Alternators keep burning out???

[Garrcus]

I have an 85 K10 with a 305. In the past year I have had to replace the alternator twice, each time with a brand new battery since it seems to be killing the batteries as well. Thankfully both are covered under warranty at Autozone so it hasn't cost me anything other that the hassel and labor of swapping them out. After the last time I swapped it out I took the new one back to be retested and the guy said the alternator was running a little hot at 14.5 volts but said this wasn't extreme. Not being very well versed in the electronics side of things I just took his word for it. Well it has been about 4 or 5 months and again my truck will not start but rather just crank very sluggishly. I put a volt meter on both the battery and alternator before crank they both read above 12 volts and during crank the battery dropped and bounced between 9 and 10 volts. However the alternator stayed above 12. Any help or where to start would be greatly appreciated. Of course I'm going to bring it in and get another alt and battery swapped out at Autozone but I imagine they will both just go out again in another 6 months. Thanks again.

[bake74]

     I will ask this now, because if I don't the next person will.
     1:  how are you hooking it up ?
     2:  have you checked the cables (both ends,ground and power) off the alt. for cracks or loose/worn ends ?  How about ohms between the ends (fully disconnected) to see if the cables are broken or partially broken under the outer coating ?
     3:  Have you done the checks after replacement of both for voltage and amp draw with only the truck running and then with acc's turned on ?  (This could tell you if you have a drain on the system or maybe a spike or even a short somewhere in a certain system).
      4:  do you have a internal volt gauge inside your cab so you can see what it is doing while you drive?
      I am sure that is only a start to the question's, but that will get you a head start from what is coming.

[454Man]

Have you changed the + Batt cable?

[Garrcus]

Thanks guys for your suggestions, bake I followed the one wire back to the starter and it seems fine at a glance but haven't done the ohm check. If I do what should it be reading and what will it read or do if the wire is damaged? Also where does the other wire go from the alt I followed it back into a plastic sheath with a bunch of other wires? And to 454 no I haven't replaced the + battery cable is that a common problem? This electrical stuff is my biggest deficit when it come to doing the work myself which I almost always try to do so I can learn but hunting season is almost here and I need this thing up and running so if i can't figure it out in the next few days I might just take it in. Thanks again guys.

[454Man]

Yeah more than one May think. Check out my thread...you may not have the same prob but it's still a Good read http://forum.73-87chevytrucks.com/smforum/index.php?topic=26582.0

[VileZambonie]

You need to do a voltage drop test. Get some alligator clips for your meter leads and start with the negative side. Go from the negative battery terminal to the starter housing and observe the voltage reading during cranking. Search "voltage drop" and you will find a deeper explanation as I'm sure I've covered this quite a few times.... If you are seeing over .3V you've got resistance.

[Garrcus]

I read your previous thread 454 and some of it sounds similar (and it is a pretty good read), this truck will sit for 4 or 5 days at a time but I've never had the voltage spikes you were describing. I'll look over the battery cables as well. But my main question for Vile and anybody else is that should I wait to do a voltage drop test or any other tests until I replace the alt and battery. Since they are both fried won't any test right now be pointless or can I still track down the issue beforehand?

[rich weyand]

It takes almost nothing to run the ignition system.  I would replace the battery and leave the alternator unconnected right now.  Do your voltage drop testing on the battery alone, turning individual systems on and off.  You can put the trickle charger on it overnight.  This will keep the problem from frying another battery and alternator while you test.  Hard to fry the battery without the alternator connected -- they fry them with overvoltage -- and impossible to wreck the alternator when it's not connected.  This will also let you check voltage drops easier, because the battery voltage is more stable than the full system voltage, and is not RPM dependent, which the voltage will be when things are not running properly.

[Garrcus]

Thank you again guys for all your suggestions unfortunately I've had some work situations arise and I'll be traveling for a little while so this has to go on the back burner for now. I'm going to try and get into this once I get back and I'm sure I'll be asking some more questions once I try out some of these tests.

[Irish_Alley]

autozone used to do a starting test. dont know if they still do but they might if you ask. whats you volts when running?