Lithium Build for Magic Mobility X4

[swalker]

Expresso,

I have had the Revoletrix PSU since early December, 2018, so for about 4 months now. I ordered it during their Thanksgiving special offer period.

I have had no issues with it so far, but it has seen limited use. I have used it to charge each of the 8 cells (from around 2.9 V, so a lengthy charge), discharge each cell for 20 Ah (2 hours each), and fully recharge each cell. I then used it too fully charge the 8S battery pack, discharge it for 18 hours (about 62 Ah), and then to charge it fully (3 hours 26 minutes).

So far it works great!

One thing to consider for my use is I don't have much power in my office/work room. I have a single 15 Amp, 120 volt circuit that powers the outlets and lights in that room and the outlets in the living room. The office has lots of things using power, such as multiple computers, copier, printers, scanners, lights, and another charger hooked to a wheelchair with lead acid batteries. I also occasionally use some high draw items such as the soldering iron, and heat gun. So, I determined that my office outlets cannot reliably deliver all the power the PL8 is capable of consuming. The Revolectrix power supply is rated at 1200 watts, which is less than the PL8 can accept.

I don't ever put 1200 watts through the power supply. I am charging the at 25 Amps, so delivering a maximum of less than 750 watts to the PL8.

Perhaps that restrained use will prolong its life.

Steve

[Burgerman]

Dont be worried. I do 40A all the time. Never had one fail yet.

[expresso]

whow very thin - which is good for me - i wont have much room - i may try that along with the tape i have here already first - then that one over it and done - no silicone inbetween- even better this way i think - i will be pressed for space so looking to keep it as tight as i can - safely - battery tray is plastic so not a big deal on the bottom - of course i would cover the bottom anyway - i cover the whole battery with the heat tape - then can use this over it .

https://smile.amazon.com/Temperature-AI ... way&sr=8-3


https://www.ebay.com/itm/150mm-x-33m-10 ... 1a000bfa91

i used these both - and then added a .05mm silicone inbetween - i will use these tapes again and see the space i have left when done - either way will always add something in between -

[swalker]

Here are some charts of the initial charge of the 8S pack (note that each cell had been fully charged before the pack was assembled), a discharge of 62 Ah, followed by a full charge.

Steve

[expresso]

@ Swalker - thanks - good to know - i have slowed down my charge rate since i charge two packs - with two charges etc, - no need to charge at 40A in my case - unless i need to - i used at first charge at 35A first summer - since adding ADD ON - i cut the charge rate to 20A - or 25A on large pack and 15A to 20A on smaller pack - gets it all done before i go to sleep - this way

if i had one large 200ah pack - then maybe charge a bit more 30A at least if used up alot - i keep that one i mind when looking for another PSU -

[swalker]

It has been an exciting day. My friend Greg came over this evening to install the LiFePO4 battery pack into my Magic Mobility X4 wheelchair.

We just wrapped up and I am pleased to report the X4 passed the first test drive, which was limited to my garage because of the winter weather we still have here. My wife's car is currently banished to the elements.

We probably ran into some pretty typical issues. There seemed to be too many wires for the space available. Rerouting the circuit breaker from between the two 12 volt batteries so that it is on the main positive lead was a bit exciting. We still have not figured out where to put the cell monitor or how to route the wire to it. But, it lives.

Accessing the battery boxes on the X4 requires removing the seat, removing a support beam, and then removing the shroud. Putting it back together is quite fiddly and took longer than expected.

The actual install of the batteries went very well. Needless to say, I could not have done any of this without Greg. He has been a great help in many things and was there pretty much every step of the way since I first started thinking about a lithium battery pack.

Here are some pictures of the install.

[swalker]

More Pictures of the install.

[swalker]

Yet more pictures of the install.

[Burgerman]

Very good. A few tiny cable ties might tidy up all the wires. Did you test?

