WheelchairDriver

Posted: **18 Feb 2019, 22:59**

I decided to start a thread to document my build of a LiFePO4 battery pack for my very old Magic Mobility X4 wheelchair.

With MK group 24 lead acid gel batteries, I reliably get a range of 4 miles and have gone as far as 5.25 miles. That is inadequate for my needs. I finally decided to do something about it and for the last 2 months have been procuring the bits and pieces necessary to make it happen.

I have a good friend that is helping with some of the heavy lifting parts of the job.

I have attached a parts list of the things I have procured so far.

So far, we have completed building all the wiring harness components. I received notice today that the batteries (ordered directly from the manufacturer in china) have made it to the US and are making their way to me in Colorado by way of UPS.

We have not yet decided what to do about insulating the cells. We have looked at fish paper, EVA foam, silicone sheets, and many other items, but have not yet hit on a solution I am happy with. If anyone had any suggestions, please let me know.

Also, if anyone has any comments on the items we are using for the build, please feel free to chime in. If there is bad news to be heard, the earlier the better.

And finally, a big thank you to everyone who has posted about their battery builds and especially to BM for providing this website/forum and the preset files for the PL8. Without all that, I would not have know how to get started.

Steve

Posted: **18 Feb 2019, 23:17**

I wouldnt add up all the tools etc, it will upset you!

Posted: **18 Feb 2019, 23:59**

I started with a pretty robust set of tools, so only needed to purchase a couple of special tools for the project.

I upgraded to a temperature controlled soldering station (should have done that 20 years ago) and bought a special crimper for the JST XH connectors used for the 8s battery monitor.

I generally prefer crimped to soldered connections and thought about buying an SB 50 crimper. In the end, I decided to solder those. If the soldered connections turn out to be too brittle and subject to failure, I will redo those with a crimper.

Steve

Posted: **19 Feb 2019, 00:18**

very nice - take pictures along the way - always good to look back and can post them here also -

which cells did you purchase ?

Posted: **19 Feb 2019, 00:28**

Here are some pictures of the wiring harnesses.

Posted: **19 Feb 2019, 00:31**

Another picture

Posted: **19 Feb 2019, 00:39**

expresso wrote:which cells did you purchase ?

They are listed in the spreadsheet. The QH brand 176 AH prismatic cells from

https://www.lifepo4-batteries.com/sale- ... f-car.html

I am certainly nervous about purchasing sight unseen from an unknown-to-me vendor in China. But, they are the only cells I could find that suit my purpose.

The only other potential downside is that the cells are rated for 2C maximum discharge and, though not shown on the web site, 1C continuous discharge (per an email exchange). I have done the math on what my wheelchair draws and think this will work OK. It may require some care not to work the wheelchair to long and hard in high draw situations.

Steve

Posted: **19 Feb 2019, 02:05**

ah ok - nice Cell - when you get them - do a review - or test them - etc, and post the results - it be fine - i dont think our chairs will use that many Amps Constant all the time - we will find out - i wouldnt worry too much - as long as they are good etc, -

Posted: **19 Feb 2019, 16:07**

Why not wire the cell checker to a male 13w3 and connect it that way. It’d save on the number of ring terminals you gotta bolt to cell terminals. Just a thought, not a criticism. What you done looks good :thumbup:

Posted: **19 Feb 2019, 17:17**

Wonder if they make a Y cable balance cable so you can use just one set of rings for the balance wires and use the Y cable to connect the Cell checker - first time i didnt know about adding it - and when i knew i didnt do it because didnt want to add more wires - but would like it on my next full chair if i can add it neatly. or if using alot of AH which today seems to be the Normal now - 180ah - may not even need it

Posted: **19 Feb 2019, 17:46**

Looking forward to this.

How old is your V4? Please take a lot of photos of the chair's battery area before and after fitting the cells. I'm very curious. :thumbup:

Posted: **19 Feb 2019, 21:05**

Expresso: I considered a variety of options for wiring in the battery monitor. In the end, I decided to keep the wiring separate from the other wiring.

