In this post we will try to learn how to diagnose and repair an inverter, by comprehensively learning the various stages of an inverter, and how a basic inverter functions.
Before I have explained how to repair an inverter it would be important for you to first get fully informed regarding the basic functioning of an inverter and its stages. In the following content I have explained regarding the important aspects of an inverter.
Stages of an Inverter
As the name suggests DC to AC inverter is an electronic device which is able to "invert" a DC potential normally derived from a lead-acid battery into a stepped-up AC potential. The output from an inverter are normally quite comparable to the voltage that is found in our domestic AC Mains outlets.
Repairing sophisticated inverters are not easy due to their many involved complex stages and requires expertise in the field. Inverters which provide sine wave outputs or the ones which use PWM technology to generate modified sine wave can be difficult to diagnose and troubleshoot for the folks who are relatively new to electronics.
However, simpler inverter designs that involve basic operating principles can be repaired even by a person who is not specifically an expert with electronics.
Before we move into the fault finding details it would be important to discuss how does an inverter work and the different stages normally an inverter may comprise:
An inverter in its most basic form may be divided into three fundamental stages viz. oscillator, driver and the transformer output stage.
Oscillator:
This stage is basically responsible for the generation of oscillating pulses either through an IC circuit or a transistorized circuit.
These oscillations are basically the productions of alternate battery positive and negative (ground) voltage peaks with a particular specified frequency (number of positive peaks per second.) Such oscillations are generally in the form of square pillars and are termed as square waves, and the inverters operating with such oscillators are called square wave inverters.
The above generated square wave pulses though are too weak and can never be utilized to drive high current output transformers. Therefore these pulses are fed to the next amplifier stage for the required task.
For info on Inverter oscillators you can also refer to the complete tutorial which explains how to design an Inverter from the scratch
Booster or Amplifier (Driver):
Here the received oscillating frequency is suitably amplified to high current levels using either power transistors or Mosfets.
Though the boosted response is an AC, it is still at the battery supply voltage level and therefore cannot be used to operate electrical appliances which work at higher voltage AC potentials.
The amplified voltage is therefore finally applied to the output transformer secondary winding.
Output Power Transformer:
We all know how a transformer works; in AC/DC power supplies it is normally used to step-down the applied input mains AC to the lower specified AC levels through magnetic induction of its two windings.
In inverters a transformer is used for similar purpose but with just opposite orientation, i.e. here the low level AC from the above discussed electronic stages is applied to the secondary windings resulting in an induced stepped up voltage across the primary winding of the transformer.
This voltage is finally utilized for powering the various household electrical gadgets like lights, fans, mixers, soldering irons etc.
Basic Principle of Operation of an Inverter
The above diagram shows the most fundamental design of an inverter, the working principle becomes the back bone for all conventional inverter designs, from the simplest to the most sophisticated ones.
The functioning of the shown design may be understood from the following points:
1) The positive from the battery powers the oscillator IC (Vcc pin), and also the center tap of the transformer.
2) The oscillator IC when powered starts producing alternately switching Hi/lo pulses across its output pins PinA and PinB, at some given frequency rate, mostly at 50Hz, or 60Hz depending as per the country specs.
3) These pinouts can be seen connected with the relevant power devices #1, and #2, which could be mosfets or power BJTs.
3) At any instant when PinA is high, and PinB is low, the Power Device#1 is in the conducting mode, while Power Device#2 is held switched OFF.
4) This situation connects the upper tap of the transformer to ground via the power device#1, which in turn causes the battery positive to pass through upper half of the transformer, energizing this section of the transformer.
5) Identically, in the next instant when the pinB is high and PinA is low, the lower primary winding of the transformer becomes activated.
6) This cycle repeats continuously causing a push-pull high current conduction across the two halves of the transformer winding.
7) The above action within the transformer secondary causes an equivalent amount of voltage and current to switch across the secondary by means of magnetic induction, resulting in the production of the required 220V or the 120V AC across the secondary winding of the transformer, as indicated in the diagram.
DC to AC Inverter, Repairing Tips
In the above explanation a couple of things become very critical for obtaining correct results from an inverter.
1) First, the generation of the oscillations, due to which the power MOSFETs are switched ON/OFF, initiating the process of electromagnetic voltage induction across the primary/secondary winding of the transformer. Since the MOSFETs switch the primary of the transformer in a push-pull manner, this induces an alternating 220V or 120V AC across the secondary of the transformer.
2) The second important factor is the frequency of the oscillations, which is fixed as per the country’s specifications, for example countries that supply 230 V, generally have a working frequency of 50 Hz, in other countries where 120 V is specified mostly work at 60 Hz frequency.
3) Sophisticated electronic gadgets like TV sets, DVD players, computers etc. are never recommended to be operated with square wave inverters. The sharp rise and fall of the square waves are just not suitable for such applications.
4) However there are ways through more complex electronic circuits for modifying the square waves so that they become more favorable with the above discussed electronic equipment.
Inverters using further complex circuits are able to produce waveforms almost identical to the waveforms available at our domestic mains AC outlets.
How to Repair an Inverter
Once you get well versed with the different stages normally incorporated in an inverter unit as explained above, troubleshooting becomes relatively easy. The following tips will illustrate how to repair DC to AC inverter:
Inverter is “Dead”:
If your inverter is dead, do preliminary investigations such as checking battery voltage and connections, checking for a blown fuse, lose connections etc. If all these are OK, open the inverter outer cover and do the following steps:
1) Locate the oscillator section; disconnect its output from its MOSFET stage and using a frequency meter confirm whether or not it is generating the required frequency. Normally, for a 220V inverter this frequency will be 50 Hz, and for 120V inverter this will be 60 Hz. If your meter reads no frequency or a stable DC, it may indicate a possible fault with this oscillator stage. Check its IC and the associated components for the remedy.
2) In case you find the oscillator stage working fine, go for the next stage i.e. the current amplifier stage (power MOSFET). Isolate the MOSFETS from the transformer and check each device using a digital multimeter. Remember that you may have to completely remove the MOSFET or the BJT from the board while testing them with your DMM. If you find a particular device to be faulty, replace it with a new one, and check the response by switching ON the inverter. Preferably connect a high wattage DC bulb in series with the battery while testing the response, just to be on the safer side and prevent any undue damage to the battery
3) Occasionally, transformers can also become the major cause for a malfunction. You can check for an open winding or a loose internal connection in the associated transformer. If you find it to be suspicious, immediately change it with a new one.
