I am wondering what amperage alternator I would need for my low option 72, there's no power anything. I'm running dual rad fans and also have electric headlight actuators. I have a monster 140 amp one from a cadilac that will create clearance problems so if I could get away with a regular size alternator that would be great. Any ideas?

Rob

 

I use a 100 amp on mine with twin spal fans and everything is good to go.

 

How many amps do the fans draw when all on? Add that to about 50 amps and you should be fine. The actuators draw a load, but it's short-duration; that can be drawn from the battery and replenished later. I would think a 100 amp alt would get the job done.

 

 

Thanks guys. Do you need to run any extra wires with a 100 amp or is the stock harness good enough for that? I know of some people running an extra wire straight to the battery from the alternator.

 

Would probably be advisable depending on stock size. 4awg should be enough if you also replace the grounds to the chassis and engine.

 

And that's probably overkill. You shouldn't need to rewire anything, just take the main power feed for the fans directly from the alternator. Or if you have other stuff to add you can install a junction block like the later year cars had

http://www.zip-corvette.com/ProductD...GR-SR&CTitle=&

Just make sure everything is protected by in line fuses. I added dual fans & electric headlight operators, headlight relays and more so I added a separate fuse block from Painless Wiring

http://www.summitracing.com/parts/PRF-70207/

Mounted it on the inner fender where the vacuum tank used to be

Jim

 

You shpuld increase the wire size from the alt bat terminal to the starter. Or you can add another wire in parallel.

Google for a wire size/distance chart for dc.

 

I've read that most electric fans run a 20amp draw per fan, so a dual set up would pull 40. Since the stock alt on a mechanical fan engine is 40(?)amp, I'd assume the draw from the rest of the car would be around 30-35amp. Add to that higher draw of aftermarket headlights, worn A/C compressor, newer stereo etc, and I would think a 100amp alt would only just be sufficient and nowhere near overkill.

I would strongly advise against running anything directly off the alternator for 2 reasons. First is the alternator will be working far more than necessary due to the direct drain from the fans, causing undue wear on the alternator.
Second is that the amperage of the alternator varies greatly depending on the revs the engine is at. This will also wear on the fan motors over time causing premature failure. The battery does not have the sole purpose of starting an engine, it also functions as a buffer for the fluctuations in current and any spikes in voltage which could potentially damage any of your electrical components.

 

What about running a wire from the alternator to a terminal strip, from there run a larger wire back to the battery and run the fans and lights from that terminal strip?

 

I'm not positive I understand what you are suggesting, but it sounds like a complicated way of achieving the same end, which is wiring off the alternator. And possibly creating a conflicting current. A minor reason I neglected to mention is putting any additional strain on the alternator will drain more horsepower from the engine, thus negating the point of using electric fans.

When thinking of a Direct Current (DC) system, it is exactly that, a DIRECT current. It only goes one way. Just like a water system, if two currents of water meet going in opposing directions, they will either stop or the stronger current will force the other back. The battery is like a reservoir which regulates the incoming flow and buffers it from the outgoing draw, and vice versa. If the outgoing draw is less than the incoming, the alternator will stop charging and the reservoir stops filling. If the outgoing draw is greater than the incoming, then you're eventually gonna run out of juice.
So you want a big enough pump and pipe feeding only the reservoir to keep up with or exceed the outgoing flow, and any outgoing to only draw from the reservoir.

Basically the only place your alternator positive wire should go is directly to the battery, a component that can sustain fluctuations for a short period (starter motor) or a regulated switch.

 

What about a 383 with a ele fan ele fuel ele water pump and ac?

 

Researching the draw from electric water and fuel pumps they seem to only pull 5-8amps each (really thought a water pump would do more than that), so you'd probably be fine with a 100-120amp alt. (1 x fan = 20) + (car draw including A/C = 40 at most) + (fuel and water pumps = 20) = 80amp draw. Add another 20 for an additional fan if it's dual or 20 for upgraded headlights/small audio amplifier/anything aftermarket and you'd have your 100.

