In this post I have explained how to build an innovative inverter circuit with a single transformer that works both as an inverter and a battery charger transformer, I have explained the details from the following discussion.
The Circuit Objective
Though you may find many inverters having an integral battery charger, the section will mostly employ a separate transformer for implementing it.
In the following post I have explained a unique design which utilizes the inverter transformer for power inverting as well as for charging the battery.
The circuit diagram below shows a design where a single power transformer is used for inverting purpose as well as for charging the battery when mains is present.
The good thing about the circuit is that the transformer doesn't employ separate winding for this, rather works with the same input winding and reverts DC to the battery with the help of a few DPDT relays.
The circuit can be understood with the following points:
How the Circuit Functions
The inverter section can be easiy recognized in the diagram, R1 to R6, including the T1 and T2 forms a general astable multivibrator circuit for producing the required 50 or 60 Hz pulses.
These pulses drive the mosfets alternately which in turn saturate the transformer by switching the battery voltage in it.
The secondary of the transformer generates the corresponding magnitude of AC which is finally used for operating the connected appliances.
The above configuration suggests an normal or ordinary inverter operation.
By adding a couple of DPDT relays in the above discussed operation, we can force the circuit to charge the battery in the prsence of an AC mains source.
The coils of the two relays are powered through a capacitive low current compact power supply, involving C6, C5, D1----D5.
The above circuit is connected to a mains AC source, this source is also connected to RL1 poles.
The second relay RL2 is wired up with input winding of the transformer.
In the absence of mains AC, the position of the relay contacts are in the N/C as shown in the figure.
In this position the mosfets get linked with the transformer input winding, and the battery with the circuit so that the inverter starts oscillating and the output appliances gets the AC power from the battery.
In the presence of mains AC the relay coils instantly get the required DC power and the contacts activate.
RL1 activates and connects the mains input to the transformer, the appliances also get connected with the mains AC in the process.
Also due to the action of RL2 the mosfets get disconnected from the transformer, while the the lower tap connects with D6.
Since the center is already connected to battery positive, the inclusion of D6 provides a half wave rectified voltage to the battery, which is effectively filtered by C3 so that the battery is able to get the required sufficient charging voltage.
The above charging process continues until mains is present, so it should be monitored manually. When mains fails, the action reverts into inverting mode without interrupting the appliance operations and by using a single transformer for both the operations.
C4 makes sure that RL1 always activates a shade later than RL2 for safety reasons.
CAUTION: THIS CIRCUIT IS DEFINITELY NOT RECOMMENDED FOR THE NEW HOBBYISTS, IT'S SUITABLE ONLY FOR THE EXPERTS. IF YOU ARE A NOVICE AND INTERESTED TO TRY THIS.... BUILD IT AT YOUR OWN RISK.
Parts List
- R1, R2 = 27K,
- R3, R4, R5, R6 = 470 Ohms,
- C1,C2 = 0.47uF/100V metallized
- T1, T2 = BC547,
- T3, T4 = any 30V, 10amp mosfet, N-channel.
- C3 = 47000uF/25V
- C4 = 220uF/25v
- C5 = 47uF/100v
- C6 = 105/400V
- R7 = 1M
- D1---D5 = 1N4007
- D6 = 1N5402
- RL1, RL2 = DPDT, 400 OHMS, 12V, 7 AMPS/220V
- Transformer = 12-0-12V, current as per requirement.
For only inverter design please refer to this ARTICLE
Using a 2-Wire Transformer
If you do not want to use a center tap transformer for the inverter, then you can use the following P-channel and N-channel MOSFET H-bridge inverter module for getting an identical single transformer inverter/charger results:
How do I charge a 120v DC battery bank with this circuit, what do I change?
If your inverter mosfets and transformer are rated to work with 120V, then the above basic setup will be the same, however the relay coils will also need to be rated at 120V
Sorry for asking much sir, but the final one now. Since a relay of about 200amps capacity would be big and probably expensive and might also not fit into the space provided, can a MOSFET of about 200ampsof current capacity be applied in place of the relay since it is going to be switching between the battery and the center-tap part of the transformer?. Thanks in anticipation
Sorry, no that might not be feasible, because an inverter/charger changeover circuit can be built only using relays and not using mosfets.
I really appreciate your kind response sir, thank you so much. But I’ve studied most high power inverters, however they’re without this high relay capacity you just recommended for me, their transformer primaries are screwed directly on the collector rails of the mosfets. Just with a single relay, I did not understand the magic they used in controlling the both the charging as well as inverting systems.
