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Need Help with off the line Ignition coil driver.

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chingyg

New Member
I recently come across a few old ignition coil lying around the house, so I decide to build a driver to use it to make arcs and etc. I started with the 555 based ones but obviously they are not giving enough power, so I moved on to off the line drivers, but my problem is that my SCR based design can only operate at line frenquency of 50Hz. which is to low to excite the coils fully. Can anyone offer me some sort of advice as to how to alter the frequency of an off the line ignition coil driver. or maybe a complete new design of a off the line ignition coil driver. Much appreciated.
I am using this design.
 

Sceadwian

Banned
What frequency are you looking for? and one quick question, what's the DC resistance of your primary coil?
 

chingyg

New Member
I have no idea, I do not have the equipment to work out the resonance frenquency, I am hoping for one that can tune from 50Hz to maybe 1 or 2 KHz. the dc resistance is about 4 ohms.
 

Willbe

New Member
It's a ~100:1 turns ratio with ~20kV on the secondary depending on the size of the gap it's powering, so you might just use a step-down xformer or dropping resistor from the 230vac., but the coil is not designed for continuous use.
Don't run the coil with the sec. open-circuited, it overstresses the insulation.
 
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chingyg

New Member
I am using a fat incendiary light bulb as a ballast, it should pump too much current through the primary. and the hole setup is in a fish tank with oil, but the main thing is that at 50Hz the arc (spark) is pathetic. When I use a 555 based driver at higher frequency then the arc is juicy and hot, but I cant get enough power. As I said earlier I am looking for one that runs off the line and have a higher frequency.
 

Sceadwian

Banned
If the primary coil is 4 ohms couldn't you feed it from a power audio amp?
 
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chingyg

New Member
provide if I have a old audio amp. The thing is no one would give a 17 year old guy in South Africa an old amp to play with, not even my parents and the other thing is people don't throw away things here. sorry man, Id look into it but don't think it would solve the problem.
 

chingyg

New Member
I still prefer the SCR based capacitor discharging driver. My thing is that The SCR cant switch it off automatically so I have to syn it with mains. I just checked that PowerLab claimed that They have got a SCR based off the line driver that can operate at 6kHz. However they offered no detail of the circuit. What a pity.
POWERLABS Ignition coil drivers page!
 

ccurtis

Well-Known Member
I recently come across a few old ignition coil lying around the house, so I decide to build a driver to use it to make arcs and etc. I started with the 555 based ones but obviously they are not giving enough power, so I moved on to off the line drivers, but my problem is that my SCR based design can only operate at line frenquency of 50Hz. which is to low to excite the coils fully. Can anyone offer me some sort of advice as to how to alter the frequency of an off the line ignition coil driver. or maybe a complete new design of a off the line ignition coil driver. Much appreciated.
I am using this design.
Seems to me your images are a good way to go. Why not try them? In a), you can switch the gate of the SCR with a 555 timer substituting for the switching of the 12 VDC. You can do that switching at a rate in the KHz, while still powering off the mains. The SCR will not stay stuck-on because the counter EMF from the coil will turn it off. In any case, a TRIAC could be used instead.
 
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Willbe

New Member
See if you can find the rise/fall time of the primary winding voltage for a 6v/12v breaker point system, using the quenching capacitor across the points. This will give you some idea of what kind of square wave you need to feed this thing.

These non-electronic systems also used a thumb-sized PTC series ballast resistor to try to maintain constant coil current as the car speed increased (which cut down on the dwell time available to build up to max coil current).

With these waveforms and currents you can design a comparable AC-fed system.

It's gotta' be on the Web somewhere. You might try auto ignition system diagnostic waveforms. There was the "parade mode" [slow sweep speed] and the other o'scope mode which let the tech look at a closeup of rise/fall times. It was slower than nanoseconds, for sure.

Also check capacitor discharge ignition systems. These had higher energy at high engine speed because they didn't depend on the dwell angle. In the late 60s, Delta made an aftermarket version. The first ones had very low current through points and so the points did not self-clean by arcing. Later versions put a few hundred mA through the points to fix this problem.
 
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imix500

Member
I had a circuit at one time doing this very thing. I think it used a triac with a diac on the gate to self trigger off the mains. I'll see if I can find it...
 

ccurtis

Well-Known Member
I've am aware of the usage of common lamps dimmers to provide the input to the ignition coil. The steep rising edges when the triac turns on near the peak of the cycle (where its use as a dimmer would result in a dim lamp) jolts the primary. I don't know any of the details.

