PINNED - 230Ah (245Ah certified) A grade cells Amy, Docan

[Scooterman]

Will do

Do you mean possible loose connection on 5 and 7, rather than balance wires 5 and 7 reversed?

[Scooterman]

Here's a zoomed in graph of charge

[Burgerman]

It ended the moment it was balanced. Setting to that 11.5A would then have made zero difference. Because the current was under 1 amp at this time already!

Also that initial part of the curve where the two lines above and below the average could be not real. That happens if you have a bad connection, or if the PL8 is badly calibrated for whatever reason.

[Scooterman]

Understood thanks

I’ll recheck the connections tomorrow with fine tooth comb and charge pack again and see what happens

[Burgerman]

What was the charge current at the point where its charge ended?

Set that to whatever this was, and make it 33% less. So it has chance to soak that final cell for 10 to 15 mins ish. While its doing this, put a digital voltmeter on each cell and check te ACTUAL voltage to see if the PL8 is calibrated correctly. All cells should be the same while at CV and balanced.

[Scooterman]

I checked all the connections and charged them again. Cells 5 and 7 still went high before all the others, but the balance phase lasted about 15 mins and terminated at 750mA.

I'm going to discharge them again by about 20Ah I think you said somewhere.

Then swap around the cells and charge them again to see if it's a problem with cells 5 and 7 or connections to 5 and 7.

[Scooterman]

.

[Burgerman]

I would sugest that cell 5 or 7 or 6. Has a bad connection someplace. Or a longer wire or something different.

If not then use a multimeter while charging and check the real voltages and see if they are all matched which they will be...

In which case you have a badly calibrated charger.

[Scooterman]

Okay thanks BM will do

[Burgerman]

https://www.youtube.com/watch?v=AGglJehON5g



youtu.be/AGglJehON5g

[Scooterman]

Thanks I shall have a watch later

Re: docan cells update.

You were correct, the PL8 I was using isn't very well calibrated.

With PL8 in. monitoring mode my Fluke measures all cells to be 3.333V

[Scooterman]

So I dug out different PL8 and monitored cells and better calibrated. Cells read 0.003V higher than Fluke

Also swapped balance cable and tried another charge. But cells 5 and 7 still went high early. All I can conclude is that 5 and 7 must be weak cells. I could swap them round in pack but don't think it'd make much difference?

[Scooterman]

Forgot to add this, this is the better calibrated PL8 that did above charge graphs.

[shirley_hkg]

The average of 5 & 6 is the same as all the others.

A component is ageing, but still safe to use.

[Scooterman]

Yes I see what you mean, well spotted Shirley

[Scooterman]

The average of 5 & 6 is the same as all the others.

A component is ageing, but still safe to use.

That makes sense as that PL8 has had the most use. I've packed it away as a spare.



Now using different PL8

I moved cells 5 and 7 to positions 3 and 4 respectively.

And on this charge 3 and 4 went high.

So, 5 and 7 are definitely weaker cells I assume?

Does it matter, should I contact Amy at Docan, or just install them in chair?

[shirley_hkg]

Cells seem ok.

You should do a full discharge to 3.00V to see their actual difference in capacity wise.

[Burgerman]

Looks pretty damned good to me.
You have to undrstand that a fraction or a fraction or an Ah difference buts the balance out right at the top. And that appens quite naturally die to minor temperature differeces, cell spec differences, etc. Thats perfect. And after a little use they will get better still.

You COULD capacity test them, but you will find as I did after a LONG time, they are all better than the 230Ah rated capacity...
My worst one wes 243.3. Best one was 244.5. In use you shouldnt really be going past say 210Ah absolute max. So just use them! The rest is a reserve, and a unused bit to make them last!

[Scooterman]

Thanks both I really appreciate that.