Ubochi, If you are using 2kva load at the output, then the transformer primary has to switch a 2kva current through the mosfets and the relay contacts, isn’t it? So isn’t the mosfet and the relay must be rated to handle that much current and load?? Moreover if your relay contacts are burning that clearly shows that the relay contacts are experiencing heavy load which is beyond their handling capacity.
Mr Swagatam, I have a difficult situation with your design here, please i really need your help.
I just designed a 2.5kva inverter using your recommended single centre-tap transformer method. I really appreciated the design on light loads, however, when I asked my client to turn on his fridge, the system shut down, then I found out that the 20am relays at the mosfet input to the transformer got burnt due to high current passage. Now, this is a very difficult situation for me now as removing the relays has cost me a lot of mosfets as the mosfets now have direct contact with the transformer primaries, especially whenever I try to input mains to charge the batteries. I don’t know what to do, please help me. Is there no other design that can work with a single relay?. Thanks
Hello Ubochi,
I am glad you could build the circuit successfully, however, you should have selected the relays appropriately according to the load.
For a 12V 2.5 kva load the relay contacts must be rated at 2500 / 12 = 208 amperes….that looks huge right, but that is how the relays must be rated, at 210 amps each for the mosfet side relays. If you replace the relays correctly with 210 amp relays then I think the inverter should start responding correctly. However for 210 amp relays the C6 capacitor will need to be increased to 5uF/400V
In a H-bridge design, transformers input volt are usually half of the battery volt. For example, a 12vDC to 220vAC inverter transformer is usually 6v-220v, while a 24vDC to 220vAC inverter transformer is usually 14v-220v. Now my question is this, with the above circuit, when AC mains is present, the transformer will return it’s winding voltage back to the battery I.e if it’s a 12v system, then 6v Wil be sent to the battery, or if it’s a 24v system, then 14v will be sent to the battery which will not be sufficient to charge the battery. So, how to solve this problem?
In an H-bridge circuit the mosfets will supply the full battery voltage to the load, if a 12V DC is connected to the H bridge mosfet drain, then this 12V will be alternately switched to the connected transformer primary.
If this is the case, then why use transformer with primary winding is half of the voltage of the battery in any H-bridge configuration? All inverters i have seen and repaired which are H-bridge configuration, uses transformer half the battery voltage. I opened a 48v -220v inverter yesterday, and the transformer is 26v primary and 220v secondary.
And if a mosfet of H-bridge gives full battery voltage i.e. 12v into 6v winding, then the output of the inverter should also double, like 440v thereabout.
Transformer winding will be half only when the H-bridge is a PWM based inverter, in which the load gets only the average 50% of the total Dc supply due to the PWM. If it is not a PWM then the load will get the full DC supply.
Thank you for the response. Now, in a PWM h-bridge, will this charging circuit be applicable?
The H bridge charger circuit shown above has nothing to do with H-bridge mosfets or PWM. In the presence of grid AC mains voltage, the transformer is directly connected with the battery through a bridge a rectifier and relays for the required charging of the battery.
I understand the circuit perfectly. My concern is the transformer. If AC mains is present at the 220v side of the transformer, then the other side of the transformer will have 6v because that is the default winding. Which is why I’m wondering if the 6v will work for charging a 12v battery.
Normally if the transformer is 12v-220v winding, then definitely there won’t be a problem. But since the transformer is not winded like that, what’s going to happen?
Yes, in that case a PWM based H-bridge cannot be used in this charger concept.
Thank you so much for the clarification sir. God bless you
You are most welcome!
Pls 24v ups my ups did not bring 230v output, it bring 170v why any help
Is your battery fully charged? And is the 170V with load or without load?
180v with load and battery is fully charge
Try reducing the load, and check the voltage. If the voltage rises with lower loads then the problem could be due to low power transformer and battery which are unable to handle the load that you are applying.
Helpful
does anyone has the PCB diagram to print a PCB form.
Thank you for your swift response.
I need your advice.
1) I want to use a 12-0-12v transformer with a 24v battery, what is your advice sir.
2) A 10amp 28VDC relay for this circuit been a battery charger inverter.
You are welcome Emmanuel!
1) It will work if your inverter frequency is PWM based and with 50% duty cycle
2) for 24v battery, the relay must be 24v also
Thanks sir.
In one of your article there is a diagram for 500w inverter. That is the diagram I am following. But in my case, my target watt is maximum of 150 to 200w. In other to achieve that, I didn’t use a transistor with the two MOSFET but I want to use every other components you have on the diagram.
So according to the diagram of 500w inverter.
1) Is it a PWM inverter or not.
