Charging / equalising Parallel Battery banks

[Marco]

Hello,

apologies if this question has been posted but search results seem to

throw up conflicting ideas.

Why is it not prudent to use too many battteries in Parallel?

some people say 2 maximum. I've heard of 9 being used in Parallel no problem.

Equalisation of the battery voltage should not be needed if the positive and negative terminals are all parallelled up as current will always flow from the higher voltage to the lower voltage cell anyway - hence batteries remain in equilibrium at an equal voltage. So what is the problem?

Again when charging: one battery could not race ahead of another as the voltage

would then be higher and contravene the above.

I am almost sure that I am missing something obvious!!

Any ideas? (I was about to by 5 batteries on ebay and Parallel them up!).

Wrong section, fixed. Editor.

[Flux]

If you have enough charge capability to keep them well up there should be no problem.

When they stand idle the lowest voltage battery will drain power from the others, slight differences in specific gravity and plate material will affect the emf.

Batteries from the same batch will be better matched than those from different batches or manufacturers.

personally I think there is more trouble with series strings than parallel.

Flux

[Fiddlehead44]

A chain is only as strong as it's weakest link..

 My understanding is that if you have 5 batteries

at 95% and one at 50%, the bank will be 50%

      Fiddlehead

[electronbaby]

Hey Marco,

I dont think the idea of multiple strings in parallel (more than 2) is a good idea. This might be alright for float service batteries, where you have a constant charging source. Although I tend to agree with Flux, voltage drop between series strings might become a problem as cells age. It is common practice to keep a very close eye on this, as it is, specific gravity readings also.

The above is true while a bank is on float, or idle mostly. When a bank is constantly charged (cycled) often, another problem is equal current distribution within the bank. It is said that one should charge the bank with the (+) and (-) electrodes @ 180 degrees apart. This is said to equalize current flow into the bank by making all the appropriately sized cables, equidistant from the main buss bars to the actual cell terminals (in parallel strings). Although hard to imagine, (lol) #0000 cable does have resistance. For current equilization between strings to be the same, all the cables must be the same resistance. Since cables of this size are expensive, moving the charging source 180 degrees apart tends to emulate this.

Hope you can picture this. It makes good sense.  :-)

Have Fun,

RoyR

KB2UHF

[Flux]

Yes Roy, that is a good point that I forgot about, the lead resistance is significant and if you lump all the batteries in parallel and take the feed from the nearest one it will take most of the load.

Flux

[Marco]

Thanks for all the advice. I understant the current thing with

resistance in the wire.

Good Gale XL315 speaker cable is massive, flexible and cheap!

SO here's what i've done

I've Ordered 2 X 85Ah (12v) deep cycle leisure batteries

I'm going to Paralell just the two. If It turns

out my genny will be 24v I can always serial them.

[SamoaPower]

All good stuff! Flux brought up the keyword of matching and Roy expanded it to include the cables. Right on! I might add another element to the matching game - connections. We're talking about milliohms here gentlemen. I have seen so many poor connections (some of them mine) that I have to believe that it probably accounts for more high-current grief than anything else.

Consider Marco's two-battery parallel system. A minimum of four cables are needed to connect them into the system which means eight connections. Right? Sorry, it's actually 16 since each end typically consists of two, the one between the cable and the lug (you are using lugs, aren't you?) and the one between the lug and the terminal point. So, we have 16 potential trouble points, any of which can cause us problems if not properly done. And that's just for the batteries. Add in the charge source(s), metering shunts, switches, inverters and other loads - all the high current paths, and it's a wonder we can get it to work at all!  Obviously, in a larger system of more banks or batteries, the potential problems multiply. Depending on the environment, connections can be a high maintenance item.

How do you put on a lug? Crimping seems to be in vogue because it's quick and easy, if you have the proper tool. I'm sure many of us have tried crimping using more common tools with various degrees of success. Okay, trying to get a decent mechanical connection is worthwhile. But, it's not enough! You MUST also solder! I know, soldering a lug on a 4/0 cable is not for the faint-hearted, but it's gotta be done. So, we crimp AND solder. I use one more step to insure the integrity of the connection. I put on a sleeve of thick-walled adhesive-lined heat shrink tubing over the connection. This offers strain relief and seals the solder joint from corrosion.