And I must admit I wasn't keen on doing a capacity test because of the time. I'd rather just get on and install them in the chair. When they arrived I put 165Ah-170Ah into them, so I know they have at least that capacity. And that's loads when compared with lead acids, and for just over £400 delivered I'm really pleased.

[Burgerman]

Trust me they have around 244Ah. Compared to the typical 80Ah lead bricks 40 to 45Ah before its stops.

So thats 5 times as far as a full set of lead bricks, with some left over. But... the higher voltage (gives more range!) and lower impedance (gives morerange) and the fact that they will STAY that way! Where lead bricks deteriorate so fast that you can tell after 6 months of hard use. So its really about 6x the range.

Think about it like this. If you manage to get them to deteriorate to HALF capacity, somehow... Then you only have about 3x as much range as 6 lead bricks remaining...

And it is cheaper than lead. And it lasts decades instead of months. Lead is so dead!

[Scooterman]

I suppose because we're so familiar with lithium in this forum we tend to take the HUGE capacities for granted.

And as you say it's not until you compare it with lead that you realise what a game changer it is for mobility devices, and the cells look cool too.

Most other wheelchair and mobility scooter users we see out and about are still running around with lead acid batteries. They need to get on www.wheelchairdriver.com!

[Burgerman]

They are almost all running around barely in control too. Every single last powerchair I ever tested, looked at in shows, users met in and around my town, the spinal injuries unit, etc have the same. Problem. Hovercraft steering.

[snaker]

In VN, I have problem in buying lifepo4 cells. The 'smallest' cells are now 314Ah and they no longer import smaller cells. Should I go crazy to fit 8x314Ah or 9x314Ah

[shirley_hkg]

I think Amy will ship to VN.

[Burgerman]

IF you can fit them. But 230Ah ones fit where the stock grp 24s come out. And give enough range to escape the country. Try amy, docan. Great quality cells.

[Scooterman]

When installing 8S lifepo4 prismatic pack in 2 x group 24 steel battery box do we need to leave room for the cells to expand?

packing them in snugly is obviously good cos we don't want pack moving about. But then I think, do we need to allow a gap at either end in particular for cell expansion over time?

Worry that if no expansion gap cells might try and swell but can't, then explode, cause fire and burn house down!!!

[Burgerman]

Its the opposite. The manufacturers insist that for long life and hevy currents we SHOULD have a steel plate either side, and a high clamping force... Because high charge voltages, high current draws etc that dont really affect us cause them to swell otherwise.

[Scooterman]

Funny you should say that because I read what you say in solar forum, and it seemed counter intuitive to me so wasn't sure if it was right? Thanks

The 230Ah fit fine in Sunrise Salsa/Jive R2. I just need to sort out some packing for sides.

[Burgerman]

You need some insulation/protection UNDER those cells, as well as around the outside edges.

All the casings are at different voltages that match the negative connections. If anything wears through that blue plastic film and they short out you are back to the

How much gap at each end?
And between bolt threads and that metal bar?

[Scooterman]

I've always found that difficult to understand. I assumed that he aluminium casing were either electrically isolated from the positive and negative, or at the same potential as the negative aka 0V. But obviously not because I suppose the manufacturers wouldn't supply the insulation boards, and you say not and I bow down to superior knowledge!

Once I'd built up pack using supplied insulation boards. I bound it together with gaffer/duct tape, put it on a sheet of thin plywood, drew round bottom of pack, cut it out and taped it to bottom of pack so that should be okay. Pack also sits on three front to rear velcro strips.

Re that cross tube there's about 20-25mm air gap to top of studs. I plan to slice a bit of plastic pipe lengthways and stick/tape it to underside of cross tube.

Total length gap is about 10mm, but I've already packed most of that. Just got to find something 2-3mm to fill up rest of length gap. I diliberately left that gap for expansion but will find something to slot in there.

BTW built pack is bloody heavy, I really struggled getting from bench onto floor. The only way I could do it was to bolt wheelchair ramp to workmate and slide pack down on sheet.