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I have had 5 group 27 gel cells paralleled for over 10 years with no such
problems. Previous setup actually had a battery fail, but it just opened up the
circuit and prevented 12v from being provided. The cruisers I know and have
sailed with also have not experienced a short circuit failure of all the
cells-in fact, I have never even read about one. If you are using gels or AGMs,
there are already relief valves built in for venting H2. The battery will be
trash, but not explode. And I also studied physics in college.;<)
ahmet erkan wrote:
>> a few weeks ago I inquery about connecting 6 100 Ah batteries parallel.
>> I received very useful relplies, thank. I just started to install the
>> cables connecting the batteries together.
>> My old technician friend visited me, and pointed out,
>> that there can be a serious problem: if one of the batteries
>> fail and be short circuited (all cells, he could not really explain
>> how it
>
> can happen) the battery will be heated up by the other batteries,
>
>> will generate H2 and finally will explde. So he suggested to install
>> breakers for each of the batteries.
>> I don't know if it is really necessery, as it will add cost, complexity
>> and more possibility for something to go wrong.
>
>
> Hi Geza,
>
> Your friend sounds like a prudent person. I concur that, individual CB’s
> for each battery is better than hardwiring in parallel. They thought me
> in school a long time ago that voltage sources cannot be paralleled
> unless they are at exactly the same voltage. Unfortunately some genius
> decided to make 12V the standard for boats and RV’s so we have to use
> heavy wires, inefficient appliances and bend the rules of physics and
> parallel voltage sources (ie: Batteries). In order to parallel batteries
> safely you have to reduce their peak current capability. When switching
> batteries in parallel, Andina utilizes various techniques and secondary
> effects of long wires, wires that are not oversized etc. As a result the
> “combiner” limits the current to a reasonable level. If the laws of
> physics are not satisfied, nasty things like burned contacts, overheated
> insulation etc will occur that will make you wish you invested in the
> initial “cost and complexity” that you are trying to avoid.
> In summary, my recommendation for paralleling batteries :
> 1. Estimate the short term peak current you expect from the bank.
> 2. Divide the total current above by the number of parallel branches.
> 3. Add 25% and round up to select an automotive CB.
> http://www.bussmann.com/library/catalogs/Buss_Auto-Fuse_Cat.pdf
> 4. Install the CB’s close to positive battery terminals with double
> insulated wire.
> 5. Use a wire gauge appropriate with the fuse rating as jumpers. (Do not
> oversize the wires)
> 6. Cut 12 pieces of wire in equal lengths (ie: 3-5 feet or so)
> 7. Terminate the Positive leads with lugs at the same node, or use a
> copper bussbar.
> 8. Do the same with the Negative leads.
>
>
> I hope this was helpful Geza,
> Best of luck with your project,
>
> Ahmet
> S/V 8827
>
>
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KO6CK
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