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Question about alternators and electric fans

Mastiff

Mastiff

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I'm finishing up some electrical upgrades, which include windstar fans and H4 halogen headlights. I have quad headlights and I wired them so they are all on all the time (either all high or all low). I used relays up on the fender, one for the highs and one for the lows, and one relay for each of the two fans.

I started with 15 amp fuses for the headlights and on high these kept popping after a few minutes with the lights on. I put some 30s in there, but I don't think they should be drawing that much. Maybe 20-25 amps on high?

Anyway, my real concern is that when the fans kick in, the charging system voltage dropped to about 12.5, like the alternator just can't keep up. That's even with the headlights off. The headlights alone drop the voltage below 14.

My question: is it normal to upgrade the alternator when doing the fan upgrade? I've never changed the alternator and I've had this Blazer since 1994. It could be the factory original for all I know.
 
This is the '83 I assume?

The stock alternators back then weren't rated for that much, although even my CS130 is rated at "only" 105 amps.

Are you triggering both fans at the same time? It may be a pain (although you obviously don't mind the electrical work), and I see where you live, but you MIGHT also consider triggering the fans separately, if you can. I'm guessing summer time a single fan won't cut it? I haven't had an issue with my single LS1 fan setup, but I don't have AC and nowhere near the temps you see I'm sure.

I suppose an alternator upgrade would be the easiest route actually, I just know those Windstar fans draw a ton of juice. If you are that low with just the fans on, you need to turn the heater/AC on high, radio on, headlights on, etc., the maximum load the alternator could possibly ever see, and if it drops below 12V, upgrade. I am probably rare in thinking that as long as it stays over 12V at maximum load you are somewhat ok, but you have to be realistic as to what the electrical load will NORMALLY be. I wouldn't think AC on high, fans going, radio, and headlights on high would be an unrealistic load.

FWIW, when I was looking at headlights (for the relay mod actually) I saw that on high beam they were normally around 55W each. Depended on brand, type, etc., but that was a pretty average figure as I recall.
 
I'm running the fans from my TBI computer which has a single wire output (grounds out to turn on fans). Given that, I decided to just fire them both up at the same time.

55 watts would be ~18 amps with four of them going. I hope that's all it is, because I ran 12 gauge wire to the lights. It does line up with the 15 amp fuses blowing.

I'm not sure what to think about the 12.5 volts. I'd be happier with 14 volts, but maybe that's asking too much.

It's a little disturbing that I have all these big wires running around the vehicle for the fans and lights, but the red wire on the alternator looks like 10 or maybe 8 gauge only. It doesn't seem like the thing has a chance to keep up.

Any suggestions on what alternator to get? The biggest I see on Rock Auto is 78 amps. If I'm going to the trouble I think I'd like to get into the 100 amp range.
 
If you just want an alternator that you never have to worry about, it's from the Pontiac Transport, and it's a CS144 rated at 200A as I recall.

Most people don't like the CS130's (they are an inferior design) but mine hasn't given me problems, and I suspect they are a bit cheaper. As it is now, a CS130/144 can probably be found in the wrecking yards pretty easily, and oftentimes those are new. Gotta love people that change parts guessing at problems. :)

At least on the fans the initial draw is massive, but while in constant state much lower. I've seen it stated that electric fans draw upwards of 100A on startup. I've been running the stock GM 30A relays for years, but then again, I've got the LS1 fans which probably don't draw as much.

Do some searching for folks that have gone the 144 or 130 route, see if they had any idle voltage numbers. I know my voltage stays rock solid fans on or off, at 750RPM idle. If I lug the motor it will start to waver, but I'm not worried about that.

As to big wires. I tend to agree that the "charge" wire from the alternator is probably undersized when we start adding electric fans and what not, but so are the battery cables based on the 300+ amp draw they see. Some searching will probably net fan steady state draw, you know headlights roughly, probably can find heater blower figures, and rest of truck at worst is probably 15A...wire gauge could probably be determined pretty safely from there, but I'll be surprised if the stock wire was "large enough" even for the minimal load it saw as original. I'm not factoring something in here, or all of us running electric fans that haven't upgraded the charge wiring would have had problems by now.
 
Sounds like the stock alternator in your truck could be in the upper 60 to ~80 amp range. Your electric fans are cutting WAY into that, you're likely running your alternator at the limit all the time.

I got a "New Tech" alternator from Summit Racing for mine (the 70's trucks had a ~40 amp alternator, with 63 amps as the HD upgrade :haha: ), I believe it's this one:

http://www.summitracing.com/parts/mci-n7294-3ho/overview/make/chevrolet

Works great, no problems at all.
 
