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

[wchl25]

When assembling everything together what does everyone use for the nuts on the batteries? The nuts that are provided, nylon locking nuts, or regular nuts with lock washers?

[Burgerman]

In this order.

Ring terminal for current. Soldered!
Ring terminal for balance. Soldered!
Quick squirt of switch cleaner.
Stainless thin flat washer.
Stainless nyloc nut.
Plastic nut cover.

Why?
Because a thin flat washer allows the rings to turn if knocked without loosening the stainless nyloc. Anti shake or locking washers or serated nuts will also turn the nut when you yank on a cable.
And the switch cleaner like De-Oxit puts a conductive anti corrosion "wetting" agent on contact surfaces and keeps it that way.
And stainless as it doesent corrode...
And nyloc as it will not come loose.
And a nylon/pvc/rubber nut cap as it stops metal shorting anything out...

https://www.amazon.co.uk/oumuik-Spanner ... B09G947BGR

[Burgerman]

https://www.amazon.co.uk/Stainless-Wash ... B0C7ML3XN6

[Burgerman]

M6 stainless nyloc nuts...

https://www.amazon.co.uk/HOLMOL-Locking ... B0DFL7TBHK

[Burgerman]

To Store INDIVIDUAL CELLS
Use a load to discharge below 3.25V per cell.

ZXD set as SUPPLY @ 3.28V 65% charged
5A
1000W
Silver (dont turn off)
set to 0.03A end +
00.10 to end charge.
(Ensure BIG wires and good contact connection use switch cleaner and Andersons. Or this will take a lot of time.)

Charging Cells or packs:
Voltage levels: See CHART!
100% charging 3.50V to 3.65V (preferably 3.50V) And you can balance!
100% at rest 3.40V ish balancing here is not effective. And may unbalance the pack. Balance only above 3.450V.
90% 3.35 balancing here or lower UNBALANCES the pack.
80% 3.32
70% 3.30
60% 3.27
50% 3.26
40% 3.25
30% 3.25
20% 3.20 time to charge! Lower than this frequently = shorter battery life.
10% 3.00 and as low or lower than you should ever go in use
0% 2.50 Never go this low unless for capacity testing in controlled conditions. Or in emergency.

INITIAL BUILD
If your system, BMS or charger is adjustable.
Charge all cells to 3.600V Initial charge INDIVIDUALLY and assemble the pack.
Initial charge and balance at 3.65V after assembly and set balance to start at 3.45V minimum. Or just at CV.

All subsequent charges ideally should be 3.550V per cell and balance set to begin at 3.45 or 3.50V. Or only at CV.

Charge should END when these 3 are satisfied:
a) ALL cells are balanced and the balance current is very low.
b) ALL cells are at 3.550V
c) charge current has fallen to a low level of around 350mA per 100Ah of battery. THIS IS APPROX! A starting pont. So as to continue charge at CV for 15 to 20 mins after all cell balancing is complete. So a CV time can set to whatever allows this, and a correct termination current will need to be fine tuned and set after half a dozen uses/cycles. To get the above right.

Storage needs to be around 30 to 70% charged. Dont charge full and then leave it that way for weeks or months. They dont like it!
I use 3.28V per cell for storage as thats around 65% if your voltmeter is accurate enough!

[Burgerman]

Remember that
1. That chart varies depending on brand.
2. that all those in green where you will be using the chair are so close in voltage that they vary more by temperature than by actual state of charge. So its a rough guide!
3. Your BMS accuracy per channel has a spread that is only around 5 to 10mV and its calibration to voltage may be as much as a 10th of a volt out anyway. And that most multimeters are anything up to a couple of tenths of a volt out...

Since theres only a fraction of a volt difference between these green voltages its EXTREMELY hard to know what the real state of charge is based on reading its voltage.

[ex-Gooserider]

Minor note on the nuts, might be useful for those that have to fit into tight spaces...

Most all size nuts come in both 'standard' and 'low profile' or 'Jam-nut sizes, with the low profile type only recommended for use in low-torque applications or sometimes as a 'jam-nut' on top of a standard one to lock it in place... They are fine for the level of torque we use on our packs.

