Pellet Burner Controller Circuit

In this post I have explained a programmable sequential timer with controller circuit which may be used for automatically controlling a homemade pellet burner/boiler system. The circuit was requested by Mr. Vasilis.

Technical Specifications

I have used your circuit on my homemade pellet burner that uses a 12V Ac motor for the feeder screw running 8 sec on, 30 sec off , and it works great, my idea for my project was similar to your circuit,

I also have a monostable circuit istalled using the famous 555 ic for the igniter which is a 12V glow plug that stays on for 2-3 min which is enough to ignite the pellets, here is the fun part now,

I run in to some problems during ignition, my idea for this project was for me to use a plc controller for all the action, money is short and i find building the circuit more interesting.

My question is if i can produce a sequence of actions for the ignition process, when power on the circuit 8-10sec on time 30 0ff time for the feeder, at this point glow plug to stay on around 2-3 min, and the fan blower which is a 220Vac to pulsate for the shortest 2-3 sec on 10- 15 off to it's lowest speed if possible,

when fire is detected using a LDR to activate the second circuit ( 8 sec On 30 sec off)and the fan blower to its regular speed via a relay..

I hope i explained everything correct!

Analyzing the Circuit Request

Can you provide your requirement in a step-wise manner because I am finding it difficult to understand the sequence in the above explanation.

If you can provide the circuit operating sequence serially with the relevant timing functions, then I can try working on it.

Pellet Burner Circuit Specifications

There is a room thermostat that I turn on, which gives power to
the circuit.

1) Timer for the pellets- 15 seconds then off
2) Timer for the glow plug - 2-3 minutes then off
3) Timer for the fan - pulsing 2-3 seconds on then 30 seconds off
(this needs to cycle until the photo cell is activated,).
4) Photo cell - when it sees fire, it is to stop the entire cycle.
Then the next cycle begins:
5) Timer for the pellets - 8 seconds on, 30 seconds off until the water
temp reaches 75 degrees C (the boiler will cut the power at this temp).
So every time power in on it should do the steps above, I hope it's clear!
Let me know if you need more info..

The Design

The presented design of a programmable timer controller circuit for homemade pellet burner system looks  quite complex, but actually it's not, the design is simply a chain of  a few monostable, and astable multivibrator stages configured sequentially.

The entire circuit can be understood with the following points:

The circuit is initialized by applying power via a thermostat, as soon as its powered, current passes through C1 and triggers the stage#1 monosatble.

T1 activates the connected relay and the relevant load, and also ensures that the reset pin of stage#2 and supply pin#8 of stage#3 gets grounded so that they stay deactivated.

After the set time elapses, T1 releases itself and the connected load, triggering stage#2 into action.
Now T2 activates switching ON the relay and the relevant load, T2 also makes sure that the reset pin of stage#3 is held grounded so that it doesn't activate.

Once the set time of stage 2 gets over, the connected load is switched OFF and stage 3 which is an astable now gets activated.

Stage three toggles the connected load ON/OFF at some specified rate as per the duty cycle set by appropriately selecting the value R16.

The above astable remains ON until the pellets ignite, and the light from its glow activates the comparator associated with stage 4.

With the detection of fire the opamp output goes low grounding the reset pin of stage 3 astable, thus deactivating its function.

The opamp triggering in the process also activates another astable at stage 5 which just like stage 3 toggles a connected load at some specified rate determined by the evaluation of R24.

The last stage is responsible for heating up the boiler water whose temperature is monitored by the thermostat. Once the water temperature  reaches the set degree, the thermostat switches OFF power to the entire circuit so that everything is reset back to the original state, ready for commencing a

fresh cycle.

Feedback from Mr. Vasilis K:

Hello swagatam vasilis k here.

I have started putting the circuit together on a breadboard then i realized my mistake at (stage #3) which toggles the fan blower on/off will go off, which is no good as the pellets will go out if there is no air, please is it possible to make an add on to the circuit when (Stage #5) is activated the fan blower should be on steady!Also please can you specify the connections made between P1 , R18, R19, R20 really stuck at this point.

Thanks in advance
Vasilis K

My Reply:

Solving the Feedaback Question

Hi Vasilis,Please do the following modification:

Disconnect D2 connection entirely, it's not required. That'a all, this will rectify the issue.

