The main reason the ACR needs to stay connected after the sensed voltage
has slightly dropped is because when it senses a charging voltage it
often then connects to a deeply depleted battery. The depleted battery
then adds a heavy load that drags the voltage down some. If the ACR
didn't allow from some drop it could be constantly disconnecting just
when you need it to stay connected the most.

Opinion: The VW way of using the alternator charging signal to control a
battery relay has some serious merit for many vans. For one thing it
allows you to have a charging device such as solar that is set to the
needs of the aux battery, whatever type battery it is. With an ACR the
ACR will sense the charging voltage from solar and combine the
batteries, even if of different types with different charging needs. One
exception is if you use a uni-directional ACR such as a 1314A.

Mark

>>> 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
>>
>