The low profile nuts can be hard to find, especially in a nylock (plain ones will work with a thread locker and be even thinner) but will save a couple of mm on the height. Probably not worth the effort unless needing to shave off mm in pack height, but worth considering if you need to.

ex-Gooserider

[shirley_hkg]

https://youtu.be/pEWmF1f-W-g?si=l_MtYoou-POGB4uq


Lithium makes it obsolete.

We did the same 17 years back, and looks silly now.


https://youtu.be/HVOpgSTRQtQ?si=WVbdncBxnnp4yVTW

[Burgerman]

Same here.

When you have decent lithium power why is all that noise, weight and vibration needed? I already have more range than you can use in a day. You gotta sleep at some point!

[wchl25]

They are in and wired!

ABS sheet on the bottom, and around the sides for isolation. I used the epoxy sheets in between them. Two thin sheets of plywood in the back to take up the gap and they are nice and snug in their new home.

[wchl25]

I have a few questions regarding the new battery installation.

1. When charging for the first time, do I need to charge all the way to 100% or can I go to 70 or 80%? I don't use this chair everyday and I'm not sure how soon I will be using it enough to run it down.

2. How much will using it in the winter for hunting affect the batteries? Going out and sitting in my deer blind for 2 or 3 hours at a time in subzero temperature, like -12c I looked at the spec shett and it said down to -35c was the operating temperature so I am assuming what I will do is OK?

3. You said when charging to set the end current setting for 800ma,but the spec sheet says to set it at .05c which is much higher than that, can you help me understand what I am missing here?

Thanks

[Burgerman]

3. first!

What you are missing is that if charging 1 cell then 0.05C is 100th of its 230,000mah. So you can end charge at its 3.650V at 2.3A.

But then we have the following...
1. theres 8 cells. We want all cells to be balanced. So the first 8 cells will get to that over the top 3.650V at different times, and sit at this voltage (or pulsed to higher than this if using some BMS if we use a 3.650V x 8 charge voltage. Because once at the 99% charged state som cells are lower than this voltage... And we are at a constant voltage supply (CV stage) on the charger or power supply for some time. Now all the first 7 cells have been sat at 3.65V (or more pulsed at Over voltage cut off by on/off if using a BMS). When the charge current sees your 2.3A which is OK for a single cell that final cell may not yet be up to the same voltage as the rest. If it is, it JUST made it, and we stop.

So now we have 7 cells that have been at 3.65V for a while awaiting that final one to catch up. And it just did. 7 cells for maybe an hour. And at a termination current that fell to a very low level, maybe a few mA on the first cell to reach 100%. And then a spread. And then your last cell.

So now, you have 2 or 3 that are 100% soaked and 100% full. So those will stick at 3.65V and when charge stops, will fall to 3.4xxV. And that last cell stopped charging as soon as it saw 3.65V at 2.3A. So it isnt AS full as the others. Maybe 98%? And as the charge ends its voltage drops to a 3.4xxx point too. But faster. At this point NON of the cells can be further balanced.

So we held a bunch of cells at 3.65V for an hour or even a week if the balance was off by a lot on initial charge. Those sat at top voltage until tail current is almost zero. And just 1 final cell for almost zero time as soon as it sees 2.3A.

In order to make sure that final cell(s) ends up closer to the same level as the other 7, we need to give it at least 15 mins to 30 mins at its final charge voltage. Non of that matters with a single cell. Its because of the way chargers, and worse BMS works.

Then, the biggest reason to charge to a rather pointless 3.65V is because it is an OVERCHARGE voltage. The cells do not like it... But in order to end up with a balanced pack with traditional old school chargers that were electrically simple (they cut off as soon as they see the CV voltage happen such as in a laptop, or mower etc) then you need a higher voltage. My drill battery for e.g RELIES on the overcharge to balance. It has no balance circuit at all. That was common years ago. As they all moved from nmh cells. Why does an elevated charge voltage balance? Same way it balances your lead bricks. If the cells top voltage is say X volts, then charging at X + A few % extra means that all cells experience a degree of overcharge. Then settle back to the max they can be with that particular chemistry. But overcharge on lithium is very harmful. Even dangerous on some chemistries. But where a BMS is crap, it ensures balance.

