Group 24 cells

[jefferso]

I have been thinking about putting a lithium pack in my chair for a few years. I haven't had the time or help to do it but I think I might go for it soon. Would anyone have recommendations for cells to buy to fit in a Permobil F5?
It has Permobil's new branded battery now but I think it can use MK gels as well, which I think are both standard Group 24 size. Last time I measured the MK gels from the C500 I got 259 x 173 x 209 mm.

Ideally I would like to get a configuration which I could use in my old Permobil C500 as well, but the battery placement is different, so it might not work easily. The F5 has them right next to each other, long side touching, with the terminals facing towards the back, both sliding out the back.

The C500 has them with terminals facing back, short side next to each other, with a metal divider between, but each sliding out to the side.

F5 battery arrangement, slid out the back

C500 battery arrangement, slid out the side

C500 batteries in place with shroud removed

[shirley_hkg]

https://www.wheelchairdriver.com/board/ ... =2&t=12134

You may not get 209 height.

Last month, I put 160Ah in a Quickie QM-710 , which is in lack of space similarly.

However, one 350mm side is needed still.

[Burgerman]

Do careful measuring. Not all cells need to be the same way around. In many cases where there is a group24 setup originally its possible to fit 8 230Ah cells. Such as these.

There many suppliers. These for e.g will or should fit.
USA https://www.docanpower.com/index.php?ro ... ption=true
EU/UK https://www.docanpower.com/index.php?ro ... ption=true

Heres a pic, layout, in a typical chair. Not yours though.
230Ah all nice and neat.

Remember that while 230Ah will give you a huge 500% or so range increase minimum and because of ultra light use and infrequent charging/low DoD daily a HUGE lifespan that will outlive the chair and maybe you, even the 160Ah cells will still give you around 3x the stock range. And last pretty well too.

Why? You will get 45Ah maximum from a set of 74Ah gel batteries because of peukert. Lithium doesent suffer from that.
230Ah div by 45 = 5.1 times as much range.
160Ah div by 45 = 3.5 times as much range.

But with the smaller pack you need a bigger percentage as reserve so say 3x as much. But even this is way better than lead. I wouldnt go less that 120Ah though as things start to get worse, with most of the lithium gains that were the very reason to do this, lost.

[Burgerman]

I may be tempted to TRY a set of these in a GRP24 chair. These are just big enough Ah to make it worthwhile, and while I dont like BMS equiped batteries for LFP cells, or powerchairs for that matter, these are at least capable of engine starting so should be OK with heavy intermittent currents...

Note that they are supposed to be GRP24 but are 2 to 3mm wider (275 or 276mm) than say a typical GRP 24. Not normally an issue.

https://www.energy-xprt.com/products/da ... ery-923536

Note that as far as I am aware these are the ONLY lithium drop in replacements that tick all the boxes that would make me consider a redy to go solution. I wouldnt do it as I prefer the PL8 and no BMS for a huge bunch of reasons. But thats not for everyone. And that they are exactly HALF the capacity of doing it "properly" with 8x 230Ah cells.

[jefferso]

I may be tempted to TRY a set of these in a GRP24 chair. These are just big enough Ah to make it worthwhile, and while I dont like BMS equiped batteries for LFP cells, or powerchairs for that matter, these are at least capable of engine starting so should be OK with heavy intermittent currents...

Note that they are supposed to be GRP24 but are 2 to 3mm wider (275 or 276mm) than say a typical GRP 24. Not normally an issue.

Looks like their specs say 242.5mm x 176mm x 197mm vs 259 x 170 x 200mm for my current ones. I guess I'd have to get someone to check and measure to see if it looks like the width would be a problem.

I thought the posts would stick up too high but I guess they have "M8 size bolts. Includes a terminal adapter kit with automotive & marine posts that screw into the M8 bolt terminal, and M8 brass terminal bolts."

https://dakotalithium.com/product/dl-pl ... rformance/

https://www.energy-xprt.com/products/da ... ery-923536

They look interesting. I don't see anyone selling them in the UK. Looks like it would be $2,318 for 2 plus $940 shipping, total $3,258.

[jefferso]

Do careful measuring. Not all cells need to be the same way around. In many cases where there is a group24 setup originally its possible to fit 8 230Ah cells. Such as these.

There many suppliers. These for e.g will or should fit.
USA https://www.docanpower.com/index.php?ro ... ption=true
EU/UK https://www.docanpower.com/index.php?ro ... ption=true

I would love to have 230Ah, but I don't know if they'll fit. The drawing on that page shows that those are 204mm high for the main body, 207mm high with the terminal posts. I'm not sure the F5 will accommodate that height. Especially based on Shirley's previous post
https://www.wheelchairdriver.com/board/ ... 30#p199432

Do cells always need to be upright? or can they be arranged on their sides?

