Battery Balancing 48V system

[LilMT]

I have a 48V bank that consists of 2P4S batteries.

I was checking voltages the other day and noticed that the batteries in the left bank are all around .2V lower than the batteries in the right bank.

Re-torques all of my connections.  Double checked by cable lengths and interconnects.  Everything looks good on that side.

I will swap main leads this weekend to see if the imbalance follows a specific lead, if it does, I will dive into the lead wires in more detail to see if there is a hidden bend or something.

However, this got me thinking about a balancer.

Do any of you use balancers?  Any suggestions on a quality one?

Are they legit or just a gimmick?  I see Victron does sell some so I would tend to think they are legit??

Thanks for any input,
LilMT

[qrper]

Hi

I'm not much into balancers for lead acid batteries. The best thing to do, and it appears you already have done it, is the make sure the cable length are the same. That's from the battery to the inverter/switch/fuse what nots...

Decades ago, Home Power Magazine had an article or two about an issue with the end batteries of a string that always went out of whack and failed earlier than the ones in the center of the string. If memory serves me, there wasn't a smoking gun as to why this was happening. They decided the best way to prevent the problem was to rotate the batteries so the end batteries  never stay at the end of the string. I don't know about you but moving 16 L16 sized batteries every other month isn't in my pay rate.

I have seen some installations were the batteries were cross connected, this seems to improve balance between battery sets.

Let us know what you find out

mike, wb8vge

[LilMT]

By cross connected do you mean like the attached images?  I came across this and am having trouble wrapping my head around it.

[LilMT]

Update,
Prior to swapping leads on the banks took a voltage reading.  Left bank reading .5v below right bank.
Swapped leads, loosened all connectors and re-torqued them.
Check voltages again, still .5v low on left bank.
1/2 hour later the voltages had come within .1v of each other.
Also noticed that my "average" current draw was down from 6.5A to around 4.1A.
checked again about an hour later, the banks had completely equalized, and my average draw is still down around the 4.1 mark.
I am running a charge cycle now and it seems that my charge time is significantly better than before.  I am nearing full charge in about 2/3 or time that it has been taking.
The only thing I can think of is maybe there was some oxidization on the terminals???  Loosening and re-torquing them then made better contact?
Seems weird.
Once I get a full charge on them, I will let them rest for a bit to stabilize and check voltages again.

Thanks,
LilMT

[LilMT]

Update 2:
Checked the voltages after a charge and rest and all batteries were even.
and my amp draw overnight was significantly lower about 2/3 of what it has been.

All seems better now.

Yeah.

[boB]

Your drawing is correct.  This arrangement help to make sure that all batteries see the same draw  or charge current due to different lengths of battery cable resistance.

Battery balancers.  We have wanted to make these for many years now.  Like, 20 years.   I think that now that lithium is getting more and more common, balancers for lead acid may eventually become unnecessary.

I may be wrong though as lead acid will be around for a while.  Balancers for lead acid would be higher current than the balancers for lithium in their BMS's I would think.

boB
 

[qrper]

Your drawing is correct.  This arrangement help to make sure that all batteries see the same draw  or charge current due to different lengths of battery cable resistance.

Battery balancers.  We have wanted to make these for many years now.  Like, 20 years.   I think that now that lithium is getting more and more common, balancers for lead acid may eventually become unnecessary.

I may be wrong though as lead acid will be around for a while.  Balancers for lead acid would be higher current than the balancers for lithium in their BMS's I would think.

boB
 

Personally, I feel lead acid battery balancers are right up there with lead acid desulfaters.

Mike, wb8vge

[LilMT]

Thank you for the replies.

After swapping the main leads all seems better again...For now.

I will think about adding the interconnect cables.  Still seems weird to adding those connections across the banks.  Understand the concept but every time I look at it, it looks like a short.  I know it is not but it still looks like one. 

Thank again.

[qrper]

Thank you for the replies.

After swapping the main leads all seems better again...For now.

I will think about adding the interconnect cables.  Still seems weird to adding those connections across the banks.  Understand the concept but every time I look at it, it looks like a short.  I know it is not but it still looks like one. 

Thank again.

Let's try this again. Apparently, i pressed the wrong button when I replied the other day...

Anyway, decades ago Home Power Magazine did an article on why the end batteries in a string seemed to fail more often than the center batteries.
While I can't recall all the details, they boiled it down to 'we're not sure' as to why the end batteries in a 48V battery fail sooner than the rest.
They suggested to rotate the batteries from the outside to the center of the string. Now, I'm all doing whatever I can to prolong the life of my lead acid batteries, but I can't see me rotating 16 of those heavy beasties every four months.

Mike, wb8vge

[boB]

Let's try this again. Apparently, i pressed the wrong button when I replied the other day...

Anyway, decades ago Home Power Magazine did an article on why the end batteries in a string seemed to fail more often than the center batteries.
While I can't recall all the details, they boiled it down to 'we're not sure' as to why the end batteries in a 48V battery fail sooner than the rest.
They suggested to rotate the batteries from the outside to the center of the string. Now, I'm all doing whatever I can to prolong the life of my lead acid batteries, but I can't see me rotating 16 of those heavy beasties every four months.

Mike, wb8vge

When you say "the batteries on the end", it matters how you wire them.

If you wire them the way the drawing(s) in this thread shows, then you shouldn't have to do any rotating I don't think.

boB

[qrper]

Let's try this again. Apparently, i pressed the wrong button when I replied the other day...

Anyway, decades ago Home Power Magazine did an article on why the end batteries in a string seemed to fail more often than the center batteries.
While I can't recall all the details, they boiled it down to 'we're not sure' as to why the end batteries in a 48V battery fail sooner than the rest.
They suggested to rotate the batteries from the outside to the center of the string. Now, I'm all doing whatever I can to prolong the life of my lead acid batteries, but I can't see me rotating 16 of those heavy beasties every four months.

Mike, wb8vge

When you say "the batteries on the end", it matters how you wire them.

If you wire them the way the drawing(s) in this thread shows, then you shouldn't have to do any rotating I don't think.

boB

It's been so long since I read that article in Home Power, I can't remember all the details other than it was a known problem. I don't recall if they recommended cross linking the batteries or not. Like I said, I'm not about to rotate 16 of those big boys around every other month.

Mike

[LilMT]

I think I found the article in their archive.  Interesting information.

https://www.homepower.com/

Issue #60 Q&A page 106.