Although it won't be that easy to learn everything about how to repair DC to AC inverter from this chapter itself, but definitely things will start "cooking" as you delve into the procedure through relentless practice, and some trial and error.
Still have doubts...feel free to post your specific questions here.
So, my inverter has a low voltage error when a first stage low DCV MOSFET is connected and it gets hot real quick. If all first stage FETs are removed the inverter turns on. The frequency at the gates of all is normal. Another problem I have before this is the AC output was 71 ACV. I tried adjusting the POT with no change and there is no frequency on the output. Please help.
Sorry can’t figure out. Without seeing the schematic it is difficult to understand how the MOSFETs stages are configured, and difficult to judge the fault.
hi!! i have a 3000 watt 12 volt eliminator power inverter that i bought 5 years ago for cottage where there is no hydro only working with solar and generator . power inverter started to act up a few weeks ago while i was there for a week battery are full charge, i have x8 27dc marine battery at 90amp each power is coming at about 110 volt, there is a voltage ,watt, power screen to monitor all the power that is coming in and out of the power inverter , that’s where my problem come in to play .
when i first start the inverter everything is showing properly on that voltage screen 110 volt is coming out no problem watt meter is showing wath power i am taking out of my battery at the time and fan are running on and off when they have to run to keep think in order but after a while that screen only show the voltage off the battery where its at and the power that is coming out (110) but it stop showing my wattage that i am using ( p.s i have a 3000 w inverter but only really using about 300 to 500 watt i have that one for a buffer i have a small 12 cu fridge runnig on my system) so when my watt meter stop working i still have all the power coming out not less then before but no fan are running at all to keep thing cool down as where before it start and stop multiple time during day or night and my battery power never go lower then 12.3 volt if there is not sun i run on a generator and recharge battery with charger .
i look for cold solder joint bad fuses , bulge capacitor or even burnt spot on back of main control board but it all look good . it all stated when i was beside the battery and inverter one day when i notice a smell of burnt electronic component but that could be from the fan not running because when fan do run there is no smell at all . any idea of what could be the cause or what i should be looking for ? i was thinking of a solder joint that get loosen up when getting to hot like i seen before on my tv board because the problem is on and off but dosent look like it is . what would cause the fan stop running when the watt metter stop showing the wattage . the watt meter dosen’t go blank it just show 000w instead of 250 w or whatever wattage i am using at the time . any tips would be apreciated thx
Hi, it can be difficult to troubleshoot a specific stage in commercial inverters because each inverter may have a unique circuit design.
If the fan stopped working it means the issue could in the circuit which drives the fan, or maybe the fan itself has gone faulty.
You can replace the fan with a new one and test the results, or you arrange a separate fan which may be permanently connected to the 12V DC at low speed during the inverter mode. This will ensure that the new fan always remains ON while the system is in the inverter mode and switches OFF in the grid mode.
The wattmeter may also have a control circuit which might be malfunctioning, and will need to be diagnosed physically using test instruments.
thx for your help ill keep looking and try to fix it . i bought a other one for now to replace this one but if i cant fix it it will be used as a spare incase something happens with the other one .
Sure, no problem, wish you all the best!
First, I know nothing about electronics. I am just interested in powering my travel trailer. I have a 2021 Jayco 24RL that has a 190 watt solar panel and a Gopower controller. Secondly, I have a 3000 watt Gopower inverter. The inverter was installed about 2 months ago and initially seemed to work ok.
In the past few days, the inverter has failed to pass AC power to the system. Based on recommendations and my research, I performed a “hard reset” by turning off all AC and DC power and waiting 30-45 minutes. Apparently this is to reset some relays. This procedure worked a couple of times and power and recharging was restored.
But, yesterday we were away from the RV for several hours. When we returned, the same issue was happening. I attemped a “hard restart”, but with no success. The battery condition at its worst was under 8 volts. I was able to get some DC power to the RV by connecting my tow truck to the RV.
I would like to understand what is causing the constant need to “hard reset” the inverter?
Sorry, It may be difficult to judge the fault without a practical checking, because the fault seems to be specific to the circuit. However, if the battery is not charged properly that may certainly lead to power shut-down by the inverter. Without the battery optimally charged the inverter may keep shutting down frequently…you can try charging the battery through an external charger and then check the response!
Hi Swagatam,
I’m an amateur electronics engineer, and currently have a very difficult problem to solve. It seems similar to Daniel’s:
IN SHORT –
10 year old conventional 300W inverter (modified sinewave) brand “Microcontrol” seems to give normal output, but when more than 1 laptop is connected (2 laptops = 80W) it cuts out completely and gives error message (red LED). After switching off, disconnecting load, switching back on, 1 pair of IRF840B disrupts immediately, causing a short circuit in both so that external in-line fuse blows. This happened 3 times.
I would also like to know how the OVERLOAD PROTECTION works; I haven’t been able to figure it out.
MORE DETAILS –
When it failed initially, only 1 half of the output circuitry worked. I needed to replace a driver transistor MPSA44 on the side of the other output circuitry, plus a diode 1N4148 parallel to one of the 4 MOSFETs type IRF840B.
There is an IC “ELAN” EM78P458AP that connects to the power output section through opto-coupler PC817 x 3, out of which 2 are connected to the base of an MPSA44 each. 1 PC817 is connected through a resistor .5 Megaohm to the same source as the power MOSFETs are (230V). From the collector of those MPSA44 it goes directly to 1 IRF840B of each of the 2 sets of IRF840B (4 in total). The general circuitry is such that the 12V input is being transformed up to 230V using 4 MOSFETs 1Nxx, then rectified and finally fed to the MOSFETs.
I need advice, please. Thank you for providing this great platform.
P.S. I made a photo of the PCB, but don’t know how to attach it to this message. If you could tell me how I will send it through.
Thank you Sven, It can very difficult to judge the fault without practically testing the board with meters and oscilloscope.
80 watt is quite low compared to the 300 watt handling capacity of the inverter, so it seems the inverter is malfunctioning severely. It cannot be just the over load protection, it could be all the MOSFETs that might be damaged fully or partially due to some reason.