The circuit additionally requires a few corrections as suggested below:

1) Put a 10K resistor across pin#4 and ground of strage#5 IC, which is missing in the diagram.2) The LDRs must be connected in parallel for better response and not in series as wrongly indicated in the diagram.

As regards the P1 setting, do it in the following manner:

initially keep the D1, R17 feedback disconnected.

Introduce the LDRs with the required amount of light from the burning pellets, and through some trial and error adjust P1 such that the output pin#6 of IC741 just becomes low or zero volts.

Now removing the light from the LDRs should make the output high or equal to the supply voltage, check this a few times to confirm the results.

That's all, the IC is all set.....now reconnect D1.R17 back in position.

Remember the LDR should not receive light from any external source, otherwise the whole circuit will malfunction.

I hope you got the points,

Prototype of Homemade Pellet Burner Design

The above circuit was designed by me as per the requirements requested by Mr. Vasilis.

Once it was completed, the unit needed some more refinements/enhancements and customizations for achieving improved optimization.

With the suggestions provided by Mr. Vasilis, we could together successfully implement the features.

The following discussion between Vasilis and me, and the video explains how things were put into place using a few add-on circuits with the original pellet burner design.

Customizing a Homemade Pellet Burner

Query: I have started putting the circuit together on a breadboard then i realized my mistake at (stage #3) which toggles the fan blower on/off will go off, which is no good as the pellets will go out if there is no air, please is it possible to make an add on to the circuit when (Stage #5) is activated the fan blower should be on steady!Also please can you specify the connections made between P1 , R18, R19, R20 really stuck at this point.

Answer: Please do the following modifications:
Disconnect the reset pin#4 of stage#3 IC from D2 and R13. Connect it to the anodes of two 1N1448 diodes joined together. Cathode of one diode now goes to collector of the stage#2 transistor and the other to the collector of stage#5 transistor. Also put a 10K resistor across pin#4 and positive. D2 and R13 are not required any more.

Put a 10K resistor across pin#4 and ground of strage#5 IC, which is missing in the diagram.

Another point, the LDRs must be connected in parallel for better response and not in series as wrongly indicated in the diagram.

I hope you got the points,

The first modification explained above needs correction.

Only D2 connection needs to be disconnected, rest of the things can be ignored. R13 is necessary do not remove it
As regards the P1 setting, do it in the following manner:

initially keep the D1, R17 feedback disconnected.

Introduce the LDRs with the required amount of light from the burning pellets, and through some trial and error adjust P1 such that the output pin#6 of IC741 just becomes low or zero volts.

Now removing the light from the LDRs should make the output high or equal to the supply voltage, check this a few times to confirm the results.

That's all, the IC is all set.....now reconnect D1.R17 back in position.

Remember the LDR should not receive light from any external source, otherwise the whole circuit will malfunction.

Feedback: Thank you! Going to work on it this weekend.

I might have messed up something up today, as i had the first 3 stages working perfect with the correct values for the timings on each stage,now i get no response, i am new to this as my job has nothing to do with electronics, i think i might stick with the 3 stages, can you please edit the schematic so i can ask help from a friend of mine, who actually makes a living from this repairing electronics...

Solution: OK Vasilis, in that case you can eliminate stage4 and 5 completely. Let pin4 of stage3 IC be connected via R13, that's all....no other amendments would be required.

Feedback: I wanted to let know that i am ready to test the circuit on the burner these days, as the first 3 stages work flawlessly with some slight accidental changes, pin 4 from stage 3 is now connected to positive leg of C4 at stage 2 with a 4.7k resistor also pin 8 from stage 3 is now connected to the collector leg of T4, I also removed the two 100K resistors as they preventing switching i guess from one stage to another, really happy with the outcome as it made me more excited to continue building the rest of the circuit, i hope you can guide me from now on with the rest of the circuit when you have some spare time!
I am greatful for all!

Reply: That's great Vasilis, but I think pin#4/8 of stage#3 IC should be connected exactly as I have shown otherwise the system might malfunction.
Removing 100k is OK, alternatively you can replace it with a 1M resistor.

Feel free to question if you have any doubts!

