Radiator Electric Fan Switch

[TurboMinivan]

I have a friend out east who used to rebuild alternators and starters for a living. I sent him a message to get his opinion on the matter. Rather than come back with an instant reply, he decided to ask a friend of his... a guy who just happens to work for Johnson Controls. Knowing how big into AGM batteries they are, I'm curiously awaiting his reply.

 

[Bobzilla]

In other words, his "100 amp" alternator is really not a 100 amp alternator. It needs the battery to handle a 60 amp startup load. I would think any battery would be able to quickly provide 60 amps.

The alternator I purchased was bench tested at G J starter & alternator in Grand Junction and was rated at 100 amps but tested at 105 amps FYI.

 

[jeep-N-montero]

The great thing with Jeeps is that there are a few higher output alternators from other Chrysler vehicles that bolt right up and can be had for under $40 or so, I'm sure the same goes for other makes as well.

 

[flexyfool]

The alternator I purchased was bench tested at G J starter & alternator in Grand Junction and was rated at 100 amps but tested at 105 amps FYI.

Yes, but it evidently can't do 100 amps at a high duty cycle. If it could, there would be no problem with it providing 60 amps for the fan start-up. I'm sure it is a good rebuild and upgrade. There is just so much that can be done to juice an alternator that was designed from the factory to do 40 amps. There are size and heat limitations.

 

[gijohn40]

ok I could be way off base here but I have worked with power systems of high amperage and low voltage (think 48 volt and 2-3k amps) and they always use acid filled batteries. The reason is that the batteries carry the load and the alternator just charges the batteries... agm/gel batteries have a hard time with instant on with high loads or spikes which the load needs so then the alternator bypasses the battery and supplies the load directly. This heats up the alternator. The battery should ramp up and take the load ok within seconds so the heat generated in the alternator doesn't get to hot right away but after running a fan on/off a few times it could start to break down.

This really is not a big issue and this is why you don't see warnings on cars about agm/gel batteries. But it does happen and causes alternators to die in shorter time periods.

There are cell towers that use 48 volt and 100-500 amp and they get away with agm/gel batteries just fine but the charging systems get replaced sooner.