An overload is detected by adding a appropriately calculated resistor in series with the inverter battery supply. The voltage developed across this resistor is monitored by an opamp comparator which is also called the error amp. When the overload exceeds the set limit, the voltage developed across the sensing resistor also exceeds the opamp’s set threshold, which causes the opamp output to go high and trigger the cut off circuitry.
In place of the fuse you can temporarily connect a heavy duty lamp, which will indicate if the MOSfETs are shorting or working correctly. You can also check the frequency output from the opto couplers to be sure that the MOSfETs are being fed with the correct frequency. I think an oscilloscope would be strictly required for all these testing procedures.
I could have requested you to send the image but, I am sure image won’t help to troubleshoot the fault, it will require an actual testing of the board
Thank you Swagatam for your excellent reply.
I won’t have access to an oscilloscope soon, but what you explained is great.
After the initial failure happened, and after the disrupting of the 1 pair of IFR840B, I left the other, original, pair of IRF840B in. Before I drew a circuit diagramme based on the PCB of the output section, I noted that when putting the Ohmmeter between Emitter (leading to ground) and the Collector of the MPSA44 of the side that was working, in 1 direction there was a resistance of 1.3 K Ohm (the MPSA44 was okay). There was no reading (only open circuit) on the side where I put in new pairs of IRF840B that kept short-circuiting. Does this mean that the original pair of IRF840B is damaged, too, and this would cause & explain the disrupting of the other pair?
In fact, I built the circuitry you suggested (the one with the LED and a couple of resistors) for testing NPN MOSFETs, and according to that nice little device the 2 original IRF840B are good. Yet they have a measurable resistance…
In light of this, would you invest into another 4 new IRF840B?
I still have to look at the PCB to find the Overload Protection according to your explanation. I expect it to be close to the input.
Sven
My pleasure Sven, MOSFETs are sensitive devices and they can blow unpredictably and suddenly without any indications.
If you are in doubt, it would be a good idea to test the MOSFETs externally before soldering them on the PCB.
Also to ensure the MOSFET do not burn unpredictably, you can connect a heavy duty bulb in series wit the battery supply which can prevent the short circuit from passing through the MOSFETs, by illuminating the bulb. It is an quick way of introducing an overload protection while doing the troubleshooting.
Furthermore, before connecting the MOSFETs check the source of the gate, whether it is creating the required frequency or not, because in the absence of a frequency in an inverter circuit, the MOSFET can burn or short out quickly.
Thank you Swagatam for encouraging me to take the remaining pair of IRF840B out of the PCB to test it again according to your instructions (https://www.homemade-circuits.com/how-to-check-mosfet-using-digital/). Both failed the test with the Ohmmeter. And both have an unchanging reading of 583 Ohm/ 593 Ohm between the Drain and the Source, with the black probe being on the Drain.
Funnily, when I had checked those IRF840B with the little device (LED, 2 resistors), the result was good. What do you think?
I then checked the voltages at the Gates of the first IRF840B of each half of the output circuitry, using the cheap multimeter I have. Both Gates received identical input values of about 4.1V= and about 8V~ which could explain that the working half of the output circuitry (even though obviously damaged, too) still gives some output as long as not burdened with more than a certain load.
Could those 2 IRF840B, that I have re-tested and seem faulty, be the reason for short-circuiting the other pair of IRF840B of the output circuitry, when the inverter is connected to a load too heavy? In light of the info above, would it seem reasonable to you to get a complete set of four IRF840B to get the inverter back to work?
You are welcome Sven, while testing the MOSFET, the gate capacitance should be correctly shorted and discharged for the testing to work, and also the gate, source, drain pins must be correctly ascertained while doing the steps….if you have done these correctly, then it is strange why its failing the meter test.
For the LED test you can try replacing the LED with a heavier load like filament lamp or a motor, and check if the MOSFET still gives satisfactory results.
Yes it may be a good idea to change the complete set of MOSFETs, but before fitting them make sure to test them on the LED jig, and also make sure to implement the safety tips which I had discussed in my previous emails
I shall proceed as instructed, and will update you.
OK thanks…
Swagatam –
It took a while to get replacement FETs, and today I put in 4 pieces of IRF840 into the inverter (after checking each one of them using the jig). I tested the inverter on 70% load, and it’s been working fine! I let it run for several minutes.
One thing that puzzles me… even the new FETs IRF840 have a resistance of about 600 Ohm between the Source (red + probe) and the Drain (black – probe). So there seems to be no difference to the old set of IRF840B, and yet it now works. I had made no other changes to the system. Would you have any explanation for that?
It’s been a great exchange with you. May God bless you for that. With your readiness to share your knowledge freely you have good cards for entering the Kingdom of God and attaining eternal life.
Thank you Sven, I truly appreciate your kind words! I am so glad your inverter is working now.
The RDSon resistance between the drain and source of IRF840 should be 0.85 ohms according to the datasheet. The resistance will be minimum only when the MOSFET is switched ON, meaning when there’s at least 10V present across the gate/source of the device. So if you measure the resistance when the MOSFET ois switched ON, that will probably show 0.85 ohms.
Swagatam, Season Greetings!
The inverter still works.
Everything could be repaired if we only wanted it to happen!
Greetings Sven, I completely agree with you, everything can be repaired if we only have the will to do it….please keep up the good work.
i have a FIEL 1001-05 board that i need repaired.any suggestions as to who i can send to?
Sorry, I haven’t studied the FIEL1001-05 yet, so I can’t troubleshoot it!
Yesterday my lights started working only very, very dimly.
The batteries are full.
The inverter runs other things just fine (fans, bread machine etc) but lights are all dim.
How do I know the oscillating stage in an inverter without center tap transformer
whether it is a center tap, or full bridge, all inveters will have an oscillator stage, which can be verified at the gate of the respective power MOSFETs
I have an ACDC 3000w/12VDC inverter and I happened to connect 24VDC now its not working because I saw some smoke coming out of the inverter. Please help was part of the circuit can be the cause?
24V is too high for a 12V inverter…if a fuse was not used in the inverter, then I am afraid it might have damaged the power mosfets and the associated circuitry.
Sir, please I have a 12v 1000w/230v inverter, when it is switched on, the output will come on and go off immediately. What could be the fault and how it can be corrected. The oscillator circuit gives 50Hz.
