How can I estimate how much alternator output I need?

[robroy]

Hello!

I'm now trying to pick out an alternator. Because of the brackets I'm going to use to mount it, I want to stick to the 1G style case (not the 3G case). But I see that there are plenty of re-done, modernized alternators out there in a 1G case, even with internal voltage regulators. They're probably just a little more expensive than over-the-counter 3G alternators from an auto parts (I'm guessing on this point).

The only electrical needs I foresee on my truck are a big electric fan (I'm thinking of using the electricity-hogging Taurus fan(s)), and maybe a couple of bright backup lights. I can imagine that those could add up to a peak 50A, but I really don't know.

With this in mind, would a modernized, 95A alternator in a 1G case be enough?

Thanks very much for the truly excellent advice!
Robroy

[70_F100]

Large, heavy-duty trucks many times use a 105-amp alternator. They have the capacity to run multiple lights (a BUNCH of them), air condition and other accessories, while supplying the charge for large batteries.

I would think that 95 would be PLENTY for your rig.

[robroy]

Hey 70_F100 thanks for replying!

It sounds like it might be indeed. It's good to know that commercial trucks often use 105A alternators!

I see many alternators on the market that are rated at 140A or even 200A. What's the deal here? Do folks really use that much electricity?

Thanks again 70_F100!
Robroy

[rjewkes]

Some do especialy with electro nic everything/efi computer and large stereos.

i recently put in the 100 amp from an 88 ford van/truck the only mods would be the end of the field wire needs changed to a female connector, and the mount brakets need changed to a slightly longer upper bracket.

[robroy]

Hi RJewkes, thanks for replying!

I see what you mean about the big stereo equipment and EFI stuff.

You know, I found out that I could get a 140A alternator for only a little more cash instead of the 100A one, so that's the route I took. I had been reading through old posts about how much current the Taurus fans take, and I read numbers like 80A or even 100A for a moment during start-up, then a constant 50A to keep them running full blast. I figured 140A would definitely be enough capacity, while 100A would only probably be enough.

Maybe it's overkill, but oh well. This way I'll be able to add a giant neon sign of Elvis on the bed if I want to later on.

Thanks RJewkes!
Robroy