the house batteries and the start batteries are isolated until they need to be combined.
Which should never be required. UNLESS charging is present. Discussed in detail in the link in my reply #5. Written by our trusted friend and guru, Maine Sail.
This is only the tip of the iceberg, please, read the entire link which has great explanatory material and much more detail and reasoning.
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Dual Circuit Plus Battery Switch Rant:
This is also a
rant or
vent about the Blue Seas Dual Circuit Plus battery switch. This owner installed one, and when his house bank failed internally last week, he had no way to switch to
only his
starting bank, in an
isolated manner. They key here is;
"in an isolated manner".
to get any sort of VHF, instruments etc. without combining a good battery with a completely failed, internally shorted battery/bank.
The start battery still likely had a little life in it, about 110 cranking amps (Midtronics) before I tried to start the motor, vs. the 1000+ it should have, but due to the Blue Seas DCP switch he was unable to take any advantage of his second bank, in an isolated manner, as a safety back up because the failure in the house bank bled it down to the point where he could not start his motor at all after using the "COMBINE" position of the DCP switch.
The owner did not realize the house bank had failed internally so when he got to his destination, and could not make a VHF call or turn on any of his electronics, he did what he thought he should do, he turned the battery switch to
COMBINE.....
When he did
combine the start battery with the house bank it was apparently into an internally shorted house bank. He left it in combine/parallel long enough, while using the VHF radio & trying to figure stuff out, that it sucked the remaining useful life out of his starting battery and he was left dead in the water and needed a tow to get home
- If buying a Blue Seas Dual Circuit Plus Switch please do your home work and make sure it is the right fit for you.
CONSIDERATION: The Blue Sea DCP switch
can not provide isolation of a bad bank while using the other bank. Your only course of action is the COMBINE or PARALLEL feature. In a case like this it forced the owner to combine his marginal condition starting battery with an internally failed house bank that was hoovering in the 7-8V range. A marginally healthy 12V battery can't charge an 8V battery for very long without being drained to the point of not being able to start the motor, especially one that has already been abused from improper practices...