Anointed, is the battery voltage alright? please check the battery voltage? If it is ok, then this could be some internal fault of the inverter which may be causing its internal relay to trip….it can be solved only by practically checking the internal situation.
Yes nice wan
ans, I have inverter of 1000w 12v to 220v – 240v digimark I put 36v instead of 12v battery then burned capacitor 10v 220uf and small ic bursting. I replaced capacitor is working but output not.
I am sure you might have destroyed all the main components of the board, because you have exceeded the supply input by a huge margin…
Hello Swagatam,
I’m looking into your circuit diagrams for small hobby projects since my grad days. You’re genius man. Really appreciate your effort for sharing the knowledge.
Today I’ve a particular problem I’m facing since last few weeks and found no online suggestion what to do. I’ve got an old Brainy Eco Solar Inverter, but when connect it to the battery, the relay doesnt turn on. Checked and found there is no signal from the uc to turn on the relay, which is expected. Hoping in case you have got into any similar situation in past, what is your suggestion for me to check. Or, if you’re familiar with this PCB board, it’d be really helpful if you tell me, where to check for the issue.!
I’m thinking if there is any wrong with any component burnt or something or the uc itself is the culprit.!
Thanks.
Thank you amlan, if the relay is not turning ON that simply means that the relay coil is not getting the supply….either due to low battery or the may be the relay driver transistor has gone faulty…so the first thing you must check is the battery voltage, next whether the supply is reaching the relay coil…if both of these are OK, then you can check the relay driver transistor to see if it is faulty or not.
Thank you Swagatam for the suggestions. What is found is, the the relay control voltage is not coming from the micro-controller itself. I tracked down almost every pin, every traces, found no component fault for not working of this relay. Another thing I noticed is that microcontroller pin (53) is not even shorted to GND when there is no power, but as soon as battery is connected that pin gives me 0v instead of 5v . So I think this must be some conditional response. Here I am tired to think of any reason for such behavior.
Thanks amlan, for updating your results, since it is a microcontroller based issue, it will be difficult for me to diagnose and troubleshoot it…I hope you are able to solve it soon.
what is likely problem when accidently connecting ac to inverter that is turned off with a soft switch
My 12v to 220v/600W power inverter just made a loud SNAP! sound with a bright flash inside the case. Now there is no power output.
I have opened it up and inspected everything for signs of scorching on any of the components but no obvious burns on anything.
What component would make that arc snap noise when frying? What should check as a likely failure point? I would like to repair the unit if it is just likely to be a simple diode or capacitor replacement job.
Isolate all the MOSFeTs from the oscillator by disconnecting all the gates from the oscillator source, and now check the oscillator output for a clean 50 Hz frequency, if the frequency is present then your oscillator section is fine, now you must check the all the MOSFETs separately by removing each one from the PCB…..only the MOSFET snapping can create a arc like sound……however, a wire shorting can also create this kind of sound.
Excellent article.
My inverter shows a grid fault (501) and has disconnected from the grid. A second inverter along side is working fine despite sharing the same grid connection as the first one.
Can you suggest an explanation to help me understand what might be going on.
Thanks
Glad you liked the post, however the issue you are facing seems to be a little complex to solve, since it is involved with GTI functioning, and a 501 fault whch I am not familiar about? I wish I could it solve it for you, but presently I do not seem to figure it out…..
Thanks for your informative and quick reply. I will take it apart (not very easy with this one) and check it out.
I’ll get back to you with what I find.
No problem, wish you all the best!
My 12v to 220v/500W power inverter just made a loud sounds with a bright flash inside the case. Now there is no power output.
Probably some sort of short circuit, causing some of the power devices and wires to blast….
Thanks for your great article and tips.
I have a Xantrex HF1000 that is intermittently either giving me a AC overload error or showing high current and power consumption WITH NO A.C. LOAD. The display now shows V=13.1V, A=39A, P=0.4KW, it is running with no errors. A week ago, I could not get it to last more than several seconds without shutting down from AC overload, but I briefly saw an output power of over 0.8KW. I am a retired ET, but don’t have the tools to check the waveform or measure such a high DC current. Do you think this is a typical symptom of shorted MOSFETs or output transformer? The local Xantrex shop here says the unit is not repairable.
Yes it could be a case of shorted MOSFET, which can be confirmed only by removing all the MOSFETs from the board. It could be a burned transformer also, however transformer don’t burn easily, and if they do it can be accompanied with smoke and smell. MOSFETs can burn quickly without any signals.
You can also try removing the transformer connections and check the results.
Sir,i have suoer 2000w inverter and 20 amp charger it always damage the positive side mosfet irfp460 whenever i replace it,it will just work like 10 minuite before the replacing mosfet will be damage again,what can i do sir?.
Without checking the circuit, it can be difficult to judge the fault, may it is due to wrong MOSFET being used…
My outback 48v inverter system has given 10 years of reliable 230v power to my off grid home
But yesterday it decided to only give 130v’s
Please advise as 2 solar experts!!! Have come up dry today.
Thank you
It cannot be judged without giving a practical check. The fault can be in the MOSFETs, transformer, or the feedback control loop, the fault may be one of these or combined
I have a 300W inverter (12V to 120V) powering low wattage electronic equipment (router etc.) in a remote area. The battery is charged by solar; however, the battery went into low voltage protection mode and shut off the power. When the power was restored the 110V inverter didn’t work, although the inverter power light was on and fan was running. After disconnecting the inverter and reconnecting, it booted straight up and worked. My problem is the inverter is critical and I cant disconnect / reconnect all the time being in a remote area.
1) What would be the issue?
2) How can I prevent this locking of the inverter when the batteries go into protection mode?
3) Is there a different type of inverter I can purchase whihc will auto start?
Is it an UPS or an inverter. Because if you are expecting an auto changeover from an inverter to mains grid, then it is an UPS.
By the way an inverter is never supposed to start if the battery is over discharged, so if your inverter is refusing to start due to low battery then it is doing the right thing, you must make sure that the battery is correctly charged either by solar or by the grid.
my 3kva inverter showing input voltage and there is no input voltage, how do i sort? please help
I have an Onan RV QD 3200 generator. The inverter has a burned out capacitor. Onan is backordered on a complete inverter for at least 6 months. Can anyone repair my inverter? Please contact me at drkehr at msn . com Thanks very much for any help you can offer
I have a 12V DC input inverter which outputs 240V AC. Is it possible to convert this unit to a 48V DC input, simply by replacing the transformer, or is it more complicated than that? The inverter is a modern design.