[Burgerman]

Well any way up I suppose! I wasnt suggesting they would fit but showing others latyout. Measure twice order once. Remember that you need something insulating below them as well as in between. All the casings are 3.6V different to each other. Ony needs to be thin. But tough.

[swalker]

I would also like to get a set of LiFePO4 cells that will fit in my Permobil F5 wheelchair and could be used in my Permobil C500 wheelchairs. I have been looking seriously for over a year now.

So far, I have not found a suitable cell.

The F5 and C500 battery compartments are not very tall, meaning any high capacity cell with studs permanently installed will not work.

Every 230 Amp Hour cell without studs I have l0oked at is still too tall. They will otherwise fit in the F5 (requires a bit of an unusual arrangement of the cells, but that is OK), but they will not fit in the C500.

So, I have been looking at smaller sizes. I don't want to go too much below 200 Amp Hour, due to the limited C rate of the prismatic cells (typically 1 or 2 C sustained).

I am still looking, just have not found the right set of cells yet.

Note that I do have LiFePO4 cells in another wheelchair (Magic Mobility X4), so am familiar with the benefits they bring. The last set came from China, and there was just too much drama involved (cells were obviously used, swollen, etc., illegal for me to return, no recourse to make things right, really). Now, I am looking for US resellers, where I can legally ship a bad cell back to them. That certainly limits my selection.

I have the budget set aside for a set for the F5, but have just not yet found the right set of cells.

Steve

[jefferso]

Every 230 Amp Hour cell without studs I have l0oked at is still too tall. They will otherwise fit in the F5 (requires a bit of an unusual arrangement of the cells, but that is OK), but they will not fit in the C500.

Thanks for that. How would you arrange 230Ah cells to fit in the F5?

[jefferso]

I think someone posted about these, or similar, before. They claim to be 240Ah and are shorter than the typical 230Ah (185mm vs 200mm), but the listed weight is 2.8kg
Seems implausible when the weight of 230Ah cells is around 4kg.

https://www.aliexpress.com/item/1005006515947627.html

Does it seem like a scam?

From the specs:

Grade: Grade A
Quality: brand new
Material: Aluminum
Rated capacity: 240Ah
Minimum capacity: 240Ah
Internal impedance: 0.1~0.5mΩ
Rated voltage: 3.2V
Size (L * W * H): 175* 48 *185mm (+/-10mm)
Weight:about 2.8kg
Recommended current constant: 240A (1C)
Discharge termination voltage: 2.5V
Recommended constant current: 240A (1C)
Charging voltage: 3.65V
Maximum continuous discharge current: 240A (1C)
Life cycle (90% DOD): 5000

[Burgerman]

This is the problem. The chinese can CLAIM anything! As long as you pay with paypal, then you should be safe. When they arrive they need the following:

Careful examination for previous use/recovering etc.
All flat sides are FLAT and not bulged in any way.
Connect to the PL8 or simiar and charge fully, and then do a discharge test. You should get between 3.6V fully charged and 2.7V fully discharged almost exactly the claimed Ah capacity from each seperate cell.
Using a chinese impedance tester measure internal resistance, all should be low and approx the same. Measure at around half charged for lowest figure. But it should still be the same across all 8 even when fully charged.

If all this rigns true, then they are good cells!
Its unlikely though at this price!

￡467.93 for 8 delivered.
(￡1,169.82-60%)
240AH Grade A Rechargeable.

If they are what they claim and look as good as the pictures they used then let me know I need about 24 of them!
If not claim money back via paypal. Or ypur credit card. Check before buying with both...

Theres many variations on aliexpress. Like https://www.aliexpress.com/item/1005006 ... ry_from%3A and we cannot know. Look for lots of good feedback!

[jefferso]

Theres many variations on aliexpress. Like https://www.aliexpress.com/item/1005006 ... ry_from%3A and we cannot know. Look for lots of good feedback!

That one seems more like the standard height and weight for the capacity:

Size (L * W * H):205*175*55mm(+/-10mm)
Weight:About 4Kg

[Burgerman]

Heres the connundrum... They keep bringing out new more energy dense cells. So it may be real. They do this by using thinner materials internally, thinner seperators etc. This is why they are generally low C rate when energy density is high. The opposite is true. Capacity is reduced when making a high C rate cell in the same physical size.

