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Alternator is screaming, but why?

skunked

skunked

phat block everything
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I have a head scratcher and need some input.

Short story- Firing a new engine in a 57 Chevy and the alternator is making all kinds of noises. Disconnected the belt, no noise. Leave the belt on and disconnect the power wire (GM single wire setup) to the alternator and it's quiet. Swapped out the alternator, same problem. In fact we can run the engine and touch the alternator wire on the + terminal of the battery and it squeels like a pig, remove it and it's quiet.

Any ideas what would cause an alternator to do this? Car runs fine otherwise.

Some specs
57 Chevy
GM performance SBC
FiTech EFI
MSD 6AL and MSD distributor
Electric Fan
60amp CS130 alt & 160amp CS130
 
Tighten the belt. There is obviously a draw the alt is responding to when it's connected, and the load causes drag. If your belt isn't tight it will scream. The alt on my 6.2 would do the screech in time with the glow plugs cycling. on my set up the pinch bolt part of the alt was stripped so I couldn't get it tight enough.
 
I've tried a few different tension settings, bought different belts and even bought a belt that wrapped around the water pump only thinking that would bite better. The last setting was stupid tight, it has a turnbuckle so you can adjust the tightness easily.

It doesn't sound like a belt screech, sounds like the alternator itself is screaming. Hard to explain but it's not like a cold belt screech.
 
That setup running the alt backwards?
Regulator on the car and alternator?
 
the alternator we ran first was on the old engine however we moved it from the drivers side over to the passenger side because we swapped out the manifolds for headers which required new brackets. It's on v-belts so rotation has not changed. CS130's are internally regulated, no other regulator that I'm aware of.
 
With 2 alternators doing it, but only when powered, it's something not being right when the field windings are active.

@6872xtc , this might be a Pat question...
 
That's what I keep thinking.

We put a new battery in it, added more grounds, replaced the charging cable.
 
I should also mention that the first alternator bench tested fine at our local alternator rebuild shop.
 
Assuming you just didn't get two bad alternators (unlikely) and the wiring is correct, the belt or pulley may be glazed from slipping or if you have new aftermarket brackets, they may not be allowing enough belt contact with the pulley.
 
The belt was wrapped around the crank pulley, water pump and alternator. I also tried around the water pump and alternator only. So half the pulley was wrapped, very tight. No change.

I was reading about the 1 wire setups needing rpm to excite, wondering if that has something to do with it.
 
So if you had one tested at a local shop, did you get to listen to it on the bench?
I know that the CS130 makes some noise when it's working, but I wouldn't call it screaming. And if it makes noise when powered, then it's working and no more RPM is required to excite it.
Did you try a bar of soap on the belt?
Are you familiar with the CS130?

@500$k5
 
It didn't make the noise on the bench test.

I'm not very familiar with the CS130, it was installed by a hot rod shop down in SoCal last year when the Ron Davis radiator and e-fan was added.

I found out late last night that the second alternator we tried is a 7127 alternator, the Napa counter said that's the correct single wire alternator. I'm thinking that one may not have given the chance to excite as I never revved it up.

No soap
 
The alternator itself shouldn't make any unusual noises,there is always a slight whine when one is charging heavily after a cold start,but other than that it would indicate shorted diodes or a heavy amp draw somewhere on it,and its struggling to put out maximum output..
Perhaps there is a dead short somewhere in the harness or at the starter solenoid where the battery positive and fusible links connect..

Also I'm not that familiar with CS130 alternators,I dont know if the "feed wire" supplies a full 12v,or has to have a resistance to it to reduce the input some for it to sense the amount of amps needed to power everything..if it needs resistance and you put full 12V to it,it'll probably overcharge ?..

When there is no load on it (as in the charge wire left off,which isn't a good idea,it can blow diodes )it shouldn't make any noises..the fact two alternators do the exact same thing points to another cause,its most likely not the alternators--kind of "impossible" to get two that are defective in the same manner..
 
The alternator shop that tested it said it sounds like it had an unusual draw, that's a theory we're trying to diagnose yesterday by eliminating circuits from the car with exception of what's necessary for it to run. Wires aren't hot or smoking which I would think we'd see if there was a short. He also said the battery, if old would put a strain on the alternator as well so we replaced it too.

Perhaps we should try starting it, removing the starter wire from the battery and see if we can eliminate the starter.

and here is a pic of the current belt configuration to eliminate any slipping. Again, I don't think that's the noise we're hearing.

IMG_2508sm.jpg

and a pic of the car because everyone loves 57's

IMG_2501sm.jpg
 
The belt should wrap around the alternator pulley at least 2/3rds of the way around--I cant see in the photo how much contact the belt has,but if its only contacting an inch or so on the pulley,its possible its not enough to keep it from slipping under a load..
But you say it doesn't really sound like a belt squeal either..
I think its maxing out too,trying to overcome a heavy draw somewhere..

I remember an old car we put a GM alternator in at the junkyard squealed like crazy,and we started un-plugging things to see if there was a short somewhere..it wasn't till we un-plugged the wiper motor that it stopped!..never did figure out why it "drawed" any power with it switched OFF...I guess maybe the way the motor or washer pump was wired up internally maybe ?...electrical issues can be very befuddling..:screwy:..we had to snip the power wire to the wiper switch and put a toggle switch in line,and leave it off unless you needed the wipers turned on--then the alternator belt howled !..
 
have you hooked the wire from the alternator back to the battery just to see if there is a short in the wire somewhere? Or is your charge wire going directly to the battery already?
 
Is it an illusion or is the alt belt to large for the pulleys. On a one wire setup where does that wire go? I had to try 4 differt belts when i first put the 140 amp alt on my Blazer. Every time it loaded it squealed like a pig.
 
gonefishin said:
have you hooked the wire from the alternator back to the battery just to see if there is a short in the wire somewhere? Or is your charge wire going directly to the battery already?
Click to expand...

Charge wire goes directly to the battery. This was the way it was wired before swapping the engine over.

frankin5 said:
Is it an illusion or is the alt belt to large for the pulleys. On a one wire setup where does that wire go? I had to try 4 differt belts when i first put the 140 amp alt on my Blazer. Every time it loaded it squealed like a pig.
Click to expand...

That's partially why I was trying different belts, the vary slightly in width between manufacturers.

diesel4me said:
The belt should wrap around the alternator pulley at least 2/3rds of the way around--I cant see in the photo how much contact the belt has,but if its only contacting an inch or so on the pulley,its possible its not enough to keep it from slipping under a load..
But you say it doesn't really sound like a belt squeal either..
I think its maxing out too,trying to overcome a heavy draw somewhere..
Click to expand...

how do you get a V-belt to wrap 2/3 around a pulley without an idler. It's wrapping about 45% around it....
 
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