If I had used a male 13W3 for it, I would have to unplug it to charge and then plug it back in to ride, doubling the connect disconnect cycles for the 13W3. The 13W3 connectors I chose only have a lifetime rating of 2,000 plug/unplug cycles. So I decided not to go that route.

Instead, I purchased of couple of 36" 9S extensions from Revolectrix (which have JST PA connectors). I connected these together, replaced the JST PA connector one one end with a JST XH connector (used by the battery monitor) and replaced the connector on the other end with 1/4" ring terminals.

Gnomatic: It is a Magic Mobility X4 rather than a V4. The X4 is a 4 wheel drive predecessor to the X8.

I purchased the X4 used in 2015. At the time, I researched the serial number and figured out a likely date of manufacture. Unfortunately, I did not write that result down and can't remember for sure what I came up with. As best I can remember, it was probably manufactured in the 2008 time frame. So, it is a very old wheelchair.

My friend and I were able to pull the brushes for the motors and they showed absolutely no sign of wear. Based on that, I am guessing the wheelchair had less than 100 miles on it when I got it. I have put about 300 miles on it since then. With a 3.5 to 4 mile safe range it is hard to put a lot of miles on it.

I have attached a set of pictures to provide an overview of what I am working with.

The battery boxes are oversized for group 24 batteries. They each should hold a battery up to 174mm wide by 285mm long by 210mm high. There is room for a taller battery if things are rearranged a bit.

Posted: **19 Feb 2019, 21:20**

Looks fairly roomy and easy to work on with the top half off -

i like your wall with all the tools hanging on it neatly - i wish i had a Larger Room for Tools and workshop area - i have to make due on my 36 inch square kitchen table

and living room is my garage

i cant believe you got 5 miles max - thats crazy - you will feel free after the 176ah are in there - :thumbup:

Posted: **19 Feb 2019, 22:36**

swalker wrote:
Gnomatic: It is a Magic Mobility X4 rather than a V4. The X4 is a 4 wheel drive predecessor to the X8.

Yes my mistake.

Looks like you're off to an excellent start with your project.

Posted: **19 Feb 2019, 23:58**

Keep the pictures coming for us. How much were the 8 batteries?

Posted: **20 Feb 2019, 05:00**

All of the prices are in the spreadsheet in my original post in this thread.

The 8 cells, including shipping, were $1,140 plus $18 for paypal fees.

Steve

Posted: **20 Feb 2019, 09:01**

expresso wrote: or if using alot of AH which today seems to be the Normal now - 180ah - may not even need it

Initially at least, I'm planning recharging based on mileage covered, and using the pl8 (powered via XLR) to occasionally measure cell voltage if need be.

Btw, how accurate is cell voltage as an indicator of DoD?

If out on a run do you check loaded or unloaded cell voltage?

If unloaded, does cell voltage move much depending on time off-load?

Posted: **20 Feb 2019, 10:32**

Btw, how accurate is cell voltage as an indicator of DoD?

It drops initially by a lot in the first mile. And then it changes bugger all all day. Then it starts to drop off a cliff. And not all cells do so at once so you need cell log to monitor the last 10%. It wont tell you much at any other time. It will change more by temperature than by Ah used.n It may even RISE as you use the first 30% instead of fall. So basically its useless to monitor voltage to find SOC.

The only way to really deal with this is to take note of Ah returned every trip till you get a feel for range. And use the cell log to be sure you NEVER let anycell group below 3V. Then you will be safe.

Posted: **20 Feb 2019, 12:20**

Burgerman wrote:The only way to really deal with this is to take note of Ah returned every trip till you get a feel for range. And use the cell log to be sure you NEVER let anycell group below 3V. Then you will be safe.

Couldn't agree more .

Just install a 4-digits voltmetre. Everyday use will tell all you need .

Have it ON all year round . Won't drain your 180Ah at all.