Proper matching can cure a lot of ills.

[Clifford]

I just have regular battery clamps on mine.  They just bolt on to the ends of the cables.

Right now I have a continuous wire that I've bolted multiple clamps onto...  so there is less chance of failure at the clamps.

Someone suggested fuses between the batts...  I don't have them, but it did sound like a good idea in case of an internal short, and I'll probably do it the next time I rework the array wiring.

All of my battery terminals have both wing nuts and clamp style lugs.  The nice thing about that is that it is easy to connect 2 cables to the same terminal.

You must be concerned about time to charge as well as reserve capacity of the batts.  And, perhaps using them heavier on weekends than weekdays.  

I believe that most batts are supposed to last significantly longer if you don't deep cycle them on a daily basis.  But, that may also be an illusion...  

Say you buy one battery and get 500 - 80% deep cycles.

Vs buying 4 batteries and get 2000 - 20% shallow cycles...

Your total cost in batteries may actually be the same.

[Drives]

On high current buss bar, I use this

http://www.cool-amp.com/

It works well, but expensive.  I don't know how it would react with battery terminals.  If you can't afford a silver based compound, then Noalox works well also, it just uses Aluminum vs. silver

Just a thought.

[scottsAI]

Do NOT use silver for battery connection.

While designing my battery bank, checked out NEC.

(national electrical code)

Requires a lead coated terminal to interface with the lead battery terminal.

Different metals when wet (moist) become a 'cell'.

The cell will increase the resistance of the connection and promote corrosion.

I had 8 golf cart batteries to interconnect.

I decided on coper bus bars, battery layout made it very easy to use.

Copper bus bar was much cheaper than buying cables.

0.25” x 0.75” x 48” was $16 on ebay. Cables were almost $80.

For me the bus bar was easier than making my own cables.

MUCH lower resistance. Like equivalent to 0000 cables!

I used clear heat shrink tubing around the bus bars.

Looks nice. ($20 adhesive type)

I soldered the copper bottom, so lead to lead connection between the copper and battery terminal.

Did make cable from battery to controller.

Have fun,

Scott.

[Drives]

Makes sense, thanks for the info.

[nothing to lose]

"Say you buy one battery and get 500 - 80% deep cycles.

Vs buying 4 batteries and get 2000 - 20% shallow cycles...

Your total cost in batteries may actually be the same."

I think there is much more than is normally considered here.

Yes if it equaled out that way, 4x's either way it would be the same. Probably is not exactly equal though or 4X's. Would you get 450 deep cycles or 550 deepcycles, most likely somehow you either win or loose but not exactly break even.

Then there is the self discharge, more batteries have more self discharge and require more charging to make up for it. So you got a bit of a loss on that end.

In todays world, what direction are batteries heading in price? Are we better off buying more today and makeing them last longer because higher demmand as more people go to RE power may drive up prices next year, or will prices drop because more sales are being made?

Will government over tax batteries because they don't like lead any time soon like they do everything else they don't like? Ciggarettes, alcohol, Freon, etc.. will Lead be next?

Right now we want our batteries to last a long life because of costs and such, in 2 years though will a much better battery be on the market for the same price or lower we would rather have? We hear alot of battery talk, when will we get them and for how much?

Buying 1/5th the batteries and getting 1/5 the life with deep cycles may not be so bad if we can buy a battery twice as good for the same price in 2 years. BUT if we still only have the same choices for batteries as now and they double in price then we should have bought them all now and shallow cycled them perhaps to get that longer life.

I think things like the above and other thoughts similar should also be considered at times. Right now we are in a rapid changing world.

Look at what happend to Solar pannels. Most people were thinking as demand increased manufactures would increase the supply and prices would drop, many waited for that drop. Instead they have gone far higher right now. So should we wait for a price drop latter this year or grab them now before they go even higher?

I have the same question about buying batteries and price changes as solar pannels.

And what about that NEW solar progress that was talked about and we have not yet seen that was supposed to lower prices? Is that the same with batteries, lots of talk about things we won't be getting?

Though with electric vehicles in the picture we may have a better chance of getting better batteries.

So for me, I really can't decide what is the best way to go, other than buying good used batteries and saving a ton of money, and I should get as many of those as I can at $10 compared to $70