The Powerstream isolator is a split-charge relay such as I described. The difference is that they add a small "black box" which controls when the solenoid gets energized.
Originally Posted by olsen_karl
I don't think that black box is really necessary, and in fact I don't much like it. It disconnects the batteries when the voltage drops below a certain point, and reconnects when the engine battery voltage gets up to a certain point.
I prefer to disconnect the battery whenever the key is off. I don't want to depend on a black box which could fail, and I don't see a need to have the batteries tied when the key is off, except perhaps if you are charging the aux and need to charge the main as well.
You can solve that by simply adding a switch powered from the engine battery to energize the solenoid manually when needed (very rarely).
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