PINNED - Lithium battery conversion/info

[ICEUK]

I wanted speed bm, i have a 6mph amd i just fancied having a chair with higher top speed, i do notice the decrease in torque but its just about acceptable.

Its my outdoor chair and my bungalow is mainly vinyl flooring, i use my 6mph jive inside

If i kill the motors i would put 6mph ones back on, with hindsight i would of selected 6mph motors but then i would of always wanted to try a 8mph on lithium.

[Burgerman]

I have tried 8.5 and 8 motors. Twice. Once you program the chair properly so it jumps to attention, turns and stops turning when I tell it, and set all the accelerations and other things high you can really feel the lack of response. It feels like the joystick is connected by a rubber band. Sort of like the batts are flat. I cant hit a damned gap or doorway unless I allow for the rubber band effect. But since it varies with load, battery state, and other stuff you cant aways guess right... It just feels sort of only vaguely in control. Of course if you drive around with mushomatic stock programming like y grandma and you cant tell because its all hidden behind the other problems. Drive it like you stole it (I do) and its patently obvious!

I never go for 8mph now, even if its the same rice. And it frequently is. Once you make them add the essential 120A controller in place of whatever cheap option they think they will palm you off with.

[ICEUK]

A few questions,

Do lithium like to stay fully charged?

How long can they be left fully charged? Couple days, week etc

If not What is storage charge voltage?

If cell falls below 2.8volts it will give no more useable amps for our chairs?

Thx all.

[terry2]

@BM

I have 8 176 amp cells(most likely 200 amp when new) I went looking for another 8.
But they are all 200 amp. Will it hurt to to have 8@176 amp and 8@200amp?

Thanks.

[Burgerman]

That depends how you plan on connecting up 16 cells. If you connect one of each together in parallel to make 8x 376Ah cells, no problem.

How will you fit 8x 176 and 8x 200Ah cells into anything anyway?

[terry2]

That depends how you plan on connecting up 16 cells. If you connect one of each together in parallel to make 8x 376Ah cells, no problem.

How will you fit 8x 176 and 8x 200Ah cells into anything anyway?

Thanks.

I should have enough room.
Will know more when I have fitted the 8 cells I have.

[steves1977uk]

A few questions,

Do lithium like to stay fully charged?

How long can they be left fully charged? Couple days, week etc

If not What is storage charge voltage?

If cell falls below 2.8volts it will give no more useable amps for our chairs?

Thx all.

LiFePO4 cells like to be between 40-70% full while being stored. Don't forget the PM draws around 5mAh+ (more if you have it fully kitted out!) if the chair is switched off but left connected to the battery pack. Charge volts don't matter if you remember to remove a third of the capacity afterwards, so 70A for a 210Ah pack. Depending on the cells natural discharge rate, you could probably leave it a few months between charges if the PM is disconnected.

Don't go below 3.0v per cell or 24v for 8 while under load as this is the best way to avoid the cells getting too low.

Steve

[funkykeyboard]

You can do 4 cells to each (7 cell) balance connector.
Or 7 to the first one (a) and 1 to the other one (b).
All can be routed through one D connector on the chair. Keep all balance wires short, or less short and a bit fatter that the short ones...

Like this-


image link wouldn't post

LC

Do you have this image any longer, it's no longer available from that link.


Any advice appreciated, Tremulous Tetra. :-)

[funkykeyboard]

You can do 4 cells to each (7 cell) balance connector.
Or 7 to the first one (a) and 1 to the other one (b).
All can be routed through one D connector on the chair. Keep all balance wires short, or less short and a bit fatter that the short ones...

how do you do 7 cells/7 balance cables from one socket, when 2 of the 8 pins are positive and negative?

[Burgerman]

Use a little logic!
Yes I know... The socialist brain and all that.

A 7S pack has EIGHT wires.

cut a candle into 7 parts. Count how many ends plus cuts you now have.

Or play with this for a few mins. https://scriptasylum.com/rc_speed/lipo.html

Seriously I dont know how else to explain. How about this. A 2 cell pack, has THREE wires...

[steves1977uk]

It's quite simple to me BM! FK needs to think and try to work the wiring out himself. I gave him a hint in his other thread, but I want to see if he can think logically!

