Could it be a winding or diode that's ok when cold, but develops a problem once warmed up by normal operation?
Overheating alternator?
- Thread starter Avery4
- Start date
At least on other Hondas, a lower charging voltage with a hot alternator is normal because the internal regulator is temperature compensated. The regulator's setpoint dropping to 13.3-13.6 volts with a very hot alternator such as from recharging a dead or shorted battery is perfectly normal. To me, the real question is why the alternator is getting that hot under normal loads.This is the only part that has me concerned. All the other results seem to be okay, IME. I'm curious as to what the rebuilder finds; keep us posted.
It takes a lot to get alternator this hot. I had a test mule years ago with an alternator bolted to a small OPE engine. A regular alternator dumping full load can get too hot to touch, but I can’t see boiling water.
212+F? I suspect the diode pack is weak.
Note, field windings at full 12V can hear the machine a good bit as well. Eventually I think those alone can probably reach mid-100s. Folks do weld with automotive alts in bursts.
Also, I’m not sure I hold to the “weak batteries wear them out” belief, as even with a weak battery, they can’t absorb big amps for more than tens of seconds before the vehicle voltage gets too high due to internal battery resistance. This can be studied as simply as with an in-dash ammeter and voltmeter setup. We can wish weak batteries could pull down big current for faster charging, but in my observations they don’t. My old school chargers output higher than the typical 14ish vehicle volts to get big amp charges in there.
212+F? I suspect the diode pack is weak.
Note, field windings at full 12V can hear the machine a good bit as well. Eventually I think those alone can probably reach mid-100s. Folks do weld with automotive alts in bursts.
Also, I’m not sure I hold to the “weak batteries wear them out” belief, as even with a weak battery, they can’t absorb big amps for more than tens of seconds before the vehicle voltage gets too high due to internal battery resistance. This can be studied as simply as with an in-dash ammeter and voltmeter setup. We can wish weak batteries could pull down big current for faster charging, but in my observations they don’t. My old school chargers output higher than the typical 14ish vehicle volts to get big amp charges in there.
Thanks for the info! Sounds like the case boiling water and 305+ degrees on the stator at idle while producing 39 amps at 12.5 volts is definitely something to be concerned about then. Seems like the insulation around the windings may start melting at around those temps or even significantly higher in the middle of summer under more load with the hood closed.
The rebuild shop should have looked at the output via an oscilloscope. That would pick up a bad diode
Yeah, they shouldn't heat up much at all. I just put a new one in my Focus and with a fully charged battery, the air coming out of it was slightly warmer than ambient, but not very much.
