80Ah ADD ON build

[Scooterman]

They are stored for a year or two .

I will charge @20A max , at least for the first few cycles .

Is that okay for 2P arrangement as well Shirley, or should I up it bit?

[Burgerman]

Just charge at about half normal rate. Dont know why he does that though. The PL8 will throttle back Amps to whatever is needed when it arrives at the balance voltage or CV.

[Scooterman]

If you were me BM, would you do the measuring self-discharge procedure like you did with your headways, to enable matching cells across the two 12v packs ?

I'm not in any mad rush to have lithium power, but would like to have it up and running by the Springtime when the weather should be better.

Do the cells have to be discharged down to say 2.8v first, and then recharged to 3.6v before then removing the required number of mAh before storage?

Or can they be charged up to 3.6v 'straight out of the box' then discharged a little bit before storage. I think you said aim for about 1000mAh from the 15Ah headways (or similar value as long as they're all the same mAh out). But I don't know whether I'd have to multiply that by 6 for 90Ah cells?

If they have to be discharged to 2.8v first before charging to 3.6v, then it will take a long time to do all 16, especially discharging through PL8. I'd be prepared to sacrifice some performance to avoid spending days doing that.

[Burgerman]

With 16 cells, yes. With 8 theres no point as you cant mix and match regardless.

[Scooterman]

And that's why 176Ah ones are a good idea.

But I'm really pleased with shirley's LF90s as they're good cells and give the option of 48v-50v in future.

[expresso]

And that's why 176Ah ones are a good idea.

But I'm really pleased with shirley's LF90s as they're good cells and give the option of 48v-50v in future.

thats a good point - i didnt think of that - in a chair that can be converted to 48V - 16 Cells would be needed then - i am thinking way ahead myself - on one chair - its an option for me but cost will be the downside to doing it - never know

[Scooterman]

I found this in a different thread

EDIT: I know first thing you do is number new batteries when they arrive, and write down on a table the voltages.

No just number them. But check that they are all simillar and above 3V. Usually 4.something.

Then you charge to 3.6v. Then what, you leave standing for a month or more, then measure the voltage levels again, add up all the voltages and arrange cells in parallel lots of equivalent average voltage?

Charge each, same exact settings, and store in a box for a month. Its healthier to charge and then remove say 1Ah (1000mA) from each cell, which means watching them discharge and clicking the mouse to stop after 999mA out... 4 or 5mA out either way not critical. Because ideally its not good to store these fully charged.

After a month, charge each one again, and at the point the charge ends, write down mA number returned, -1000. That gives you the amount of SELF DISCHARGE each one had over the month. It will be a very small figure, say 30 to 100mA. Make sure that the charge termination setting is quite high, like 250mA when doing this. Both times, the same figure. Actual figure not critical, but dont change it.

Then you connect the parallel lots in series to give you approx 24v

Then you need to make groups of 2 in parallel. Since you have 16 cells. Make them add up to the same figure. So if some cells are 50mA and some are 25mA then the two together will be 75mA. With only 16 cells, thats not going to be easy but it prevents you from putting say 2 cells together that have say 100mA self discharge, and 2 that have 25... Because you can mix the right ones together to get a reasonable average.

THEN asssemble your parallel groups of 2, in series to give 8S or 24V.
THEN charge as a series pack with 8S and 24V.

Or can they be charged up to 3.6v 'straight out of the box' then discharged a little bit before storage. I think you said aim for about 1000mAh from the 15Ah headways (or similar value as long as they're all the same mAh out). But I don't know whether I'd have to multiply that by 6 for 90Ah cells?

Sorry to be a nuisance BM but I was gong to start doing this shortly. I just wanted to check with you first how many mA I should remove from the cells before storage?.

[Burgerman]

As long as its similar, and as long as you are not storing full, then it doesent matter. They dont like that. On large cells maybe 3 to 4000mAh. If you take 3020 or whatever it doesent matter, just write it on the cell. When recharged you are only interested in how much it lost, so how much it took to recharge. Take one from the other.

Set the CHARGE termination point to aroung 200th of capacity for the initial charge, and the recharge on those large cells.

[Scooterman]

Thank you BM I do appreciate that.
I will make a start on them tomorrow.