Alternator Recommendations

[elwaupo]

After 15 year it’s time to replace the old 100 amp alternator, bought it off of Ebay but I want a good one this time. My question is what size do I need? It’s going on my 69 Camaro and I’ve converted it to a Holley Sniper EFI. Other then it’s just stock. Any brands recommended?

[Vimes]

Depends on how much juice you want. Mechman can get you up to 500 amps. I've used a couple of them, and they're now my go-to when I need one. If the 100 has been enough, another one like you have would work. Or, if you just need a little more, you can get a factory alt that makes 130 to 150 or so.

[Jim Streib]

Yep if the old one kept up, get the same size or a little larger.

Getting 15 years out of an alternator could be good and maybe take it to a place and see what is broke or worn out. If it's something as simple as a set of worn out brushes and the rotor rings are good, replacing the brushes has to be more cost effective than a total replacement.

JMO

Jim

[elwaupo]

Hmm, good advice. The concern I have is it enough for the Sniper? It has been in the past but since I’m replacing it I thought I should check on amperage

[Vimes]

Check your paperwork on the Sniper for its max possible power draw, and get an alternator that makes that much more over 100 amps at a minimum. But really, I'd suggest getting at least a 200 to 250 amp alternator. You may decide to add electric fans and an electric fuel pump down the road and if you're replacing the alternator now there's no reason to not plan ahead. The alt won't draw any more HP off the engine regardless, since the alt only actually makes the amperage the car is calling for, and not what the alt is rated for.

[Jim Streib]

I've been doing car audio since the late 70's and when I've added a bunch of amplifiers there is always a concern of having an alternator large enough to keep up with them as well as whatever else might be on the car at the same time.

Let's say you are drawing 90 amps of power, then if you had an alternator putting out 100A then all would be good and the battery voltage should stay up at the alternators output voltage.

If though you had a 100A draw and then only a 63A alternator you will see a high voltage at first but then the longer this 100A draw is being pulled with only 63A being supplied by the alternator the system voltage will keep going down and down and down the longer you drive the vehicle. The remaining 37A would be supplied by the battery and since the battery is only a storage device and not a generator, then eventually the battery will only be able to give less and less out of it as it becomes depleted and then if the voltage get's too low, the car will not restart.

So, with that said, if before your battery voltage was staying up and solid with what you needed on like the air conditioner, the headlights, parking lights, fuel pump, and whatever, then you had enough but if in the future you want to add something, it might be the time to get a larger output one. Even if you had one of these new ones that are capable of outputting 400A or more, the voltage regulator will keep things in line and if the alternator needs to output 110A, and it's designed to do that or more, then it will only output 110A. If more things come online and the demands grow to 140A, then the regulator senses this and adjusts things.

Jim

[elwaupo]

Thanks guys, great information

[Richard454]

Just a few tips- I worked in the car audio business back in the day and set many an alternator on fire!!!

MORE important than the rated output- is the amount it can deliver at idle.

The alternator puts out max power around 1500-1800RPM depending on the pulley set-up.

At idle the alternator might be only producing only 40-50% of the rated output. Add heat into the mix and the output is even lower.

Think of the alternator as income - and your battery as your bank account...at idle you are only working part time!!!

If the alternator can't handle the electric fans- AC blower- fuel pump ETC at idle- you are looking at problems.


And think of the alternator as a fuel pump- a big pump with a small fuel line doesn't do you much good. So you want to up your charging wire's size too.

Wire is rated at maximum current before it melts at 70° F- so under the hood rule of thumb- is to go up one size to handle the underhood temps

Richard