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Ignition coil driver?

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LAN_403

Platinum

Thu Nov 29 2012, 05:31PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

There's been an ignition coil sitting in my junk box for months, and I've never driven one at they frequency they like. Only on ZVS (I couldn't get ZVS frequency quite low enough.) So I want to dive it via dimmer switch.

I'm going to buy one of them tomorrow at B&Q, should I get the highest wattage one? and also what capacitors do I need to use in series with the coil? And also is there any type of dimmer switch that only works with this type of driver?

GrantX

Fri Nov 30 2012, 02:35AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

I believe you need a trailing edge dimmer (that means it cuts the waveform short after allowing it to rise slowly. A leading edge dimmer will switch on hard then allow the waveform to drop slowly to zero). This resultant sharp waveform allows flyback style ringing. I used a 400W dimmer, but you might get away with using a smaller one.

Usually the best cap is an AC motor run capacitor, some where from 1uF to 10uF, with a decent voltage rating. When I played with the dimmer circuit I used a 450VAC 4uF PP motor run cap. The cap is essentially just current limiting, so you just pick a rugged cap of suitable ratings.

As usual, take precautions when working with mains power, it may be best to fit a bleeder resistor to the cap, believe me a few uF at a couple of hundred volts hurts like hell.

Eventually my dimmer gave out and died, for unknown reasons. It could perhaps be reasonable to protect the dimmer with a snubber of some sort?

Platinum

Fri Nov 30 2012, 09:39PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

They are cheap enough so I won't mind if it does give up. I'll buy a 700watt one tomorrow, also will mkp or MOC's works?

zippotix

Sat Dec 01 2012, 12:03AM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86

MOC will work. The wattage should be above 400, if I remember correctly, I used to drive a ignition coil with a 400W dimmer and 1uF MOC, and it runned fine, no overheating or anything.

Platinum

Sat Dec 08 2012, 10:56PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Right then what do I do, the dimmer has L1, L2 and com, can anyone show me a simple schematic for this?

zippotix

Sat Dec 08 2012, 11:12PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86

I have the old type of dimmer, just two connectors and some clamps for mounting. Anyway, the dimmer must be in series with mains and capacitor, you could try using L1 and L2, im not sure what this com is. Here is a simple schematic

The cap in this schematic is rated at 600V, but 2100v MOC will be just as good if not better.

GrantX

Sun Dec 09 2012, 01:54AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

Hmm, all dimmers I've encountered only have two connections, to allow the dimmer to be wired in series with its load. However it is possible that other dimmer models may need a neutral connection (com), however I can't be sure why.

Also, an interesting note: All ignition coils I've tried that possess a FULL core, without air gap, which are mainly the "high performance" E-core coils (and perhaps C-core) perform very poorly on a light dimmer, possibly due to saturation, honestly I don't know. In order to achieve a decent spark you will want the old oil-can type, which only has a straight piece of iron for a core.

Platinum

Sun Dec 09 2012, 10:05AM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

The type of coil I have is old I think, it's shaped like a taller thinner pop can. It's the old type.

Proud Mary

Mon Dec 10 2012, 11:32AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Platinum wrote ...

The type of coil I have is old I think, it's shaped like a taller thinner pop can. It's the old type.

There are two basic types of these ignition coils: the ballasted, and the unballasted.

The ballasted type has a lower primary impedance and is designed for operation in low battery and hard-to-start cold engine conditions, where it allows a bigger spark at start up. Once the engine has started, a relay connects a ballast resistor in series with the coil primary, reducing its current. If a ballasted type were to be used without the ballast resistor, it would overheat and perhaps damage the distributor points and erode the sparking plugs too.

The unbalasted type does not have this high power at start feature.

The HV experimenter will get bigger sparks for their money from the balasted type - used without the ballast, of course!

Newton Brawn

Sun Dec 23 2012, 04:35AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi !

Some old ignition coil are oil filled and aluminun case that are connected to the primary and secondary. SOOoo be careful to avoid the electrocution or short circuit,

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