Does this matter. Not if the capacity is high enough. And at that size its plenty.

Another thing to consider is that you PROGRAMMING makes a huge difference to C rating or rather the max current that your chair will draw from the batery.

Why? Because while with QUALITY low impedance motors the motor current can be 120A each, at stall, or as you accelerate at full power or rapidy swap direction (acceleration setting, turn acceleration settings matter a LOT here) then the battery current may be 25 or 30A only. So the motor current at stall and LOW speed such as just rolling may be many times higher than the battery current. I can explain why if you want but its a page...

However only if your forward acceleration is set high enough will it reach a really high battery amp figure as speed INCREASES. So if you set forward acceleration to say 100. And your motors are hit hard as you accelerate away at max acceleration, the motor current may be 120A each at stall, all the time as you accelerate. But the battery current will slowly rise from around 30A or so as speed increases. This is because the motor is a generator. As you speed up the voltage needed to be supplied to maintain that 120A increases. When it matches battery voltage, then 120A per motor is then 240A at the battery. So now ALL the current is needed at the battery. This only happens at 1 specific speed, under full load for an instant. After this the current drops away as speed continues to increase. This is around half the chairs max speed. However if you do this up a ramp or slope then the speed increases slowly or doesent actually increase past the half speed point even under full power. At this point you see a full 240A at the battery for a longer time.

This almost completely depends on programming and driver "aggression" I can repeatedly do it. Most people dont actually drive that way and cant anyway if the chair is programmed in grandma mode even if they wanted to.

So C rate isnt as important if you are one of those people. For some it is...

[jefferso]

Ah, I think I see. So that's why swalker doesn't want to to do 160Ah on his Permobil F5 or C500 because at 1C the pack would only deliver 160 amps.

[Burgerman]

Well it would deliver that 160, or 260 if needed, but its about lifespan. The further you go away from the rated 1C the longer they last. The higher the regular peak currents the worse it is for the cells. If you want a pack to have a long safe reliable life, much greater than the typical expected lifespan then you need to keep well away from its limits.

Example. When flying things like my helis or quadcopters we are using 20C up to 70C lithium packs. Not 1C!
Even 130C packs are available. And we do take upwards of 100A from a 4Ah pack at times.
And typically get just 30 to 50 flights before the pack is swelled or unhealthy.

The same applies to A 1C lifepo4. Take up to 1/2 C from it and thats half what its rated at and get 3x the service life.
Likewise lithium do not like the following:
Being stored full... Store at between 40 and 70%.
Being charged to 100% (3.65V) or discharged to zero% (2.50V). So ideally never discharge below around 80% deep. And only charge at 3.5 to 3.55V per cell. This actually is 99% charged but it must happen to balance.

And obvously the bigger the pack the further away from all these destructive things you stay. A pack of double the size sees half the load, half the depth of daily discharge, or can be charged half as often. Weekly in winter for eg. So with lithium, the bigger the better. With the advantage that you also end up with so much range that all range anxiey is removed. And of course the very reasons for fitting lithium are:

Better range.
Better lifespan.
Less frequent charging.
Longer service life.
Thee things are all possible with lithium if you take advantage of the higher energy density that lithium offers. Which is why it totally misses the point to swap say 80Ah lead for 80Ah lithium. Because you throw out all the advantages! (Well most of them.)

So with lithium always maximise capacity. This also increases the effective C rate headroom too as the current draw remains the same and the battery is bigger. By doing this the bigger pack should last decades. And even if after 30 years its capacity is HALVED then its still as good as 2.5 full sets of MK gels!

But 160Ah at 1C is enough. More than. Because unless your chair is programmed like mine and driven like you stole it you will only very very occasionally reach 160A battery draw. So it shouldnt impact service life noticibly. Like most things its a compromise.

[shirley_hkg]

Usually you have 100A fuse.
I saw many heavy chairs have 80a fuse, and seldom get blown.
BM said his motors took 120a each, but they are not at 24V, I guess, are they ?
Over 100 amp at 24V is not very often.

[Burgerman]

Yes it IS possible. With the Salsa, which had a 100A fuse It can take 200 plus amps quite easily if you gun it up a ramp or something from a standstill. And yes I blew a 100A fuse. And with my programming I can repeat that quite easily. And that takes much more than 100A.

And yes at 24V. If it was at 45V then the battery current would be halved.
Remember that my acceleration is set to 100 and so the chair goes when I tell it!