So its BETTER to limit voltage to 3.600V or even better to 3.550V. But both of these are not so much of an overcharge. Now we do not hurt the cells as much. So now its SAFER and in fact required to have a longer CV time to allow a balancer to work. And this still ends up 100% full. Just takes a little longer at CV. Hence a lower termination current. Longer at CV to allow balancer to do its thing properly at the right voltage.

WHAT we are trying to do is this.
1. Charge cells to 100% at the lowest voltage we have to use.
2. Allow time for balance to complete + say 4 or 5 mins at 3.65V, your (2.3A). Or 15 to 30 mins at 3.60V. Or 30 to 120 mins at 3.55V. ALL of these will end up at the exact same state of charge. 100% Full. In order to get say 30 mins you adjust that tail current.

We do this because a lower voltage allows full charge, allows balancer time to do its (sometimes very slow) thing, and is nicer to the cells.

Does that help?
++++++++

A simpler way to look at it... By exaduration.
You COULD charge each cell to 4.00V and KNOW that its 101% full even with a zero time CV stage. Stop charge at that 30A charge current, the moment it sees 4V. Its still going to be completely full. The battery would last maybe 200 cycles? I dont know exactly how many. But it will hurt the battery.
But its much worse. That BALANCE circuit will have almost zero time to balance if you chop off charge current when the 1st cell to see 4V causes he charge to end. Now you have 7 undercharged cells, and the FULL cell and those other 7 will drop voltage in a matter of minutes down to 3.4xxx at which point balancing is no longer possible. And you cooked that cell that reached 4V. Alternatively, if that BMS or charger allows charge to continu until all cells see 4V then 7 of these cells were held at 4 Volts for extended time while the rest catch up and cooked them even worse!

Better to hold all cells at a safer lower charge voltage for longer while it balances. Thats your 3.550V and 800mA and that 800 is a guestimate, you must fine tune that to give:
ALL cells balanced on YOUR pack in daily usage charge scenario.
PLUS 15 to 30 mins to ensure that last cell to reach 3.550V actually ends up with adequate soak time at this lower voltage to end up 100% to match the rest.

[Burgerman]

1. When charging for the first time, do I need to charge all the way to 100% or can I go to 70 or 80%? I don't use this chair everyday and I'm not sure how soon I will be using it enough to run it down.

That 1st charge should be completed fully. It also should be done on the bench. So that you can see and fix problems as you look at the charge graphs (PL8) or spot bad connections etc. And it may take anything from an hour to a week depending on initial balance state above 3.5V.

2. How much will using it in the winter for hunting affect the batteries? Going out and sitting in my deer blind for 2 or 3 hours at a time in subzero temperature, like -12c I looked at the spec shett and it said down to -35c was the operating temperature so I am assuming what I will do is OK?

That cold temperature thing I do not know. The coldest I ever saw here was minus 8 centigrade in daytime. For half a day. At that temperature I (or anything else) at minus 2 or 3 degrees C is far too cold to leave the house! Why would you?? If you did, the BATTERY wouldnt be at minus 8 as its got thermal mass and is at 20C at home... And it gets slightly heated in use by a couple of degrees too. Also dont feel the need to blow holes in the innocent deer.

Remember that all batteries are chemical reactions. All chemical reaction are speeded up or slowed down by temperature. So all batteries perform MUCH worse as temperature is lowered. But just dont charge until they warm up.

[wchl25]

3. first!

What you are missing is that if charging 1 cell then 0.05C is 100th of its 230,000mah. So you can end charge at its 3.650V at 2.3A.

