PINNED - Lithium battery conversion/info

[shirley_hkg]

It's hard to find M4 lugs that accepts 10mm2 wire.
Steve

This is the biggest barrel for a 4mm lug.

[shirley_hkg]

APPEARS TO TRY AND BALANCE REGARDLLESS OF VOLTAGE. YOU DONT WANT THAT!

No. It doesn't.

Balance Start Voltage,
Cell voltages diffidence ,
are user defined. Balance will start only when BOTH are true.

[shirley_hkg]

This one seemed promising. It seems configurable. Most pricey….of course. Thoughts?

https://www.amazon.com/gp/product/B0CMP ... A0R09&th=1

Thanks

Not that pricey on Taobao , <$70 US.

[Burgerman]

Thats great. Set accordingly!

[shirley_hkg]

BM, would like you to advise on the charge and discharge voltages for lithium-ion pouch cells, compromising longevity and practical usage.

BTW , below is the basic settings of a JK bms.

[Burgerman]

BMS work OK on thithium ion cells. Unlike LiFePO4. As long as they dont fail and cause a firework explosion...

Voltages.
If you want maximum capacity then the usual 4.200V full. (up to 4.3v on some HV high capacity ones - read specs)
And 3.4 to 3.5V low end. GENERALLY.
On SOME high capacity types this can be as low as 2.7 volts, see spec sheet. Be sure you get this part right or you waste a lot of capacity and run the risk of killing your cells if its wrong in the opposite direction. They all vary by type of lithium ion. And cell manufacturer. Theres now many slightly different chemistries used. So no hard and fast accurate rule of thumb possible.

They live much longer (many times longer) if you only use say 70% of rated capacity. I generally charge to 4.100V per cell on hobby stuff like transmitters. And run them down to 3.7V if I have to. On flight stuff, where apacity matters I charge to 4.200v and discharge to around 3.4V if needed in an emergency. To get back on the ground gently.

Its all a compromise. If you use less capacity they last a lot longer. If you charge and discharge at a low rate they loe a lot longer. If you keep cool they live a lot longer. If you store below 85% charged by capacity as I do on my laptops then instead of getting a year and a half they last a decade or more.

Tesla charge to 85% in normal use. And read "empty" at 85% discharged. And that way their lithium ion last the life of the car with around 20% loss of capacity at a decade of normal use.

So its completely up to what you are trying to achieve.
If I am going to use a ithium battery laptop at an airfeild all day, I will charge it to 100% at 4.2v. Most of the year its sat plugged in to the AC and at between 80 and 85%.

So you can have the best of both worlds if you understand the compromises and adjust according to circumstances.

[Burgerman]

Electric bikes. On news just now. This last year (2023) there were 149 house fires in england only, attended by fire services. To put out fires caused by ebikes stored or charged indoors. 4 deaths, 22 serious injuries. 60 injuries needing hospital treatment. Of course theres a lot more that were not indoors, or didnt need the 999 services so not included.

This is why I would not use lithium ion in a wheelchair. We have bigger packs, and cant get off and run away. And when a small pack decide to go its violent and sudden. Just like a massive firework display. Ending is a fire.

With LiFePO4 cells that we all use in wheelchairs that cant happen as the cells themselves dont burn - at least not without external heat applied (such as in a fire). But if you use a BMS then this CAN cause a fire on its own. Every LiFePO4 fire that can be, is inevitably traced back to a BMS failure. And its not the cells that burn but the wiring, and the balance wires melt and cause the main wires to become shorted. Then everything else that can burn follows suit. That then causes the cells to be "in a fire" which boils the oily electrolyte out. That stuff is like cooking oil. It can burn if hot enough. But needs an ignition source.

So as long as we charge with hobby type chargers then theres no BMS to fail and short out anything either. So we do things in the safest way possible. Actually safer than lead batteries. Since when overcharged or faulty those give off hydrogen and oxygen which is a bad thing! The hindenburg was full of hydrogen... Theres many photos of exploded lead bateries on the internet. When they do they throw acidic gel or AGM matting out as well as start fires... But we accept this as we are acustomed to its risk level.

[shirley_hkg]

Always bear in mind.

It is another power bank for wheelchair, and it is not a fixture.

The ultimate add~on for dummy turns out to be more versatile than we thought. It does not just extending range when we are out for a longer ride. Many, who are waiting for new batteries, borrow these power bank to resume their daily lives. Application for new batteries usually takes months.

Will use 21700 cells this time.


Pouch cells are my project.



https://www.wheelchairdriver.com/board/ ... +for+dummy

[Burgerman]

I have the samsung 21700 5000mAh ones here for various things. 50G. Very good cells. Especially regarging self discharge. Absolutely no change on any of them over a year and a bit.

https://www.thunderheartreviews.com/202 ... rison.html

Note that THESE cells are capable of being discharged to 2.5V although I limit this to 2.7V. Which seems extreme but they dont seem to mind! And to get near to 5000mAh you must.

So 7 of these will be 29.4v charge (around 29v afterwards) down to just 17.5V cut off and so wheelchair own display should be fine. And the chair will stop probably long before a cell goes too low anyway.

[Burgerman]

Or you can use say 8S and 4p 21700 cells and build a physically small firework 20Ah 35V battery in a small bag carried on the chair push handles. And use this, to give say constant 27V and 3 to 5A limited CC/CV charge via XLR all day long. So adding 50% or 60% to the range. https://www.ebay.co.uk/itm/226087828265

Been planning to build one to lend out myself for years. Never get around to it!
It would extend the lifespan of lead by a long time, maybe double or better if set as suggested above.
4 or 5 Amps isnt enough for continuous rolling. But it would still more or less keep up as it catches up when you stop for a few mins or eat etc.
Remember that 4A charge is 20Ah restored every 5 hours. About the rate most people use up the battery. So low DoD average.