I am repairing my underhood wiring in my truck and i'm putting in a fuse panel for my HEI ignition and a electric fan. What I am wondering is what amp fuses to use and also how many amps does the alternator field use?
thanks for any help

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85 d-100 HEI 2BBl
06 Toyota Corrola

If memory serves, most of our Mopar alternators draw only about 4-6A for the field winding. Chrysler didn't fuse them in any of the models I worked on, just tapped the ignition power. A stock Mopar electronic ignition can draw up to 12A, the point ignition about 8A w/ ign on & engine not running. I doubt the HEI draws any more.

I'd consider using an auto-reset breaker rated 20A for the ignition; probably a 30-40A for the fan. Electric fans usually need a lot of current and you don't want to trip the breaker prematurely.

Thanks KBB_of_TMC
I was planing on using a 30A auto reset breaker for the fan and a 10A fuse on the ignition. The fan is out of a 94 grand caravan and draws 25A at start and then drops to 10-12A when it gets up to speed. I like your idea of using a breaker for the ignition. 20A seems a bit high, but if the coil draws more than that i bet i will need a new coil any way. As for the alternator field I will just tap into a ignition wire.
Thanks for the help

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85 d-100 HEI 2BBl
06 Toyota Corrola

Having just adjusted a mechanical point voltage regulator, they were actually fused.......

There's 2 fusible links inside the regulator to act as fuses.....

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Good point emsvitil; on the grounded field models the regulator could be fused since it was upstream of the field winding. I opened up a solid state replacement for the mechanical regulator and didn't see any fuses inside, but it could have had internal current limiting circuitry - I didn't test it.

For the isolated field electronic regulator, it's on the low side of the field winding so there's less need for a fuse. The high side is connected directly to the ign feed, so if you let the field feed wire get sucked into the alternator you can short everything out (from personal experience).

Carl, remember that when cranking the ballast is bypassed and the full 12V is applied to the coil, so it could draw as much as 20A (with a hi-po coil) then. Generally, most people like to be generous when it comes to fuses and breakers. A fuse or breaker operating too close to its trip point for long can give give problems.

It's rare, but I've seen some fuses burn or fail when operated right near their rating for a long time. I generally put in a fuse or breaker that exceeds the max anticipated current by 1.5 - 2x.
My experience is that some inexpensive auto-reset breakers get weak if cycled too many times and start tripping at progressively lower currents.

good advice, the cheap breakers I think are a thermal switch so its not nessalry the amps that trip it. Also it has the coil from a 89 S-10 and HEI module, if i remember right it should draw less than 10 amps not shur tho.
thanks, the members of this site are always helpfull

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85 d-100 HEI 2BBl
06 Toyota Corrola

I'm surprised that takes so much current for ignition!?

Truly?

Cheers, Wizard

When cranking the 1ohm factory ballast is bypassed. I read that the Pertronix II coil is 1.5ohm and the III 0.32ohm, I measured my Accel coil to be 1.1 ohm, and I looked at others that were advertised to be 0.6ohm, giving 8A, 37A, 11A, and 20A while cranking. (I wouldn't plan on using the Pertonix III in a stock setup. )

My old 1968? FSM actually lists the current draw in the specs; those point systems used a ballast resistor that changed resistance by heating up. The effective resistance was about R=0.5ohm+0.633ohm/A (from both the FSM and my measurements).

The actual time-averaged current needed will depend on your coil, ballast, electronics and RPM - in general in a Kettering-based system, the faster you go the less current you draw.