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Old 11-03-2011, 10:23   #1
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Batt Selector with 1, 2 and NO Both ?

Hi;

Does anyone make a battery selector switch to select from one battery, or the other, but NOT allow you to combine the two? I am installing LIFEPO4 cells, and I want to be able to bypass the BMS. THis seems like the easiest way to do so. Must of course be make before break - combining for that small time is not an issue.

Chris
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Old 11-03-2011, 10:53   #2
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Re: Batt Selector with 1, 2 and NO Both ?

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Originally Posted by witzgall View Post
Hi;

Does anyone make a battery selector switch to select from one battery, or the other, but NOT allow you to combine the two? I am installing LIFEPO4 cells, and I want to be able to bypass the BMS. THis seems like the easiest way to do so. Must of course be make before break - combining for that small time is not an issue.

Chris
I don't know of one....

Most pros use on/off or a combiner or connector relays if not using a 1/2/both/off switch ( which most pros I know don't like). So a make/break feature is not important is you use the other setups.
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Old 11-03-2011, 11:01   #3
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Re: Batt Selector with 1, 2 and NO Both ?

What about 2 switches?
Thanks
Ed
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Old 11-03-2011, 11:05   #4
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Re: Batt Selector with 1, 2 and NO Both ?

I have 3 switches fitted, a common negative for house and start banks, and an individual positive switch on each bank. With both positives "ON" banks are common, otherwise they are separate.
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Old 11-03-2011, 11:06   #5
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Re: Batt Selector with 1, 2 and NO Both ?

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What about 2 switches?
Thanks
Ed
i'm guessing that's exactly what I am talking about...actually you often want 3...on/off for each batt...one for an emergency crossover...that's where combiners and relays come in too...
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Old 11-03-2011, 11:50   #6
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Re: Batt Selector with 1, 2 and NO Both ?

I am not using this to switch between two banks, but between two paths to the same bank. One will bypass a battery management system. We have a seperate starter battery that is charged via a Echo Charger.

Chris
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Old 11-03-2011, 16:39   #7
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Quote:
Originally Posted by witzgall
I am not using this to switch between two banks, but between two paths to the same bank. One will bypass a battery management system. We have a seperate starter battery that is charged via a Echo Charger.

Chris
Why ?
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Old 11-03-2011, 17:56   #8
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Re: Batt Selector with 1, 2 and NO Both ?

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Why ?
The house bank is LIFEPO4. If the Battery Management system fails, I want to be able to get power from the cells. Also, the BMS disconnects the batteries at 90% discharge, in an emergency, I want access to that last 10%.

Chris
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Old 12-03-2011, 02:31   #9
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Then just put a switch bypassing the BMS disconnect relay. There's no need for anything else. ( other then a normal battery switch). With lifepo4 you need battery fuses with the highest interrupt rating you can find as well as the short circuit current is huge.

You will do significant to the batteries if you drain them flat

Dave
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Old 14-03-2011, 08:34   #10
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Re: Batt Selector with 1, 2 and NO Both ?

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Then just put a switch bypassing the BMS disconnect relay. There's no need for anything else. ( other then a normal battery switch). With lifepo4 you need battery fuses with the highest interrupt rating you can find as well as the short circuit current is huge.

You will do significant to the batteries if you drain them flat

Dave
I imagine that putting in such a switch, along with turning off the bms (it has it own switch) would accomplish the same thing. I was hoping to not add to the complexity with yet another switch.

I am aware of the potential damage to be done to flat lining LIFEPO4 cells, but in an emergency, it of course would be worth it.

Chris
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Old 14-03-2011, 21:09   #11
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Re: Batt Selector with 1, 2 and NO Both ?

This is the setup on our Mac. 3 switch - 1 for each battery, and one switch to combine them (emergency start, etc) Has a voltage sensing relay to charge the starting battery first, then the house.

Only way to go IMO. Wish my Ohlson had this instead of the 1,2,n,b switch

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Old 14-03-2011, 22:15   #12
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Re: Batt Selector with 1, 2 and NO Both ?

Here is a switch that may do what you want. It is arranged that from "OFF" you can get to "1" or "2" without having to transit/pass through "Both/All." I have used these switches for emergency engine starting cross connects. You can also modify the switch by putting a blocking screw system to physically prevent the switch from being positioned in the "ALL" position.
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Old 20-03-2011, 11:43   #13
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Re: Batt Selector with 1, 2 and NO Both ?

What about this?
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Old 20-03-2011, 13:53   #14
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Re: Batt Selector with 1, 2 and NO Both ?

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What about this?

That is EXACTLY what I have in my post (#11) above - 3 switch solution with a voltage sensing relay to charge both batteries (starting first, house second). That picture was the inspiration to me installing that in my Mac 26M.

I wish I had it in my Ohlson. the 3 switch solution is a great way to go. You NEVER have to touch the switches..ever.. unless you need to do an emergency jump start to combine them.

2 separate and distinct systems - 1 starting only, one house only. Never the 2 shall meet (unless you jump it with the 3rd switch that is).
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Old 20-03-2011, 15:25   #15
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Re: Batt Selector with 1, 2 and NO Both ?

Only one problem with that diagram - if you look closely the output of the alternator is going to the "other" side of the right hand "on/off" switch and the alternator has no direct connection to a battery except through the switch. This is a recipe for a burnt out alternator should that switch be off or turned off while the alternator is operating. Alternators need a good load for the output or they can go to infinite voltage and burn themselves out.
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