Dual fans What size alternator?

[EvilScamp]

I recently built a 383 for my Duster, i installed an aluminum radiator with dual fans. When the fans turn on it charges about 3/4 of the way up on the factory gauge.
It's a 60amp alternator on it now, will a 75amp be big enough or do i need to go bigger like a 90 or 100amp?
Not sure exactly what amps the fans are drawing, it has a 30amp circuit breaker if that helps any.

 

[C130 Chief]

What is the amp rating of the fan motors? If they are protected with a 30 amp fuse, I would think the factory alternator would support them just fine.

BUT your post hints at a far bigger problem! Where exactly are these fans getting their power?!? If the amp gauge goes up when they come on, it would suggest that their operating load is traveling through the amp gauge which means it is also traveling through the ignition switch and most importantly the BULKHEAD CONNECTOR. You should fix this as soon as possible, as it WILL cause problems (think ELECTRICAL FIRE)! Connect the main power lead for the fan relay directly to the output post on the alternator (best), the supply side of the starter relay (good), or the positive battery post (OK). Any of the three will make the fans work better and the 40 year old harness last much, much longer.

 

[EvilScamp]

It's getting the power supply straight from the battery.
I wired it exactly according to directions that came with the kit.

 

[BB73Challenger]

I went with dual fans on my Challenger and they draw a ton.
I just bit the bullet and went with powermaster 100 amp and figured with add ons
I'm covered down the road.

 

[desmo900]

You will need to find out what the maximum draw of your fans is and whether or not they will both be running at idle. Alternator output at idle is a more critical value than maximum output of the alternator overall. You will need to make sure you alternator can support your amperage draw (along with lights, radio, electric fuel pump etc.) at idle.

 

[67Dart273]

What have you got for wiring?

Completely factory?

MAD ammeter bypass

Aftermarket?

Start by reading this article:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

If you don't have 'a lot of other stuff' a 60A MIGHT do it, but the wiring needs to be "up to snuff."

Even Ma knew that the factory wring was marginal. If you can find the documentation (it's in some of the factory service manuals) of what is called "fleet" or "taxi" wiring, this was done with factory 65A optional alternators. It involved abandoning the original ammeter wire and running them in through the firewall in separate grommets.