230 X .05 = 11.5 not 2.3...
This is where you are losing me?

I didnt do the maths because I thought I knew the figures in my head!
You are correct. Again, that is basically the same result when you charge a single cell. I am trying to show you that it doesent make any difference what termination current you set here. On ONE cell.
As you charge at say 20 or 30 Amps then the voltage climbs very gradually from 3.2xx to 3.3xx over most of the usable charge at say 20A for 10 hours. And then voltage shoots up suddenly when full in a couple of mins. It doesent really climb at all much until the cell is basically 99% full and then it shoots up in a matter of a few mins to 3.55, 3.60, 3.65 or 3.8 and well above in seconds if you let it. In seconds. To stop that a good charger drops the charge current to whatever it takes. Or terminates charge.

Right up to this full point it will stay solidly in the CC stage at your fixed 30A. The flat part of the current Amp curves below. The difference between 11A, 5A, 2A etc end tail current is all irelevant. That cell is basically full (+99%) at their 3.65V level at this point whatever the current.

If you look at a charge curve for just 1 cell, or bunch of ALREADY balanced cells then you will see that the current basically stays at 30A or whatever you use, then drops off down like you rode a bicycle off a cliff. So 11A (or any) cut off current here results in a full cell. In order to keep that voltage at CV, you have to set a much lower cut off current. Guestimated at 800mA ish for 230Ah ones. (PL8.)

Look carefully at the CURRENT curve shape.
If the cells are
a) all balanced (so no long CV stage needed)
b) charger set to stop as soon as it sees the current drop to any low level (like in this case the 230ah cells suggested 0.05C).

Then it pretty much makes no difference at what point you cut off charge! When its full, and when CV stage occurs, its pretty much fully charged.

But if its not yet balanced you cant turn off the charger! Since the voltage will rapidly "settle" and drop and go below the point where balancing works at all.
So you need the following logic to fully charge and balance a pack!
End charge when
a. all cells are balanced at 3.550V (less voltage is better for cells, but needs a little longer at CV.) Cut off at 11A, bad as this balancing hasnt yet happened!
b. final cell to reach (climb) to 3.550V needs some extra time at this lower voltage (to stop its voltage "settling" more than the other 7 that have been at CV for long time). And because of low current.

Why low current? A balancing charger, or a BMS will not allow the full cell(s) to exceed 3.550V and so in the case of a good hobby charger as soon as the first cell sees CV voltage it reduces the power (Amps) to enable the cell balancers 1A to keep that cell below the limit. That means that we are now at 1A charge while the rest catch up. If you set it to stop at 2.3A or 11A that also stops the other cells balancing or catching up. Depending on logic on charger/BMS.

Do you see this?

[wchl25]

Thanks for clearing that up, the math wasn't mathing so I was confused.

So I am going to charge it up for the first time. I will be using my Junsi X8 charger, with ZXD for power.

These are the settings I'm thinking are good?

20A charge rate
3.45 start balance
3.55 cell voltage
2.5% end current 5.75A (Junsi is %) or should I go lower?

The charger should be set both to end current and balanced

I found a data analyzer for my charger so I should be able to monitor on my pc

I also need a way to discharge it to storage voltage. I was thinking about getting one of these, what do you think?

https://www.amazon.com/MakerHawk-Batter ... _hp_d&th=1

[Burgerman]

All OK except

>>>2.5% end current 5.75A (Junsi is %) or should I go lower?

Set it less for initial charge, and watch it. Maybe 1 or 2 A.
It may take a long time for initial balancing and may take a couple of charges to end up with a fully balanced pack.
Note the current that it is at as it gets to balanced Voltage and low balance current, + say 30 mins. And then set THAT as your termination current.

Then adjust it so that it ends charge when the cells are all balanced, plus around 30 mins at 3.550V after the next few charges until its right. Thats then going to be perfect. We cant know that final figure until you charge it in use for half a dozen times. Let me know what it is for my own interest!

You wont get it perfect as it varies a little charge to charge too. Is not critical at all so dont worry as long as it turns off as intended and they are all balanced. An extra half hour or just 15 mins is OK. Just monitor it and fine tune a bit at first.

Depending on how well balanced/matched your cells are and depth of discharge it will vary. At 3.55V compared to the 3.65V you can spend more time safely without hurting them anyway.