Yes it is definitely possible by upgrading the transformer, MOSFETs and the battery specs accordingly
Thank you Swagatam for your response.
Possibly, the MOSFETs may not have to be changed, if they are already rated to 60V or so. I would have to test to find out what the AC voltage coming out of the transformer/s is/are (there is probably two high frequency transformers), and then look for transformers with the right number of turns ratio between primary and secondary windings, so that I get the same output voltage, even though I have increased the input voltage 4 times.
My present 12V DC to 240V AC inverter is rated at 10,000W (20,000W peak), so it takes a lot of current at 12V to output that amount of Watts. The inverter cost about $1,700 AUD, so it is worth looking in to the feasibility of converting it to 48V DC input, rather than forking out that kind of money on a new 48V DC input inverter.
You are welcome Chris! That’s right, you don’t have to change the MOSFETs if they are already rated at 48V
If you are having a 12V transformer, you can probably add 4 times more number of turns to the existing 12V winding, to make it a 48 V trafo.
Thanks for this great blog. I have a 2.9kw grid inverter. The inverter is not detecting DC voltage but I do not have a warning message. I have checked that the DC voltage reaches the inverter input (350v), but when I turn on the inverter DC input the voltage approaches 0. I have continuity between the negative and positive DC terminals (1.5 ohms). I suspect that the problems could be the transformer. What is your recommendation? Thanks.
Thank you for liking this blog, it seems like a clear short circuit across the input supply terminals, this may be most probably due to shorted or blown off power devices. Transformers usually don’t become shorted without burning or smoking, so it must be the power devices….
Thank you very much for your reply. You are absolutely right. I have two Mosfets with continuity between their three pins. However, I also have the transformer with smoke in one of the terminals (I have not opened the transformer since it is sealed). Please see the photo (nearest connector-https://1drv.ms/u/s!AhgrRnWDjB9pgYxbi85lEno_ZJQ1rQ). However, the circuits are different. Do you think I have a burned out transformer too? Thank you again.
OK, then it seems the shorting of the MOSFETs might have burned some sections of the transformers too due to high current passage….in that case you might have to replace the transformer also, along with the MOSFETs, but only after confirming through appropriate testing
Thanks you for your orientation.
Hi Swagatam, when you talk about power devices are you referring to the mosfets? I have a similar issue on my 1kw 12v inverter where the input supply terminals are shorted on one orientation of the test probe but not on the other. There are 4 rows of 4 mosfets each, 1 mosfet on row 2 and 3 are blown physically. I removed all the mosfets on the row but I still test a short to ground. Where else should I check?
Hi Serolf, yes power devices refers to the semiconductor devices that switch the transformer and the battery current. They maybe mosfets or IGBTs.
Do you mean the battery terminals of the inverter show a shorted indication? Then you must track the wires and check each and every location and isolate the locations to test which specific region of the circuit is actually showing the shorting. It can be the IC, a resistor, a voltage regulator or the power mosfets. Before doing this you will have to remove the mosfets entirely from the PCB.
Mosfets cannot be checked while they are soldered on the PCB, they can be checked only after removing or isolating them from the PCB
Thank you for the quick reply. Yes I still test a short on the main 12v rail of the battery input terminals after removing the physically blown mosfets. I will check next on the oscillation area. I appreciate your response and it was great to find your article!
Sure, please check the oscillator section also, if it s working then your main circuit board may be still intact….
good morning sir…can share circuit diagram for inverter 5000w
I have a new Edecoa 3500W pure sine wave inverter.
I installed it on a boat that has existing shore power, and generator wiring with a double pole switch to switch between Breaker bus, and Inverter.
When I plug into inverter directly it works great.
When i wire to outlets, (disconnected from power bus by switch, verified No contact, and no voltage until inverter is switched on), it trips ALL of the GFCI outlets on the boat in all circuits.
When I disconnect the ground from the inverter to the ship ground, (still connected inverter ground to GFCI outlet ground, it works, and powers all devices just fine.
left inverter – right Ship breaker bus with Shore, and generator off.
Inverter HOT to Ship ground = 0 VAC
Inverter Neut to Ship ground = 120VAC
Inverter ground to Ship Neutral = 120VAC
Outlet monitor connected directly to inverter shows Open Ground. (probably not enough voltage to light the neon bulb).
measuring at inverter.
45vac Hot to Ground
45VAC Neut to ground
120VAC hot to Neut.
With ALL devices disconnected the GFCI doesn’t trip, but any current draw, even a phone charger is enough feedback on ground to trip GFCI outlets.
Hot & Neutral are bonded at breaker panel, (and shore power panel).
Both main plug for shore power, and shore power pedestal have GFCI outlets.
There might be some AC leakage from the inverter circuit into the ground which could be causing the ground-fault circuit interrupter to trip, because these devices are designed to detect ground leakages and trip on sensing even the slightest amount of AC interference…
I just pulled it apart to have a look, several things i Noticed.
Instead of 6 or 8 big mosfets, there are around 50 tiny of them.
Little guys that look like 10 amps.
Instead of several large gauge wires, there are a dozen small gauge connected in parallel.
There is a tiny circuit card inline with the neutral with several components that look like diodes, or resisters, a very small gauge (20) is connected between the ground terminal, and a pad on this board that the screw goes to the case.
3 small transformers are connected in a bank (1000w each?)
It appears this inverter was scaled from a small inverter design by tripling the component count.
It powered a 2KW load no issues, but I’m not impressed.
Since I’m reading 45 volt from each leg to ground, what will happen if I hard ground the neutral?
I have a separate neutral buss for the inverter that I can connect, or disconnect with a switch.
the panel neutral is bonded to ground, and also battery negative.
My best guess is the feedback is on the DC negative since there is no other connection to the boat ground common.
I don’t think the inverter circuitry might be having any problems, rather it’s some kind of AC getting into the GFCI and tripping it.
You may have to diagnose the wiring, and what exactly the GFCI is detecting and tripping, you can one by one disconnect the wires from the GFCI and check which wire is causing the issue.
It can be difficult for me to judge the fault without referring to the complete wiring details.
Neutral shouldn’t be hard wired with the ground line, that’s not recommended
Basically, You may just want to replicate the wiring that we have in our home wiring system
In US homes the neutral is grounded at the panel.