Feedback: I get the same result over and over when i connect the ic the way its shown on the schematic, when power is applied to the circuit first stage gets activated and within the predetermined time second stage gets activated as well, the problem is that both stages stay connected for ever. Also by changing the 100K resistors with 1M it made a difference the circuit works properly, only when its connected the way i reported it works as it should.
Thanks for your fast reply
have a nice day.

Answer: OK Vasilis, thanks!
Let's see how things work out finally.

Feedback: Well, it didn't work as i thought it was, i have stage 1&2 working properly with the timings and all set, problem is with stage 3, it's connected the way it's shown on the schematic, the problem is when it's switched on to stage 3, when off it's going back to stage 2 continuously this is the kind off problem i had since i started putting the circuit together!

I hope you have a solution for this, also thanks for your patience with me!!

Solution: Stage3 has no connection with stage2 so there's no possibility of the above thing to happen so it's difficult to understand the situation, may be it's producing false triggering of stage2. You can try connecting a 1uF/25V capacitor across base of T1, T3, this might stop from stage two or stage 1 from false triggering.

Feedback: I only have 2.2/50v will they do?Also when pin 8 from stage 3 when it is connected to the positive rail stage 3 comes up momentarily and stops, other than that it switches stages alright without the need of the extra capacitors, this would have worked out fine, running out of patience today as i have the burner all the wiring ready to test it..

Analysis: Stage3 is an astable meaning it will switch ON and OFF (oscillate) at some specific rate determined by its R/C values. For checking you can connect its pin8 to positive but you should connect it back to where t is connected after checking. Yes 2.2uF/25V will do.

Feedback: You didn't fully understand , language gap here, when power is applied to the circuit and pin 8 from stage 3 is connected to positive it's gets activated only once along with stage 1, when time elapses from stage 1 and 2 (2-3 min period) then stage 3 gets activated like its suppose to, i hope it's more clear now, i don't wont to bother you again today, i am just looking for a solution to my problem so i can troubleshoot this issue!!

Reply: yes, when power is applied stage3 might only momentarily activate. But as soon as stage1 relay driver activates, the transistor instantly grounds pin8 of stage3 making it dead.
If you want to avoid this, you can try adding 2.2uF capacitor which you have already have across positive and base of T2 via a 1K resistor. So now you don't have to connect the cap across the transistors which I had referred before.

Feedback: Thanks for all your help so far, i think i might stick with the first tip, having the two 2,2uf caps connected to base and ground solved the problem, stage 1,2,,3 are connected as shown on the schematic and working like a charm, also i will keep on working with the rest of the circuit as i don't like to quit that easily..

Reply: That's great news Vasilis, surely you will be able to complete it

Feedback: I have tested the other day the burner with the first 3 stages on the breadboard, the circuit so far works like it's suppose to work,i have a question if it's possible, when stage 2 elapses which is the glow plug, stage 3 gets activated. problem is pellets don't ignite within the predetermined time most off the times, with the result that the burning chamber gets filled with pellets and they go out, so here is my request, how to connect the op-amp to stage 3 so when the ldr's detect light only then to activate stage 3 and completely discard stage 5 which is over kill for my project, this way its more trouble free as it takes time for me to disconnect it from the boiler, take it apart and clean it, so it can start over again.

Analysis: For this to happen you will have to do folowing steps.

Remove D1, D2, R17, R25, R13, T7 these won't be required now.
Connect pin#6 of IC741 directly with pin#4 of stag3 IC.
Connect pin#7 of IC741 to T4 collector.
Use the LDRs in parallel and not in series as wrongy shown in the diagram.

Swap the pin2 and pin3 of IC741 with each other, this is IMPORTANT.

Once you do these, your circuit will respond as you have mentioned.

Make sure the LDRs do not come in contact with any external light.

Feedback: hanks for replying back ,a quick question just to make sure so i don't mess anything up, were do the ldrs and R19 connect now? Along with pin#7 that connects to the collector leg of T4? or to the positive?

Reply: It would be better to connect them to pin#7 so that all get the positive supply from a common point.

Feedback: I hope everything is well, i am having trouble with the op-amp as everything it's connected as you mentioned i don't get the expected results, pin#4 is connected to the output of the ua741 ic, the output is down to 1.9v but it keeps oscilating at power on, whenever i connect pin#4 via a 4K7 resistor to the collector leg of T4 the astable stays grounded, reply to this please when you get some spare time, i hope you have solution to this.

