Split charge vs parallel set up - Defender Source
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  #1  
Old March 9th, 2010, 10:08 AM
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Split charge vs parallel set up

Hi everyone,

Got a quick question and hope not to start a big argument here. My 110 was supposedly well kept by an EXMOD mechanic (says the previous owner) and instead of using a split charge system, it came with 2 optima blue tops wired in parallel. It also has a Warn winch which is directly hooked up to the batteries. Now I remember a little bit from my Circuits class, something like V=IR and that the voltage across a parallel system is the same. So while starting or winching, it should be drawing from both batteries. Would also charge both batteries at the same time although a little slower. I am just wondering why an EXMOD mechanic would wire it this way instead of using a split charge system? He know something we don't? Just trying to plan my rebuild. Thanks
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  #2  
Old March 9th, 2010, 10:24 AM
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Charles Galpin
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I think because it's simpler and there is nothing additional to fail. It's like having a bigger battery which I think is all most people need anyway (if they even need a bigger battery).
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Old March 9th, 2010, 10:38 AM
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biggest drawback to the two battery parallel system is that it does not provide any redundancy as when one fails, the other will quickly drain into the flat one rendering them both useless. Unless you can somehow detect that beforehand and quickly disconnect one of them. Which is basically what managed systems do.

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I think because it's simpler and there is nothing additional to fail. It's like having a bigger battery which I think is all most people need anyway (if they even need a bigger battery).
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  #4  
Old March 9th, 2010, 10:42 AM
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Charles Galpin
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Do you really see batteries fail suddenly though? My understanding is they will both get drained/charged equally and this shouldn't really happen. I can't recall ever hearing of a battery going from "working" to "dead" without being drained beyond repair or something.
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Old March 9th, 2010, 10:47 AM
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If you go parallel, just use a combo switch so you can run both together, but isolate them if necessary.
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Old March 9th, 2010, 10:49 AM
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Originally Posted by dmarchand View Post
If you go parallel, just use a combo switch so you can run both together, but isolate them if necessary.
Yes this is what I plan on doing.
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Old March 9th, 2010, 10:57 AM
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true it is not the most common failure mode. but i have had batteries lose a cell for whatever reason. anyway, it really isn't much different from the failure mode of one single battery so I say go for it.

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Originally Posted by cgalpin View Post
Do you really see batteries fail suddenly though? My understanding is they will both get drained/charged equally and this shouldn't really happen. I can't recall ever hearing of a battery going from "working" to "dead" without being drained beyond repair or something.
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  #8  
Old March 9th, 2010, 11:00 AM
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I have both systems... They both have their advantages and disadvantages. I run dual yellow tops in parallel in my ST and have not had any problems. In my yukon, I run a wrangler NW set up.

Since I drive the Yukon everyday, I like the ability to use the batteries separate and together. But, in my ST, both batteries get used together, so they charge and discharge together. I think that this keeps them better maintained vs. the second battery rarely if ever being used.

I think of this like a cordless phone in a spare bedroom this is never used, only kept on the charger so when needed the battery does not have a long battery life.
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  #9  
Old March 9th, 2010, 12:04 PM
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Depends on what you're doing with the truck.

My 110 (with 8274 warn) has 2 optimas connected in parallel, so just like one "big" battery.

I don't do heavy winching, and don't have much in the way of accessories (apart from my carPC, but that automatically shuts down when the voltage drops to a set level) so i don't see any need in having a split charge.

incidentally, some of the rovers direct from the factory are set-up this way.

If i were to go on an overland trip, i might consider having a split charge and using the second aux battery for powering a fridge/lights etc
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  #10  
Old March 9th, 2010, 04:12 PM
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Hi the parallel connection method works well as has been said above however it is not recomended to use a mix of types or sizes and you must avoid mixing a new battery with an old one.

the reason is as Ren said is they will try to even their charge which is achieved if they are very similar and you will have a large capacity battery, however if they are mis-matched they will cycle between each other which will warm both cells - it can be felt on the case. it is this that causes the batteries to eventually fail as the weaker of the 2 fails and will pull down the good one.

so .. put 2 new ones of the same size and brand and it will be all good.

regards all
Gren
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  #11  
Old March 9th, 2010, 04:18 PM
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The first time I installed an existing yellow top with a refurbished red top...I did not realized that I should not have done that, but they last over 3 years connected together in parallel. Then I put two brand new yellow tops together.
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