I’ve found the issue, but don’t have any good solutions.
With the inverter output completely isolated IE an appliance directly plugged into the inverter outlet, and no connection to the boat wiring, no problems.
Without grounding the Neutral, the ground shows open on an outlet tester, and GFCI outlet does not trip on ground fault.
I measure 54VDC between the Negative 12V input, and the Neutral output of inverter.
Same between Negative 12v, and Inverter Hot.
The issue is the HV difference between the Inverter output, and the 12V DC in.
On my boat the 12vDC negative is grounded to the frame.
The AC ground & Neutral are also grounded to the frame at the panel.
When the inverter is connected to the boat battery pack, it’s negative 12v input is also tied to the boat’s frame. Grounding the inverter output puts 54vDC (pulse) on the ship ground tripping all GFCI’s on the boat.
I currently have it “working” by having a separate ground for the inverter.
One GFCI outlet is inverter only, and only grounded to the inverter ground, which floats at 54vdc compared to the rest of the grounds.
The other GFCI is grounded to the common ground which includes a connection to the DC negative, the shore power ground (green wire), ALL ground wires for all devices, and outlets, (except inverter), and the frame, and a jumper to the neutral Bus on all outlets (except inverter).
I don’t know if this meets any codes, but it works without tripping anything. This is an Edecoa inverter supposedly made for US. 3500w pure sine wave with terminal for direct connection, and several plugins on case.
In India we don’t short the neutral with the ground, the ground or the earth line is inserted deep into the soil, and this line is also associated with the body of all metallic appliances so that any chance of a mains leakage on the body is absorbed by the earth line.
I think what you have done is fine, since your inverter seems to be working normally, so it’s the GFCI whose wiring specs will need to be reviewed from an expert, to exactly know the reason behind its strange tripping behavior.
Great write up and informative. What is the chance someone would know the specifics of the 120vac voltage sensing transformer in a Xantrex RV2012M inverter? Mine has a burned up primary and Xantrex refuses to give me any information on this part.
Thank you very much, however, without seeing the schematic of the inverter it is difficult to understand the specs of the transformer.
Yeah that was the argument I ended up in with Xantrex tech support on the second call. I don’t think he liked it when I told him his JOB was technical support not sales! Then I told him if he didn’t want to technically support me I would be pleased to talk to the manager and recommend he be transfered to sales! Lmao
I hope your problem gets solved soon.
Good afternoon,
I have just bought at a good price a 1000 w pure sine wave inverter fitted with 2 120v 60hz plugs that each support 500 w. For a larger single load can I join the two outputs together (hot to hot, neutral to neutral, ground to ground) to get the full 1000w capacity?
Yes that may be possible, however it would be safer to first check the phase angle of both the outputs with an oscilloscope, to ensure that the respective AC sockets are perfectly in phase or synchronized with each other.
Alternatively you can connect an AC bulbs, each in series with the parallel wires, if the bulbs don’t illuminate would confirm that the ACs are phase, and are safe to be tied up in parallel.
I have Microtek EB700 inverter. Inverter is working fine but when main power goes out. The output from the inverter is 298V. My two led bulbs blows out. Any method to reduce the output voltage from inverter.
It can be corrected by opening the inverter and adding an automatic voltage correction feeedback, or by using an external voltage stabilizer unit
Good Day Sir,
I found this lamp online https://amzn.to/2KrnUpe. This they named it inverter lamp. What is interesting here is during power failure it takes over by a Lithium battery inside and keep the light on. My query is that how it detects power failure and actual switch off by a switch?. Even after power failure if we flip the switch to off it goes off. One more is if we touch the two pins of B22 base with metal it lights up. How they made this circuit what is the logic behind this. If you have time please explain. If you do have circuit of this please post it too. Thanks in advance.
Hello Kumaran,
It works by detecting the resistance between the two input pins. When mains is not available and the switch is in ON position, the input pins of the bulbs detects the resistance developed from the grid transformer, and this switches ON the inverter side LEDs, when mains returns, it turns off the inverter side LED driver through the stepped down voltage, and switches ON the mains side LED bulbs. When bulb switch is in the OFF position, no resistance is detected across the pins, and mains AC is also cut off, so both side LEDs remain switched OFF
Sir, thank you for your replying promptly. If you can suggest a DIY version circuit for the above explanation will be useful for the beginners like me. Thanks in advance. Your work is greatly appreciated as always.
No problem kumaran, if possible I’ll surely post a related article soon…
Thanks alot.i really appreciate your article on how to repair an inverter.it was well explained and comprehensive.i am just a beginner.i believe it will be very useful and helpful to me…. thanks a million times.
Thanks and Glad you found it helpful!
My inverter started making lights pulsing, bright and then dim, and then it stopped making power.
I turned inverter off and waited 1/2 hour turned on and watched display. The voltage starts a 0 and increases until it gets to about 80 volts and then drops to 0 and keeps cycles up and down.
It also has ruined 3 breakers that are between batteries and inverter.
Do you have any ideas?
In most cases, related to inverter output voltage issues, the fault is with the output power devices. So you can try checking the MOSFETs or the IGBTs to know whether they are working correctly or not. You can also try adding a DC bulb in series with the battery. If this bulb glows brightly without a load on the inverter will further prove that the power devices are shorted somewhere
Good morning sir, I have an issue with my 1200VA crown inverter, it is SMPS based.
I plugged it in to charge as usual and everything was fine, after a while I noticed it wasn’t charging again.
I then decided to try inverting, I noticed that on no-load, the output voltage was 340V instead of 220v and within two seconds the system trips indicating a fault (over voltage I guess).
but when I add a load , the output voltage comes down to normal , please what could be the reason for this and how can I solve these problems ( charging and over voltage ). Thanks sir
Hi Daniel, it seems there’s no RMS control or over-voltage feedback control in the inverter, which looks strange? You may have to check whether or not the feedback is present or malfunctioning, or add a new feedback for the same.