And also the fact that most chairs have 100 or 125 amp fuse with a 120A controller doesent tell you what the peak current it. Because an 100A fuse can do 3x this 100A current for a short spikes, and 200A for quite long enough as to accelerate through the 100% pulsewidth period. (maybe 1 second) Without blowing. It will only fail if you significantly exceed 100A for a significant time.
Breakers perform the same way.

I now have 150A fuses in all my chairs. And can blow 100A fuses at will. And even sunrise have started doing this. I have a loom bought for a sunrise chair with a 150A fuse already in it that I didnt fit!

Theres a reason that sunrise are fitting these 150A (double that rating intermittently) now. Rnet 120, heavy chairs, and ramps/steep hills mean that it can spike to 240A intermittently if programmed to go...

[jefferso]

Are there any good UK suppliers of cells? Looks like ordering from China means delivery in June.

[Burgerman]

https://shop.gwl.eu/en/By-Brand-Manufac ... hparam=230

EU?

https://www.fogstar.co.uk/collections/l ... ll-grade-b
OUT of stock, grade B and super cheap!

[jefferso]

Looks like the UK places are out of stock and might take as long as shipping from China to get more.

I'm leaning towards these:

https://www.docanpower.com/index.php?ro ... ption=true

China Stock EVE 106Ah LiFePO4 3.2V Prismatic Cell with Laser-Welded M6 Studs

Width: 174mm, Height: 154mm, Thickness: 54mm

There should be room for these cells in the space of 2 Group 24 batteries. Does this diagram make sense for placement? That would mean they are on their sides, so it might not have enough room for the terminals?
They might need to be squeezed into the space upright, but then there might not be room for insulation between them if the space available is really only 348mm total.

[Burgerman]

Why would they be on their sides?

[jefferso]

Why would they be on their sides?

I'm not sure if they'll fit upright with the 174mm width into the space if they need some insulation between them. The last time I measured MK Gels I got a width of 173mm and they seem pretty tight in the F5 configuration. If they're on their sides, that's 154mm which leaves 20mm or so for the posts and wiring in between.

Permobil claims their new batteries are 259x170x200mm, and I haven't tried MK Gel in the F5 yet, but I've heard at least they will fit.

[Burgerman]

Permobil are a law unto themselves. But if they made the chair to actually fit BCI GRP24 then thats actually an "inch" size and the mm part is a conversion.

They should be capable of fitting:

https://www.thebatterygenie.com/latest- ... ize-chart/

Group 24
Metric mm 260 x 173 x 225
inch 10 1/4 x 6 13/16 x 8 7/8

So if they built the chair properly then any battery that is GRP24 or 260, 173, 225 tall should fit...
The 230A lithium are 206 tall. And with them aranged as a row of 6 and 2 turned, should fit with space to spare at both width and length as well as being around the same height with terminals connected.
https://www.docanpower.com/index.php?ro ... uct_id=523

Laid out like:
6 together and 2 turned



I I I --
-- I I I
It ends up leaving lots of room for cell spacers, and a 1mm plastic/nylon/pvc/polythene base for safety.

[Burgerman]

Like this or with one cell on the opposite side.

[Burgerman]

I know you are not getting it so I did an unbelievably bad drawing in about 2 mins... After !

I appologise.

But the cells are not 55 wide. And are not 175 long. They are less. But even if they were it all still fits!

With ONE possible exception. Height. Now a group 24 is usually around 200 to 220mm tall. I have some here that I just measured from the salsa. Those are 225 tall. So these 230Ah cells will fit in the space that 2 grp 24s came out.

[Burgerman]

Seperate with these https://www.amazon.co.uk/Essential-Arts ... 0155?psc=1

Tape the whole lot together on the bench as one pack with a roll of duct tape. Tape a thicker plastic sheet like 1mm under the pack. Then it should just slide in neatly. Will weigh approx the same as one lead battery.

There will be a about half inch gap each side. Fill with foam. Like the stuff you sit on. But use the hard stuff. Can be ordered pre cut on eBay You need 2 bits 200 x 340 x 15mm.

Of course being permobil will probably complicate everything! Like height.

Then dont wory about range ever again.
Or battery meters...
Why? Because you will have 5.2x as much range as lead. So around 100 miles. At full speed, non stop then that would take around 18 hours without a break! Which is impossible.

[Burgerman]

Incidentally I assured Dorcans representitive that I would be measuring and testing Ah and capacity. And heres my quote:
These are A GRADE EV type cells, complete with original factory capacity and resistance measurements and serial numbers and bar codes.

