Monday, December 14, 2015

Battery Separator Upgrade to Blue Sea ML-ACR 7622 Automatic Charging Relay

My Roadtrek came with Sure Power Battery Separator Model 1315-200, a 200 amp solenoid version. The separator works fine, but draws about 1.5 amp when solenoid is energized and that is a significant solar energy loss.

I replaced mine with Blue Sea ML-ACR model-7622, a 500 Amp magnetic latching (bi-stable) automatic charging relay with manual and remote control. It is pretty expensive, about $200 US, but for me it is well worth it. Per manufacturer, it draws very low current (<40mA to monitor terminal voltage) in the "ON" or "OFF" states, and draws moderate current for very short time when changing state. It is dual sensing, senses charge on both batteries. It also has a start and engine isolation feature, but I did not use those. With the remote switch, I can manually isolate and combine batteries from the driver seat. I usually leave it to auto mode and turn it off (isolate) when house battery is charging from solar panels. For most applications, the cheaper 120 amp continuous rated Blue Sea SI-ACR should be plenty enough for alternator charging.

The replacement is pretty straight forward, same wiring were used from the old Sure Power isolator. ML-ACR terminal studs wiring for the batteries are interchangeable, so no need to trace what wire goes to start battery or house battery. I only needed to run 3 new wires (red remote, red (+), and yellow led wire) to the remote switch which I mounted on the dashboard next to the headlight selector switch. I also have to slightly enlarge the (+) cables ring terminal holes as ML-ACR terminal studs are slightly bigger (size 3/8") than the old isolator. You can change the (+) cables terminal rings at this point if you prefer going that route.

Blue Sea ML-ACR automatic charging relay wiring diagram.

Blue Sea ML-ACR automatic charging relay wired and mounted on passenger side firewall.

The remote switch location has a factory cut-out and was covered with a plastic snap cover. You can easily access the area by removing the light grey dash panel below it. With the panel removed, the plastic hole cover can be easily pushed out from the back. The factory cut-out has to be enlarged to accommodate the much bigger auto charging relay switch. I use a box cutter to slowly enlarge the hole.

Remote switch wired and mounted. The switch LED indicators are little too bright for me, that is the only thing I did not like with it.

Remote switch ground connection.

Wires were routed from cab to engine compartment through this factory firewall opening with weather tight rubber sleeve.

(+) wire to remote switch with 2 amp inline ATO fuse. All wires to remote switch were 16 gauge size as per Blue Sea manual.


  1. One of the best mods I have done to our RV!! I did not modify the dash. I used one of the switch blanks already in the Sprinter to mount the switch. Again, best mod that I have done to our RV/MH.

    1. Nice idea using the switch blanks. Thanks.


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