Recommended amperage for an alternator

[Woodfin]

Duster,

It is completely acceptable to have more alternator output than your system requires. An alternator only puts out the amperage required by the load.

It is common to see 85 amp - 100 amp rated alternators on drag race cars.

Personally, I chose pulley sizes that spin the alternator about 20% - 25% faster than the engine.

Example - 7200 engine RPM x 125% overdrive = 9000 alternator RPM.

Another example - 1200 engine idle RPM x 125% overdrive = 1500 alternator RPM. That is enough alternator speed at idle and does not over speed the alternator at high engine RPM

[FireSale]

Make a list of the amp rating of everything your electrical system might be driving and total that up to find a starting range.

The problem with alternators on dedicated drag cars is that they don't usually put out a full charge at idle rpm and that's where your engine tends to spend most of it's time at the track.

If you pick a one wire alternator be sure to set it up correctly with the jumper to the right terminal. Use the remaining wire for a warning light of some sort. It comes in handy when you lose your adjuster hardware and drive belt at the track like I did Sunday. The light popped on so I took a look and everything was just gone.

The short version: 85 amps for the strip. 120-140 if it's a street car with lots of electrical stuff.

Dale