[Scooterman]

This isn't a criticism, what you've done looks really good

But I was wondering whether you could have got away with thinner series links between the cells? What I've learnt from feeling cables during charging is that (for the same csa) it's the longer cables that get warm and shorter cables stay stone cold.

[shirley_hkg]

You should insulate against the centre beam too.

[Scooterman]

You should insulate against the centre beam too.

Good point

But is there room?

[expresso]

nice job Swalker - cant even tell when chair is back - i like those yellow wiring you used for the connections - did you add extra balance wires for a external cell monitor ?

with a large pack - you may not even need it but whos to say - never know - looks like you do outdoor off road riding and that may use alot of juice - it may be handy for you even with a large pack - unlike me - mostly road riding - i never used one - just got used to my riding style and distance - PL8 checking at home - after a while you get used to what it can do and cant - but dosnt hurt to have a cell monitor -

looking forward to results when in use

[swalker]

Here are some responses to questions and comments:

Scooterman: I could have gotten away with smaller wires (for the yellow wires connecting the cells in series). In the worst case (a failure condition), those could have to carry the fully load. I calculated that 10mm2 would be appropriate. Unfortunately, in the US it is impractical to buy 10mm2 cable. The closest would be 7 AWG, which is also impractical to buy. So, I went one size larger, which is 6 AWG, or about 13.3mm2. Fortunately, those larger wires did not cause any wiring or space issues. Other wires sure did!

Shirley_hkg: You are right. I should have added insulation around that beam. There is not much space, but I could have at least wrapped that beam in an insulating layer, perhaps something 0.25mm thick. The next time I have the chair apart I will do that. For now, each cell has the original shrink wrap that came on cell, 0.25mm thick electrical insulation paper (fish paper), and 0.25mm thick PVC shrink wrap. I think that will be enough, but still should have wrapped the beam. The foam you see between cells is non-conductive EVA foam, whose primary purpose is to fill the gaps between the bulged cells and make sure there is a secure fit in the battery box (which is quite a bit longer than needed for a group 24 battery).

Scooterman: You are very right. There is not much space at all between the cells and that beam.

Expresso: Yes, I have one set of balance wires for charging and another set of nine 22 AWG wires for a cell monitor. This wheelchair is primarily for outdoor riding, though it has been indoors a time or two. I use it extensively in the winter because I live in a place where it snows a lot. I also use it for back country adventures in the summer both around where I live as well as in national parks such as Yellowstone and the Grand Canyon. It has been spectacularly useful in that role, even though its range has been limited to a paltry 4 to 5 miles with lead acid batteries. I am hopeful the LiFePO4 pack will extend that range to at least 12 miles. It uses a LOT of energy.

Steve

[expresso]

whow - i see - you need alot of lithium to keep you out there the whole day - i sure hope it gets you more than 12 miles - that would be double at least than you get with lead - so its a big improvement - in that case - it may be wise to have a cell monitor -

i wonder if you can carry your PL8 and PSU with you - would you be able to charge anywhere ? maybe take a short break charge at 40A - and gain more range - i know it may be hard to find a outlet where you ride - you can make some nice videos - on your rides - would be nice to see -

[swalker]

I slept really late today. When I got up, the first thing I did was head to the chair to see if I could finish up cable routing on the exterior of the chair on my own.

I needed to reposition the chair slightly so I had better light. I turned it on and was greeted by a flashing LED and no response to the joystick. After a moment of panic, I remembered that the last thing we did last night was to take the seat down from its elevated position. I elevated the seat slightly and that restored normal operation.

I found the wire that was temperamental with seat height and addressed that. I was able to clean up the wire routing and install some zip ties without assistance.

I then went out on a test ride. I was planning to go just a few hundred yards, because I did not want to be too far from the house. Also, we were supposed to have snow all day today (and tomorrow). It was not snowing when I departed, but it looked like it would start soon. Because I was going on a short test ride, I did not dress very warmly.

