Ignition Driver Modifications

[Suraj143]

Guys I build this ignition driver & all its working.I use this circuit for a small distance fence.

The only problem is sometimes the NE555 is burning out while in the running mode.At that time I can say the 555 frequency varies.

How to overcome this problem?

I use an oil type ignition coil.The pulse timing is 30mS ON time for a 1 second period.

Thanks

 

[alec_t]

I'm guessing voltage spikes when the FET switches off are somehow getting back to the 555. The 1N4007 used for D3 is probably too slow to prevent the spikes. Try replacing it with a suitably-rated Schottky diode.

 

[crutschow]

Try adding a larger capacitor (>1μF) in parallel with C4.

 

[DerStrom8]

I've built circuits like this a few times as well. I've had problems with circuit spikes, primarily when using Silicon diodes (1N4007). A proper freewheel diode is very important, and as mentioned already, schottky diodes are ideal, as they can be fast enough to suppress the spikes. So in short, I agree with alec_t, and I speak from experience. You wouldn't believe how many 555 timers I've destroyed on circuits like this when using a standard silicon diode instead of a schottky. I personally recommend a heavy-duty STPS1545D. However, if you can't find one, a 1N5817 will probably be ok, though the forward current is rather low (1 amp).

 

[Suraj143]

Brilliant information guys.Never heard such a thing.

Thank you very much for the modifications.I'll add them.

 

[KeepItSimpleStupid]

I would agree with no diode across the coil.

Also, I think it would be OK to use a series resistor with the coil, to limit the current. You don't want to kill anything.

Lifetime could be increased if you changed to a switching regulator for the power supply and you may even be able to use the CMOS version of the 555.

My $.02.

 

[DerStrom8]

I would agree with no diode across the coil.

KISS, you NEED a freewheel diode across the coil to prevent dangerous reverse EMF spikes.

Also, I think it would be OK to use a series resistor with the coil, to limit the current. You don't want to kill anything.

I wouldn't recommend this, personally. These coils need a fair amount of current to operate at the proper level (usually around 5-7 amps). A resistor is not only unnecessary, but would actually decrease the efficiency and output of the coil.

 

[ronv]

He has a snubber with C6/R5, but I think R5 should be 10 ohms not 10K ohms.

 

[KeepItSimpleStupid]

My comment came out wrong. I meant it to be interpreted as "I agree with the comment of there is no free wheeling diode across the coil"

The resistor.

As for the resistor. I think you would still want to current limit the output. Secondary side current limiting might be tough. It was customary to use a resistor in automotive ignition circuits to prevent burning of the points. The resistor was switch in, after the car started. There was usually a big white ceramic resistor on the firewall. So, I firmly disagree.

For reference: **broken link removed**

 

[DerStrom8]

My comment came out wrong. I meant it to be interpreted as "I agree with the comment of there is no free wheeling diode across the coil"

Oops, that was my mistake. Misunderstood what you said. There is a freewheel diode of sorts across the FET, but it is a 4007 and should be changed to a Schottky.

The resistor.

As for the resistor. I think you would still want to current limit the output. Secondary side current limiting might be tough. It was customary to use a resistor in automotive ignition circuits to prevent burning of the points. The resistor was switch in, after the car started. There was usually a big white ceramic resistor on the firewall. So, I firmly disagree.

Ah, I see where you're coming from now. You're talking about the ballast resistor. In an automotive application it's used to prevent the battery from draining too quickly when the alternator isn't running at full speed. It's connected to the primary, not the secondary. There probably isn't any real need to limit the output current unless you plan on having almost steady operation. However, since the OP said it's on for 30mS per 1S interval, I don't think it's necessary. The system should be able to cool down enough between pulses for it not to pose a threat. I suppose it couldn't hurt, but I don't think it would really help much. If you have a high power ceramic resistor hanging around somewhere, go ahead and throw it on the output. Otherwise, I wouldn't worry about it.

 

[KeepItSimpleStupid]

A resistor if picked properly, could also act as a fuse.

I don't particularly like this thread because of the lack of current limit controls on the system and the POTENTIAL of being lethal to people. I'm wooried more about something happening like this: https://www.ebaumsworld.com/jokes/read/80833133/

How do you know if the system is working?

There is the old trick apparently my grandfather played on somebody when someone had to go to the bathroom on the farm and the electric fence was nearby. I don't know if it was true or not. Aside: I do remember when my uncke and grandfather were castrating pigs with a sharp razor blade on top of a 55 gallon drum and they said "you want to be next". I was probably under 10 years old at the time.

