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Battery bank mid-point problems


incagarcilaso

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9 hours ago, The Terrible Triplett said:

I would think the only real benchmark would be 2 identical setups, one using the batteries, one carefully nurturing them with balancing to see which bank last the longest ito Ah drawn out of them over their lifespan i.e one lasting 5 years at max Ah usage, the other 8-10 years with min Ah usage = waste of funds.

What do you guys think?

I like that idea.  Will you please sponsor the batteries; I'll perform the tests.  :D

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9 hours ago, The Terrible Triplett said:

In the back of my mind I keep on wondering why the guys whom are off-grid, only generators as backup, using large Ah banks with 2v cells, who's banks last +-15 years. Why do none of them have balancers, and they do know about them. I know they do keep painstaking records of each cells gravity, and handle it when there is a discrepancy by equalising.

That is the advantage of vented cells. Balancing is how you equalise VRLA batteries. More and more 2V VRLA cells are coming onto the market so its a problem that is going to be more common.The hassle is a HA02 was not designed witha 1500Ah bank in mind.

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56 minutes ago, Chris Hobson said:

The hassle is a HA02 was not designed witha 1500Ah bank in mind.

Could you elaborate Chris? What can't the HA02 do with a 1500Ah battery composed of 2V cells? Just to be clear before I buy them.

Referring to other posts about this becoming more of a problem, why is there only this one balancer on the market, why can't it cope with 2V cells and why is it so difficult to source? I've seen quite a few forums with people in my boat trying to find a balancer with very little luck. Why on earth don't the battery manufacturers produce and sell a balancer for their cells? Would make life a lot less stressful - I buy Enersys and have an Enersys compatible balancer. I suppose that would just be too easy.

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12 hours ago, Chris Hobson said:

4th pair of wires on cell No 21's positive and cell No24's negative

After a while and having spent time balancing cells and monitoring during late absorb on can start identifying the weaker cells - the ones with highest voltage under charge and position them in the middle of the bank where there are two balancers acting on each group of cells. It is going to be quite a tall order to balance 1500Ah cells  the balancer can shunt 5A but the charging current could be as high as 45A during late absorb. Balance is not going to be achieved easily it is going to take time. I would double up on balancers if you have spares so that on could shunt 10A for cells 1-6 and 19-24. One would be able to shunt 20A for cells 7-18.

 

Edited: Replaced the incorrect term battery with the correct term cell.

Thank you very much for this Chris, it is going to help greatly. I had no idea you could overlap the balancers so that some cells have two chargers working on them. As you say, the literature on this is extra double 'lite', so I will be following your advice in this post for the set up.

I get why you suggest working with groups of 3 initially - it is also what I thought as there is no specific reference to leaving two disconnected from the HA02 (even though the specs for voltage ranges might suggest it is possible).

Do you overlap cells 7-12 and then 13-18 for any other reason than that it gives you a nice grouping in the middle where you know you can swap in the worst looking cells to bring them back to health? I ask this because I am going to have a real job moving cells around in the bank. If this were the case I might just try to double up equalizers on the whole bank to avoid moving cells around - i.e- move the equalizers around rather than the cells.

I also understand from this that I could add in more balancers anywhere within the bank to try and increase the amperage used to equalize. On sunny days in summer the inverters show charging currents in excess of 70A but I'm not sure if that is a 'true' reading of what the batteries are taking. Does this mean that the work of the equalizers is going to be defeated because they can't shift enough of the charge onto the weaker cells and the stronger ones will continue to race ahead? I suppose I could also use the inverters' controls to help me, i.e. restrict and/or increase the charging current on some occasions depending on what I am trying to achieve?

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36 minutes ago, incagarcilaso said:

Could you elaborate Chris? What can't the HA02 do with a 1500Ah battery composed of 2V cells? Just to be clear before I buy them.

A battery bank tends to go out of balance during late absorb. For my bank that is a charging rate about 10A and each balancer can "move" 5A so it copes. You are looking at a charging rate of about 45A hence the idea of doubling up. If moving cells around is a problem then doubling up your battery balancers is the way to go. 

After a month or so I would still casually invite your brother-in-law over for a weekend braai and the after his second beer say would he mind helping you move a couple of cells round in the battery room - putting the weaker cells in the middle where you would then have 20A balancing capability. 

It is going to take a while but the balancers will get your cells back into balance. Doubling up is going to help tremendously as you are going to reach your goal sooner and extend the cells' life.

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5 hours ago, incagarcilaso said:

It suddenly occurs to me after all the discussion about how to deploy the HA02s - they do work OK with gel batteries, right? The Enersys OPzV is a gel, not a lead-acid battery. Not sure if that was clear. Don't want them blowing up on me or anything.

Yes they work with Gel batteries and the good news is that the optimising current is 10 A (not the 5A I previous said in this thread)  according to the manufacturer's website. Gel batteries are lead acid batteries just a specific subset of lead acid where the electrolyte has had silca gel added to it immobilising the electrolyte so that they are non-spill and so do not have to be kept upright.

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20 hours ago, Chris Hobson said:

Yes they work with Gel batteries and the good news is that the optimising current is 10 A (not the 5A I previous said in this thread)  according to the manufacturer's website. Gel batteries are lead acid batteries just a specific subset of lead acid where the electrolyte has had silca gel added to it immobilising the electrolyte so that they are non-spill and so do not have to be kept upright.