Once I had ridden a few hundred yards I rationalized that it did not matter if I needed to call my wife to come rescue me from 100 yards away or miles away:). So, I just kept going. My short test ride turned into a 5.2 mile ride. It was magnificent. The first flakes of snow started falling when I was 1/4 mile from home. I was very chilled, because I was not dressed nearly warmly enough to be out for over an hour.

The results were what I was anticipating, but experiencing the result was even better. With lead acid batteries, the X4 would do 3.6 mph on the flats and drop to 3.2 mph going up any kind of hill. With LiFePO4, the chair felt snappier (as expected), and was a bit faster (as expected). On the flats, I consistently ran at 4.0 mph. Going up even the steepest hills, we puttered along at 3.6 mph. Those are all certainly slow speeds, but as fast as I am able to tolerate moving over rough terrain. It suits my needs wonderfully.

With lead acid batteries, I usually limit my trips to 4 miles in the X4. I can make it as far as 5.5 miles, but is quite dicey getting home. If there are hills involved (and I live in the mountains, so there always are), the practical range is 3 to 4 miles. With the LiFePO4 battery, I went 5.2 miles and the cell monitor showed all cells still with at least 3.3 volts.

I am charging the chair now and will post a graph of that charge when it is finished.

Steve

[swalker]

you can make some nice videos - on your rides - would be nice to see -

Here is a short video of part of a ride down a steep slope in Yellowstone National Park. We are on the trail from Artemesia geyser to Morning Glory pool. My wife is walking in front and my sister took the video.

https://swalkeratvail.zenfolio.com/img/ ... 42-200.mp4

Steve

[expresso]

nice - i didnt realize where you live and the riding is very outdoors - that would eat up alot of juice - but thats great at least now you can double your range easily and enjoy more time outdoors -

must be nice to enjoy that - being in the city - i dont get to enjoy that at all - the little bit that i manage is far away from me - reason i do 40 mile rides - to get out there a bit - but still not the real off road like you do - its very nice - peaceful out there - i would enjoy it - not sure if i could live in such cold and snow -

looks like you will enjoy the summer this year unlike others - now if you can have a spot to recharge with the pl8 at 40a - a rest area etc, then you can sit for a hour - get 40A back in and ride on even longer - you can turn your trips into 20 miles round trip about 4 x more than lead - if you can manage a recharge along the way -

[Gnomatic]

nice - i didnt realize where you live and the riding is very outdoors - that would eat up alot of juice -

Not to mention his chair is turning 4 motors instead of two!

[Gnomatic]

Once I had ridden a few hundred yards I rationalized that it did not matter if I needed to call my wife to come rescue me from 100 yards away or miles away:). So, I just kept going. My short test ride turned into a 5.2 mile ride. It was magnificent. The first flakes of snow started falling when I was 1/4 mile from home. I was very chilled, because I was not dressed nearly warmly enough to be out for over an hour.

The results were what I was anticipating, but experiencing the result was even better. With lead acid batteries, the X4 would do 3.6 mph on the flats and drop to 3.2 mph going up any kind of hill. With LiFePO4, the chair felt snappier (as expected), and was a bit faster (as expected). On the flats, I consistently ran at 4.0 mph. Going up even the steepest hills, we puttered along at 3.6 mph. Those are all certainly slow speeds, but as fast as I am able to tolerate moving over rough terrain. It suits my needs wonderfully.

With lead acid batteries, I usually limit my trips to 4 miles in the X4. I can make it as far as 5.5 miles, but is quite dicey getting home. If there are hills involved (and I live in the mountains, so there always are), the practical range is 3 to 4 miles. With the LiFePO4 battery, I went 5.2 miles and the cell monitor showed all cells still with at least 3.3 volts.

I am charging the chair now and will post a graph of that charge when it is finished.

Steve

Awesome! I'm interested to see how many Ah the PL8 returned to your battery after charging.

[Burgerman]

And a note of Ah returned!

[swalker]

The charge finished and here's the graph.