Trying to achieve this with a BMS is much more difficult. But again its not critical. Since charging 100% full isnt needed all we really want is all cells at say 99 and balanced. That extra bit after balance is just to be sure the last cell sticks, so it doesent drop away a bit faster than the others when you stop charging.

[Burgerman]

To level all the voltages I connected all the POS terminals together, and all the NEG terminals together. They took 2 days to get within 3mv (3/1000th of a volt). all the pos:1 to 2, 2 to 3, 3 to 4 etc. And then 1 to 8. Same with the Negs.

They took 10 days to get to exactly 3.3431V resting for each cell, once all the cables were removed, a day full later. All are now sat at the same exact voltage measured with a calibrated fluke 289 meter. That means all are identical to 1 ten thousandth of a volt!

When I connect a PL8 which are pretty accurate, it shows a 3mV spread. When I connect a BMS it shows 8mV spread. Those figures are good enough for charging. But these cells are showing as unbalanced! The PL8 would try and balance them. The BMS would try and balance them much more to level that 8mV.

If I were to charge 1 cell by just 8mV with a PL8 to simulate what a BMS would try and do to that pack, what would it show? Well it takes about 14Ah to achieve that new voltage point. So if you were to allow it to balance at this 3.3431V point it will actually unbalance the pack by about 14Ah.

[Scooterman]

Strange Graph?

Cells charged in cold garage.

Started charging and graph looked slightly odd so stopped charge and restarted charge twice. Graphs 1 & 2

Then I noticed PL8 was charging at 3.55v due to 50mv compensation due to less than 10 degrees.

So I thought as the cells had probably warmed up a bit I'd turn off cold weather comp and allow pack to charge at 3.6v.

But still got an odd graph, see Graph 3.

I'm guessing it's due to cells being cold?

TC was set to 700mAh, so have now set it to 650mAh to see if it gives me a slightly longer CV balance phase next time I charge them.

[Burgerman]

Is everything soldered?
If not then theres the problem.
If it IS all soldered, then you have something loose on an interconnecting strap, or maybe a balance wire connection.

Either way theres a bad connection somewhere. Likely cell 4 and 5.

[c500user]

I have just finished replacing two 10 year old Odyssey PC2250s in my Otto Bock C2000 by eight EVE MB31s (bought from Docan a little while ago). I decided to use the plastic snap-on brackets (https://www.docanpower.com/china-stock/china-stock-plastic-holder-280ah-345ah-size-raw-cells) to ensure cell separation and minimise risks of short circuits. I decided to use flexible copper bus bars rather than making cables but swapped the standard nuts for thin stainless M6 washers and nyloc nuts. Everything went fine and all connections are torqued to spec (5Nm) using insulated tools (not cheap but worth not having to worry about accidental short circuits).

My balance wires terminate at a 9 pin round SP28 connector (rated at 10A per pin, so more than enough for balancing) that is mounted on the chassis. The balance cable I will be using for PL8 charging (SP28 on one side and standard balance connector on the other) can also be connected to an IDST 8s battery checker (https://www.isdt.co/bg-8s-2.html). We connected it and all cell voltages were fine.

I have left the main 100A fuse (that is accessible without tools) in place but connected it at the 0V side of the 8 cells, rather than in the middle where it originally sat (between the 2 lead acids).
The C2000 has a non-standard charging port using a Neutrik PowerCON connector. I have not checked the rating, but I think the charger that came with the wheelchair was a 20A charger so it might be fine up to 20A. I never used that charger but should have it in my shed and will check the rating before charging the batteries using a PL8!
I have no need for a high charging rate, so even it were 10A it would be fine because it is not my daily driver. The most I ever recharged with the lead acid batteries was less than 70Ah, and now with >300Ah on a wheelchair I only use occasionally when I go for long walks, even charging at 10A would be fine.

My helper drove it for a bit to see if everything was ok, and everything seems to be ok. Next week I'll take it on a 10km walk to see if everything works as expected.

I have learnt a lot from the info on this site and have now bought (and installed ) the last batteries that I will probably ever need for this wheelchair. Thanks!

