Electronic spark generator/igniter

[kwame]

I want to harness LPG gas to provide heat for my birds at night during power outage.I have read at length about the spark generator but it is above my head as the hardware is virtually non existent in this part of the world.
I want to use a 121VDC thermostat (powered by car battery) to turn the spark generator on/off to provide optimal heat within the brooder.
Folks i need help to identify the right affordable , 12VDC ,reliable spark generator for this task.It is intended to ignite a gas burner ;a solenoid valve will put out the fire when necessary by shutting of LPG to the stove.

Kwame

 

[MikeMl]

Here in the USA, I would run over to the local Recreational Vehicle dealer (trailers, caravans) and buy a replacement 12Vdc igniter for the LP Gas furnace, refrigerator, or hot water heater. Do you have any similar appliances that run on LP Gas?

 

[tcmtech]

A simple DPDT relay set up to make itself cycle on and off with one set of contacts and power a basic automotive ignition coil and condenser with the other set works very well as a simple spark generator.

Just put a capacitor in parallel with the relay and it will make nice slow spark pulses.

With the right resistance in series with the primary of any common ignition coil and condenser from a small engine like a lawn mower or chainsaw this setup will work just fine as well off of any 12 volt battery.

 

[dr pepper]

Excellent idea tcm.
I was going to suggest an ignition coil driver circuit, they are all over google, just a 555, fet and a auto ignition coil, I've used a similar setup as the hf start on a vehicle based tig welder, vibrating relay contacts is a very similar system as used on the 1930's ford model T ignition, it worked for many thousands of them.

Strictly speaking for your application safety wise you really ought to have a burner control module, so that safety functions are included so you dont get the gas valve open without a flame, amongst other things.

 

[dr pepper]

Well it just so happens I have a coil and other bits in my bench so I tried tcm's suggestion.
My version doesnt have a cap in parallel with the coil, that I havent got, and its very violent with the relay contacts, and probably intereferes with everthing around it, the relay contacts light up nicely.
Heres a quick and nasty vid showing the relay, coil and the resultant spark, the latter would be very much bigger with a cap accross the coil.
Operation for more than a few secs would get the coil hot, most later cars have constant energy coils which operate at a constant dwell angle therefore they have a very low dc resistance and pull lots of current.

https://www.youtube.com/watch?v=dr0ezNggX48&feature=youtu.be

 

[tcmtech]

I see I need to elaborate. The capacitor in parallel with the relay coil needs to be a few hundred uf or more so that whenever the NC contacts hit they charge up the capacitor and keep the relay energised for a second to two before resetting. Tick.... tick.... tick.... tick.... at one to two second intervals should be what you are getting.

Also for the ignition coil the condenser is necessary and needs to be parallel to the NC contacts that are controlling the ignition coil. ost any non polar higher voltage rated (250 VAC or more) with a .2 - 2 uf rating should get you going.

Ideally the capacitors/condensers uf value needs to be a good match to the coils inductance so that it creates a nice uniform LC tank circuit. That make the ignition spark the hottest while keeping the contact arcing to a minimum.

Relating to the ignition coil if the primary resistance of the ignition coil is low enough to allow it to conduct more peak current than what the relays contacts are rated for a series resistor will be needed. For a 12 volt ignition circuit you will need a total of 10 - 30 ohms of primary circuit resistance depending on the size of your coil and how hot of spark you want.

When designed right you should get a nice hot popping spark off the ignition coil every second or two with very little arcing at the relay contacts.

 

[dr pepper]

Yes of course.
I threw this together with junk at hand just to see if the idea works and it does, I dont have large caps suitable for either the relay coil or and esp the tank circuit part of the ignition coil.
The circuit is very much like the old marconi oscillator, one of the first radio transmitters.
Heres the hf start circuit I put togther for my mobile weld set, the circuit below is the spark gap osc with cap array (in series for extra volts rating), and the board above is just a 555 pwm circuit, I think it generates 100hz or so, the big black thing covered in heatshrink is the coupling transformer, its full of ferrite rings, hf from the spark gap osc goes in on 7/0.2 cable and effectively comes out in series with 200amps of weld current on the 12 guage black cable, you can see the hf spark where the tie wrap is:



Its also really good for stick welding rusty old junk too, it bites through rust, with an agrresive 6010 rod you can weld better than you'd think through paint, rust and crud.