I want to be clear on that sir.
2) And if it is not, how do I make it a PWM inverter with 50% duty circle as you have said sir.
Emmanuel, you can try the first or the second circuit from the following article, which are compatible with your transformer specifications.
The IC must be supplied 12V from a 7812 or any step down converter
https://www.homemade-circuits.com/modified-sine-wave-inverter-circuit-2/
Thank you for your apt response always.
Kindly help me with these analysis on the battery charger diagram if I am correct.
Relay 1 and 2 coils are connected before and after D5
The common pins are connected to the transformer
NO is connected to the appliance
NC is connected to mains input.
Please I want to know if I am correct with this analysis.
Thanks
That’s right, N/O of RL1 are also connected to the transformer 220V wires.
Thank you for your response. Please, how many pin does RL1 and RL2 has. Or probably not all the pins are used in RL2. Kindly help with this.
8 pin each, please Google DPDT relay you will easily get all the details.
EngineerSwagatam.
Good evening.
I am pleased to have found this page interesting and useful, as it teaches about power electronics. I am a hobbyist who recently dabbled in this investor issue. I have assembled this circuit in Proteus to be able to simulate it. But of course, the simulation is not given in the first instance since you have to understand the design. My big question: can this circuit work with the load and at the same time it can feed back the battery, in order to be able to work continuously 24 hours x 7 days? My thanks in advance for the attention given to this.
Atte.José Javier González.
Thank you Jose, I am glad you found this site useful!
Yes simulation might not sometimes give us the desired results, and we have to ultimately build and test a given project practically.
No, sorry, it is not possible to discharge a battery via an inverter and simultaneously charge the battery from its output, because the inverter will work with 10 to 20% losses which will never allow this process to succeed.
Swagatam Engineer.
Good evening. Thank you very much for your precious reply. I am studying all this topic regarding CA – CD Invertor based on your valued page www. His answer reveals the principle of energy: it is neither created nor destroyed. So based on this principle, do you mean I should design the circuit adding a second battery of equal voltage and amperage that feeds back the first battery? Or will the initial battery increase its capacity for the same inverter in question? My thanks in advance for the attention given to this.
Atte. José Javier González.
You are welcome Jose, no, even using two batteries will not help to produce power 24/7, eventually both the batteries will get exhausted.
Good day sir, an inverter I use well at home and charges well, when I give it to someone , it never charge a single volt with generator in that house because they don’t have power in the house. They use the generator to pump their 1.5hp pump. The inverter is serving during automatic changeover but not charging the battery at all. Please what could be wrong sir.
Adeyemi, please check the DC voltage from the generator which is used for charging the battery, that will clarify the situation.
Thanks for always being there, Swagatam. How can I appropriately rate the breaker in auto changeover inverter charging system against sulfation tripping off.
Sorry Adeyemi, I do not have any idea about it.
Thank you for circuit more grace.actually what if the relays fails won’t the be any disavantage on the mosfet.wont dey butn plz reply
If the relays fail, the circuit will burn, you can add a fuse to prevent that….
Dear Sir,
If seen carefully in the circuit, when on an idle state the relays are not activated and the mosfet drains have access to the trafo taps via relay 2……this will make the inverter function normally when battery is connected.
But the oscillator circuit is being continuously powered when the mains is active…….this has been un-noticed when you designed this circuit…..I found this through mental simulation.
The oscillator gets a half wave unregulated power from the transformer and remains continuously on while the battery is charging……how to avoid this?
I have bought all components and ready to make the circuit….please help here.
Dear Sherwin,
There’s no easy way to eliminate that, and anyway it does not matter because the oscillator wouldn’t draw more than some milliamps.
hi Sir, I need pure sine wave inverter without microprocessor
Hi Sunshine, I have explained many of them in this website, you can find them here:
https://www.homemade-circuits.com/category/dc-to-ac-power-converters/
Thank you sir for helping by posting circuits . How much is the current rating of the transformer if I want to charge 24v 18ah battery ?
Hi Nikhil, you can use a 24-0-24V/3 amp transformer, make sure the filter capacitor is rated at least 6800uF/50V
Ok thank you Sir . And Sir I am using eg8010 as inverter section , so how can I connect both battery and H bridge configuration in transformer .
sorry, it can be done only with the above shown configuration, other configurations may not work as inverter/charger using a single transformer.
Sir swagatam,do you mean h bridge inverters don’t use single transformer for inverter and charger? Many inverter chargers I have repaired only uses one transformer,and most of them you will see the transformer primary connected directly to the drains without the relays but they do charging,pliz enlighten me what happens and infact the mosfets uses for inverter are the same that do the charging. Help me understand more so with a non centre tap transformer.
