Is there anything dangerous with a parallel battery bank

[picmacmillan]

hello all..i was reading a post recently and one of the responses indicated that it was a "no no" to string long lines of batteries in parallel?  does anyone have any info as to why this is the case? i thought it was very intriguing, and i had never heard this before?  any and all responses would be appreciated..take care all..pickster

[whatsnext]

I was the one who posted that and did not intend to infer that there was any danger. It's just that every battery is a little different so they will not charge evenly when placed in long parallel strings. All your batteries will act like your weakest one and if one battery developes a short all your batteries will then discharge into it or just not charge at all. Keeping your SpG matched will also be a headache.

John..

[asheets]

I'm told that if the imbalance between the strongest and the weakest parts of your bank is really big, the strong battery will try charging the weak battery (with bad results, including leaks, cell reversals, explosions, and other -- I've personally only had the 1st two happen).

I stick plenty of diodes between my batteries when I can when i build parallel packs...  My $.02 ...

[ghurd]

Hey Pickster!

I haven't seen any VERY bad experiences.  Meaning if 2, 12V are connected in parallel something very bad happens.

I have seen a bad battery drain the others, fast or slow(1), keep the others from charging(2), interfere with the others from suppling amps at a decent voltage(3), etc.

(1) If one battery 'leaks', as its V drops, it is sucking power from the others to stay charged.  Like if one battery leaks 1A at 12.4V, the other battery can't get past 12.4V if the charge amps do not get past 1A.

(2) Some batteries seem to 'leak' a lot faster as the voltage increases, meaning the 2nd battery never gets up to regulation because the leaky battery takes all the charging amps.  Like one battery leaks 1/4A at 12.4V, but it leaks 5A at 12.45V. The good battery can not get higher than the bad battery will let it even at high amps.

(3) Related to #2?  As the better battery supplies the majority of the amps, the 2nd battery volts drop fast and it starts using part of the power to charge itself. (?)  Very strange but I have seen it. No guess at an explaination for that.

It is best to have the batteries at about the same age.

Probably very important to have them at the same voltage, when they are first connected.

I have seen batteries that should never have been connected... connected!

Many worked fine together for years.  Others did not.  That leads me to currently believe if the charging system can keep up, it should be OK if you keep an eye on them individually.

You gotta do what you gotta do.

G-

[windstuffnow]

  I don't see a major problem with it as long as there are fuses between the junctions.  I run 6v batteries where 2 are series'd and the 4 pairs are paralled.  At each point where the 12v pairs are connected to the main line there is a fuse.  If for any reason one of a pair shorts it will blow the fuse and leave the balance of the battery bank intact.   If their not fused there is a possibility that the shorted battery will draw maximum amps from the others creating some very hot leads which in turn could cause a fire or explosion.   It's good to protect your investment with a few more dollars worth of fuses.  Its not good to mix batteries of different amp hr ratings and as well you shouldn't replace just one or two from a battery bank where there is a mix of new and old batteries.

.

[Shadow]

Good advice, What size fuse do you recommend? I have 3 banks (8,6volt batteries to a bank)of 48 volt. So I should have 3 fuses one on each positive side?..or either?

[windstuffnow]

  Hi Shadow,

    I'm using 100 amp fuses on each pair and seldom does my system draw that much on the entire bank.  You'd have to size them for your system.   I imagine the 100 ampers would work as well on your system.  If any one of the batteries shorted it will draw alot of amps quickly and blow the fuse.  You might be able to use smaller ones since your at 48 volts.  I figured the maximum draw from the inverter was 400 amps and since I have 8 batteries ( 4 pairs) making up a 12v system divided the inverter draw by the 4 pairs.   Yours would be divided by 3... not very scientific but functional.

.

[picmacmillan]

ahhh...thanks john for the info..i was a bit confused  i run my battery bank series/parallel, and thought it would be better to ask in case i missed something, than to have someone get hurt or worse...thanks for the reply...pickster

[picmacmillan]

thanks men for the comments and suggestions...helps for sure...below is a photo of my battery bank i am currently using...the picture shows aluminum wire, but i have since changed to copper...both kinds of wire were donated and the batteries are 6 volt bought used for 15 bucks canadian each..they work great and i am currently running a fridge, all lights and my stereo  off of these batteries in our remote cabin in northern ontario....i even had a moose comeo ut to the shoreline of the cabin to see what all the noise was...i was playing bob seger good and loud....kinda cool to see a moose come out to se what all then oise was...apparanly he has never seen anyone running their camp from alternative energy before ..have a good one..pickster