Alternator Question

[77 casa grande]

Two weeks ago my alternator went. No problem, I went to Autozone and picked up a remaned. I went there only because they are the closest to me.
Last week i noticed my volt gauge was reading low, I pull the battery cable and the truck dies. OK bad alternator. Back to Twilightzone for an exchange.
I put the new alternator in and I'm on my way.
This mornning I,m getting ready to go to the beach, and sure enough my volt gauge is reading low. I pull the cable, truck dies. Back to Twilightzone
and get another exchange.
I put the new alternator in and I'm on my way,again.
I have a dual battery setup, one starting and one deep cycle with an electronic issolator.
OK now my questions;
Could the issolator be blowing out the alternator and if so, how do I check for that, or did i just get two crappy alternators?

 

[454Sub]

Not sure about the battery, but i went to Autozone, Advanced and Napa and got a bad PS pump from all 3 of them, in one day, in a row winning

 

[lovebomb_69]

I got a friend who got 3 bad alternators in 3 weeks from autozone several yrs ago

 

[ktmoutfront]

Find a local rebuild shop. We have a local guy who does turbos and electronics. Just him and his kid. He said they get more work because of the crappy Mexican rebuilds.

Have him add some juice to it also. With 2 batteries, you could use a bigger output.

 

[Fordum]

OK, couple of points.

First NEVER pull the battery cable to check the alternator any more. That was fine in the days of points and no electronics.
These days, its seriously risking fried parts.

Second, depending on how you have the isolator wired, there may be nothing wrong with your alternator.
The most common way of wiring it, splits the output of the alt. to the two batteries, but only one side has the voltmeter hooked to it.
Usually along with the power to the engine.

So, if that side is blown, then it is not getting anything from the alt. even though it is putting out what it is supposed to.

Fastest way to check it without a meter, is to hook the two positive battery terminals together with a jumper cable and see if the voltage comes up to normal after you crank it.

Of course, if both sides are blown, then it will fail that test too, but its unusual for both sides to blow out at the same time unless something major has occurred.

If you have a meter, then just crank it, measure each output from the isolator to ground, and then the input to ground.

If you have normal alt. voltage at any of those points, but not all, then the alt is good, but the iso is bad.

Note, the two outputs will be slightly lower than the input even if its working right.

 

[77 casa grande]

When I returned the alternators, both were dead when they benched tested them.
(which took them longer than it took me to remove and reinstall)

I questioned the isolator because it was the only other variable I could think of, as I have no other electrical issues.

I've had the isolator wired in for three years now.

 

[azblazer]

On a side note....a pet peeve of mine is that in those years gm routed the battery ground cable to the altenator bracket instead of straight to the engine block. Even though said bracket is bolted to the motor it seems to be worth half a volt or so on the gauge if it is ran to the block. Also make sure the ground strap from the back side of the cylinder head is attached and ran to the body is clean and tight.

DW