Evans, Actually it can be done by isolating the transformer from the H-bridge through a relay, such that the relay disconnects the transformer from the H-bridge and the connects the transformer with a bridge rectifier and filter for charging the battery….it may be actually easier than a center tap transformer.
Hi swagatam thanks for your reply, please help me know this
1. Inverters with a non centre tap transformer and those with centre tap which one is more efficient in terms of service delivery and output wattage?
Evans, 2 wire topology is more efficient in terms of cost, size, wattage.
Also sir as you have indicated in your reply above concerning the use of a relay in isolation of transformer from h-bridge to bridge rectifier,help me know how to select the size of a relay that would be capable of handling the primary current of a 5000W inverter transformer to be able to charge 2×200AH batteries.
The relay contacts must be 2 times more than the specified charging current, for 400 Ah this could be a 80 amp relay
Also the relay should be able to handle current during Inverter and charging, urgently waiting to hear from YOU.
If you do not see the details, please tell me where to upload the pictures. Thanks again
the links which you are trying to send can be visualized only by you in your PC, it cannot be visualized by me or anybody else.
You can send the specifications in written, that will be enough, image is not required.
Technical data
maximum head MCA 5,7
maximum flow cm/h 2,7
power supply v/hz 230/50hz
fluid temperature grdC 2-95
ambient temperature grdC 0-40
storage temperature grdC -20-70
mahimum percentage % 40
ECM equipment regulations cf EN 610-3-2/EN 61000-3-3/EN55014-1/EN55014-2
Ferroli Energy Saving (ES) 25-60 /180 is an eficient electronic glandlles pump driven by a permanent magnet synchronous motor,fitted with frequency (inverter technology) The pump body is made of cast iron treated by cataphoresis to withstand the corosive action of the condensate.
TECHNICAL SPECIFICATION UM lt it 25-60 / 180
Gelu, I only need the voltage and wattage of the pump, and whether it is a DC or AC, please provide these info, the voltage seems to be 230V AC, so just provide the wattage…
Hello Mr Swagatam. I very much appreciate your posts. Coming for years. I have to help with an inverter scheme for this pump. What scheme do you recommend? Thousands of thanks. Excuse me for my bad english. Please email me gogutu68 @ gmail.comfile:///home/probe/Desktop/pompa_es_2_dr_web.png
Thank you gelu, the shown link is not working in my PC. and also you will have to provide the technical specification of the motor in detail so that I can suggest you the right circuit
I have 600 va ups transformer but i dont know its secondary winding there are so many wire. How can i identify this??
Could you identify the primary winding which is supposed to be connected with the mains AC?
Sir i know the 12-0-12 winding detail what i need is the coils connected to ac mains
Elec, take another 12-0-12V known transformer, connect it to AC mains and feed its 12-0-12V AC to your UPS transformer’s 12-0-12V wires, now check randomly across the output wires to find which one gives the accurate 220V, or 230V
Thanks for helping now i got the right winding
If i want 500 watts from 12v 7ah battery how much amp transformer is needed
getting 500 watt from 12V/7AH is not possible…you will need a 200 AH battery for that
If i use 2n3055 transistor instead of mosfet do i need to change the resistor
you will need to add additional driver stage as this
https://www.homemade-circuits.com/50-watt-inverter-might-look-quite/
Can i use 12-0-12 1 amp transformer and 4 ampere transistor for working 15 watts soldering iron
yes will do!!
The transistor heats up when i use ferrite transformer but when i use iron core it didn’t get heatup at all. The ferrite transformer i use is got from from a old 120w inverter i am only using your Oscillator section of your circuit
ferrite trafo will require a high frequency in the order of 20kHz, for iron core it is just 50Hz which is not compatible with ferrite core trafo
Is there any problem if i overlap the winding of the transformer because i am making the transformer my self
yes, the efficiency will be greatly affected.
Hie Sir
Is the polarity of C5 correct?
Hi Francis, sorry it’s a mistake, please connect the positive lead with positive of bridge….
I have just constructed a similar inverter /charger but for the oscillation I used SG3524 ic. When I powered the inverter it worked great and when I plugged the AC mains it stopped inverting and stated charging the battery. But when disconnected the mains, I heard a continuous clicking sound from the relays and powered off the inverter but mosfet were shorted. Replaced mosfets again did the same but am sure I labled my relays correctly and I just switched the relays and no problem now worked. JUST DON’T KNOW HOW?
