Need a bit of advice asap please:Ignitions

[911hillclimber]

Trying to get my race car going this weekend.

The ignition circuit is classic distributor, Electronic module (Aldon Automotive) coil to suit and that's it.

The circuit has a 5 amp fuse in it and a red light to show Ign On etc.

Came to switch the lot on very briefly, the red light came on and the fuse went splat.

What level of current should I expect the circuit to take?

Graham.

[Rich7se]

Depends on the type of coil you have, I have taken the two most popular values and worked out the following.

All based on a 13v supply.

3 ohm coil - 4.3 amp
1.5 Ohm coil - 8.6 amps

Rich

PS, have you ever owned a beige 911?

Edited by Rich7se on Saturday 16th May 20:02

[singlecoil]

Is the coil designed to run with a ballast resistor? If so, and you were feeding it 12v without running the starter motor at the same time, then it would certainly draw more current than it was supposed too. Maybe not enough to start blowing fuses, or maybe yes.

Also, check the wiring again and take nothing for granted. Fuses blowing are often a sign of short circuits.

[911hillclimber]

Thanks to you both.
I think there was a short, now fixed.
The circuit is without a balast resistor and the coil is 1.5 ohmes!

A friend tonight has said 5 amps will not tolerate the current, so will try 10 tomorrow.

And yes, I own a beige 911 hillclimb classic, but this problem is on a special hillclimb car I'm close to finishing.

[Rich7se]

No worries Graham, thought it might be you. Yes you need a bigger fuse in there if its 1.5 ohm.

Was hoping to get the Westy out for the Loton season, but I am afraid the credit crunch dictates I wont be doing much this year. Hope to get sorted for 2010. Your special looks great, what class is that sports libre?

Rich

Gulf painted Triumph Spitfire 1997- 2001.

Edited by Rich7se on Saturday 16th May 22:06

Edited by Rich7se on Saturday 16th May 22:10

[Mr2Mike]

Ignition circuits were traditionally never fused on older car that used points ignition.

If you must fuse it, you should bear in mind that the purpose of the fuse is to protect the wiring, not to protect the ancillary device the wire is feeding. It should therefore be fused according to the current capability of the wiring. As battery voltage can be over 14v with the engine running, peak current will be too high for reliable long term operation with a 10A fuse.

[911hillclimber]

Ok, I'm with you.
I was stepping-up in units of 5A untill the circuit held.
5A popped, if 10A held then I was staying with that.

Are there any peakes (ie when the ignition switch is first made) that can pop a fuse that would normally sustain the running current?

Thanks for the help!
Graham.