24S4P 2volt batteries acceptable or not?

[GeorgeF]

Ive been reading here and elsewhere that parallel connection of batteries (12v monblocks) is not recommended for offgrid use (CyclicUse)

But, is 24S4P with 2volt batteries in an offgrid situation (24S or more than 24) acceptable ??

[Mike90250]

first, what sort of batteries are you talking about - lead acid or Li-Ion ? Li-ion (any flavor) has strict brand restrictions on parallel and series configurations. Never violate them.

Lead acid, 2 parallel can be made to work. more gets real complicated fast, to keep things balanced . LA in series, no restrictions, other than system voltage limits.

[GeorgeF]

Lead acids like these for example.

added:
these batteries are being cycled daily and being charged with PV only.

[littleharbor]

That's a large battery bank for sure. I'd consider separte charge controllers for each, or every two strings at most.

You asked, "

But, is 24S4P with 2volt batteries in an offgrid situation (24S or more than 24) acceptable ??

"
It doesn't matter how many cells are in the strings as far as even charging goes, it does change the string voltage though. W

ith lead acid batteries

24 cells in series is going to give you 48 volt nominal . With so many connections, high quality interconnects and properly torqued connections is imperative. Many times you'll see solid copper bars being used instead of stranded cable. Solid bars don't have crimped terminals to add resistance and possibly become failure points.
Large battery.jpg

[GeorgeF]

24x2volt cells is like one big 48volt block battery. If 24s4p they parallel 4 big blocks of batteries, and I thought that such a design is not recommended to be used in an offgrid application.

See attached screenprint from this forum.

Will this also reduced lifetime although perhaps installed by pro's comparing to small simple SHS systems?

[sdold]

We have used similar configurations (24s2p, 24s3p, 24s4p) a few times and it seems to work,when we needed more capacity than we could find in a single cell. I assumed the conductance of all of the cells "averaged out") but I don't know if that's true. But ten years of daily cycle service was common.

It's surprising how the current can differ between parallel strings. Here is a 2040 AH 48V system that I measured yesterday at one of our solar sites that happens to be a microwave site, so it's under continuous 20A load 24/7. It's 12V 170 AH batteries arranged 4s12p (four in series to make 48V, than 12 of those in parallel). With the solar disconnected, two strings showed 0.8A, a couple were around 4A, and everything else was in-between.

They were installed about two years ago and great efforts were made to make the cables perfectly with solid bars in the series strings, paralleled with same lengths, properly installed terminals, etc. This is the result of an attempt to use the same make and model 12V battery for every site in the name of cost-savings, whether it be 12V systems, 24V, 48V, float or cycle service. With some cells sourcing 0.8A and some 4A, there will be an obvious difference in DOD between them. I measured them with the solar connected and saw huge differences in charge current too, but didn't have time to write the numbers down. I don't expect them to last anywhere near the 13 years that old batteries lasted, which were 2V cells 24s2p.

batts.JPG

[littleharbor]

I got just over 4 years out of a 2s4p set of similar batteries. I was careful to make all parallel cables from the batteries to the buss bars exactly the same length. In the end charging currents were varying wildly.

[inetdog]

Take a look at smartgauge.co.uk/batt_con.html for tips on paralleling batteries or strings of batteries. You can minimize the unequal currents, but there are too many cells and interconnections to be confident about it. When directly paralleling two large batteries you can usually be assured that the internal interconnections are as close to identical as possible. And there are a lot of them....

[GeorgeF]

SDold,
If your example with 12volt monoblocks works for cycle service and only being charged by PV it amazes me that the batteries will last more than a couple of hundred cycles if they are NS thin plates telecom red batteries and you cycle them everyday and only charge with PV. Your are talking about 13years lifetime. Is it not floatservice?

I more understand the setup of my example with 2volt batteries cause you can monitor (and correct) each 2v battery cq each cell.


I've read in another thread, even if you balance perfectly on day one it will imbalance if you cycle parallel 12v monoblocks (offgrid).


I am curieus how IEC look at this. Anyone knows?

[sdold]

SDold,
If your example with 12volt monoblocks works for cycle service and only being charged by PV it amazes me that the batteries will last more than a couple of hundred cycles if they are NS thin plates telecom red batteries and you cycle them everyday and only charge with PV. Your are talking about 13years lifetime. Is it not floatservice?

I don't expect them to last 13 years, that's how long the old set lasted which were 2V cells in a 24s2p configuration. BTW what the heck is a "Monoblock"? (Edit: Never mind, just looked it up)

I've read in another thread, even if you balance perfectly on day one it will imbalance if you cycle parallel 12v monoblocks (offgrid).

I suppose this is correct, I'm really interested to see what we get out of this set.

[GeorgeF]

We have used similar configurations (24s2p, 24s3p, 24s4p) a few times and it seems to work,when we needed more capacity than we could find in a single cell. I assumed the conductance of all of the cells "averaged out") but I don't know if that's true. But ten years of daily cycle service was common.

It's surprising how the current can differ between parallel strings. Here is a 2040 AH 48V system that I measured yesterday at one of our solar sites that happens to be a microwave site, so it's under continuous 20A load 24/7. It's 12V 170 AH batteries arranged 4s12p (four in series to make 48V, than 12 of those in parallel). With the solar disconnected, two strings showed 0.8A, a couple were around 4A, and everything else was in-between.
...

I am trying to learn about the fascinating world of lead acid batteries. A lot of interesting threads here and elesewhere and from what i've learned is that 12v UPS batteries designed for floatservice can not give a lot of cycles if you daily cycle them.

If you load 20amp @ 48volt 24/7 is about 23Kwh per 24 hours.

Amazing that these thin plates red telecom batteries already last 2 years.

So, it is suitable for offgridUse then ???

[sdold]

So, it is suitable for offgridUse then ???

If you're aslking me, I'm not sure, they are sold as Telecom batteries and we normally use them in float service where they are rarely cycled (normally only during a power outage) and I assume the calendar life would be a greater factor.

[GeorgeF]

I think guarantee = 5 years or 400 cycles 😣