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Date:         Wed, 1 Apr 1998 15:32:16 -0700
Reply-To:     "Michael A. Radtke" <m.radtke@ELM.AZ05.BULL.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         "Michael A. Radtke" <m.radtke@ELM.AZ05.BULL.COM>
Subject:      Re: auxiliary terminal on alternator
Comments: To: "Vanagon@VANAGON.COM" <Vanagon@VANAGON.COM>

Hello,

I have had several discussions with Bob Hoover on this subject, and while he is certain, I am not.

The issue is whether the Motorola alternator/regulator senses voltage remotely or not. Bob Hoover says no, I say I just don't know.

1) No remote sensing. The output terminal of the alternator is regulated to the voltage necessary to fully charge a battery. This is somewhat temperature dependent, but usually taken to be 13.8 volts. If this is the case, there seem to be two options:

a) Rather than using a diode battery isolator, use a solenoid switch that connects the aux battery across the base battery only when the engine is running.

b) As was mentioned in a post sometime ago, there may be an internal connection in a Motorola alternator that can be used for remote voltage sensing. If so, connect this to the base battery and use a diode type isolator to automatically route the charging current to both batteries.

2) Remote sensing. If it has it, it would have to be through the idiot light wire, since this is the only other wire on the alternator. There are a number of other cars that do exactly this, so it isn't far fetched. However without a schematic of the alternator/regulator, I just can't tell.

The advantage of this setup is that the real battery voltage is sensed, the resistance of the wiring harness need be of no concern.

If this is the case, either type of battery isolator will work just fine.

So, can anyone verify what the Motorola system does for sure?

Thanks, Mike '84GL


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