# Battery Selector Switch - proper use



## nightowle (Aug 2, 2006)

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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## Idiens (Jan 9, 2007)

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 No joke - I had one on mine, but it had been replaced by a diode bridge and had no wires were attached.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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## Faster (Sep 13, 2005)

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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## camaraderie (May 22, 2002)

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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## Omatako (Sep 14, 2003)

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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## BarryL (Aug 21, 2003)

*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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## camaraderie (May 22, 2002)

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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## PBzeer (Nov 11, 2002)

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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## BarryL (Aug 21, 2003)

camaraderie said:


> 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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## sailingdog (Mar 19, 2006)

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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## Omatako (Sep 14, 2003)

Cam

That's an interesting observation.

The most common thing that will cause the diodes to pop in your alternator/regulator is if you open-circuit them. In other words, disconnect the charge line from the battery bank while the alt is spinning. This will only happen if the switch turns one circuit off before the other is turned on. The four way switches commonly fitted to boats don't do that. They always make the second circuit before breaking the first.

If the switches you get in the US are different to that then they must be custom-made for the American market just to piss you guys off. I can't recall in thirty years of boating having a four-way switch that breaks without making first and all the switches I have had have always been made in the USA and the only time I've ever blown diodes is when SWMBO has turned the switch from One past Off to get to Two.

Or else I've had 30 years of charmed boating  

I have seen some boats that have a bank of separate switches to switch this on and that off and then if you follow the wrong sequence you'll have problems. But a four-way? Not in my experience.

Cheers
Andre


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## TSOJOURNER (Dec 16, 1999)

PBzeer said:


> 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.


Really? With a "1/2/Both/Off" switch isn't the starter and the panel wired to the common terminal on the switch. The switch ordinarily selects what battery you're using, not what's being powered.

What you're describing is a dual circuit switch, maybe? Perko doesn't supply those.


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## camaraderie (May 22, 2002)

Omatako said:


> Cam
> 
> That's an interesting observation.
> 
> ...


My guess is that you have such good luck because you have an isolator in the systems you've worked with. As this article states...without one, damage is a real possibility:
*An optional component for installation is an automatic charging relay or battery isolator, two names for similar, solid-state devices that allow all batteries to be charged by the alternator, regardless of how the battery switch is set. Without one, only the batteries that are currently selected at the switch will be charged. If the battery selector switch is in the ALL, BOTH or 1+2 position (depending on how the switch is marked), both batteries will be charged, but if only battery ONE is selected, battery TWO wonâ€™t be charged. An ACR or battery isolator also protects the boatâ€™s alternator from possible damage if the battery switch is operated with the engine running.

Boating World: Hands-On

Further data: 
"*
*Off, 1, 2 Both Battery Selector Switch*









The next step up is to install a "Off, 1, 2, Both" switch for the batteries. It is then up to the user to select either Off when leaving the boat, 1 for starting the engine, or for charging the engine start battery, 2 for running the domestic side, lights, instruments etc., or both to charge both batteries. Unfortunately, "both" can also be used to ensure that both sets of batteries are discharged together, thus ensuring that you *cannot* start the engine, a source of comfort when being blown onto a lee shore! *An added "bonus" of these switches is that when the engine is running and the switch is changed from position 1 to 2, through the off position, the alternator is disconnected from the battery, thereby burning out the diodes in the alternator.

From:Sailing Boat Battery Charging

*Can you read the small print under the off position on that switch? It is there for a good reason!


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## Omatako (Sep 14, 2003)

Cam

Yes it is there for a good reason. It's there for people who don't know about this stuff. I never, at any time, said that the switch should be turned through the off position?!? That's really dumb. Off is Off.

If you read my last post properly you'll find that I said: *the only time I've ever blown diodes is when SWMBO has turned the switch from One past Off to get to Two.*

Try turning the switch from 1 to 2 through the *Both* position. You'll get a pleasant surprise. Your alternator will carry on charging and by a miracle, the diodes will be safe!!!