[Burgerman]

All sounds good. The only downside of charging at low speeds like 10A would be that it takes a day and a half (about 35 hours for an empty pack. But also that even if only adding say 30Ah you nessasarily hold it at its full voltage a long time during that last few percent. Which isnt iseal. But if you only charge if now and again due to large pack then probably not so much of a problem.

[wchl25]

So I am finally charging the new pack up for the first time. I will post all the details when it gets done. I have a question though. I was looking at the internal resistance of the cells on the charger and there is a lot of variation. Is this normal?

[Burgerman]

Are all connectors soldered.
Are all are all connectors plated. Not bare copper.
Are all wires and link wires similar lengths.
Are all connectors tight.
Are all cell links wired rather than the bus bars they ship.

If the above is all true then you can ignore those figures.
Because to measure cell resistance requires a special 4 pin connector, direct to the cell, not to a connector. And a special meter that injects AC at 1000hz as the signal to measure. Trying to measure in the mOhm range with anything less is a waste of time.
All it can really show is if something is absolutely miles off.

The ACTUAL resistance of all of my 20Ah cells was 0.22 or 0.21 mOhm. That is so low its like measuring the resistance of a foot of 1 inch rebar.

Like this below.

[Burgerman]

Heres the ACTUAL cells, by serial number on the manufacturers spec sheet.

Note that my measured resistance matches the actual specs exactly.
And that the cell(s) all lost 0.007V (7/1000th of a volt) between manufacture and arriving in my hands.

Your cells will be similar. So all your readings are all absolutely miles off. You are measuring the connectors, wires, induction across wires etc. All of which far exceeds tha actual cell resistance.

[Burgerman]

If those resistance readings are so useless then why are they included?

Because hobby batteries are usually charged with either cables that are a few inches long or directly. So the cable resistance is almost negligable, and the only connectors are the ones straight into the charger. The battery end is directly soldered.

So it gives a "better" reading. Still useless, but better than down a meter of cables, across 16 battery connection ring terminals, via an additional plug and socket with another 2 power and 9 balance friction connections...

[wchl25]

Are all connectors soldered. Yes
Are all are all connectors plated. Not bare copper. Yes
Are all wires and link wires similar lengths. Yes
Are all connectors tight. Yes, with a torque wrench for good measure
Are all cell links wired rather than the bus bars they ship. Yes

A little over 6 hours in.

[Burgerman]

Ist charge may slow right down, and then spend a very long time trying to balance everything up. On a bunch of cells that is a good few Ah out, that can take an hour to a day. Or it can be rapid.

2nd charge after some use will then be faster. Usually a LOT faster...

3rd charge after further use will be about as fast as it will get. Because all cells are now top balanced already.

On a set of MK Gel grp24 batts, you can take out around 40Ah from that supposed 74 before the chair stops.
On a Lithium battery you can take out all of the Ah. My 230Ah cells actually measured 244Ah when measured - matching the spec test data sheet. Yours will be the same.

So far you have returned or charged 126Ah... Thats the same as THREE FULL 24V SETS of fully discharged MK batteries. (And a bit!)
Your lithium battery was at around 45% for storage.
Because the voltage of lithium is a little higher, the battery current as you roll is a little less. So in reality thats around 6x the range of a set of MKs. Now you can see why you need to charge at around 6x the Amps of a mobility charger!

[shirley_hkg]

Need not to pay much attention to those.

Just watch out if any cell pops up during charge, except it is near the end.

[emilevirus]

According to Bounder themselves, box is 290 x 375 x 304. It'd be snug but it'd fit. Not sure if I trust them tho. It seems oversized for grp 24. I don't want to pay $500 for it to not fit.

Some bounders have a grp27 batter box fitted. They look like they are taking a dump at the rear with the batt sticking out the back even more than normal. Thats a longer box than 24s.

Which is why:

Postby Burgerman » Sun Oct 26, 2025 5:18 am
No. Well it might, but MEASURE VERY CAREFULLY.

Wel well well it doesn't fit it's not 290mm but 260mm.

[wchl25]

Well it took 10 hours but we got there.

It took about 55 minutes once it hit CV to finish down to 1 amp termination current.

183.9 ah returned.