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Author Topic:   Perko Dual Battery Switch
pcrussell50 posted 04-11-2011 04:32 PM ET (US)   Profile for pcrussell50   Send Email to pcrussell50  
My Alert or Montauk was set up by the previous owner for dual batteries. [The battery switch] has [positions marked] OFF-1-BOTH-2. "Both" would parallel [the two batteries]. Right now, the OFF position kills all engine functions, such as tilt-trim, and cranking for start, but the rest of the electronics still work in the OFF position, so the whole boat is not electrically dead, even with the selector in OFF. This is the way the previous owner set it up. He is a very experienced and careful mariner, as well as a CWW member. I'm thinking I'd rather change it so that the OFF position kills power to everything, but I don't want to do something not recommended or smart. Further, I don't even know if the switch will allow such a thing anyway.

Here are the electrical customers that will still work even with the switch in OFF:
-bilge pump
-bait tank pump
-color GPS map
-nav lights
-VHF radio

Thanks for any tips/advice, or if this can even be done.


jimh posted 04-11-2011 08:15 PM ET (US)     Profile for jimh  Send Email to jimh     
There must be a direct connect to one of the two batteries which is supplying power to those loads. If you want to move those loads to be controlled by your OFF-1-BOTH-2 battery switch, disconnect the feed that powers them from one of the batteries and move it to the COM terminal of the battery switch.
andygere posted 04-11-2011 08:31 PM ET (US)     Profile for andygere  Send Email to andygere     
The direct connect may be on the batteries, or it may be on the hot lug on the battery switch. You may find a cable wired to the hot side that powers a terminal block that all those items are wired too. I like your idea, off should mean off. If the boat were kept on a mooring, keeping power to the bilge pump may have been required.
jimh posted 04-11-2011 09:21 PM ET (US)     Profile for jimh  Send Email to jimh     
Yes, I agree with Andy: OFF should mean everything is off. On my boat that is how I have it wired, except for one sump pump which is fed directly from a battery. In that way, I can have everything electrical shut off except the one sump pump. That pump is controlled by its own switch and can be left in an automatic operating mode so it will evacuate water from the deepest compartment in the boat. In that way I can leave the boat for a few days without worrying about it being flooded with rain water.
contender posted 04-12-2011 10:22 AM ET (US)     Profile for contender  Send Email to contender     
Yes and Yes, Off is off and everything should be off period.
Jefecinco posted 04-12-2011 07:31 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Many non-trailerable boats are wired so that when the battery switch is in the OFF position the bilge pump continues to be connected to a battery for obvious reasons.

The reasoning may be applicable for smaller boats kept in the water.


jimh posted 04-13-2011 12:10 PM ET (US)     Profile for jimh  Send Email to jimh     
In general, one can say that distribution of DC electrical power on a boat normally does not involve any devices which are self-aware, and the behavior of the devices will conform to the fundamental laws of Physics, according as they are wired together. If you experience an unanticipated behavior from electrical devices, the root cause is most likely from the manner of their interconnection and not from some new phenomenon previously unobserved.

As for the question of what is the proper way or the best way to interconnect devices in the distribution of DC electrical power on a small boat, there is some room in this realm for a variation of opinion, and we have seen that demonstrated here.

pcrussell50 posted 04-13-2011 03:31 PM ET (US)     Profile for pcrussell50  Send Email to pcrussell50     

Yes, there is a terminal block that the non-engine-function customers are wired to. I'll look into wiring it so that OFF is off this weekend. And yes, it is trailered only, so I don't need auto-bilge-pumping capability.

Thanks to all.


pcrussell50 posted 04-30-2011 02:05 AM ET (US)     Profile for pcrussell50  Send Email to pcrussell50     
OK, I finally did it. I wired it like this:

Now, OFF is officially, off.


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