Solution: I would suggest that you isolate the 741 stage and test it separately first for studying it's performance. You can use artificial light source on the LDR to see how the output of the IC responds. Connect an LED with series 1K resistor across pin#6 and ground to see the output response.

Please refer to this link to know exactly how you need to configure the stage:

www(dot)technologystudent(dot)com/elec1/opamp3.htm

As shown in the link, you may try adding a transistor stage at the output of 741 for powering the astable.

Feedback: That did it, all 4 stages working like they are suppose to, I can't thank you enough for the time and effort, cold weather is on it's way, I will post a small video of the finished project soon!

Response: Congratulations Vasilis, that's great news!
You are most welcome!

Feedback: Hi Swagatam, I have a question regarding the 4060 ic wired as "one short timer." If it can power on the two monostables from the pellet burner circuit, output will be taken from pin #3 which is the last to count to the C1 stage, will that work?

When power is applied to the circuit, the first 2 stages should stay low until the time has elapsed. Pin #3 should be set to activate the cycle, so when I leave home in the morning, I will be starting the timer via the thermostat. Then when I get home, the burner should be running. Thanks so much for your help.

Analysis: I could not understand this "first two stages should stay low.."can you explain the procedures a bit elaborately.

Feedback: As per the circuit design there are 2 monostable circuits(Stage 1&2) when power is applied via a room thermostat it activates the cycle (Stage 1&2), my request is when power is applied after the predetermined time of the 4060 has elapsed, is to activate the cycle(Stage 1&2), as there is no need for the burner to run when no one is around, plus this would be ideal as it takes about an hour for the water temperature to reach at 75 celsius , I hope this is more clear now!

Reply: Please check out this post:

TESTED&WORKING, really happy with the outcome, i used the 2nd circuit with the relay as i didn't have that specific transistor, that would be my last request for you, i hope i wasn't that much of a pain, again really thankful for all the help and effort, god bless you!!

I have put both circuits on a pcb board, everything is working like a charm, ready to burn some pellets soon, i am looking for a 220 vac to 12 vdc transformerless power supply for both applications, can you recommend me one?

Thanks in advance!

Vasilis K

Response:

That's great Vasilis!For power supply i think it would be better to go for a ready made 12V/1amp smps adapter for this, because making a capacitive type cheap transformerless power supply could be risky and dangerous for your circuit.

Regards.

Feedback: I think this may be my last question for you regarding the pellet burner circuit. I was wondering if I can connect a simple latch circuit at the junction of T2 and C4, I want the relay to latch right after the time from the first monostable elapses, is this possible? Thanks.
Vasilis K.

Solution: yes it's possible. Actually you won't need an additional latch circuit because the first stage itself can be effectively used as a latch. You just have to integrate another transistor relay driver stage with the collector of the first relay driver transistor. Do the connection via a 10k resistor and that's it, as long as the first stage stays activated, the added relay driver will remain switched off, as soon as the first stage time lapses and it switches OFF, our second relay stage will latch up for the intended change-over actions.

Final Thoughts and Results

My pellet burner project is finally complete, everything works the way its suppose to work thanks to you. I have tested it several times with no problems at all.

I have used pins 1&2 from the 4060ic, pin#1 activates the fan blower and pin#2 is responsible for powering the pellet burner circuit.Pin#1 is connected to the fan as a normally open connection.

When it gets activated it runs for about 2min(Cleaning the ash).Then when pin#2 is latched, the fan gets disconnected and the 1st stage is running.

This is the auger feeder, for 30 sec, feeding pellets to the combustion chamber(with no air blowing the pellets away).

When time elapses from the 1st stage, the new relay driver you recommended, activates the fan blower along with stage#2 which is the glow plug(igniting the pellets), it runs about 3min.

Stage#3 is diactivated until fire is detected by the (LDR) which is placed behind the combustion chamber detecting light through a small hole.

I will build another timer with the 4060 ic which will power both circuits for greater time delays!
I made a short video of the burner running, you may see it here!
Homemade pellet burner

Really greatfull for everything!
Thanks again

Vasilis K