Hi
My 1200watts Thunderbolt inverter went off after lightening struck, but has suprised me is that none of all circuit breakers in the Live line trip off. I get an overload messege on the display.
what could be the problem
Hi, It could mean that the the power devices and the wiring were unaffected, but the sensitive electronics might have been damaged due to the lightening surge. It could be just a single part or multiple parts…will need to be diagnosed
Hello Swagatam,
I have a Chloride make (Jenus board) Home UPS cum inverter(800 VA). Though it is old but works fine.Recently it is observed that machine moves to inverter mode where as input AC main exists but goes more than 240 volts. If INPUT voltage decreases slightly again it recovers to AC Power ON mode automatically.
Pls help me with possible cause and its solution/repair.
Best wishes,
SANKAR KUMAR CHATTERJEE
M: 9163576074
Hi Shankar, does your UPS have a feature to switch the unit in the inverter mode during a high mains voltage detection? If yes then it could be due to this feature. Otherwise, the changeover relay section of the UPS could be malfunctioning, which will need to be diagnosed
Dear Swagatam,
You are correct. This machine has feature high input voltage detection and switching to inverter mode.
Specification: Main AC Higher Voltage limit : 290 ± 5V (Inverter mode)
260 ± 5V (UPS mode)
Main AC Higher Recovery Voltage : 270 ± 5V(Inverter mode)
250 ± 5V (UPS mode)
Selected mode in machine is INVERTER Mode.
But Device switching from MAIN to INVERTER mode when voltage raises ≥ 242V. On slight decrease of AC main voltage it comes back to AC Main mode. In my residential area AC Main somewhat higher side ≥ 240V (Specially in morning time as load are low). However changer over relay are OK and performing fine.
Pls help me to locate exact circuit in JENUS make Home UPS/inverter .
Best wishes
S K Chatterjee
Dear Sankar, OK, then it seems the internal preset adjustment of the UPS might have slightly changed due to mechanical vibrations. You may have to locate this preset and try adjusting the cut off threshold to the desired 270V mark and then seal the preset with some glue.
Sorry, I do not have the schematic for the mentioned UPS with me.
Dear Swagatam,
Thanks.
One more help pls.
Instead of Schematic of that particular make , idea of control circuit (without mentioning component value of commonly available Home UPS/inverter will serve my purpose.
Brief on working of the said circuit towards force activation/de-activation of relay beyond upper/lower cutoff is also requested.
best wishes,
SKC
Dear Sankar, You may have to check the relay circuit of the UPS, and find out which op amp or comparator and the preset stage is controlling the relay tripping point, and then you may have to adjust this preset to change the tripping point of the relay.
Halo Sir,
I have this microtek xp sw 2300va inverter. A fault occurred blowing the fuses but upon replacing them, the inverter mode failed but works on mains on. when testing the charging voltage, shows 26 volts. when mains is switched off , the contactors click to shift to inverter mode and suddenly goes off with beep, tries to come on a few times but switches off eventually.
What could be the problem under such circumstances
Hello Nelson, it could be due to s short circuit of some kind in the inverter power stage. Therefore, the fault is being detected by the protection circuitry and the contactor is getting tripped OFF.
You may have to check the power stage of the inverter through appropriate steps.
Hello, great article.
I have a grid tied 300W inverter however I found it to be short circuited. The fuse is still ok but the battery connections (+ and -) are SC on the PCB level.
What would be my next debugging step? Or should I take it as a lost cause?
Thanks in advance
Hi, Thank you and glad you liked this post!
There could be a short-circuit connection directly across battery leads on the PCB, bypassing the fuse….you can track the wires from the battery and check where it exactly leads to, and locate the precise spot of the short circuit on the PCB…
Hi, i have 5kva must p1800 hybrid inverter, some 2 capacitors swallowed sometime ago causing the inverter to stop working i replaced them with the same same size i put it on it came alright output and everything but it stop charging the batteries from both utility power and the solar panels it displays bypass mode on the screen dont know what to do please help me.
Hi, it could be the changeover stage that may be malfunctioning, which is responsible for reverting the battery to charging mode when the mains fails.
Please check if there’s any form of relay or MOSFET control stage which connects the DC from the mains supply with the battery. Check whether this stage is connecting the battery with the DC or not.
Hello Swagatam
Thank you for the valuable support. I have a G50 5KVA 48V Inverter in my shop it was reporting the following problems.
1.Initially Fault code 8
2. Then Fault code 7 upon day of removal from installation
3.It was blowing MOFETS one by one each time it was switched on in Inverter mode.
4.With AC input it would blow blow a Mosfet and then go into bypass mode
5.Conditioning capacitor fitted on the drive board was disconnected but tests on it were OK.
6. Bypass mode works well meaning transformer has no problem
Now in the shop I replaced all the ten blown mosfets(five each side). I did no change the other ten they tested good on the board so I did not remove them from circuit for further testing.
At first after this initial repair it was not responding to power when it then responded. it blew one more Mosfet and after replacing it together with its a gate resistors, there is no more short circuits and the inverter can switch on on battery mode and on ac mode. But there is still one big challenge, the inverter output when in inverter mode is not uniform.
I have recorded some values coming out on display every 3 seconds or less
I have observed the following voltage readings every 3 secs: 2.9;0.0;0.0;108;8.1;0.1;0.0;209;0;0;108;0;0;0.1;0.1;0.8;0;0;209;0.0;0.0;0.3;206;0.0;0.0;0.0;0.0;184;228;0.0;0.0;0.0;228;0;0;0;0.6;0;0;0;0.;.;.;.;.;…224;0;0;029;0;36;0;0;0;220;220;0;0;29.1;0;36;0;0;0;220;220;0;0;33;3;0;0;0;220;0;0;0;220;0;0;61.2;17.1;0;0;0;220 and it goes on like that hence I have fluctuating AC output.
What am I missing now, could this be caused the other ten Mosfets which i did not replace, could it be a driver issue?, or is it an oscillator issue? How should I proceed from where I am now. I have also noticed too much overheating on one mosfet on the oscilator board I cant even touch it it is the only component overheating. It is very unfortunate this inverter came without a manual so I am figuring out everything on my own.
Regards
Trymore
Hello Trymore,
The condition indicates that something’s not right in the driver section. Unless the driver section is checked and corrected, the MOSFETs might keep blowing or the output may continue to be unpredictable.
You will have to isolate the oscillator section from the MOSFET and check its response using an oscilloscope, frequency meter, and voltmeter. Once the driver oscillator section is corrected, the MOSFETs will need to be checked and confirmed by either removing them from the PCB individually or making sure that the MOSFETs pins are totally isolated from any associated circuitry while being soldered on the PCB.
