what is the battery selector switch selecting?

B

BillE

New member
I have the Perko 4-position switch 1,2,OFF, BOTH.

Is the switch selecting:
What is being charged by the alternator?
or, what is being charged by the battery charger?
Or, which battery is powering what?
Or ?

Yes, even after searching and reading many threads here it is still possible to be confused.
 
With a bit of hesitation, let me take a stab at this. The selector switch selects what source of energy is being used. Most setups using this setup will have two batteries. When selecting 1, you select one battery that you decide is either the start battery or the house battery. When selecting 2, you have selected the other battery. When you select "Both", you have selected to use both batteries at the same time, which might make sense if your start battery was low and could not turn over the engine on its own. Selecting "Off", isolates both batteries so no drain on either battery is present. Of course that only applies to loads that go through the switch, which are the majority of the loads. (There are loads, ie bilge pumps, that go directly to a battery and not through the switch).
Common use of this switch would have you select the start battery (1), to start your engine. Then switch to both for charging while underway. Upon shut down, when away from an exterior charge source, switch to the house battery. (2). Again, "Both" might be used if for some reason the start battery did not work on the next attempt to start.
 
Excellent explanations by both DW and Locallboy. I am like to just add a "combiner" voltage sensitive relay, or automatic charging relay, as Localboy suggests, keeping the 1/2/all off switch, and using it to select the primary load which runs off the batteries.

The ACR or VSR, will combine the start and house batteries, once the start battery reaches a voltage of approximately 13.7 volts. They will remain combined as long as there is a charging source, keeping the battery voltage above 12.7 volts (can be a battery charger or the engine generator/alternator. When the battery voltage of the start battery, drops to 12.7 volts the batteries are isolated. Thus there is no chance of running down the start battery.

In some boats I take that a little further, since the biggest draw we have is the refrigerator / freezers, we have a battery, or set of batteries dedicated to that, and they may have their own ACR, which begins to charge the dedicated 3rd bank of batteries when the house battery reaches 13.7 volts.
 
BillE,
Everyone was once a newbie, and they learned from others.
A PO may have already installed a VSR since they are cheap, easy to put in, simplify ‘switchcraft’ and mitigate against the most common switchcraft errors that lead to dead batteries on the water.
A few additional comments I hope may be helpful:
The 110v battery charger outputs will be wired directly to the positive studs of the batteries. (Neg goes to a common ground bus bar). When the shorepower and charger are ON, both batteries will be getting charged regardless of the Perko switch position. As above, think of the Perko as selecting the SOURCE of 12v power on the boat.
There are likely fuses on those outputs at the charger. There should also be fuses within 7 inches of the battery. Mine didn’t have those, perhaps the standards changed. If you need those, Blue Sea MRBF are simplest to wire.
https://www.westmarine.com/buy/blue-sea ... cordNum=33
An additional change to standards is that now yellow wire is used for 12V Negative (will be black wire on older boats).
The ‘BOTH’ position on the Perko switch is equivalent to what Blue Sea and some other switches label as ‘COMBINED’ you may have read about. You’d think there would be a standard, but no.
Items which SHOULD be direct wired to a battery (these are not affected by the Perko switch position) include any bilge pumps, CO detectors, and (often) stereo memory. A PO may have also installed a N2k network with sensors with parasitic loads and goodness knows what else.
Get a mulimeter (I like Fluke) and test around the boat.
Have fun learning how things work! Happily, it’s a never-ending quest.
John
 
----"Have fun learning how things work!--"

Well, some of it is fun. But boats get really hot in the summer and crawling around and under trying to trace a rat's nest of wiring is a bit less than fun!

I have also discovered that just "doing stuff" on a boat--in the water--- uses some neglected muscles, and I is sore! It is also more tiring than doing the same job on land, as one is always keeping their balance and reacting to the shifts.
Should be good for me!

Thanks to all for the helpful replies.
 
FWIW, the manual for my Guest battery charger said that the charger should not be operated with the battery switch set to BOTH. Any other position was ok.
 
ssobol":1atujjoy said:
FWIW, the manual for my Guest battery charger said that the charger should not be operated with the battery switch set to BOTH. Any other position was ok.
Click to expand...

That is correct, because at least some battery chargers will sense each battery individually, and then apply the appropriate charge. If you have combined batteries, you will have a "average" and the charge will not be ideal. The combiner does the same thing--and there is an argument to turn off the combiner when using the battery charger.

I am toying with buying a lithiumFE PO4 battery, to be dedicated to my refer/freezers. If I do so, that battery cannot combined when charging or discharging with lead acid or AGM batteries, because of both the different charing characteristics, but also the discharge characteristics.
 
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