What Happens When Your Alternator Gets Hot?

When your alternator gets hot it does not technically "Lose" any amperage, it just changes its design in a way. It is not "struggling" or "breaking down" and not able to produce the same amperage anymore, it’s just changed its parameters.


The main design attribute in an alternator stator is the resistance from phase to phase, basically the resistance of each coil. (1 coil per phase) The less resistance each coil has, the more output the alternator is capable of.


The hotter the wire, the more resistance, which equals less output capability. You are basically making it a higher resistance stator (less output)


There is a lot more going on than phase resistance, but it has the biggest contributing factor in why the output is less when the alternator is hot.


Voltage is something else altogether.


About every voltage regulator has temperature compensation built in. Batteries are supposed to charge at a lower voltage when hot, so the regulator compensates and lowers voltage. Again, it’s not because the regulator can’t handle the heat, it’s just doing what it’s supposed to.

I have charged and closely monitored a LOT of batteries in my day, and one thing I have noticed is when a battery gets hot from the charger, you may as well turn the charger off and let the battery cool down before you try and finish charging it.


  • Let us say your charger is 8 amps on a big AGM that is real low, let’s say 10 volts. A lot of times the battery will hit the 12's and get extremely hot. Hot enough that 8 amps will not really be doing anything anymore. You can turn the amperage up but now you are just going to make the battery exponentially hotter and will more than likely result in damage. If you let the battery cool, you can put it back on 8 amps and let it finish.


When you have heavily drained batteries like that and you try and shove your 320 amps worth of alternator power down its throat, you can imagine how hot your battery would get if your tiny charger makes it get hot. This is the main reason I NEVER recommend playing with voltage. Too much can happen.


The best thing to do is when you leave a show after bangin' all day long is to actually turn your voltage DOWN to 13.0-13.5 and when you get home put your batteries on a charger overnight.
AFTER your batteries are topped off, ... you can turn your voltage back to mid to upper 14's and not have any problems.

Alternators are NOT battery chargers