[SOLVED] Ignition Circuit Query

[betwixt]

The 555 works independently of the rest of the circuit, all it does is produce pulses. If the pulses are not there it isn't oscillating and that can only be a wiring problem or faulty parts. If your market sells power MOSFETS, look for one with > 100V VDS and at least 10A current rating, it shuld make a better replacement for the bipolar transistors.

Brian.

 

[RMMK]

I removed the 0.01uF capacitor connected at Pin 5 because it was faulty! Now the LED blinks rapidly when connected at pin 3!!!! Is it gonna make any difference if I just dont connect any capacitor at pin 5 of 555 IC???

 

[betwixt]

You can leave pin 5 disconnected but it is prone to picking up interference and in your circuit where there are high voltages and large current pulses there is likely to be a LOT of interference!

Any reasonable value will do, 0.1uF will be fine. It you make it too big (> 100uF ?) it will take a long time for the frequency to settle down after applying power.

Brian.

 

[RMMK]

You can leave pin 5 disconnected but it is prone to picking up interference and in your circuit where there are high voltages and large current pulses there is likely to be a LOT of interference!

Any reasonable value will do, 0.1uF will be fine. It you make it too big (> 100uF ?) it will take a long time for the frequency to settle down after applying power.

Brian.

Well I havent connected a capacitor at pin 5 yet because i am kinda in short of them! maybe I will do so tomorrow! I also reconnected the 5.6k ohm resistor at pin 3 and at the output where coil is supposed to be connected; i connected an led and it blinked rapidly! I think its a good sign! What do you think?? I am going to connect my Ignition Coil to it now and will see what happens next!

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Ahhhh!! It didnt produced any spark even though I was getting blinking LED at the output where Coil was supposed to be mounted!!!!! Is it because there is no capacitor I have connected at Pin 5 of 555 IC???

 

[betwixt]

Pin 5 is an input to the 555, in astable mode it gives you fine control of the frequency, the resistors and capacitor are the main frequency deciding parts. Leaving it disconnected or fitting a capacitor will not change how the spark is produced. The danger of leaving it without a capacitor is it will pick up some of the interference form the spark which in turn could shift the frequency, instead of getting a rapid 'click click click click' of sparks you could get irregular sparks or even screeching noises.

It is good you now have the blinking LED, it means the pulse that triggers the coil current is now being produced. I think the reason it doesn't work is that the transistors are not being changed from fully non-conducting to fully conducting as the pulse is fed to them. Try the changes I suggested and see if it works. As I said, it isn't how I would design it but it's good you are learning by experimentation.

Brian.

 

[RMMK]

Pin 5 is an input to the 555, in astable mode it gives you fine control of the frequency, the resistors and capacitor are the main frequency deciding parts. Leaving it disconnected or fitting a capacitor will not change how the spark is produced. The danger of leaving it without a capacitor is it will pick up some of the interference form the spark which in turn could shift the frequency, instead of getting a rapid 'click click click click' of sparks you could get irregular sparks or even screeching noises.

It is good you now have the blinking LED, it means the pulse that triggers the coil current is now being produced. I think the reason it doesn't work is that the transistors are not being changed from fully non-conducting to fully conducting as the pulse is fed to them. Try the changes I suggested and see if it works. As I said, it isn't how I would design it but it's good you are learning by experimentation.

Brian.

Umm the thing is that I have found out just now that my TR1 is faulty! the same was not the case when I connected it at first........ I will buy a new one tomorrow! As for the circuit u proposed, I will also buy the components needed for it tomorrow and will make it and tell u the results! Umm tell me should I use BJT's or MOSFET's in ur proposed design?? If u say MOSFET plzzzzzzzz redesign it for me and also tell me the part name of those MOSFET's....... that will be a great help to me! THANKS!!

 

[betwixt]

You can try this:

Sorry about the quality - it was scribbled and photographed on my phone!

It is completely untested, just drawn while I was working on something else and the values are not optimized but should work. I tried to keep as much as possible to the parts you already have but made these changes:

1. The 555 was producing a 66% on 33% off waveform, I changed the resistor values to make it about 90% / 10% because you only need short pulses of current.
2. (if I got it right) the output of the 555 is high most of the time so I added the bipolar transistor to invert the signal. It's collector should go high for about 10% of each cycle.
3. I changed to a MOSFET output transistor, these have much lower input current requirements than bipolar types so I increased the gate feed resistor to 470 Ohms, this also reduces the collector current in the bipolar transistor making it easier to find a suitable one.

You can use almost any small NPN transistor, and I would suggest easy to find MOSFETS are IRF530, IRF540 or IRF640 but any rated at >100V and >10A should work.

As I pointed out - it isn't tested!!! In a commercial design it would have several additional safety components but I kept it a simple as possible.

Brian.

 

[RMMK]

You can try this:

Sorry about the quality - it was scribbled and photographed on my phone!

It is completely untested, just drawn while I was working on something else and the values are not optimized but should work. I tried to keep as much as possible to the parts you already have but made these changes:

1. The 555 was producing a 66% on 33% off waveform, I changed the resistor values to make it about 90% / 10% because you only need short pulses of current.
2. (if I got it right) the output of the 555 is high most of the time so I added the bipolar transistor to invert the signal. It's collector should go high for about 10% of each cycle.
3. I changed to a MOSFET output transistor, these have much lower input current requirements than bipolar types so I increased the gate feed resistor to 470 Ohms, this also reduces the collector current in the bipolar transistor making it easier to find a suitable one.

You can use almost any small NPN transistor, and I would suggest easy to find MOSFETS are IRF530, IRF540 or IRF640 but any rated at >100V and >10A should work.

As I pointed out - it isn't tested!!! In a commercial design it would have several additional safety components but I kept it a simple as possible.

Brian.

Thanks a lot man........ I will definitely test this circuit out!!!!!!

 

[RMMK]

Thanks everyone especially Brian! My circuit is now working just fine...... BUT I will definitely make that circuit you proposed!!! THANKS!!!!!

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But now I require a Regulator supply for charging the 12V battery! 8-O!