# Correct Battery Conection?

Discussion in 'Solar Power' started by zaskar, Aug 29, 2011.

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Given that I have 2 x 110amp batteries connected in parallel, is it better to connect my solar panel (via a controlller of course) to the POS and NEG of one battery only, or to the POS of one and the NEG of the other?
Does it make any difference in a parallel bank and if so, why?

Ta

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3. ### jonandshellFunster

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It won't make a blind bit of difference!

4. ### chrisgreenFunster

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i have my inverter connected as in method 2 in your link jim:thumb:
dont know why i done it,it just seemed to make sense:thumb:

5. ### scotjimlandFunsterLife Member

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you are serious ?

perhaps all the theory and experts are wrong ? ..

Last edited: Aug 29, 2011
6. ### jonandshellFunster

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Hi Jim

I work on electric warehousing equipment and stacker cranes.
DC voltages are up to 80v, Ac up to 415V 3 phase. The batteries we deal with go up to 80v 800Ah.

I have never, repeat never, seen any evidence of pos and neg cables from a charger ever being connected across paralleled cells or batteries as a design feature. From an electrical standpoint, as long as all interconnecting cables, busbars and connections are up to the job and are tight, parallel is parallel!

I would say, that there is truth in the theory, but for connecting just two batteries, drawing low amperage?

The voltages at all points along the pos and neg sides of paralleled batteries will be equal. The argument on the link you posted for unequal current flow will only hold true where the batteries are connected with cables and terminals not up to the job. Ie, of insufficient cross sectional area, or of differing materials, causing resistance. It must be remembered, when planning cabling for an extra battery, that resistance increases in your cables the longer you make them. For our extra battery in the garage, we have run a length of 35mm sq cable to it to combat the inevitable voltage drop.
Resistance in power cabling usually results in heat and heat in our game is a fire risk. Most of our customers have a thermal camera survey carried out on their charging banks as a condition of insurance.

This is only an opinion based on industrial experience, however. As is my opinion that any battery labelled 'leisure' is only fit for scrap. I am sure there will be a man in a white coat in a lab somewhere who will have a different opinion though!:BigGrin:

7. ### scotjimlandFunsterLife Member

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Hi John..

I am not questioning your experience ..

I am also well qualified with 45 years experience in industrial electrical maintenance including DC power generation and storage. .. but won't start on that as I see no point as it would fill a page and make very boring reading .. and it could all be a pack of lies.. but it's not..

The OP asked a simple question, I gave what is consider the 'best practice' answer .. the last thing an electrical novice wants is for two "experts" to lock horns over DC theory and what is the best practice.. all they want is a straight forward answer to a basic question.. I gave that and some further reading as he also asked for an explanation ...

a "blind bit of difference" is not an accurate or helpful reply and also called into question my answer, knowledge and experience.

We sparks must stick together .. :Wink:

8. ### jonandshellFunster

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Hi Jim

I was perhaps trying to over-emphasize the small difference differing connection methods would make on two batteries subjected to the low amperage draw of a MH.

I didn't mean to trivialize the subject too much! :Blush:

I believe most of our power problems as MHers come from dreadful batteries, not how we connect them!

9. ### scotjimlandFunsterLife Member

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I meant to say, I agree that at 80v the volt loss will be insignificant .. so it would make no difference, but we are talking about 12v battery banks.. where even small voltage differences and drops can significantly affect the banks performance .. both charging and discharging

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Thanks guys, much appreciated.:thumb: