Electrical: What size (amps) of alternator would be best for my car? (update)

[junior]

Ok very looooong story made short....

I am upgrading the alternator on my '54 coupe and need to know what size of alternator to get.

The car has been converted to 12V, and has no real modern electrical accessories added to the stock Studebaker electrical system other than a power antenna and electric cooling fan. The antenna is rarely used and has a 3 amp fuse. The engine cooling fan is used constantly in traffic jams... I don't know how many amps it draws, but do know the two leads to the fan motor are 16 ga. wires so assume no more than 25 amps draw. The present alternator in the car is an ancient Delco Remy, external regulator style...I think it came off of a '63 Chevy. The ammeter in the car usually reads in the plus zone unless it is at idle with the headlights turned on and the cooling fan running. Bringing the rpm up to about 1200 will bring the ammeter back into the plus zone when this happens. From my reading I think I want to go with a GM 10 or 12 SI alternator…only I can`t figure out how many amps output would be ideal for my car. So any ideas or suggestions? Thanks, Junior

[fiveftsix]

45 amp should be plenty, your not running vast amounts of power there and any larger will only put a load on the motor if you go crazy and install an 80 amp+ one.
Geoff

[sweetolbob]

Are you eliminating the external voltage regulator? If so, then pick a common, readily available one so you can find it locally if you need one. If you are keeping the external VR then I'd probably go at least 45 as suggested above possibly somewhat higher. If you add up headlights, blower motor, wiper motor and other things to the fan draw 45 is probably close.

Avanti, Bob

[jclary]

I'm not very qualified to make an authority type statement on this, but if your car has a good well insulated wiring harness rated for the current draw of a six volt system, twelve volts should not be an issue. Also, to me, the major limiting factor would be the capability of the voltage regulator. Since it is the regulator's job to handle the current demands of electrical devices, and circuit breakers and fuses to protect the circuits, the key must be the voltage regulator. If you use an alternator with a built in regulator, then it most likely will be rated to handle anything the alternator puts out.

[junior]

Thanks for the responses…yes I want to eliminate the external voltage regulator…that was part of the long story made short. I was thinking that the stock Studebaker was equipped with a 45 amp generator, and I have added a 25 amp load to the system with the cooling fan that would mean something in the neighbourhood of a 70 amp alternator. From what I`ve read I would not want to go with too large of an alternator because at idle the large one will not be putting out enough amps to satisfy the cooling fan, yet I don`t want to go too small because then the alternator will be working at its max. capacity most of the time and eat itself up with heat…. Thanks, Junior

[Michidan]

I wouldn't guess on the cooling fan draw, check with the manufacturer. Some can really take a lot to run.

[Dan Timberlake]

If the ammeter is wired "properly" wouldn't running the fan with the engine off show the fan amps as the change in discharge?

Dan T

[Dan Timberlake]

"any larger will only put a load on the motor if you go crazy and install an 80 amp+ one."

I'm thinking alternator output (and the power required to drive it) depends on the electrical load. If the lights, wipers, stereo etc are drawing 25 amps, and the battery is already charged up, then 25 amps is all the regulator will ask the alternator will provide.

Similar to what happens to a gasoline back up generator when I start a 10 amp circular saw. The sudden increase in power required will change the intake roar of the engine when the throttle opens to maintain rpm while pumping out extra amps.

[41 Frank]

What I have been told by a Powermaster alternator vendor is that with one electric fan and AC the suggested amp rating to buy is 100 amp. An alternator will only put out enough to keep the battery at a satisfactory voltage determined by its regulator. While lower amp alternators may keep things running, my experience has been that the electric fan will not run at optimum speed. End result is insufficient cooling in traffic.

[karterfred88]

Not knowing which Delco alternator you adapted from what 63 Chevy, makes it hard to guess what you have vs. what you need. That alternator output could be as low as 25-35 amps, thus your needle dip with headlamps and fans running. My guess would be a 55-65 amp replacement would be more than enough and leave you room to add some other accessories. I don't know what most Studebakers came with, but my Avanti's Prestolite was only good for 40+/-2 per the workshop manual, it's taxed at idle (650 RPM) with factory lighting, wipers and heater fan running. Not sure about how to handle the original amp gauge though might need some wiring fix to work right with increased output (past its range).

[fiveftsix]

Think were going a little overboard over this.
Were not confusing Watts with Amps are we ???
Most modern cars today run alternators in the 35 to 45 amp range
Why is it that one believes they would need 100 Amps ??
Electric fan ???
Don`t most modern cars have those ??
As well as A/C ??
An electric fan shouldn`t be running constant,it should have a thermo couple switch installed in the system so as to switch it on and off as needed.
If anything an older car would require less amperage than our modern counterparts with electric everything.
The advantage of an alternator over the old Generator was the fact an alternator gives out higher amperage at lower Revs
So when running at idle with Lights etc it would still be charging
Geoff

[48skyliner]

The cars I have been working with are from the 1980s-early 90s, and they all have 50-60 amp alternators, with internal regulators. A lot of newer cars have 100 amp alternators, and some are going to single wire, with internal voltage referencing - don't ask me how it works.

I would go with something common and very modern, and if you run a higher rated unit it will never have to work very hard. There certainly is no harm in running a 75 amp alternator if you only use 40 amps.

[StudeRich]

/Cut/I would go with something common and very modern, and if you run a higher rated unit it will never have to work very hard. There certainly is no harm in running a 75 amp alternator if you only use 40 amps.

All except the fact that if you get too crazy with these High powered Alternators, the Wiring will smoke!

These Cars never had more than 35 Amp Systems in them and they worked just fine, so unless you have a 200 AMP Stereo Amplifier there is NO need of all that Power. Going beyond about 50-60 AMPs is just overkill and may burn the Car down.

[karterfred88]

Think were going a little overboard over this.
Were not confusing Watts with Amps are we ???
Most modern cars today run alternators in the 35 to 45 amp range
Why is it that one believes they would need 100 Amps ??
Electric fan ???
Don`t most modern cars have those ??
As well as A/C ??
An electric fan shouldn`t be running constant,it should have a thermo couple switch installed in the system so as to switch it on and off as needed.
If anything an older car would require less amperage than our modern counterparts with electric everything.
The advantage of an alternator over the old Generator was the fact an alternator gives out higher amperage at lower Revs
So when running at idle with Lights etc it would still be charging
Geoff

Where did you get your info on "modern cars" even my late 90's and up cars all had 100+ amp alternators? My 2013 Mustang comes standard at 135 Amps. Yes it has more load, since computerized injection and high pressure fuel pumps arrived they have been way more than 35-45 amps. But a little more doesn't hurt.

[JoeHall]

Anymore than 60 amps on a Stude is overkill. My experience with a 70+ amp on a Stude was that it had a light whine. The 50-60 amps are always nice and quiet. I use the 1-wires, with a diode wired in to that it comes on instantly. With EFI, AC, etc., a 50-60 amp has always been sufficient for my Studes.

If a Powermaster vendor advised me to use a 100 amp alternator, I'd simply consider the source. After all, the guy SELLS them for a living...