Just a hello

[rcyoung]

Introducing myself ... My name is Robert Young living in the USA. I do not use a chair myself but my wife has been in an electric wheelchair for 36 years. Currently she likes the Quickie V121 since it will break down for travel more readily. Speed is not a concern as she is also visually impaired, but battery life is always an issue as the 14in version only uses U1 batteries. Nice for indoor use but a bit iffy for walking the dogs for any distance. I noticed the description of Li batteries used on a wheelchair and that looks very very interesting!

[Burgerman]

Hi, welcome. Lithiums are interesting. But not simple.

See here http://www.wheelchairdriver.com/BM-MK3- ... rchair.htm

[rcyoung]

How true. My own background is not sufficient to design or build a Li battery pack, but I did forward a link discussing it to an electronics engineer friend of mine. Back when I worked at a US Dept of Energy facility, he borrowed the idea of my wife's wheelchair to make a remote controlled radiation monitoring robot. He is retired now, but still "tinkers" in such things.

[Martin O Refurbisher]

Welcome Robert,

I think we all see Lithium as the next big advance to improve powerchairs. However, there is no "plug-and-play" solution, at least not yet.

Many are working on this however, and with BM pulling hard, we will get there sometime soon I hope.

Best,

Martin

[Burgerman]

Well it already IS plug and play if you understand whats going on. And what you need. Just not simple enough for most people. Everybody wants a lead brick straight swap...

[rcyoung]

That's understandable. Most people do not have the necessary background to do much beyond plug-n-play. Not their fault, just not their "forte". It would be like me trying to install plumbing in a new house....NOT advisable!!

Similarly, I can not do all that much in "do it yourself " electronics, as my expertise is as a PhD in nuclear chemistry. On the other hand,I realize my limitations, and I have no qualms about finding those with the expertise I require to do all sorts of little projects.

I live by the mantra "98% of everything I might want to do or have done has ALREADY been done by someone, somewhere".

Look at your case....I was toying with the idea of Li batteries in a wheelchair, and you have already shown it is possible.

[Burgerman]

Soon there will be "lead brick" lead acid copies in lithium batterie. They WILL just swap. But to do so kind of defeats the object of going to lithium in the first place.

The idea is that lithium MAXIMIZES the capacity you can get in the same space. So improves both range or range AND performance. But sticking lithium cells and a built in "universal" BMS system in every brick case just reduces the capacity by around a third. Or it reduces the C rate. Because theres only certain ways to package it all.

The idea is that lithiums will LAST 10+ years (probably 15+) and this requires care. The sort of care a bundled BMS cell balancer doesent give...

The idea is that it saves weight. But adding all the extra casing, built in BMS systems, etc all decreases the capacity/weight advantage.

The idea is to gain efficiency. So get extra FREE range (by using a higher voltage) for eg, since the higher C rate than lead allows thie use of smaller capacity/higher voltage batteries. This advantage will be lost.

But this is the way things will go for the manufacturers and dummies...

[ex-Gooserider]

I would say that the key question for the OP, is if there is a size of Headway or equivalent cells that works to make a U-1 size pack, the way that BM's pack is the same size as a pair of Group 24's?

Once that is figured out, it seems like a quite straightforward thing to do the same sort of thing that BM is doing, as I don't see that much else is different... Same Anderson setup would work (though it might be possible to go to the smaller PP-45 size connectors?), same Hyperion charger / BMS, etc... Different numbers plugged into the Hyperion, but that's no big deal...

ex-Gooserider

[Burgerman]

I would say the only bit that would be complex to some was making the 9 (10 actually) conductor loom with plug/socket to the balance ports/battery cells correctly.

[Burgerman]

Lets see...

The smaller packaging is way less efficient, with wasted volume on the ends of the headways, etc. But:
Approx U-1
Length : 7.8 ins (200mm)
Width : 5.2" (135mm)
Height : 6.3" (160mm)

???

Or whatever battery compartment allows.

Then a 10Ah headway is 135mm including screw tab, 40mm x 40mm with building block.
So width - same or a fraction more with connections etc. May fit, would need to see/measure battery box.
4 high 160mm
5 long is 200mm

So 2x 20 cells is possible I think. So 40 cells. In 5 cell groups, to give 5p 8s. Or a 50Ah battery in place of a 35Ah lead U-1 system.

But at high rate the usable lead Ah is almost halved. Lithium is unchanged. No peukert. So range would be improved by approx 2.5 times and it would be much lower resistance, and last around 10 to 15 years.

The ONLY dificulty is the length of the cells, with srews and connectors will be about 3 to 5mm more than the U1 batteries. This may not matter, I cant see the battery box. Make 2 cardboard boxes, 140mm x 200 x 160 and see if they will fit. If so order today!
www.evassemble.com