LiFePo4 for Permobil C500S

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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 04 Aug 2019, 13:50

Intersting question:
Can LiFePo4 cells be mounted upside down?
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Re: LiFePo4 for Permobil C500S

Postby Irving » 04 Aug 2019, 14:10

quadcopter wrote:Intersting question:
Can LiFePo4 cells be mounted upside down?

Don't see why not, they're solid electrolyte.

But don't rest them on the terminals, they won't like that loading..

But why would you want to?
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 04 Aug 2019, 16:18

The electrolyte is like oil, thin, clear and a bit like vegy oil. Not solid like in the lipo packs or lithium ion cells. But theres not much in there, a few CC, and theres no reason they should work any better any particular way up. But probably better to have the vent not at the bottom. It will puke oily electrolyte rather than what looks like smoke/steam out if drastically overcharged or shorted out or heated up. Its on the pos end of the headway style cells and the top of the prismatics. It wont matter unless the pressure release vent is needed...

If you want to see this oily stuff, put a headway on the fire. When hot enough it leaks out via the vent. And like cooking oil it will burn if hot enough and ignited by external source.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 05 Aug 2019, 22:50

Irving wrote:
quadcopter wrote:But why would you want to?

I reworked my pack after Burgerman note about isolation between cells. I added isolation tape and special isolation film.
The cells were placed in powerchair case but they stay very tightly. Also there are welding seams on walls of the case.
I'm sure that isolation will be damaged one day.
So I want to rework the pack again: 4 cells inside the case and 4 outside at the back + thick good isolation between cells and case.
I'm thinking how to place them to have shortest interconnections.
Lay them on a side seems the best for me right now.
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 09 Aug 2019, 22:18

Can I use AWG 10 and these fuse holders with rectangle fuses 40A instead of Revolectrix 40A Safety Banana Plug Cable?
fuse_holder.png
Fuse holder
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 09 Aug 2019, 22:55

Screw connectors?

I wouldnt. You just need a normal ring terminal and solder it, midi fuse, and a M5 nut/bolt. Covered in heat shrink. Its smaller neater and wont screw up, come loose, or be a high resistant point.

Will it work? Yes. Is it as good, no its bulky, and less good. And more expensive. Those are really for boy racers adding car sterios. Or just use blade fuses, and solder + heatshrink. Or if you are careful, skip the fuse. I have given up fitting any on charge cables. Because I am careful...
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Re: LiFePo4 for Permobil C500S

Postby expresso » 09 Aug 2019, 23:08

BM - how big of M5 nut and bolt would be needed ? to make a good contact and keep it flush ? do you know the length size -

etc, -

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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 09 Aug 2019, 23:33

Use a domed (round head type) M5 stainless bolt, 8mm long and an M5 nyloc. No washers. Not nylon!!!
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Re: LiFePo4 for Permobil C500S

Postby expresso » 10 Aug 2019, 00:20

any reason a M6 screw wont work - i have the m6 nut already

https://www.amazon.com/10-M5-10mm-Stain ... =1-13&th=1

like this but 8mm long ?
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 10 Aug 2019, 01:12

You could. But the hole in those fuses is designed for M5 bolts and so is drilled to 5.5mm. You would need to drill 6mm or a fraction bigger, and then the bolts and nuts are physically bigger and will stick out more. Probably better to use 5mm bolt.

Yes as above. With nuts.
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Re: LiFePo4 for Permobil C500S

Postby expresso » 10 Aug 2019, 01:25

ok - will look around if i can find a few here -
i have a fuse holder but this would be less bulky - mines is compact though

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Re: LiFePo4 for Permobil C500S

Postby expresso » 10 Aug 2019, 03:32

BM are you sure 8mm is good enough size - what if the ring on the wire end is a hefty size - not very thin ?
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 10 Aug 2019, 07:25

On M5mm bolt it should be perfect, as the nut is smaller too. And on a ring terminal for 5mm bolt there should be no problem. The next size is 10 or 12mm. But bolts are cheap. So order a few different lengths if your ring terminals are thicker metal. Or order 10mm long. Or measure yours... The nut is 1.5 x the 5mm (so 7mm tall) The bolt is 8mm long... So 1mm left for the ring... Order 10mm. If you can find any. Or 12mm but there will be 2 or 3mm sticking out extra.

https://www.westfieldfasteners.co.uk/Da ... High_M.pdf


Looking at this, then ideally you will need 10mm for a nyloc nut inc fuse/ring.
Or 8mm for nornal nut including ring and fuse.

But I dont think 10mm is easy to get. So you have a choice of 8mm (normal nut) or 12mm which is a little longer than needed, for nyloc.

