camelot-forum.co.uk

(nowtyproject for searching)

Well, as its a new forum, we will have to have a short recap of where I was up to with my battery system.

Over the past few years I was buying up mostly faulty 5kWh lithium Growatt Battery packs from the SP2000 controller range which I believe are no longer manufactured as they are pretty old technology now, compared with the Sofar and Lux, etc. And Growatt seem to have a new unit now, no idea how good the new one is. So unfortunately not many old units seem to come up for sale anymore.

So although each battery unit was somehow faulty with a red light (or no light), I found it was always, very low charge level, or a cell imbalance or the protection board had expired in some way. It was never the actual lithium cells. Even one with practically zero volts came back to life and accepted the correct amount of kWh's charge.

Feb 2018


So I ripped out the cell modules (which were in handy 24V modules) and ran them first with my old 24v Off Grid SMA Sunny Island. No cell balancing seemed necessary as they worked OK for a full season with ALL cells paralleled up with fused links.

April 2018


But then I upgraded to a 48v SMA On Grid Sunny Island with full house backup system with G100 compliant export limitation.



So I had to reconfigure 24v modules into 48v modules by connecting each original 24v pair together with a heavy duty string fuse so each 48v battery pack is from the original 5kWh pack and is individually fused. I ended up buying several more faulty battery packs until I had 10 of them.



But being lazy and reusing the fused links, I only paralleled up every two or 3 cells, hoping that any drift between two or three adjacent cells would be minimal.

April 2019


Occasionally I checked the cells manually for imbalance but there were too many of them to do the job properly and after about a year I had several cells which ran very low. So I had to install some sort of automatic balancing system. Some were quite expensive, others were too small or too complicated. In the end I found some cheap Chinese sourced active balancers which could be cascaded to work with any number of cells and could shift up to 5A from each adjacent cell proportional to the imbalance.

Balancing Board Specification
Operating voltage: 3.0V - 4.2V
Working power drain 15mA
Termination voltage: 2.9V (into under voltage sleep state <1mA)
Maximum Balance current: The Cell difference V / Balance current 0.1V/1A 0.5V/3.5A 1.0V/5.5A
Balance accuracy: < 5mv
No external power supply is required, internal energy in each high cell is transferred to the lower adjacent cell in the pack to balance the entire battery pack.

Front Side


Back Side


Remote Test Point with the Balance Boards - Aug 2020


I split the 1 bank of 10 batteries into 2 banks of 5 batteries, each capable of full 6kW charge / discharge. I connected the balance boards remotely to ONLY the middle battery of each 5 battery banks and relied on the parallel fused links to trickle down the balancing to the other batteries. I added a few more fused links so apart from the middle battery with ALL its cells on the balancer, only each pair cells were paralleled up on the adjacent batteries.

This worked very well indeed but it made me even more lazy to check any imbalance in the cell pairs. After another 6 months or so I was randomly checking the odd cell and found a significant cell imbalance on a pair. Which meant I needed to do a full check on ALL 140 cells.

The battery balancers are on Battery 3 (yellow) on each bank which is connected to all 14 cells.
The bold vertical lines show which cells have the parallel fused interconnects.
The red numbers are pair's of cells which I found as unacceptably imbalanced.

Feb 2021


So my conclusion was I had to parallel up ALL cells, that meant I had to make up another 48 fused leads and install. Well that was back in Feb this year and although I bought the bits and pieces early on, its been on the "TO DO" list until very recently. Finally I've pulled my finger out and made them up and I have now installed them. So now finally, ALL cells are now paralleled up and therefore ALL cells are now connected to the balancing boards.

June 2021


In a week or so I will report back with another full table of cell voltages to see if my full paralleling up of the cells on the balancing boards has worked.

Phwoar, battery porn par excellence, just promise me you wont dig anymore holes under the house, my heart couldn't take it

Spear deet

Always very impressed with the work you do with these batteries and the life you have had from them after they were effectively scrapped. When my Growatt system finally gave up I just sold it and bought a more up to date AC coupled system.

Inskip75 wrote: ↑Tue Jun 22, 2021 6:17 am Always very impressed with the work you do with these batteries and the life you have had from them after they were effectively scrapped. When my Growatt system finally gave up I just sold it and bought a more up to date AC coupled system.

Whether you are the seller or the buyer, both parties are doing a good thing rather than scraping them.

I even sold on the SP2000 controllers which I thought no one would want as others were for sale on ebay and never sold. But the sellers were asking unrealistic prices, I still got between £100 and £150 for them. And the metal cases and bits of copper cables from the battery packs went into the recycling bins.

Wow - amazing stuff.

nowty wrote: ↑Tue Jun 22, 2021 11:49 am

Inskip75 wrote: ↑Tue Jun 22, 2021 6:17 am Always very impressed with the work you do with these batteries and the life you have had from them after they were effectively scrapped. When my Growatt system finally gave up I just sold it and bought a more up to date AC coupled system.

Whether you are the seller or the buyer, both parties are doing a good thing rather than scraping them.

I even sold on the SP2000 controllers which I thought no one would want as others were for sale on ebay and never sold. But the sellers were asking unrealistic prices, I still got between £100 and £150 for them. And the metal cases and bits of copper cables from the battery packs went into the recycling bins.

I totally agree and I described exactly the fault and sold both the battery unit and controller and asked the chap I sold it to let me know how he got on with getting it up and running but have heard nothing - so no idea whether its in use or not, which is a pity as I was interested in whether he was successful or not.

Well, I promised to report back now ALL battery cells are paralleled up on my cell balancers and I think the results speak for themselves. The batteries are fully charged on my 90% full regime to extend their life. No cell anywhere near the dangerous 4.2V+ zone, in fact none over 3.97V, so I think I finally have a fully automatic balancing system and not need to worry too much anymore. In fact there was some fluctuation because the sun was coming in and out of cloud whilst I measured them so the batteries were fluctuating between charge and discharge so in reality the cells are probably even closer than I measured and are probably all within the spec of the balancer +/- 5mv.

I think all I need to do now is check the voltages at my remote test point from time to time to ensure the balancing boards are still operational.

As a reminder, the battery balancers are on Battery 3 (yellow) on each bank which is connected to all 14 cells.
The bold vertical lines show which cells have the parallel fused interconnects which is now ALL of them.

July 2021


Some of these batteries have been in use for 6+ years now and absolutely no sign of any reduction in capacity. In fact they seem to have more than the quoted capacity, maybe because I am charging and discharging them at very low rates as I have such a large battery bank. So I am thinking a usable asset life of 20+ more years.

Thanks to SWMBO for writing down the cell values on a matrix as I measured each of the 140 cell measurements and relaying them via my mobile phone as I was some distance from her in a claustrophobic environment.