Balancing LiFeP04 cells

I have made up a 12v battery using Headway 38120 10A cells -a pack of 8 cells with 4 pairs of cells in parallel to make what a charger sees as a 4cell 12v nominal voltage battery.

My idea was to have it as a General purpose 12v battery for camping and as an emergency starting battery for a 40 HP Yamaha outboard (but not to be charged by the outboard motor)

My only issue is with balancing the cells- the voltage readings currently for each of the paired cell s are- 3.41v 3.61v 3.37v 3.36v and this is after balancing and charging them with a Volt 680 AC multi function charger.

They were assembled with the proper metal connectors with all surfaces cleaned with fine sandpaper before fastening together.

There is a low voltage Zeva LVC12 cutout on the battery. Would you believe made in Australia.

The charger has many modes for these cells- eg balance,fast charge, storage and so on-all a bit complicated.
Plainly I am doing something wrong here.

Regards

Peter

Before you start get all to same voltge a bms is not meant to balance a home made out of all over the world voltages. Only build your battery with match voltage cells. How new are the headways ? What they used for ?

How did all the testing go that was recommended in your previous thread that you didn't reply to?
https://endless-sphere.com/forums/viewtopic.php?f=14&t=86080&p=1259883#p1259998

If you don't want to do all that testing to build a balanced pack, then the only other thing I can recommend is to disconnect the three series connections of your pack, and take the four paralleled pairs of cells and connect all of them in parallel.

Then charge them with your Volt charger as a 1S pack.

If you want to find out which cells are causing your problems (if any are), then either do the testing suggested previously, or at least do this part:

After charging as a 1S 8P set, disconnect all the paralllel connections, and let all the cells sit at least overnight without being connected to each other or anything else.

Then measure their individual voltages. Ones that have dropped a lot more than others may have internal issues, and then you can decide what to do about that, if anything.


Once you've got them all tested, you can then reassemble the pack into the 4S2P pack you want to actually use it as.

I'd just put your charger in single cell lifepo4 mode, and try charging each string one by one. FWIW, anything over 3.5v does not matter. just a second or two of discharge will bring those cells over 3.5v down. Its called surface charge. So don't fret those too much, unless they go over 3.8v to 4v. Just try to bring up the low ones. Or,,, bring down the high ones, using a 12v incandescent bulb, like a turn signal. That's how I do balancing out in some camp, bring down the high cells with a light bulb.

That should get them all to the same voltage. If some won't charge to more than 3.4v, then they are weak, and you will always be out of balance about to that degree.

and if so,, so what? Just monitor the weakest string, and stop discharging the whole pack when that string is too low, or let a bms do that for you. Sure, you wont have full capacity, but you will have capacity to 3.4v, which is still plenty usable for the purpose you have in mind.

For tent lighting, check out the 12v led stuff for cars. I got the neatest little string of 12v led lights meant to light the back of a truck bed. instead of one blinding point light, it's 6 in a string. Hung in the tent, nice even light through the whole tent. WAY better than anything in the camping lights section of the store.

Thanks for those suggestions-will work through them and come to an answer for sure.
Regards
Peter

All is going well with this 12v battery-the balancing feature works-all cells now sit at 3.32v however I am having difficulty raising the cells to a higher voltage-I would like each cell to be around 3.5v which is around 90% charge.

I have bought a Volt 680ac charger which has a few features for LiFePo4 batteries- eg balancing,fastcharge and so on. I put the battery on fast charge at 4A and it cuts off with each cell around 3.4v and says the battery is full-the cells then settle to the 3.2v mentioned above.

I have tested the battery with starting a 40hp outboard motor and it does that-also used it to power camping lights and so on-it does the job.

I would like to get the battery to a fuller state of charge however the charger won't get it there. Any ideas?
Peter

First of all, 3.5v is 100% charged for lifepo4. But it is very routine to overcharge lifepo4 to 3.65v, which forces them to balance. Everything above 3.5v is surface charge, which when it dissipates, or is removed in the first seconds of discharge, leaves the cells holding the maximum voltage they are capable of holding.

Fast charge means it stops a bit early, the last bit which goes slower takes a lot of time.

Lifepo4 can be charged past 3.5v safely, so you need a way to get each cell to 3.65 or so, but not really needing to be balanced past 3.5.

Try a balancing charge, or at least the slow charge of course. If that does not do er, then,,,

One way would be to manually, while watching intently, hit each cell with higher voltage than 3.5v. 5v from a cell phone charger for example. Get each cell to 3.6v or so. Careful! they will go to 4v very quick from 3.4v!!!!

Then put them on a tiny load for like 2 seconds. That will discharge the surface charge, the voltage they cant hold. At that point, you will know the max voltage your cells can currently be charged to. Ideally, it will be 3.5v on each cell. If not, no point in charging higher than the voltage the worst cell can hold.

As the cells age, they will of course hold lower and lower max voltage. 3.4v is still plenty usable cells. 3v would not be.

I thought it I would contribute for a change rather than ask questions. Attached are a few pics-one shows an arrangement on the front forks to prevent the front forks doing a 180 and wrecking the wiring to the front hub. Pretty rough but it works.
The other photo shows one of the bikes-it is used to get around the 5 acre property so as long as it does that all is well.
The milk crate on the back is standard practice around here-they are almost indestructable and freely available. The front basket holds tools which would otherwise fall through the holes in the milk crate,

Back to batteries-I am thinking that a BMS can be a source of problems(they have been for me) so I am thinking to put the takeoffs to each of the ten cells to a 10 lug terminal on the outside of the battery box and monitor the cell voltage manually.
The battery charger I have now will charge and balance the pack in two stages.
Any ideas on this?
Peter

having a way to verify what the bms is doing, with a plug you can use to monitor cells one by one, is a great idea for any battery.

Beats the hell out of me why they are not built in to all bike batteries, though perhaps under some security screws. For the shop tech to use, I mean.

Attached is a photo of how I have setup a method of reading individual cells. I have removed the BMs from this battery and am going to give manual balancing a try for a time. I see now how surface charge can be misleading-after charging the voltage readings are misleading-a load settles the voltages to their true values.

Balancing the cells is still something I am practicing-I have light bulbs setup-singly and in series for various voltages and I have been putting a load on cells (or a group of cells) that are reading high to discharge them to approx the low reading cells then recharging the battery.
A bit painstaking but it seems to be working.
What is an acceptable difference to have between cells? If I finally get some to 3.55V and some at 3.45v is this as near enough for practical purposes?

If the manual balancing becomes a pain i will buy another BMs. Do some members use manual balancing? I am aware that a BMS has other features other than just balancing (for eg low voltage detection of a cell)
Thanks for the help here-I am finally getting somewhere with this.
Peter

Are these new or used cells.

The cells are mainly used-I have 2 batteries and they are now a mixture of cells. One has 10 old and 2 new-the other has 11 old and 1 new. The new cells are Headway-good quality with threaded ends. The original cells seem to be not as good quality as Headways- all spot welded together and difficult to get apart.

If these batteries get more unreliable I will buy 12 Headways plus joiners and holders etc and make my own battery