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circuit help

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TACAMO

New Member
I going to build this circuit and was wondering what the 10k pots controlled, which one controlls what
.
 

MikeMl

Well-Known Member
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BrownOut

Banned
I built this circuit. The 555 blew after only a few minutes of operation. High voltage surges propagate from the coil and destroy everything in it's path, including regulated power supplies. Better, I think, to isolate the output to the coil, and use a high-voltage transistor. I'm working on a better circuit, but haven't found the time to build it yet.
 
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chemelec

Well-Known Member
Try My Circuit. It Works Good.
Car Ignition Coil Driver

But If you use these types of Circuits from a Power Supply, You need a LARGE Capacitor across the 12 Volt terminals of the Circuit Board. The Switching of the Coil Creates Large Voltage Spikes, that can Damage the 555.

This is Why "BROWNOUT" Blew his Circuit.

When Connecting to a Car Battery, Connect BOTH the PCB power and the Coil Power SEPERATELY and Directly to the Positive terminal. The Battery will act as a Low Resistance to Short out these Spikes.
 
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MrAl

Well-Known Member
Most Helpful Member
Hi,

One thing to keep in mind is that these circuits are boost circuits even without
the coil secondary. This alone could generate very high voltages for the transistor
and other parts. Some sort of clamp across the transistor or some other way
to manage the high voltage kickback spike of the primary would be a good idea.

Another thing to watch out for is the primary DC saturation. This could cause
very high currents to flow during the normal pulse time.
The telltale sign is when the current in the primary ramps up as usual, but
then suddenly exponentially spikes up really fast. The sudden current rise
is due to the inductor core saturation and hence a sudden decrease in
permeability.

I dont have much experience with automobile coils so i dont know how much
leakage they design in at the factory nor how much primary resistance there
is. The primary resistance may be set to limit current in the event of saturation.

Since the coil primary ends up having some DC current flowing too, it would be
interesting to try to drive the primary with an H bridge :)
I bet there would be some huge peak to peak output!
 
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TACAMO

New Member
I was exploring my junk box and found 4 IRF630 MOSFET. I was wondering if I could drive the 4 IRF630 with the 2N3055. So it would be 555 output> 2N3055> 4 IRF630> Coil.
 

Mr RB

Well-Known Member
...

I dont have much experience with automobile coils so i dont know how much
leakage they design in at the factory nor how much primary resistance there
is. The primary resistance may be set to limit current in the event of saturation.
...
Older car coils (for use with mechanical points) typically draw about 3 to 4 amps at 13v, and are driven from close to 50:50 duty cycle. They will also stand 13v for 100% of the time if your car stalled with th epoints closed.

Newer electronic ignition coils are usually about 7 amps and meant for around 10% duty cycle. Generally they will melt down (literally!) if the ignition fries itself and they are left at 13v.
 
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