Overvoltage from Alternator Runaway Under Load

[nanook12]

Wow, that goes back decades! Hasn't been an issue since at least the 1980s.

Just dealt with this a couple of weeks ago, on a 24V system (airplane) took out some expensive avionics. You need to get out of your garage more often…

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[ShadowsPapa]

Max charge current for AGM batteries is 30% of capacity, for 100Ah 30 amps.

So with my JT running 14.8 volts for several weeks, during the day, no headlights (it's all LED anyway) - it's not pushing out more than 20 amps?
These are voltage-regulated rather than amperage regulated.

 

[ShadowsPapa]

Just dealt with this a couple of weeks ago, on a 24V system (airplane) took out some expensive avionics. You need to get out of your garage more often…

I thought we were talking cars/trucks.
Motorola grounded their regulators to the alternator itself to prevent and issues with engine to chassis ground connections. It could still suffer a bad connection in that area, but it helped compensate for other grounding issues.

In general, the regulator will believe that there's a low voltage situation because of voltage drop across a bad ground and pump up the field current to try to compensate.

On Jeeps, there hasn't been a discrete voltage regulator since the late 1980s or early 1990s.

 

[J Sierra]

I went from Arizona to Washington with a current meter on my battery and alternator. Never more than 25 amps into the main battery. The current meter on the alternator had 130 amps max. To be clear two current meters one on the battery and one on the alternator.

 

[ShadowsPapa]

Yes, AGM batteries take less charging current than standard L/A batteries (my car can peg the amp meter if the battery is low - non-AGM - at 50 amps).
It's one reason most of us here stress use a charger with an AGM setting - something that will work specifically for AGM, not your 20 year old charger.
.....and why I don't run AGM in my cars, the regulated voltage is set in stone.

Were the batteries damaged? Perhaps, but a lot will depend on how long that went on. Maybe not if they didn't get too hot. The IBS is supposed to watch the temperature and the system will cut voltage to prevent over-heating the battery.

However, now we get back to - was his system connected into the Jeep's system properly???

Which "alternator" was being referred to - that got tangled since the stupid DC/DC system stupidly is named "Alternator" but there's nothing AC about it.

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