I can get 230Ah, 8 cells, for the same price as a decent set of miserable 80Ah (50Ah usable) lead bricks.
Except these have around 10x the lifespan at least, and 5.2x the range, and save the weight of a full lead brick.

So...
I get 5x the range, 10x the lifespan, for the same cost as lead. Why would anyone buy lead bricks in 2024?
This is 579UK. Thats CHEAPER than the lowest priced MK 74Ah lead bricks. And it includes all import duty or VAT.
https://www.mobilityworld.co.uk/collect ... el-battery

Here is my reply/quote after our discussion. All cells tested and gave 246 to 249Ah (from a 230Ah rated cell. And all are 0.19mOhm.

_______________________________________________________________________



Thanks for your enquiry, this is Amy Zheng from Docan Power

Very sorry, EU stock can not arrange shipments to UK area, but we can ship by DDP sea shipping from China to UK address.

EVE 230Ah we supply is HSEV grade A cells, welcome to test the capacity and performance, and we also support original EVE manufacture test report for your reference:
DDP sea shipping quotation from Docan Amy
LiFePO4 cell with laser welded M6 studs Unit Price: US$68/each*8pcs=US$544
DDP sea shipping cost: US$210
Subtotal: US$754 (£579 UK inc shipping)

Payment Options:Goods and service fees (PayPal/CC/Visa, etc.) is 5%, Alternatively, bank transfer with a bank fee of approximately $48-$100 per payment
Details:
*Free Gifts:One copper bus bar and two nuts per battery & epoxy boards between battery cells
*Original EVE factory test report whole lists send to you help for searching your QR code test value; Matched shipped votlage and internal resistance；
*DDP Sea Shipping (International): All fees included; no VAT/duty/tax; 40-60 days delivery via DDP sea shipping;Local delivery by truck/DPD/FedEx/UPS to your door.

Warm Regards
Amy Zheng
Docan Tech
---
Make faster shipping and dependable service for your order, don't hesitate to contact me directly:
Directly Work Email: amy@docanpower.com
Personal Gmail: docanpower22@gmail.com
Tel/Whatsapp/Wechat: +0086 135 304 12339
https://www.facebook.com/AmyZheng1990
Warmly invite you to share the battery DIY experience via my facebook group to help more solar battery beginners: https://www.facebook.com/groups/1156652185086422

[shirley_hkg]

The 3+1 / 1+3 zigzag arrangement is brilliant.
EVE-160 is a sensible pick.

230Ah cells are very risky in height wise. I lost the measurements , but it was very clear that my cell phone couldn't slip through between the MK Gel top and the chair. That was not yet taken into consideration of top & bottom insulation layers.

[Burgerman]

Brilliant? Thanks! It was the only way to fit 230Ah into many chairs that have very tight "made to fit" battery compartments. Its not nesassary on many chairs but on my Q700 and Salsa it will be. I figured it out when doing a pack for a freind when the 230Ah cells first appeared. And I am about to do both my chairs.

It allows the 2 175 long cells that are turned to overlap slightly length wise. So they dont add up to 350... Keeps overall pack footprint shorter and means that it should go into any normal grp 24 chair. Permobil it seems managed to make even this hard! On BOTH their C500 and the F3

It would frustrate the hell out of me knowing I was giving up some 70Ah. Thats almost 4 complete MK gel batteries worth of lost range! But it is what it is. Are there non that are say 10 or 20m shorter like 200Ah or anything? I cant say I saw any but wasnt looking! Maybe modify the chair a little.

Dorcan say that their 230Ah cells all test at 246 to 248Ah too. And invite me to test their claim. Maybe they really are A or rather EV quality as they claim. Even at their cheap price. What do you think?

Acording to Amy on a video they can ship with the welded terminals or just threaded holes. Saving a fair bit in height. Total height is then 207mm. MK total height 208mm... So same! I emailed her again for details. And height WITH the welded terminals.

More info.
4000 CYCLES AT 0.5C which means we will get much more in a wheelchair.
And 2C for intermittent pulse loads. 1C for normal max continual. So thats 230A and 460A capable.
4.2KG so 8 is 33.6KG complete. Thats around 2/3rds a set of lead. 2MKs is 47KG from memory weighed in my garage!
Int resistance under 0.2mOhm. So 8 is just 1.8 mOhm or less total. Compared to MK gel 4.5 getting higher as it discharges.

[Burgerman]

OK..
Without welded terminal, 207mm
With weldd terminal, 227mm
MK 208mm So its 19mm taller than MK... Although not qite as then theres the connectots and a bolt so thats around 6mm. So its really 13mm taller.