Wait'll you get the proper gap on the plugs to compensate for the lack of compression.

You should have about a 3/8" to 5/8" gap for the spark to jump across, depending on actual compression ratio and the specification for spark plug gap.

Since we don't know how you have things laid out, it'll be really tough to suggest how to improve things.

 

SgtWookie,

Actually I did read that post, but was myopic on protecting the mosfet.

Perhaps something with a diode in series like this would help (Source: http://www3.telus.net/chemelec/Projects/Car-Coil/Car-Coil.htm):

John

 

Thanks, I will read up abit more on the subject and see if I can figure it out.


Do you maybe have any idea to filter the high voltage spikes from the spark plugs thats interfering with the control circuit?

 

Why don't you post an image of what you have wired up?

If it's on a breadboard, you should know you won't get rid of it until it's built on a circuit board with suitable grounding.

 

THanks SGTWookie.

Im not 100% sure what you need, the circuit layout or how I built it.

Ill give both,

first is the control circuit layout(how i generate my pulses, use the displays through registers and decoders etc.)

/////PIC CONTROL CIRCUIT>

Then the complete driver circuit.
Please note this driver has 3 inputs, and for each input it can generate a GND pulse, +12v Pulse, and a +5v pulse , these are all for different model coils.

///DRIVER CIRCUIT>

Then the pictures of how I wired it up.
I am using a switch mode 12v 8.5A power supply.
The complete unit looks like this, note i made a bracket to mount the spark plugs on the front, which the casing is grounded on the switch mode supply.

And then the next picture I drew blocks in colour around the sub components..

RED BLOCK - SWITCH MODE POWER SUPPLY
GREEN BLOCK - CONTROL CIRCUIT
YELLOW BLOCK - DRIVER CIRCUIT
BROWN LINE ON RIGHT RUNNING AROUND THE POWER SUPPLY - THE EARTH CABLE TO GROUND THE SPARK PLUGS(WHICH I BELIEVE ARE PROBABLY CAUSING THE INTERFERENCE TO THE CONTROL CIRCUIT)

 

Oh and the gap on the spark plugs are 0.8mm

many thanks for the help

 

Let's see... you're using a plastic box with no shielding, and you're running 30,000 volts through wires mere inches away. Wonder what the problem could be?

 

i dont know if i should laugh or cry on that comment hahah!!

Sorry not too sharp on knowledge yet, and this is the first time ive really worked with something like this.


How could I shield it then?

I realised that with single ignition coil it seems to be fine up until about 70Hz, , but with coild that spark more than one cylinder at a time interferes from the start.


How could I properly shield it in a plastic box?

 

It's going to be kinda tough with your existing setup.

I think I would've started off using something like a steel breaker panel box for a housing. Aluminum would not be much help against the inductive coupling you're likely getting.

You're not using shielded wires. They can get to be a bit expensive though. However, if they're not shielded and run in parallel, you'll get lots of inductive coupling.

You might try using some MU-metal. Electronic Goldmine has some on sale:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G16600A

 

Thanks for the reply.

I understand what you mean, on the next one I will be sure to do that with the steel breaker box Idea.

Im almost sure I can get that MU-Metal here in South Africa. If I do get this, where should I stick it to? Just on the inside walls, or around the ground leads to the spark plug?

 

Anywhere you might have inductive coupling.

I didn't know you were in SA. You should put your location in your profile. Click the "User CP" link near the top, and fill in your location about 2/3 of the way down the page that comes up. Click the "Save" or "Update" button at the bottom of the page.

I really don't know where you can buy things there.

You might find it cheaper to just go with a steel box.

You're going to be getting a lot of noise on the ground side. That'll be a problem if your wires to your power supply are of any length.

 

Ok not too good of news but I guess Ill have to do it then, I see that it even interferes with my switches on the input to the pic aswell..


Many thanks for the help

 

Just to report back I got the unit working stable..

Turned out to be the spark plugs being the issue...


I installed spark plugs with a internal resistance, and there is no interference anymore..

I want to thank everybody for there help I really learned alot!

Cheers!

 

Gee, I didn't even think about that.

Here in the States, automotive ignition systems use resistive ignition wires. They're basically a carbon-impregnated string with high voltage insulation. The old "rule of thumb" was 1k Ohms per foot, no more than 10k Ohms for any one ignition wire.

Vehicles that are set up for racing use copper wire and non-resistive plugs. It's not hard to tell if someone is using those in a vehicle on the road, as their ignition noise will drown out even FM radio stations on your car's radio if they are nearby.

The resistive plugs and wires cut down on the spark intensity somewhat, but eliminate most of the noise.

 

thats how i thought about it lol!

I remember quite a few years ago I had this moped scooter thing, and then I installed a plug without a resistance this one time.

And when close to a car it could be heard...

So thought Id give it a try

but many thanks!