I am at the point of installing my power steering and alternator and was wondering what alt. choices there are. I want an int. regulated around 100 amps and not a one wire to fit a 351W out of a 69 car.Part number and vendor would help.

 

Howdy,

I am using a 12si 90A "3-wire" internally regulated alternator. I think it's sourced for a 70's or 80's Oldsmobile.

It doesn't really matter whether you use a "3-wire" or a "1-wire" because pretty much any 3 wire alt can be used as a 1-wire. Unless you have a reason for wanting a 3 wire, a 1-wire is FAR more convenient to hook up and use. (the main reason for a 3-wire is the "sense" connection for regulation.....if you are going to have a main DC power BUS, that is a fair amount of distance from the alt, you do need a 3-wire)


Your main choice should be based on what you have for mounting.

Here's some great info on how the 10si & 12si Delco alternators are set up.

Catalog

 

Don't you mean, if it's a fair distance away from the alt, you DO need a 3-wire? In any case, you want the voltage sensed as close to the load as possible to compensate for losses.

Unless you have power windows, A/C, and other big loads, 100 amps is not needed. If the engine has V-belts, not serpentine, they may not even have the capacity to drive a 100-amp to full capacity.

 

Um.... YEAH! I meant you DO need a sense connection! (I sometimes get stuck in a double-negatives)


You have to look at all the accessories you could conceivably have operating on a continuous basis.

heater blower, A/C clutch, , headlights, wiper motor, running lights, ignition system, EFI computer, radio/stereo equipment, radiator fan... etc.

ADD the average current requirements of ea together

One thing to think about is what might run continuously.

A set of (2) 55w halogen headlights would draw about 4A each.

A heater blower motor could be as high as 15A

A/C clutch. Approx 4A

A radiator fan could be around 20A (and as high as 50A)

Wiper motor 10A

Ignition/EFI system up to 15A or so


(btw I have estimated somewhat "high" on the above components)

But for illustration, lets summarize shall we?

Just using the above common components we get 4+8+15+20+10+15 ==72A !!

And we have NOT even tried to charge the battery or listen to the 200W stereo!!

Now understand, a 200W stereo doesn't "draw" 200W (approx 14.5A) continuously.

(That would be "peak" power requirements during audio peaks when the audio gain is turned to) maximum) The average current requirements can be (and usually is) a LOT less than 1/2 the peak....but you need the peak power available to prevent audio distortion.

I would NOT size an alternator for any car that wasn't AT LEAST 20-30% higher than the average current draw for a typical rainy night pulling a trailer ( lights, wipers, rad fan running continuously etc)

AND, I would NOT size an alternator that would be required to produce rated current at any time. I would want it to "loaf" along at 50-60% of rated power for longevity.

The battery is not a factor here.

The battery is (and should only be) ONLY for starting. It is completely "out of the picture" and is actually a current "DRAW" item when the engine is running because it's being charged........ when it's finally fully charged it's still out of the picture, because it is NOT supplying power (nor drawing current)

I selected a 90A 12si alternator for my F-600 because I am planning on A/C, and still vacillating on a radiator fan (55A).

I will be using LED lights wherever I can put them which will save a few amps.....

 

LOL, I suppose you could be using the A/C on High while it's raining, in a car with EFI... but those kinds of engines (modern) typically have a serpentine belt. Driving a 72-amp load on a single V-belt will make all kinds of belt noise, you really need a double belt at the least. I do have a 90-amp alt on a single belt, but I know it will never see anywhere near the full load.

For your fan Rick, keep in mind that converting crank HP to electrical power is only 35 - 40% efficient. If the fan will be running much of the time, a belt-driven fan with a thermal clutch is more effective.

 

Not only that, but most electrically driven fans for 3/4-1 Tons trucks are huge, and draw a LOT of current.

It's for this reason I elected to go with a 19" aluminum fan driven with a viscous clutch.

I also have a double sheave 2 belt drive for my 90A alt and A/C pump.

If you have A/C, you SHOULD be using it during defog since it'll clear the cab and windshield of moisture MUCH faster!

 

Thanks for the info. Thats what i was looking for. The catalog was perfect.