Scooby Jonni

I was just browsing a forum when I came across this diagram for a flame kit: Webshots - Full Size Photo

Out of curiosity (and no i'm not thinking of making one) I tried to figure out how it worked as I would have thought you'd need a 555 timer. I couldn't but being a bit interested in electronics I thought i'd build it in a simulator and see if I could figure it out but it doesn't seem to work

Does anyone have any ideas how its supposed to work and what i've done wrong

Here's the simulator: Circuit Simulator Applet

And if you import the below code, you should be able to see my circuit.

Thanks.


$ 1 5.0E-6 10.20027730826997 56 5.0 50
178 288 96 416 96 0 1 0.2 -0.0013038439252010911 0.05 1000000.0 0.02 20.0
g 240 128 240 160 0
w 240 128 288 128 0
c 192 240 192 176 0 9.92E-6 -12.155407425567855
r 304 272 384 272 0 2.0
162 384 272 464 272 1 2.1024259 1.0 0.0 0.0
R 288 96 224 96 0 0 40.0 12.0 0.0 0.0 0.5
w 288 144 288 240 0
w 288 240 192 240 0
w 192 176 192 64 0
w 192 64 288 64 0
w 288 64 288 96 0
w 304 272 288 272 0
w 288 272 288 240 0
r 320 368 368 368 0 100.0
c 208 320 208 384 0 1.0E-5 0.0010
w 416 112 416 176 0
w 416 176 336 176 0
w 336 176 288 144 0
g 464 272 464 304 0

D4VEW557

well i cant see how it works either but i like that simulator where did you come by that.

john_s

iTrader: (1)

The lower relay switches on and off, causing the capacitor to charge and discharge (which keeps the relay switching on and off) and also allowing and breaking the current flowing through the coil, which creates the high voltage for the spark.

AndyC_772

iTrader: (2)

Nice little simulator, that Can't say I'll stop using LTSpice myself, but as a tool to help visualise what's going on it looks great!

When I import the circuit it looks incomplete, with a couple of components at the bottom not connected to anything. I can't view the original diagram either ("This photo may only be saved by friends ")

If you can fix either problem, I might have a chance of explaining how it's meant to work.

TimH

iTrader: (11)

Have had a quick look, and although I haven't 100% checked the relay pinouts, I'll hazard an educated guess.

In order to generate repeated sparks from the igition coil, you need to interrupt the +12V feed to the coil in some kind of repetitive way.

If you feed a relay coil through it's own "normally closed" contact, power is applied to the coil...which causes the contact to open...which causes the power to the relay coil to be removed...which causes the contact to close...which causes the power to the relay coil to be restored...etc.

Basically, a relay oscillator.

You can then feed the switched/oscillating +12V to the ignition coil and generate continuous sparks.

As an aside, the relay coil produces some lovely back EMF...I used to rig this kind of circuit up from a 12V power supply when I was a teenager. No ignition coil or anything, but by connecting a wire from the relay coil to my bedroom door handle, I could give my younger brother a nice (but safe) jolt when he tried to come in to my room

Scooby Jonni

I finally get it! after reading and rereading your replys and look at the diagram I finally understand how it work, it does seem obious now Thanks guys

Still not sure why the simulator circuit doesn't work, i think i need to do a bit more reading about capacitors and resistors then maybe i'll be able to figure it out.

Yeah I never thought of using a simultor before but my MAF died so I was looking into making a MAF sim and was chatting about PICs and ADCs with a coleegue and he mentioned it.

Yeah LTSpice does look good, just a shame about the price. There seems to be a few open source copys of it that I may try out. Ideally i'd like one that can simulate a PIC but I think i've got a bit of learning to do before I start doing anything like that. It's pretty good for a freebie though I must admit.

Ah yes thats my fault. I kept forgetting the default values do I put a couple of components at the bottom to remind me. Hmm, thats weired, it seems to work in firefox


I made an alarm once when I was younger but didn't thing of rigging a coil up to the door hendle

AndyC_772

iTrader: (2)

LTSpice is free...

The only trouble with using a relay like that is that it'll wear out in no time at all, especially if the design generates any arcing at the contacts. It's fine for something that's only required to oscillate slowly, like indicators, but to generate continuous sparks I'd look to use a transformer, an oscillator and a high voltage MOSFET.

Might just build one and wire it to the door knocker for Hallowe'en...

AndyC_772

iTrader: (2)

Got it... you have the relay contacts the wrong way round in your simulation, that's all:

$ 1 5.0E-6 10.20027730826997 56 5.0 50
178 288 96 416 96 0 1 0.2 -0.021278043592764733 0.05 1000000.0 0.02 20.0
g 240 128 240 160 0
w 240 128 288 128 0
c 192 240 192 176 0 9.92E-6 -11.522914889369343
r 304 272 384 272 0 2.0
162 384 272 464 272 1 2.1024259 1.0 0.0 0.0
R 288 96 224 96 0 0 40.0 12.0 0.0 0.0 0.5
w 288 144 288 240 0
w 288 240 192 240 0
w 192 176 192 64 0
w 192 64 288 64 0
w 288 64 288 96 0
w 304 272 288 272 0
w 288 272 288 240 0
r 320 368 368 368 0 100.0
c 208 320 208 384 0 1.0E-5 0.0010
w 416 176 336 176 0
w 336 176 288 144 0
g 464 272 464 304 0
w 416 80 464 80 0
w 464 80 464 176 0
w 464 176 416 176 0

Scooby Jonni

Hi Andy, I imported your example but it still didn't seem to work on my machine

I played around for awhile and did come up with the below that seemed to do the trick..

I have no idea what a MOSFET is but it sounds like a challange , I did wonder how long a relay would last.



$ 1 5.0E-6 5.023272298708815 37 5.0 50
178 256 192 400 192 0 1 0.2 0.04791207349136211 0.05 1000000.0 0.02 20.0
c 256 224 160 224 0 1.0E-5 -3.9062036246106784
R 256 192 256 128 0 0 40.0 5.0 0.0 0.0 0.5
g 256 240 256 272 0
w 256 192 160 144 0
w 160 144 160 224 0
w 256 224 176 336 0
w 176 336 496 256 0
w 496 256 400 176 0
162 176 336 352 368 1 2.1024259 1.0 0.0 0.0
r 352 368 464 368 0 100.0
g 464 368 464 416 0
o 1 64 0 35 20.0 51.2 0 -1
o 7 64 0 35 20.0 51.2 1 -1

ALi-B

iTrader: (1)

I've not really looked at your circuit as the simulation didn't really make any sense to me, however some pointers that may help:

As long as you use a ballast resistor for the coil (or high resistance coil off a really old car with points ignition) the relay should cope ok.

Alternative to a relay is a coil driver circuit; however, don't re-invent the wheel, either nick a ignition driver off an old car or buy this: Ignition Amplifier Kit : Automotive Kits : Maplin

That should be capeable of being driven by a 12volt pulse, which you can generate how you like, be it a RC flip-flop or 555. OK, it won't give you the correct dwell, but set at say 50hz (3000rpm) should be enough to get a decent spark duration.

Tip: don't use a modern (or not so modern) high energy ignition coil (low resistance) off a car with electronically triggered ignition without a ballast resistor, the current and arcing from back emf will quickly burn out the relay contacts: I once ran points on a standard high energy Lucas EFi coil on a Rover V8 without a ballast...the contact breaker lasted about 10minutes before it melted! The same coil also killed a Luminition Optronic controller due to the lack of a ballast resistor.

Scooby Jonni

Thanks for the info mate, interesting stuff. I not actually thinking of making one, I was just curious as to how the circuit works but that's good to know none the less