 

When thinking of a Direct Current (DC) system, it is exactly that, a DIRECT current. It only goes one way. Just like a water system, if two currents of water meet going in opposing directions, they will either stop or the stronger current will force the other back. The battery is like a reservoir which regulates the incoming flow and buffers it from the outgoing draw, and vice versa. If the outgoing draw is less than the incoming, the alternator will stop charging and the reservoir stops filling. If the outgoing draw is greater than the incoming, then you're eventually gonna run out of juice.
So you want a big enough pump and pipe feeding only the reservoir to keep up with or exceed the outgoing flow, and any outgoing to only draw from the reservoir.

Basically the only place your alternator positive wire should go is directly to the battery, a component that can sustain fluctuations for a short period (starter motor) or a regulated switch.[/QUOTE]

You're a plumber aren't you? Can an ignition wire off the fuse block handle the power/amperage for the fans? I thought that it couldn't, I could be wrong. Thats why I suggested stopping at a terminal strip before heading back to the battery with the larger wire. I would power the headlight motors and fans from this strip.

 

You're a plumber aren't you? Can an ignition wire off the fuse block handle the power/amperage for the fans? I thought that it couldn't, I could be wrong. Thats why I suggested stopping at a terminal strip before heading back to the battery with the larger wire. I would power the headlight motors and fans from this strip.[/QUOTE]

The battery terminal on the starter because of the large battery cable from the battery literally becomes the new battery post. No need to run separate all the way back.

Ideally you should use relays to switch all the heavy load items any any switch can trigger them adequately.
The wires feeding your term block should be heavy enough for the total load they will feed. Always keep 12vdc wires a s short as possible.

 

I'm an EE and I don't follow what you're trying to post.

#1 reason doesn't make sense because the power has to come from the alternator or the battery goes dead. So, the wiring at the battery does not reduce the load on the alternator.

#2 doesn't make any sense because the alternator is capable of producing more current as the rpm increases. It doesn't just produce more current unless the loads require it.

Finally, the fans don't care what current the alternator is producing. the fan will draw a certain current depending on the voltage at the alternator terminal. The voltage is regulated to approximately 14.2V.

Also, DC current does not mean that the current only flows in one direction. It can flow either direction depending on the situation. In some situations, current will be flowing to the battery and in other situatios it will be flowing from the battery. Being DC means that the voltage does not regularily reverse direction X number of times per second like the 60Hz power system in your house.

Personally, it would be fine to run fans off the alternator. If you want to make the electrical system more robust then replace the wire from the alternator to the starter solenoid with something heavier. #8 would be the minimum for around 100A and #6 would be more than enough.

 

I worked with Adam at Nations AutoElectric for a 170A CS144 alternator in a custom case (the new case resembles a 10SI but a lot larger). Alternator came complete with the harness adapter that is required. Best of all; the alternator installed with ZERO modifications.

http://www.nationsautoelectric.com/

The new alternator has no problem running the dual spal fans on high, both high and low beam headlights, and running the air-conditioning with fan blower on high; everything at the same time.



Dave

 

Cool, I'll bow to your superior knowledge as an Electrical Engineer.

I'll also ignore the advice of 2 auto electricians and an alternator builder who recommended against wiring directly to the alternator.
And I'll ignore the fact that all car manufacturers neglect to wire the entire electrical system off the alternator, instead only having the starter motor wired to the positive pole.
My experience is limited to car audio applications which require a massive draw, some 700amps for my planned build, and those applications aggravate potential wear tenfold, causing them to show much sooner in weeks rather than months.

For the OP and others who have asked, go ahead and wire everything you have to the alternator. Get back to me in 12 months if nothing has failed.

 

Oh good I love a good pissing contest

 

Ummm...not in my thread please.

Also, wiring is worked out. I'm only asking about supply power.