It saved my chair once , when I noticed exceptional big voltage drop. I stopped and checked. It was the piggy trolley wheels broke and grinding the floor HARD . Chair went as fast as usual with helper standing on it. Would have blown chair's PM, if I didn't see that voltage drop. cheers

Posted: **21 Feb 2019, 00:29**

swalker wrote:All of the prices are in the spreadsheet in my original post in this thread.

The 8 cells, including shipping, were $1,140 plus $18 for paypal fees.

Steve

That leaves me out of ever doing this

Posted: **21 Feb 2019, 01:23**

You must realise though that its like buying 10 gallons of fuel, and comparing it to 2 gallons. So obviously its going to cost more.

Its about 3 times the cost of a set of MKs to buy, but gives 5 times the range. So a big win based on cost per mile already.

But instead of degrading from a miserable 40Ah usable, over a year to 18 minths, they are still good after 10 or more. And if you consider that when they are completely knackered after say 15 years, at about 50% of original Ah or range, that means they still give 2 or 3 times more than the MKs did when new!

Look at it like this.
73.6Ah MK gels will give about a years hard use. And will give about 50% of rated Ah at best before you stop... So 36Ah usable.
A set of 8x 176Ah cells, or a set of 16x 90Ah cells will give a full 176 or a full 180Ah. 5 times the fuel!

180 div by 36 is FIVE times the range or Fuel.
So how much would it cost to buy 10 MK gel batteries to store the same power? Then consider that if you discharged them fully, that you would pay that every year to 18 months.

So I dont think it makes any sense to buy lead at all.

Posted: **21 Feb 2019, 10:10**

swalker wrote:
expresso wrote:which cells did you purchase ?

They are listed in the spreadsheet. The QH brand 176 AH prismatic cells from

https://www.lifepo4-batteries.com/sale- ... f-car.html

I am certainly nervous about purchasing sight unseen from an unknown-to-me vendor in China. But, they are the only cells I could find that suit my purpose.

The only other potential downside is that the cells are rated for 2C maximum discharge and, though not shown on the web site, 1C continuous discharge (per an email exchange). I have done the math on what my wheelchair draws and think this will work OK. It may require some care not to work the wheelchair to long and hard in high draw situations.

Steve

I have got the same cells from the same place coming to me hopefully end of next week.
This is a picture of the connector. They had non in stock.

Posted: **21 Feb 2019, 10:19**

Its a connector of something. Not a cell. They would be 4 inches apart. :geek:

Posted: **21 Feb 2019, 10:26**

Burgerman wrote:Its a connector of something. Not a cell. They would be 4 inches apart.

I did say connector in my post drunk2

I have got to find some or build my own.

Posted: **21 Feb 2019, 11:33**

Ring terminals. Cable. Solder. Heatshrink. Anything else is a bad idea.

Posted: **21 Feb 2019, 12:09**

Burgerman wrote:Ring terminals. Cable. Solder. Heatshrink. Anything else is a bad idea.

What is the best size for the cable? 8 AWG?

Posted: **21 Feb 2019, 12:41**

10 sq mm we are not using swg, awg, or those funny american sizes. Tinned marine. They take around 3 or 4 mins each, 7 needed.

Posted: **21 Feb 2019, 17:35**

https://www.alibaba.com/product-detail/ ... 78413.html

if in fact thats the correct buss bar they were going to send - you can get them from the above link i believe - send them that picture and ask for 10 is the min.

wont be a bad idea to have - but you can use cables like i did with one pack - and will work fine also. buss bars makes it easier but then its only 8 cells - so not bad at all -

unlike headways - having 50 60 cells etc, to connect - without the buss bars - thats a pain in the ass -

Posted: **21 Feb 2019, 21:19**

expresso wrote:https://www.alibaba.com/product-detail/auto-bus-bar-insulated-flexible-busbar_60721878413.html

if in fact thats the correct buss bar they were going to send - you can get them from the above link i believe - send them that picture and ask for 10 is the min.

That's a good find.

Posted: **22 Feb 2019, 04:40**

I ordered connectors from the same place I ordered the battery cells (https://www.lifepo4-batteries.com/sale- ... f-car.html).

The specs for the connectors are : 70*20*2MM copper

Steve

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