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  #1  
Old 04-14-2007
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Battery Selector Switch - proper use

I have a Perko 2 battery selector switch on our 27' ODay. I was just wondering how others use this handy device:

-Do you start your engine with both batteries?

-Do you run the engine with both batteries selected so it will charge (or will both batteries charge even if only one is selected)?

-While sailing, or not using shore power, do you use just one battery?

-And, do you use battery 1 or battery 2 for individual purposes?

Looking forward to your input.

Brad
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Old 04-14-2007
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Depends how (and if) its wired. No joke - I had one on mine, but it had been replaced by a diode bridge and had no wires were attached.
I would guess you can start and charge with both batteries or take all the power (and insert all the charge) from/to one or the other. Normally, one battery is reserved for just starting the engine, in case you run the other flat, or if both are loaded, both flat - and then not be able to start the engine. I think there is one snag with a switch, depending on how it is wired. At no time while the alternator is running may it see "no battery" - without the load, it blows its electronics.
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Old 04-14-2007
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As Idiens said - it depends.

Are both batteries deep-cycles? Is the switch a "make before break" or not?

We have one starting battery (high cranking amps) and a deep-cycle house bank. We use the starting battery exclusively for starting, and the house bank exclusively for house loads. Our boat is wired in such a way that both batteries are charged regardless of switch position via diode protection.

In a previous boat we had all ccts through the switches, and were able to selectively use and charge each battery individually. Then we still had a starting battery and a house bank, but through switch selection we could choose to charge one set over the other.

The important thing here (if charging cct is also switched) is that you mustn't switch while the engine is running if the switch "breaks before make". You can test this by simply having a radio or a light on and switch from "One" to "Both" to "Two" and back. If the light/radio goes off between settings - don't switch while running. If they remain on through out, then you have a "make before break" switch. Most decent switches are "mbb", only the real cheap ones are likely to break between selections.
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Old 04-14-2007
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Suggest...
1. Using only start battery when motoring keeping the other one out of the system in case of charging failure and need to restart.
2. At anchor shift to battery #2 and use for lights etc.
3. At the dock...keep the switch on both to allow both to be charged.
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Old 04-14-2007
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It sounds like you don't have any fancy charging systems that can look after your batteries for you.

I've been told that if one battery is at say 13.2 volts and the other at 11.9v and you set the switch to "Both" the regulator will sense the higher voltage and will go to float charge mode and the flatter battery will stay flatter.

At present I have a little motor boat with a simple two-batteries-through-a-Perko system. This is what I do and I never have flat batteries:

- Before I start the engine I check my volt meter to see where each battery's voltage is switching alternately to both sides.
- I always start with the switch set to "Both".
- I then set the switch to the flatter battery and let that charge for a dominant portion of the trip we're about to do. That way the regulator senses the lower voltage and charges at a higher rate.
- Near the end of the drive I switch over to the other to top it up as well.
- When on anchor and using domestic stuff, I switch to one battery (could be either one) and don't use the other one at all until the process above starts from the beginning again. That way one battery is always preserved to start the engine and if we run out of electricity on the other (result of "electrical abuse" which doesn't happen often ) then we do without power or we charge up again.

If we're out for a few days, we use kerosene lamps in the evening, an LED anchor light, use the 12v fridge and radios sparingly. I never use the windlass without the engine running. I can't actually remember the last time I had a battery that wouldn't start the engine.

Hope this helps
Andre
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Old 04-14-2007
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It Depends

As others have written the correct answer FOR YOU depends on a few things like what type of batteries do you have, do you have regular access to shore poower, what kind of sailing do you do, etc.

On my Newport 28 (which for sale) I had two group 24 marine batteries, and the boat was on a mooring (no shore power). For a typical day sail, I would put the battery switch to ALL and leave it there. both batteries would be used to start the engine, both batteries would be charged when the engine was running, and both batteries would be used to run the GPS, autopilot, etc. For a few hour day sail I would not use enough power to really load either battery.

For a night sail, or an overnight at anchor I would set the battery switch to 1 or 2 and run off of that battery. The next day (or when it was time to start the engine) I would switch to the other battery to start the engine, and then back to the original one to charge it. When it was charged I would switch back to 'all'.

If one battery is discharged you don't want to tie both batteries together for starting, because all that does is have the good battery try to start the engine AND try to charge the weak battery.

Good luck,
Barry
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Old 04-14-2007
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Doing what Omatako suggests...switching your perko switch with the engine and alternator running will result in burned out diodes and a major alternator repair. Don't try it. I don't know what setup he has that allows him to do this but it is not the "standard" USA type alternator 4 position switch.

Omatako...you said...I've been told that if one battery is at say 13.2 volts and the other at 11.9v and you set the switch to "Both" the regulator will sense the higher voltage and will go to float charge mode and the flatter battery will stay flatter...
Actually once your batteries are paralleled by the "both" position on the switch, the charger only "sees" the combined voltage and (assuming identical batteries) this would be approx. 12.5 volts and would charge both until they reached 13.2. This is less efficient than simply charging the flat battery as you can bulk charge it more quickly when it is isolated.

Barry...running the engine with the battery switch in the both position is fine for a day sail...but should be avoided on a cruise. If while running, the alternator fails...your instruments will run down both batteries leaving you no way to se-start the engine once you've realized the problem exists. Don't ask me how I know this!
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Old 04-14-2007
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Something else you will need to do, is determine what your distribution panel is connected to. It should be connected to either one or the other batteries via the switch terminal. Ordinarily, Position 1 is connected to the starter and Position 2 to the rest of the electrical system.
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Quote:
Originally Posted by camaraderie
If while running, the alternator fails...your instruments will run down both batteries leaving you no way to se-start the engine once you've realized the problem exists. Don't ask me how I know this!
Good point.

I carry one of those portable battery jump start things in case something like that happens. Fortunately, I have not needed it, but a number of friends have!

Barry
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Old 04-14-2007
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The problem is even worse if you have a gasoline engine... as without an alternator, the engine will drain the batteries to power the ignition coil...
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