It will need to be examined carefully by switching the operations repeatedly, it will be difficult to judge without a practical test
Hi sir, I have successfully completed the project, but I just wish I could increase the power of the inverter through mosfet, can I use six mosfet in parallel in this circuit instead of two?
That’s great Frank, yesy ou can use 6 or more mosfets in parallel for increasing the power handling capacity along with the trafo and battery which will need to be equally upgraded
Please sir can I use100v 10uf in the place of c1 c2 c5 because I can’t find the real values in my area
No!!
Hello sir please c1 c2 c5 can I use 100v 10uf because I can’t find the real values
I would recommend to do exactly as specified in the diagram, any other values can be dangerous….for C1/C2 the values can be slightly changed, for C5 also the uF value can be changed but it must be strictly 400V rated
Hi Swagatam, thnx for the huge efforts, very helpful. I've a question plz, I am troubleshooting an inverter, it's not charging the battery anymore, the output goes to the battery is 7.5v, which should be no less than 12v. Plz what could be the reason for that?
Thanks in advance.
Thanks Taher, please disconnect everything that's connected with the transformer or the source of the supply, and check whether it reads around 14/15V or not, if yes then the problem could be somewhere in the adjoining electronics or controller which will need to identified appropriately….if the source shows less voltage then it will need to be replaced with a new one.
I get 474j/250v for c1 nd c2, will it be ok for the same value of r1 nd r2 which is 27k
(2) What if I use 1n4007 to protect my mosfet?
Tnks
it will do.
mosfets already have built in freewheel diodes there's no need of an external diode.
anyway 1N4007 will not be enough….you can try 1N5408 instead for your satisfaction.
Tnks for the reply
another question sir, (1) pls what will be the value of r1 nd r2 if I use 0.22uf electrolytic cap for c1 nd c2 to get the 50Hz, (2)what value of zener diode can I use to protect my mosfet from damage. tnks
1) you can use the followin softare for calculating them
https://www.homemade-circuits.com/p/transistor-astable-multibivrator-amv.html
use 1/50 = 0.02 for the time period slots
2) you can use 12V zeners although it won't be required if the supply is 12V
Hy I m bravo pls I don't see dat 0.47uf 100v cap in my area pls can I use 0.33uf electrolytic or pls give me any close value I can use anD for that relay I whan to use small 12v 500ma trafo to power d coils and the C3 I get 4700uf by 16v will all this be ok pls help me out. Tnks
Hi, 0.47uF, and 27K together are supposed to determine the 50Hz freq, 0.33uF will reduce the frequency….in that case you might have to increase the 27K to 33K or 39K to correct the frequency to the 50Hz level
Good Evening Sir,
Sir, can I replace C5 (that is 47uF/100v) with anyone bellow the or little above the specified on?
And for C6 (that is 105/400V) with 104/630v or 104/250v.
Thanks you Sir.
Aminu, the value needs to be little bigger, 105 or 104 will not be suitable, you can try 10uF/250V
C6 cannot be less than 105, otherwise the relays will not operate, in fact you must use two 105 in parallel
Hey Swagatham there let me know your E-mail. So i can send you my design which has better charging and cuttoff option
Hi Syed, you can send it to admin @ http://www.homemade-circuits.com
Thanks i got it.
You are welcome Syed, yes it will work, but the heatsink will need to be adequately dimesioned and if possible cooled with a fan…
Thanks Swagatam this means alot. One more question if you don't mind "Do you think that two IRF3205 will do the job for 500-600W transformer with 200Ah battery." I'll share my design with you soon.
the load here are the relay coils which are strong enough to neutralize the initial switch ON surge…
Why there is no surge protection that is done because of the capacitor no polarized like 2.2uf 400V between the mains terminals LIVE and NEUTRAL
Thank you Syed, Half wave charging will not affect or harm the battery in any manner, you can improve the DC by increasing the filter capacitor value to some higher value….for example a 10,000uF could be tried t enhance the DC quality for the battery.
Hello brother, as i look the diagram i see that battery charging system is half wave rectification when relay switches by mains 220v doesn't this damage the battery? Your design is simple than mine i designed using microcontroller. But i am still looking for the best charging method with cutt off for a 200Ah battery. I am using irf3205 mosfets and a 600w transformer. Any suggestion ? I will appreciate! Thanks and your posts are always amazing and informative
Hi Swagatam? What controls the charging time so as not to overcharge the battery? Thanks.
Hi Joseph, over charge cut off is not included in this design but since the battery is charged only upto 70% it won't harm the battery
Ok thanks.
Hai, great cct