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Powered Wheelchair 7S3P
#1
Ok so not an ebike or cart but not sure where else to share the post.

My wife's disabled sister and brother in-law came to visit a few days ago and we were looking at her new chair.
The conversation turned to the numerous 18650 cells that are slowly over running the house and soon to the story of my homebrew Powerwall.

While we were talking my brother in-law mentioned that the new chair only came with one battery, a 24V 4A 96W lithium-Ion and that it was going to cost an extra £450 to get a second battery.

He then showed me that the battery slid into a slot in the frame and the connecting lead used 15A Anderson connector. In the other side of the frame was a empty dummy battery case.

Ok so here i am with a ton of 18650's that are good cells just not up to the capacity i want for my Powerwall Sat in a box just waiting for me to find something to do with them.

Light bulb moment lets knock together a test battery.



30mins, 21 cells, a cheap Chinese 7S BMS later we have the start of a spare battery 24V 4.2A. Total cost to me so far £13.45.
Waiting for the Anderson connectors to arrive then we can take it out for a test run.?
jdeadman and Korishan like this post
UK Southwest.

6 kWp Solar Panels
APS YC500i Micro Inverters.
Still sourcing and processing cells for powerwall.
Planning on a Sofar Mass Energy ME3000SP AC coupled grid tied inverter.
Reply
#2
Not enough space to double the width of the pack up? Effectively making it 7s6p.

Another idea, could you possibly lay the cells down length wise to the case? Would you be able to get more cells that way? Probably still end up with 7s3p, though. hrmm

Nice work, none-the-less Smile
chuckp likes this post
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at https://discord.gg/c7gJ5uA
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#3
(09-13-2018, 12:36 AM)Korishan Wrote: Not enough space to double the width of the pack up? Effectively making it 7s6p.

Another idea, could you possibly lay the cells down length wise to the case? Would you be able to get more cells that way?  Probably still end up with 7s3p, though.  hrmm

Nice work, none-the-less  Smile

Thanks Korishan

Yeah we did try several options but could only get it to a 7s3p, battery case is exactly the depth of the cell holder, just enough room for the bms and some sticky back foam to pack the top and bottom, should stop any vibrations.
We measured the amp draw on the existing battery with a clamp meter at 2,8A going at max speed on the flat, guessing it will be a little higher when going up hill.

The charger for the chair has a 2A output so around 666mA per cell should be ok for used cells.

When I get the Anderson connectors in and take it for a test run I'll post the results.
UK Southwest.

6 kWp Solar Panels
APS YC500i Micro Inverters.
Still sourcing and processing cells for powerwall.
Planning on a Sofar Mass Energy ME3000SP AC coupled grid tied inverter.
Reply
#4
Connecting two of the in parallel will halve the amp draw. That's good. Even though electric motors can pull 3x - 5x their rated amps on startup, in a wheelchair, they are so geared that they probably don't pull a whole lot. It's designed more for duration, not acceleration Tongue

Later on you could always upgrade the battery pack with LiFePO4's, and get better performance out of them if amps is an issue.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at https://discord.gg/c7gJ5uA
(this chat is not directly affiliated with SecondLifeStorage)
Reply
#5
(09-13-2018, 01:22 AM)Korishan Wrote: Connecting two of the in parallel will halve the amp draw. That's good. Even though electric motors can pull 3x - 5x their rated amps on startup, in a wheelchair, they are so geared that they probably don't pull a whole lot. It's designed more for duration, not acceleration  Tongue

Later on you could always upgrade the battery pack with LiFePO4's, and get better performance out of them if amps is an issue.

I have thought of that too, maybe for future upgrade.
I found this online for the actual chair.

https://wheelchair88.co.uk/pw999ulO
UK Southwest.

6 kWp Solar Panels
APS YC500i Micro Inverters.
Still sourcing and processing cells for powerwall.
Planning on a Sofar Mass Energy ME3000SP AC coupled grid tied inverter.
Reply
#6
link didn't work. You added an extra "O" to the end. Tongue We'll chalk it up to tired fingers.

Interesting chair. I didn't know they could fold up so small.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at https://discord.gg/c7gJ5uA
(this chat is not directly affiliated with SecondLifeStorage)
Reply
#7
(09-13-2018, 01:06 PM)Korishan Wrote: link didn't work.  You added an extra  "O" to the end.   Tongue  We'll chalk it up to tired fingers.

Interesting chair. I didn't know they could fold up so small.

I know cool isn't it.

Makes it so much easier for Di to open and close herself.

Sorry about the link probably was tired fingers I should have been asleep at that time in the morning. LoL

Cool Anderson connectors arrived.
I've been a little naughty as I'm not supposed to be doing anything since my spinal surgery.
But they are now fitfed, battery case assembled, now need to wait for Di to come over with her chair so I can test run it.

I think I'm also going to make up a patch lead to parallel link it to the original battery, should share the load nicely and hopefully double the range she can travel.


Korishan likes this post
UK Southwest.

6 kWp Solar Panels
APS YC500i Micro Inverters.
Still sourcing and processing cells for powerwall.
Planning on a Sofar Mass Energy ME3000SP AC coupled grid tied inverter.
Reply
#8
So back to the drawing board, in my haste to be helpful and making use of components i had to hand i completely forgot that 2 motors with a combined demand of 12.5A is likely to draw between 6 to 9 X that on start up. So could be i the realms of 100A+, oops little Chinese 20A bms just wouldn't cut it.

So quick trip to EB and ordered in the following.

https://www.ebay.co.uk/itm/24V-7S-18650-...2749.l2649

Wheelchair battery V.2 on its way.
hermitdave, Korishan, Dala like this post
UK Southwest.

6 kWp Solar Panels
APS YC500i Micro Inverters.
Still sourcing and processing cells for powerwall.
Planning on a Sofar Mass Energy ME3000SP AC coupled grid tied inverter.
Reply


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