 

[DerStrom8]

A resistor if picked properly, could also act as a fuse.

I don't particularly like this thread because of the lack of current limit controls on the system and the POTENTIAL of being lethal to people. I'm wooried more about something happening like this: https://www.ebaumsworld.com/jokes/read/80833133/

Quite the story. The benefit of using an ignition coil is that they can't usually produce much output current, especially not with a 555 timer driver, and at that frequency. It sounds to me like the transformer in that story was a heavy-duty, constantly-running one. It'e extremely unlikely that an ignition coil driven by a 555 timer with the described duty cycle would be really dangerous. I've gotten my fair share of bites from those things. They hurt, sure, but the frequency is high, current is low, and it's easy to let go.

I understand your caution, though, and I agree. As with all high voltage projects, I strongly urge the OP to exercise extreme caution when using this sort of thing. Electricity can be very unpredictable. You need to develop safety rules, warning signs, and emergency shutoff options just in case something goes wrong. Be very careful and use common sense.

 

[Suraj143]

I understood guys.

So the same thing happens to me in my earlier project.It uses a 16X2 character LCD.When the contactors are ON/OFF the LCD gets blank out.The noise is being added to the LCD module.
The same freewheel diode is being used 1N4007.I think thats the problem. I'll replace it with a Schottky as well 1N5817.

I just noticed for the snubber I used 10K & 0.1uF(400V).As ronv said I'll change that resister to 10 Ohms.

Thanks

 

[KeepItSimpleStupid]

Some 40 years ago, I made probably 10" sparks from an ignition coil. I think they would have hurt. The sparks burnt holes in paper. The frequency I used to drive the coil was probably around 300 Hz 50% duty cycle.

 

[DerStrom8]

Some 40 years ago, I made probably 10" sparks from an ignition coil. I think they would have hurt. The sparks burnt holes in paper. The frequency I used to drive the coil was probably around 300 Hz 50% duty cycle.

The largest I ever made was about 6 inches, and it would have hurt like the dickens! I used a light dimmer/capacitor setup and was able to get quite an output from that coil. Unfortunately it also burnt it out pretty quickly

 

[Suraj143]

Form the above design I get only 2cm spark length.

I use 30mS for a 1second period.Never tried varying the frequency higher.Because I need to use this design for 24hours.

 

[DerStrom8]

Form the above design I get only 2cm spark length.

I use 30mS for a 1second period.Never tried varying the frequency higher.Because I need to use this design for 24hours.

2cm sounds about right. The circuits I used to get 6 inch arcs were over-driving the coil. 2cm is roughly 20kv, which is generally the voltage ignition coils are designed to run at. Higher-end ones produce closer to 50-80kv.

 

[KeepItSimpleStupid]

I was overdriving too. I think I used a 6V coil. fun stuff when your 15 YO, right.

My science experiment required me to make a 3 KV power supply. I won an Honorable mention in a regional science fair.

 

[Bob Scott]

Hi guys.

I have some on-topic questions:

1. Do any of you guys know what is the turns ratio of a typical ignition coil for a car?
2. The typical inductance of the primary winding of the ignition coil?
2. The value of the "condenser" capacitor wired across the points in the older style auto?

I also once made (in 1985) a circuit similar to the one posted, but with a tiny half wave dipole antenna at the spark gap for use as a TVRO C band satellite jammer. Don't ask, there was a labour dispute at the TV station where I worked. My circuit also kept eating output transistors, so it was never used. After the lockout and the dispute was over, I learned that another team of locked out employees had climbed up to the station's roof and completely destroyed the station's main 20 foot fiberglass antenna using axes. In little pieces it was.

 

[DerStrom8]

Hi guys.

I have some on-topic questions:

1. Do any of you guys know what is the turns ratio of a typical ignition coil for a car?
2. The typical inductance of the primary winding of the ignition coil?
2. The value of the "condenser" capacitor wired across the points in the older style auto?

I also once made (in 1985) a circuit similar to the one posted, but with a tiny half wave dipole antenna at the spark gap for use as a TVRO C band satellite jammer. Don't ask, there was a labour dispute at the TV station where I worked. My circuit also kept eating output transistors, so it was never used. After the lockout and the dispute was over, I learned that another team of locked out employees had climbed up to the station's roof and completely destroyed the station's main 20 foot fiberglass antenna using axes. In little pieces it was.

1. Turns ratio is usually 100:1
2. Primary inductance is about 8mH
3. I think it's about 0.2μF