I've only taken a couple apart but the ones I looked at were just big double diodes. And diodes, being semiconductors, are never 100% on or off which means your batteries are never totally isolated.

Diodes work by blocking DC current in one direction but not the other, but not absolutely 100%. Charging current flows through the diodes to both batteries but no appreciable amount can flow the other direction. This isolates the loads. But if you were to remove the terminal off one battery and measure across the wires with a meter you will measure the other battery's voltage.

Thanks, Tom Hargrave
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-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of Mark McCulley
Sent: Tuesday, April 28, 2020 9:40 AM
To: vanagon@GERRY.VANAGON.COM
Subject: do all ACRs work like this?

I have a Blue Sea m-ACR installed in my van, there is one aspect of how it works that I'm not sure that I like. It does not isolate the house battery from the starting battery unless the voltage on one of the batteries goes below 12.75v. When I installed the ACR I thought that the batteries would be isolated whenever they weren't being charged but this is not the case.

Regards,
Mark
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