Steve

[Burgerman]

He cant. He thinks socialism is a good plan. Worse communism. We already established this on a different thread!

[expresso]

why not just try to help him with his issues - who cares what someone is or isnt - has nothing to do with the issue hes not understanding -

we dont all have the ability as you do - give the guy a break - i was same way not understanding at first - and still dont get it all - its fine -

thats why we ask on here ??

[Burgerman]

I did previously my my best to explain it several times. I am now at a loss as to know how. He doesent ever seem to understand what I said. So was waiting to see if anyone else would do it.

And elsewhere several have.

[steves1977uk]

I think FK's problem is he doesn't understand electrics/electronics, hence his mis-understandings of wiring and stuff. Maybe that's why he let others do that part and they get things wrong.

Steve

[ICEUK]

Need a bit of advice, i built my 210ah lithium pack and all has been well, charged a dozen or more times and chair has been in use, it has balanced fine charged at 30amp but i have just pugged it into pl8 and cell 8 is at 2volts and the rest our at 3.2volts. I dont let the cells get below 3volts. I am assuming a loose connection? Or is there another possibility?

Its like cell 8 gave more ahvthan the rest or it self discharges alot faster than the rest

[stevelawiw]

Any signs of arcing on the connections, loose bolts? What does tab 2, the IR tell you, is it higher than the other cells? Can you check the voltage with a multimeter?

Hopefully it's a loose connection

[ICEUK]

We have pulled the pack out and its a loose connection. We are just going through them all.

[expresso]

how did you connect them - did you use lock washers or locktite ? curious how it came loose - i had one loose set screw also which i since changed and been good since

[ICEUK]

We used nylon nuts but we put no locitie on nuts, i have replaced all the nuts now with new nylon nuts and loctite too.

[expresso]

did you use set screws on the cells ? then the nuts to hold down the wires ?

in my case - i used locktite on the set screws only - then the nylon nuts to bolt down the wires - one of my cells - the set screw was the issue - i removed it and applied red locktite this time on the set screw that goes in the Cell only -

[ex-Gooserider]

We used nylon nuts but we put no locitie on nuts, i have replaced all the nuts now with new nylon nuts and loctite too.

All Nylon nuts are not suitable for use where they are under load... Over time the nylon distorts and flows just enough to come loose (but it won't come off, just be a partial turn from "tight", which is enough to be a problem in this application) You should us 'NyLOCK' nuts - metal nuts with a nylon or other plastic insert on one side... With a Nylock nut the metal threads hold the load and the insert just keeps the nut from loosening. Loc-tite is not really needed but won't do any harm.

ex-Gooserider

[expresso]

I am saying it wrong in my case I used nylon lock but not a nlyon nut. It's a steel nut with the nylon Inside half way. I think it's being said wrong as I have. But I think he used the same kind of steel nylon. I believe. Could be wrong. The correct wording is. Nylon lock nut ?

[Burgerman]

A NYLON nut is made of nylon. As used on say a number plate fixing.

A NYLOC nut is a steel nut with a nylon insert.

You should be using red loctite on the stud in the battery. So it never moves.
And a NYLOC nut with a flat washer and no loctite on top. And not any other type of nut or washer. No flanged or shoulder nuts.

[expresso]

Nyloc is what I used

[ICEUK]

It was nyloc nuts we used however i think the problem was we built pack on bench and charged it up and made sure all was well, then disasembled pack and placed in wheelchair but we reused nuts which I think caused the issue of them coming loose.

[expresso]

I hope nyloc nuts don't come loose on there own ? Once in a chair ? That would be a big prrobelm if they did. I have my 200ah pack that mAy be goin in a friend's chair soon. I would hate to have to remove it after it's installed because of the nyloc nut

[shirley_hkg]

That sounds ridiculous the nuts are good for once.

[expresso]

Sounds is one thing. Alot of things sound ridculiouss till they happen to you

[LROBBINS]

Laptop manufacturer's say to use Nyloc just once, but they really do hold for multiple re-uses. Nevertheless, adding a drop of medium loktite when using them may not be a bad idea. Aircraft all-metal lock nuts have a deformable thread and they are indeed use once then throw away. They're also not allowed only on non-structural assemblies or where there are load reversals- in those situations, castellated nuts and cotter keys or safety wire are required.