So probably better to use normal M5 nut and a dab of loctite, and 8mm long bolt. Because that keeps it all thinner and neater easy to heatshrink.
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Re: LiFePo4 for Permobil C500S

Postby expresso » 10 Aug 2019, 16:35

this is a compact fuse holder - smallest i can find - but still would be larger than without using it - i think maybe 8mm 5M size can work - will order a few - fuse holder is about 20mm high - - i was thinking of using it but maybe will see without - depends on space - this makes it easier to change out fuses if ever needed without cutting up heatshrink
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Re: LiFePo4 for Permobil C500S

Postby quadcopter » 27 Aug 2019, 19:54

How should I charge my pack?
I.e. what is better - charge it every time I return home or let it stay till next trip and charge only before?
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Re: LiFePo4 for Permobil C500S

Postby jefferso » 24 Nov 2019, 15:26

Are you actively using the Lithium pack in your Permobil now?

My current MK Gel batteries are over a year old now so I'm starting to notice how much less charge they hold. I am about to order some replacements but I also really want to build a pack that will fit in the group 24 spaces of my Permobil C500S. I don't have the strength to do any of it myself, so I have to direct someone (of varying spatial, mechanical and electrical ability) to do each task. I've started a few projects which never quite got anywhere, so I'm a bit concerned I'd start building a pack, then not get it finished.

What size could I make now to fit? 176Ah, or are there cells that can make 200Ah?

I have a PL8 charger, but I'd need to get the right cables for it too.
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Re: LiFePo4 for Permobil C500S

Postby Burgerman » 24 Nov 2019, 15:31

16x 105Ah cells usually fit the gp24 space. So 210Ah.

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Re: LiFePo4 for Permobil C500S

Postby jefferso » 24 Nov 2019, 22:39

Burgerman wrote:16x 105Ah cells usually fit the gp24 space. So 210Ah.


Wow, that would be nice. I've looked at alibaba.com for some options and found quite variable prices. The sizes vary a bit, but for example there is one which is

37 x 130 x 196 mm

That would require 8 cells on each side if I'm understanding correctly, which could be arranged in two groups of 4 side by side, then end to end as:

148 x 260 x 196 mm

if they were packed closely. But from what I've read in the various build threads, they require some kind of insulation between cells, so that would add several mm at least.

The MK gel batteries are

173 x 259 x 209 mm

so it looks like there would be some leeway on the top, and the width, but the length might be a squeeze. It doesn't look like there's much length leeway with the MK Gels batteries installed in my C500S.

I couldn't figure out which cells quadcopter used. Are they twice as thick?

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Re: LiFePo4 for Permobil C500S

Postby ex-Gooserider » 26 Nov 2019, 03:23

Quadcopter almost certainly is using a different chemistry type, which you emphatically do NOT want to use in a power chair....

There are several different sorts of chemistry used in Lithium batteries, and the ONLY one you want in a chair is Lithium Iron Phosphate, usually abbreviated as "LiFePO4" or sometimes just "LiFe".... These offer the lowest power density, but are very safe, they won't catch fire or explode, and they have the longest life if properly treated....

Quadcopters and other flying models tend to use Lithium Polymer (LiPo) batteries - which have fantastic power density, but will also catch fire, and possibly explode violently if mistreated, and at best have a relatively short lifespan...

Lithium Cobalt, and other similar variants, are used in laptops, cell phones, and so on, and fall in a middle ground where they can catch fire if mistreated, but are less likely to, and have better power density than LiFePO4 (but not as good as LiPo) and slightly better life span than LiPo, but not as good as LiFePO4....

Because most of us that use chairs will have problems running away if things start going up in flames, the only battery chemistry that we think is suitable for chair use is LiFePO4. It is also the most economically viable in terms of cost per stored Ah of power and lifespan.

There are several other threads that go into the details of building a pack, charging, etc. - I will let you read those on your own...

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Re: LiFePo4 for Permobil C500S

Postby jefferso » 27 Nov 2019, 01:40

ex-Gooserider wrote:Quadcopter almost certainly is using a different chemistry type, which you emphatically do NOT want to use in a power chair....


I thought quadcopter (the user vs the device) was using LiFePO4. It seems he is using an LiFePO4 charging profile.
viewtopic.php?f=2&t=8675&start=150#p141379
But his cells look to be twice the thickness of the ones I've been looking at.

ex-Gooserider wrote:There are several other threads that go into the details of building a pack, charging, etc. - I will let you read those on your own...


I've been following many of the build threads for a while, but looking back, it can be hard to figure out which supplier has been used and with which cells. And the capacity seems to be continually rising. The best latest capacity seems to be 105 Ah. I've seen prices from $28 to $94 on alibaba for 3.2v 105Ah cells that seem to be in the size range of about 200 x 130 x 36 mm, 2 to 3 kg each.
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Re: LiFePo4 for Permobil C500S

Postby Irving » 27 Nov 2019, 09:40

The 200h X 130w X 36d cells are the best fit for Gr24 replacement. 2 side by side is 263mm wide (with insulation) and 8 groups are 300mm long (ditto), comfortably shorter than 343mm of 2 X GR24. Although the 263 is slightly wider than the 260 of the MKs it fits in many cases (eg the Puma has 5mm rubber packing strips each side with MKs)
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