OK. Higher transfer of amps is good news. The manufacturer/distributor website I have found for these is http://www.diytrade.com/china/pd/16161520/48V_Battery_equalizer_balancer.html Is that the one you are referring to? The description there refers to "lead-acid (VRLA)" type batteries. Does that include the OPzV gel batteries? Include image of the HA02 product description I have read and of the top and connects of my cells (completely sealed).

Edit. I have just found a paragraph on recharging in the OPzV documentation where it talks about equalization, but it doesn't enlighten me much. Image of paragraph attached. I also attached the full OPzV product document.

ha02descrip.JPG

OPzVConnects.jpg

OPzVLabel.jpg

OPzVrechargepara.JPG

EN-zV-OM-004_0613.pdf

Edited by incagarcilaso
Added info and documentation
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FWIW. Solder close or on a battery pole is a combination I don't like very much. If ever there is a problem, and the pole gets hot, the solder could start melting causing even more issues.

Got it from the web where guys use solder when the attach a lug to the end of a cable filling the caps with solder. One guy then goes and shows you why it is a bad idea. Will look for the video again.

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1 hour ago, The Terrible Triplett said:

FWIW. Solder close or on a battery pole is a combination I don't like very much. If ever there is a problem, and the pole gets hot, the solder could start melting causing even more issues.

Got it from the web where guys use solder when the attach a lug to the end of a cable filling the caps with solder. One guy then goes and shows you why it is a bad idea. Will look for the video again.

To my mind it's swings and roundabouts. A dry joint may cause the heating one is trying to avoid.

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4 hours ago, Chris Hobson said:

To my mind it's swings and roundabouts. A dry joint may cause the heating one is trying to avoid.

Crimp the joint right one time and you do not need anything else.

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2 minutes ago, The Terrible Triplett said:

It never is with solar.

FWIW - I would not cutt-off anything that works well as is.

Yes, understood. The leads on the two HA02s that span the two strings of 12 cells aren't going to be long enough either so I am going to have to totally adapt these. The string length is just under 2 metres so, even placing the HA02 box in the middle, it won't reach the last cells. I'm just hoping that extending the length of the leads won't affect performance. I imagine not for that amount (I may have to add about 30 cms).

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4 hours ago, Mark said:

I extended my cables and when I did that I added 5a fuses for safety.

Have just noticed that @Chris Hobson mentions that these can transfer up to 10a, so perhaps it would be better to add 10a fuses in my case as I certainly may have that or more running through the batteries? Having said that, if I have the 24 cells charging at, say, 75a from my panels (probably a max) I'm not sure how many amps enter each cell - is it just the max total divided by the number of cells?

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One other clarification that would be useful. I think @Chris Hobson mentioned that in this situation, the "weaker" or problematic cells are identified by the ones that accept the higher charge. I thought it was the other way around, that the weaker cells were the ones that could not charge up to the float charge or absorb charge set by the inverter. Could anyone explain why it is the cells that charge "too easily" that are the weaker ones?

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2 hours ago, incagarcilaso said:

 Having said that, if I have the 24 cells charging at, say, 75a from my panels (probably a max) I'm not sure how many amps enter each cell - is it just the max total divided by the number of cells?

Hi 

Since you have a single string of batteries you will have 75A going through each cell. If you have multiple strings you then divide Amps by the number of strings.

2 hours ago, incagarcilaso said:

One other clarification that would be useful. I think @Chris Hobson mentioned that in this situation, the "weaker" or problematic cells are identified by the ones that accept the higher charge. I thought it was the other way around, that the weaker cells were the ones that could not charge up to the float charge or absorb charge set by the inverter. Could anyone explain why it is the cells that charge "too easily" that are the weaker ones?

As a battery charges so electrons are used to convert Lead sulphate into lead oxide on the positive and lead on the negative side. The reaction will continue to take places so long as there are free electrons availableand lead sulphate in the electrolyte. As the available lead sulphate diminishes this reaction slows down and the voltage rises. Now if there is insufficient electrolyte or due to sulphation there is less lead sulphate available this reaction is going to slow prematurely and the voltage will rise. During discharge the cell will discharge to the same voltage as the other but will contribute less as a smaller amount of lead and lead oxide converted will result in the same voltage drop as the other good cells. Once a cell starts to short then obviously its voltage is going to be way lower accompanied by heat and quotes for a new battery bank.

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19 hours ago, incagarcilaso said:

I thought it was the other way around, that the weaker cells were the ones that could not charge up to the float charge or absorb charge set by the inverter.

Depends on the failure mode. As a battery ages the internal resistance goes up. If the battery is still in fairly good shape (just slightly further gone), and because V=IR (and I is the same for all cells in the string), you will see a higher V across the "weaker" cell.

On the other hand, if the battery develops an internal short of some kind, then the reverse happens and a charge current fails to raise the voltage in that cell.

What the balancers do is bypass some current if a battery runs too high, thereby causing I not to be constant and therefore getting the Vs in line :-) A balancer is not going to help with a shorted cell.

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1 hour ago, plonkster said:

On the other hand, if the battery develops an internal short of some kind, then the reverse happens and a charge current fails to raise the voltage in that cell.

What the balancers do is bypass some current if a battery runs too high, thereby causing I not to be constant and therefore getting the Vs in line :-) A balancer is not going to help with a shorted cell.

Great, that explanation helps with the diagnosis and cure. From testing, I think in my case it is not because of shorts so I hope the balancing will do it.

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