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Old 08-29-2011, 08:06 PM   #13
FlyWright
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City: California Delta
Vessel Name: FlyWright
Vessel Model: 1977 Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 13,728
RE: House Battery Bank Switch

My system uses a Yandina combiner which is not as stout as the Blue Seas ACR, but I think the combining logic is similar. For the purpose of this discussion, let's assume a single engine with the alternator charging the start battery and the ACR between the start and house banks. The windlass is on the start bank and is only operated when the engine is running.

My understanding is that in a normal non-charging state, both banks are isolated and load on one bank cannot draw the other bank down. All house loads come from the house bank and all start and windlass loads come from the start bank. When charging is present and the start battery reaches a predetermined voltage indicating a significant charge (i.e. 13.0V for 90 sec or 13.6V for 30 sec), the ACR closes to allow the charge to be shared with the house bank. If, during charging, the start battery voltage drops below a predetermined level (12.35V for 10 sec, 12.75V for 30 sec) due to a high demand windlass operation, the ACR opens to allow the start battery to receive ALL of the alternator charge. In all cases, when the charge stops, the ACR opens and disconnects the tie between the banks, regardless of battery voltage. In the event of a voltage regulator failure and the charge voltage reaches 16.0V, the ACR opens to prevent overcharging of the house bank (note that this will not prevent overcharging of the start bank). The installation of an override switch allows you to combine or separate the banks at will, regardless of charging condition or battery voltage.

If your system is tying the banks together when no charge is present and you don't have an override switch, you might have something miswired. I had similar problems with my boat until I discovered the PO had miswired the battery switch which caused both banks to be paralleled when I selected bank 2. This caused both banks to draw down when I thought I was drawing only from the house bank. It took a while for me to figure it all out, but once I did and I replaced all batteries and recabled correctly, all has been well.
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