However, if the driver is a full bridge type, the troubleshooting can become a little difficult due to the involvement of the special driver IC and the bootstrapping components which all must complement and work together perfectly with respect to each other.
I have a 1000W inverter that recently started giving a weird loud crackling sound whenever it’s connected to the mains and charging the battery. This crackling however stops when the battery is either fully charged or when the mains is disconnected and the inverter is running on batteries alone. Please what do you think could be the cause? I don’t wanna cause further information damage to the unit
There might me some loose connection a faulty part which may be causing arcing and cracking sound. The arcing stops when the current draw decreases at battery full charge level. Please check the entire line from the mains AC, up to the battery charger and its output connections.
Hello sir,
I have a 1000W solar inverter, when i connect my battery it causes a short circuit to the battery thereby producing a burning smell from the battery terminals(wires). Please what should i do? Thank you
Hello Ahmad, It indicates a short circuit somewhere in the inverter which needs to be checked, it cannot be judged or guessed without a practical checking.
Hi swagatam
I’m into repairs of Inverters and solar installation…Though I’m new in it.
My issue I with my stabiliser it’s showing delay and refusing to supply, could it be from the relay? If yes how do I rectify it a db how do I read the relay with a meter to know if it’s working or not,?
Hi Joseph, without a schematic it may be difficult to judge the actual issue. If you want to know about the working of a relay you can check out this article, and then troubleshoot your circuit’s relay problems:
How a Relay Works – How to Connect N/O, N/C Pins
Sir,
I am a fresher and working in power inverter field, my inverter is showing a problem of ” No feed back” while turned on the system . I have checked the in from the transformer and still it is showing the same. Could you please help me out of this..
Varsha, if the inverter is displaying “no feedback” indicates that the existing feedback protection system of the inverter may be malfunctioning or broken. The feedback circuit can be different for different inverters, and could be fixed only by referring to the specific schematic and then troubleshooting the stages. Without knowing the exact schematic it can be difficult to solve the issue.
Hi Swagatam
Congratulations for your excellent forum.
I have a mascot inverter, 300w, type 2285
I replace some capacitors, bad mosfets and a burn KA7500C.
This was made by an electronic technician. After that He give me as repaired, but it only gives about 220v with 15V or more, for 12v input it gives an output of 190v.
He try another time and gives up, now with 12v input I measure and it gives about 12v AC, strange…
He gives up and give me the inverter.
I am not a beginner in electronics, but not an expert, do you think I can put it working with your help?
Best regards
Carlos
Thanks Carlos, you will have to check the output from the IC KA7500, its oscillatory frequency, and then check the MOSFETs whether are burned or not. You will have to isolate all these stages from each other and then check them individually for confirming their working condition
Hi Swagatam
As I told you the mosfets were checked and replaced by the technician.
The IC KA7500 was replaced for a new one.
Do you have the repair manual or circuit draw?
Best regards
Carlos
Carlos, sorry I do not have a repair manual or a circuit diagram.
Sir, am shri and i have a problem with my inverter (CFL3). Will u help me to solve my problem…
Hello, my inverter have recently started giving a problem. The fuse blew two days back and everytime I replace the fuse it blows again. The fuse also gets very heated. The load on the line is not more than 3 amps and its a 1400VA inverter so can handle upto 900Watts I think. After the fuse is replaced the fuse takes a bit of time before blowing while running on mains
This started happening just after some electricity work in house.
Incidentally a week back the fuse had blown due to my mistake caused while trying to convert a point from regular like to inverter line and I had replaced it and it ran fine for a few days until this new electricity work was done in house. I checked with a multimeter and the power it is taking from mains is about 2.5 amps and the fuse is 10amps. What could be the problem ?
Hello, first of all whenever a fuse blows you must find the reason behind it, and rectify it before replacing the fuse. Replacing fuse without rectifying the issue can lead to further faults and permanent damage of the unit.
At this moment you can replace the fuse with a filament bulb of relatively high wattage and check if the bulb remains ON without any load onthe inverter, this will prove that there may be a shorted MOSFET or a power device which is causing this malfunction
Hello Sir,
I have a Whirlpool Elantra 700VA inverter. Yesterday there was a thunder lightning and after that it is giving problem. When mains is off the output is fluctuating with a sound inside (the sound which comes after mains is cut off or given) and after few seconds it is showing overload with a continuous beep. Can you please help me to solve the problem? I can send you the inside pic of the inverter.
Hello Dipankar, it can be difficult to guess the fault since a thunder lightening could cause serious damage to the sensitive electronics of the inverter. You may have to isolate the MOSFET stage from the oscillator stage and check them separately to verify whether any of the two stages are still OK, or the damage is across both the stages.
Thanks for your reply. Will I remove all the mosfets and check one by one to find is there any problem with them?
Yes, you should remove the whole MOSFET stage from the oscillator, and then first confirm whether the oscillator is producing the required 50 Hz along with the programmed PWM etc. Once confirmed then you can check the MOSFETs one by one through appropriate steps.
I saw a 500w inverter having Ac breaker rated 6000A, sir is this appropriate
No, that doesn’t look reasonable
Hallo Swagatam
I bought a Meissner Minivert 2000W low frequency inverter at an auction. I can’t find any documentation on the internet about this inverter. I am not sure what the input DC voltage should be. There were no cables for connecting the batteries. Only a plug to connect the DC voltage. I have tried 12V & 24V. The battery light comes on with some beeps with both voltages. I only used 7AH batteries so I am not sure if the voltage is too low or the batteries not big enough. Should I try using batteries with more AH or should I try 36V & 48V. Is there any other way to determine what the DC input voltage should be. The output voltage is 220V.
Greetings
Andre Brink
Hello Andre, a two pin plug is normally not used for connecting a battery, so it is not sure whether the input supply is being correctly connected or not.
Yes, if the DC supply is low then the inverter will auto switch OFF, so you may try little higher voltages, although that may be risky.
Ah of the battery will not matter as long as the inverter AC output is not loaded.
Hi Swagatam, how can i reduce the threshold of my inverter automatically shutting down from 10v to 5v or less if possible because my suoer inverter keeps turning off my battery voltage gets to 10v. Thanks
Hi Chidubem, you can add a low battery cut off circuit which will cut off the battery from the inverter, and stop from draining further