Alternator Hot While Charging Battery - ??

[nvrenuf]

I've had my Blazer on a trickle charger for about 3 hrs and I noticed the alternator is pretty hot to the touch (almost too hot to leave my hand on it). The engine has not been cranked in a couple of weeks so everything should be stone cold. Doesn't seem likely but is this normal?

I did have some wiring issues from a starter wire that grounded on the header but I've fixed everything I've found. The grounded wire did cause the 12v lead to the alternator to melt (insulation melted off of the entire wire from firewall junction to alt terminal). I haven't been able to have the charging system checked yet or even crank it to see voltmeter reading.

The alternator is the factory type for a '91 K5 w/ 350, "CS130" I think?

 

[nvrenuf]

Now an hour after disconnecting the charger the alternator is still hot, no discernible change. I've disconnected the battery. I'm assuming there must be a short inside the alternator.

 

[diesel4me]

It's possible one or more of the three diodes in the diode trio has failed,and is letting the current from the charger short to ground --this will also let the battery be drained overnight too,diodes act as a one way valve for electricity--this lets it charge the battery,but not let the battery discharge through the alternator when the engine is off

--if there is still one or two diodes "good" the alternator can still put out a charge and either not cause the "ALT" lamp to light up,(and make you assume its OK)-or it may glow dimly during night driving when the headlamps are on high beam and you have the heater on,etc (high amp loads)...it wont charge at 100% without all the diodes intact..

It is best to take one battery cable off when charging a battery--sometimes a charger will harm the diodes...usually what kills diodes fast is hooking jumper cables up wrong or a dead short,or a loose connection that causes arcing,and the resulting voltage spikes can fry them..

 

[nvrenuf]

that's good info - THANKS! Some of what you described sounds like my K5; I did have the dead short that melted some wire and then the next weekend the battery was completely dead (0.4v) after just sitting in the shop.