The charge had a duration of 1:25:57 with a Capacity IN of 28908 mAh.

I don't want to get too excited, but... I figure that I can safely use at least 140 Ah from the 176 Ah pack. If I was able to go 5.2 miles with 28.908, there is some potential I could go 25 miles using 140 Ah. That would far exceed my expectations. I was hoping for at least 12 to 15 miles.

Looks like I have more endurance testing ahead of me:). Snow is predicted here for most of the next 10 days, so the endurance tests may have to wait a bit.

Steve

[expresso]

nice - i bet you can do it also - and maybe use more than 140ah - you should discharge test it - if you want to know how low it go safely

would take a long time if full - using the pl8 alone - or did you do that already ? discharge it down to 2.9v or 3.0v to be safe - and see what the Volt is when it stops -

you can have an idea more or less - not accurate- cell monitor better for the alarm feature at least - going from 5 miles to 25 miles is a HUGE jump - down the line if you have to redo it- maybe can even find 200ah cells that fit or more -

[swalker]

Expresso,

I have a cell monitor for the pack and thus can stay informed of the cell by cell voltage during my excursion. I have tested that cell monitor against the readings output by the PL8 and it appears to be accurate to within 20 mA or so. Of course, the cell monitor results should only really become interesting as the cells start to get low.

On one cell, I did a test of fully charging it to 3.6 volts and then discharging it to 2.9 volts. That took out about 167 aH.

For all the cells (including the one I did the more thorough discharge/charge on) I charged them all from their initial condition of about 3 volts to 3.6 volts. That took a similar amount of time for each cell and resulted in a similar Capacity In for each cell. I subsequently discharged each cell by 20 Ah, which again, took a similar amount of time for each cell.

Based on this, I have some indication that all of the cells behave roughly similarly and that I should be able to use about 165 Ah when I discharge the entire pack from 3.6 V to 2.9V.

So, I am hoping that my target number of 140 Ah available for practical use in a full pack is conservative. I am excited about doing some real world endurance tests.

Steve

[Burgerman]

Your figures are correct if a little conservative.

But remember that terrain type, hills, and turning, esp on those low pressure tyres that range will depend greatly on actual trip and might vary greatly. You might get 50 miles in along a road with a little extra air in tyres. But less up steep hills etc.

Also that it can be charged from your car via PL8.

[Scooterman]

Also that it can be charged from your car via PL8.

How many supply volts is PL8 happiest at?

Also I noticed that amps on shirley's psu is a bit higher than charge current. But reading what you just said I twigged that CV is higher than PSU V so to deliver equivalent power (reality slightly more cos of losses (heat, etc)) then PSU amps have to rise to balance power (amps/volts) seesaw.

Learning all the time

[steves1977uk]

I leave my PSU set to 30v as this is less stressful for the PL8 as less Amps are drawn. But 24v-30v is recommended SM

Steve

[Scooterman]

I leave my PSU set to 30v as this is less stressful for the PL8 as less Amps are drawn. But 24v-30v is recommended SM

Steve

That makes sense Steve. I will up my PSU volts too

[Burgerman]

Volts x Amps = watts Output.
Because Volts x Amps + 10% Approx losses = Watts input.

Remember though that the charger is both a buck and boost inverter. If you begin charging as a buck (voltage lowering) converter, and as you start to charge the battery voltage rises, it then has to stop being a buck, and switch over to boost. As it does, the battery voltage drops... So now it has to swap back. Rinse and repeat and maybe error...

[Scooterman]

Volts x Amps = watts Output.
Because Volts x Amps + 10% Approx losses = Watts input.

Remember though that the charger is both a buck and boost inverter. If you begin charging as a buck (voltage lowering) converter, and as you start to charge the battery voltage rises, it then has to stop being a buck, and switch over to boost. As it does, the battery voltage drops... So now it has to swap back. Rinse and repeat and maybe error...

ooh i never knew any of that

its currently set at 24v. Should i leave as is or up it a bit?