Andre


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## Blue Eagle (Jun 29, 2006)

*perko battery switch*

Perko switches are Make Before Break, so switching whilst charging is no problem: Perko Dual Battery Switch
in terms of battery management, what I'd recommend is to nominate one battery as your primary, and start the engine on that battery. Use this battery for everything - nav lights, the lot, until it goes flat. Always charge it first until the amps drop off to zero, and then switch over to top up the secondary, and you'll always have power for starting your donk.

As a backup measure, I like to have the ability to hand-crank the engine to start it, and use a camping gas or paraffin lantern at night if light is required for prolonged periods.

Clearly these methods aren't necessary on modern boats with gennies

Best,

Blue Eagle


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## Blue Eagle (Jun 29, 2006)

camaraderie said:


> *An added "bonus" of these switches is that when the engine is running and the switch is changed from position 1 to 2, through the off position, the alternator is disconnected from the battery, thereby burning out the diodes in the alternator.*[/FONT]


It seems that the builders of the boats and accessories you guys equip yourselves with have great faith in the sailor's native ability to get things right first time.

The designers of the "vintage" ones I have experience with have no such faith: You CAN'T turn my battery switch through "off" to get from 1 to 2. first, it only moves through an arc of about 120 degrees. Second, the order goes "off", "1", "both", "2".

Cockups not an option! Progress eh?!

Blue Eagle


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## camaraderie (May 22, 2002)

Blue...that's the way they should be built. Unforunately the most common switches today leave you open to the very real danger of a clockwise turn!


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## TSOJOURNER (Dec 16, 1999)

my switch is "2" "both" "1" "off" from left to right & it is a make before break once it is left of "off". The alternator and starter is only connected when the switch is other than "off".
Unless the switch is in the "both" position when starting, the GPS will go off because of the drop in voltage when starting the diesel. I do have a .5 v drop to the instrument from the instrument panel connection altho i am using 16 guage wire to the Garmin pigtail harness. I am thinking about soldering an other wire in parallel to all the panel connections.
I already mentioned in an other thread the finding that an other guy found by measurements that the battery switch in "both" does not cause a higher charged battery be drawen down by a lower charged battery unless there is a cell failure.


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## camaraderie (May 22, 2002)

Rick...sounds like you think I disagree with you. That may be because I was quoting others responses to my original comment as I replied to them. Here is my original statement which I think is entirely consistent with what you said:
*
..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 too may have been blone in a former life! (G)


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## jrd22 (Nov 14, 2000)

Brad-

-Do you start your engine with both batteries?
Not normally, if batteries are low you may need to. Usually have a designated start battery(#2 in my boat)

-Do you run the engine with both batteries selected so it will charge (or will both batteries charge even if only one is selected)?
Both batteries will charge in the both position, but I prefer to switch from 1 to 2 at scheduled time intervals while running the engine.

-While sailing, or not using shore power, do you use just one battery?
Yes, I use the house battery(8D) and leave the start batt. for starting only.

We have a switch like yours and routinely switch from #1 to #2 while the engine is running with no problem so far(15yrs this boat, Yanmar). Normally you will have one starting battery that is a heavy duty diesel starting battery and then a second deep cycle "house" battery that you use for everything else. Hope this helps. John


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## sailhog (Dec 11, 2006)

RickBowman said:


> Cam,
> I agree with you but I disagree that you thought that I disagreed with you when I was agreeing with what you posted but not for exactly the same reasons, and is the reason why I posted that I was in agreement basically with what you posted from a previous posting.


I agree with this, but found the tone disagreeable. Hope you agree. If you don't agree, lets just agree to disagree.


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## camaraderie (May 22, 2002)

I more or less agree maybe, I think.


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## sailingdog (Mar 19, 2006)

So, are we agreeing to be agreeable even when we disagree?


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## Idiens (Jan 9, 2007)

Anyone had experience with Voltage Sensitive Relays as a way to automate charging of two banks?


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## sailingdog (Mar 19, 2006)

Idiens-

They make automatic combining relays, like the BlueSea ACR..


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