As a read the OP, though, he wants to experiment with higher frequencies.
 

chingyg

New Member
The thing is I am also greedy, got 2 coil in anti phase, so the DC resistance is something like 2 ohms.
 

chingyg

New Member
Seems to me your images are a good way to go. Why not try them? In a), you can switch the gate of the SCR with a 555 timer substituting for the switching of the 12 VDC. You can do that switching at a rate in the KHz, while still powering off the mains. The SCR will not stay stuck-on because the counter EMF from the coil will turn it off. In any case, a TRIAC could be used instead.
That might actually work. but then I tried it on a simulator (MultiSim) it failed. Isn't that because the counter EMF is only generate when the current in the coil is interrupted when the SCR or TRIAC turns off? So one need to turn off the SCR to turn it off, if you know what I mean.

But I am not so sure, I am only into electronics for a few month.
 

chingyg

New Member
I had a circuit at one time doing this very thing. I think it used a triac with a diac on the gate to self trigger off the mains. I'll see if I can find it...
Something like this?

It doesnt work on a simulator though.
 

unclejed613

Well-Known Member
Most Helpful Member
i've driven ignition coils with amplifiers before..... they self-resonate at about 2khz. you could try a 555 driving a power transistor. run the 555 at 2khz. connect the transistor across the primary side of the coil with the coil common grounded. connect a 3 amp fast rectifier from ground to the transistor collector with the cathode going to the collector. set up the 555 so that it's on time is about 10% of the total cycle (10% duty cycle). this will turn the transistor on for 10% of the time. during the on time, the collector is close to ground potential, placing a short across the primary terminals of the coil. when the 555 output goes low, the transistor becomes an open circuit and current flows through the coil building a magnetic field. when the 555 goes high again, the transistor shorts the coil, collapsing the field. the current through the coil (from the collapse of the magnetic field) flows through the diode and a voltage spike is created on the secondary. you should use a heat sink on the transistor, since it's on current will be very high (which is the reason for such a short duty cycle). even better would be a large power MOSFET instead of a bipolar transistor since it doesn't put too much of a load on the 555. i can work up a schematic if you want....
 

ccurtis

Well-Known Member
That might actually work. but then I tried it on a simulator (MultiSim) it failed. Isn't that because the counter EMF is only generate when the current in the coil is interrupted when the SCR or TRIAC turns off? So one need to turn off the SCR to turn it off, if you know what I mean.

But I am not so sure, I am only into electronics for a few month.
Your reasoning is sound. But, the secondary field will collapse, after the capacitor is discharged, which gets reflected back to the primary. This effect might not be included in your simulation.
 

chingyg

New Member
i've driven ignition coils with amplifiers before..... they self-resonate at about 2khz. you could try a 555 driving a power transistor. run the 555 at 2khz. connect the transistor across the primary side of the coil with the coil common grounded. connect a 3 amp fast rectifier from ground to the transistor collector with the cathode going to the collector. set up the 555 so that it's on time is about 10% of the total cycle (10% duty cycle). this will turn the transistor on for 10% of the time. during the on time, the collector is close to ground potential, placing a short across the primary terminals of the coil. when the 555 output goes low, the transistor becomes an open circuit and current flows through the coil building a magnetic field. when the 555 goes high again, the transistor shorts the coil, collapsing the field. the current through the coil (from the collapse of the magnetic field) flows through the diode and a voltage spike is created on the secondary. you should use a heat sink on the transistor, since it's on current will be very high (which is the reason for such a short duty cycle). even better would be a large power MOSFET instead of a bipolar transistor since it doesn't put too much of a load on the 555. i can work up a schematic if you want....
Thanks man, I know what you are talking about. The thing is my The only power supply i got is a 30V 4A transformer and a 12V battery. And I hate replacing MOSFETs. Their don't live long. (I think I am to clumsy, Last time I was tuning the pot of the 555 and guess what I accidentally pulled it out of the socket, making the 555 constantly on, and I got no switch on my circuit and have to get up and pull out the plug form the other side of room, by the time I got there the mosfet is almost melted on the heat sink. Haha)
is it something like this?
 

chingyg

New Member
Your reasoning is sound. But, the secondary field will collapse, after the capacitor is discharged, which gets reflected back to the primary. This effect might not be included in your simulation.
Ha Eureka, never thought of that. You are a star.
 

tcmtech

Banned
Most Helpful Member
Here is an actual Line voltage driven CD type ignition coild driver circuit.
This circuit is very adaptible and forgiving.
 

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