When I had a stock alt, 4 headlights, electric fans, A/C, stereo, etc., it was only good when driving around. Sitting at idle the voltage went way down. I just added a 2nd stock alternator and then everything was fine. That's like 150A+ for maybe $40 (reman alt and new belt). Dual alts do better at idle than a single high-output unit. When I went serpentine I switched to dual CS-series. But I know it's not for everybody.

Otherwise, best bang for the buck is to drop in a later model alternator. Many of the 2000+ trucks have 160A stock. But if you have V-belts you'll have to research a pulley swap.
 
Is there a downside to the giant output alternators besides up front cost? Do they drag more at low draw?
 
Well you need detailed specs. Some stock sized units have a higher max output, but don't do any better at idle than stock ones. Usually the giant cased units (ambulance, etc.) rule if you can find (and fit) them. The only other disadvantage I can think of to an aftermarket alternator is that you can't just grab a new one in whatever town you're driving through.

An alternator doesn't have much parasitic drag, it's the actual electrical generation that loads the engine.
 
I don't see why there would be, output is going to be based on demand, it's not going to "push" anymore at idle than the system is drawing. Theoretically the higher the amp rating, the longer the alternator will last because it's not working as hard. In practice I think most "failure" comes simply from age and environment.

The load on the engine comes from the load on the electrical system. Not sure if your TBI programming has an idle step based on fan apply (like there is with AC, right?) but if so, it's there because the load on the motor through the alternator when the fan(s) are on is enough to affect idle.

Edit: Blue85 beat me to it.
 
That all makes sense. The mystery is that it doesn't seem like it would be especially more expensive to wind the alternator differently, so why even bother making low amp ones at all? Maybe it has to do with the required downstream wiring to keep the big alternator from frying things.
 
I haven't had them apart enough to check, but I suspect there are more changes than just the way it's wound...I suspect the rotor itself is a different piece, and then of course when you talk the 130 vs the 144, a different housing, etc.

I do tend to agree, you would think the cost of making X number of different output alternators would exceed the cost of simply making a billion of exactly the same part. Maybe newer vehicle alternators have gotten to that point? Now that many are coming with things like power windows as standard equipment, there would be less reason to have different output alternators. At most maybe two.

Then again, if you are going to charge a premium for a "heavy duty" vehicle then why not tack that cost on that allows you to keep lesser vehicles more appealing cost-wise?
 
Remember, when you make millions of something, pennies add up. The wire in a 140 amp alt is going to have to be a lot heavier than the wire in a 60 amp alt.

Plus, the diodes must be heavier, the heatsink for them bigger and thicker, and the bearings heavier to handle the side loading.

Since alternators are fairly efficient, most of the load it takes to turn one is caused by the electrical load on it, as stated before.
But, that additional mechanical load causes more side loading on the pulley also.


Don't forget, the best alt in the world will not have a good output if the belt is loose and slipping.

I found the test I came up with for checking belt tightness at the end of this first post..........


http://coloradok5.com/forums/showthread.php?t=250361&h
 
Don't forget to take a look at your stock electrical wiring, too. All the amperage in the world isn't going to help if your stock wiring isn't up to the task. I know the alternator wiring on my 85 is pretty skinny, I plan on upgrading prior to getting a better alternator.
 
Figure electric fan takes 30A continuous (not sure if both on, or just one), headlights are 15A, everything else (heater blower, radio, ignition, running lights, etc) 20A, you are at 65A.

Handy chart here: http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

At a point bigger wire does nothing but add cost. A margin of error however, is never a bad thing.
 
Maybe you should find a way to kick the fans on separately. I have the same fans, and TBI, with a big output alternator, and my idle actually drops when I kick the fans on. Both of mine are on one toggle switch for now. If I was you, I would use one fan on the TBI wiring you have, and hook one to your choice of Summit/Jegs thermostat electric switch things and have it come on by itself only when needed. They have a few temp ranges to choose from. Thats my master plan anyways.
 
I ordered this:

http://www.streetsideauto.com/p/powermaster-47294/

I'll see how things look with this thing installed. I don't remember the idle dropping with the fans, the TBI may adjust since it's controlling it. The lights did cause a temporary drop until the idle readjusted.

I'd like to keep things simpler if possible, like not adding yet another controller, but if I need to it would be easy to change one relay to run from something else instead of the TBI. Either manual switch or some simple thermal switch. The thing with a thermal switch is that it will keep the fans running even after the engine is off, right?
 
That should do it. Alternators don't put out their full power at idle. A person needs to get one larger that what the need by a fair amount. All the ones I have bought came with a graph showing their power out at various RPM's. They seem to put out half the power they are rated at idle. At about 1500 rpms they ramp sharply up to near full power.
 
I know you already ordered a new one, but I have seen some high output 12SI alternators that would quit charging at low idle speeds. It is an inherent problem with the 12SI. That is why lots have gone CS130. Hopefully this fixes yours.
 
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