Last Tuesday I replaced my alternator because it wasn't charging. The charge light was on and I was watching the voltage drop at the battery as the motor was running. I jump in the truck this morning to run errands and the stupid charge light is on again.


What kills alternators? Was this one just defective? I got the limited lifetime warrenty, but swapping it out in the rain is going to suck. Oh, the one that died a week ago was only a year old too. Any thoughts?

 

Probably the cheap autozone alternators... it's usually hit or miss with those.

 

If your battery is dead you need to charge it. The alternator won't. It will run wide open & burn out fairly quickly.

 

That's probably what happened then.

It was also a cheap Kragen alternator.... I guess I'll pull it out, charge the battery, and get the new warrenty replacement today.

 

I'd check the battery for dead/shorted cells. If there's a shorted cell, that's a hella load on the alternator, which will cause it to overheat which will kill it.

 

I've never heard of cells shorting, how do you check for that?

 

You'll be in a catch-22 spot here, but... Most batteries are made up of 6 cells, each cell produces appx 2 volts of electricity. The cells are wired in series, so the voltage from the cells is summed together: 6 * 2 = 12.

If you test a battery and find that, with a "full" charge (there's the catch-22) it's only producing 10 volts, then you know that you have one "dead" cell. To ID that cell as open or shorted is tricky and there's some asumptioning going on... Generally if a battery is only 2 volts down, then the "dead" cell is shorted - this is based on odds. If it was open, then if the affected cell was anywhere except at the "end" of the series of cells, then it would be blocking the current from all the cells that came before it thus kicking out less than 10 volts.

If a battery is, say, 4 volts down, then you know you have two dead cells, and you can start working out the possibility of the combinations of open/shorted cells that could produce the math. This of course includes that cell #5 could be "open" (see previous paragraph).

You can also hook up the battery to a high capacity charger that has a decent ammeter on it. A battery that seems to charge at an abnormally high current probably has a shorted cell. This is because the short is decreasing the resistance of the load by 17% (1/6) which will increase the current draw of the charge.

Bottom line... you have the first step right - put the battery on a known good charger for 6-12 hours. Disconnect the charger and test the voltage. If it's not 12v or higher, something's wrong with the battery.

In the end you don't really care what the specific problem is - you only know that the battery is shot and it's probably causing you to go through alternators.

 

Wow, thanks for all the info. The battery 'seems' good (keeping my fingers crossed) as it had 11.70 volts when I pulled the alternator. I have killed the battery a few times over the past few months.... I bet that extra load killed the alternator.

 

Bingo!

Do what Midiwall suggested and toss it on a charger for 6 to 12 hours first. Attempting to charge a battery will fry most alternators...

 

Steve- 11.70 is not good....12.70 is. FWIW....I was once an assistant manager at a Checkers in SLC,UT.....and their alts suck. I would go with a Bapp import one before a Checkers....AutoBone is kinda low on my list also.

 

i'll never by electrical parts like an alternator from schucks again. a few months after i bought the '79, the alt died(while warming it up in the driveway, phew!) and i went to schucks and got a replacement. spent several hours trying to figure out how to get the old one out(i was naive at the time, didn't want to pull the lower radiator hose), got the new one installed in the pouring rain lying on my back in a puddle.

and it didn't work.

the next day, i pulled it out, took it back to schmucks and had them test it. it was no good! they pulled another one off the shelf and told them they're gonna test it or i'm walking out. it was junk too! i got my core back and went to napa, paid a little more, and it's never had a problem since! that was almost 3 years ago...

 

I had to stick an alternator in my 85 4Runner some years back and did the Autozone bit since they were near where I was living and I had to walk to get the parts. Carried the old one over and the new one back.
It lasted about 3-4 months. So, again I had to do the alternator walk (these things start feeling a tad heavy after a mile or so!) Had them load test it and it put out absolutely zero. Got smart, had them test the new one before I took it home and it tested ok. When I went to take it out of the box I noticed an odd sound. There was a flippin' screw floating around inside it!!!
I was very PO'ed, but didn't feeling like having to do the walk yet again so I pulled it apart, found the screw, looked to see where it had come from and apparently it had fallen in as an extra during assembly. Luckily, this one has lasted for a few years now, but you can imagine how long it would have lasted with a screw floating around in it.
Go somewhere that sells good product which will generally be reflected by a long(er) warranty, have them test it before you even leave the store and give it a shake and listen for good measure!
Get your battery load tested while you're at it. No reason to have to do this all over again and most places will do it for free. You might, however, and yes this may come across as dishonest, go somewhere else to have the battery load tested. Your battery may have fried as a result of a bad alternator, but it could be the other way around as well. Depending on where you got the alternator you have now, you could find yourself not having the warranty honored due it's being hooked up to a bad battery and you wouldn't have any proof. Sort of a chicken and egg thing.
Just an opinion.

 

11.70 was after driving it a little with the charge light on.

At full sitting charge today, the battery was only at 12.30v... but I've heard Optima's hold less of a charge over a conventional.... is this about right?