Ultimate Lithium Add-on for dummy users .

[shirley_hkg]

Received a request to make an add-on ,which will be plug & play for dummy users .

- low voltage cutoff to protect add-on (meant for free lending ).
- disregard of DOD and can be connected any time .
- through XLR charge port with no modification on chairs .
- enough for a day in accompany with chair's own battery .
- rechargeble by dummy charger .
- compact and light weight < 15 lb.


Li-ion cells will be used for higher energy density . The 50Ah cell below will be a good pick .

[shirley_hkg]

More likely , it's gonna be a cordless Step-Up / Step-Down, adjustable CC / CV power supply of Max 600W output with 1 KWh energy density (equivalent to a pair of G24 lead bricks ) of just 15 lbs.

Found this regulator module :
- input voltage 8V -- 60V
- output voltage 8V -- 32V adjustable
- output current 1A -- 50A adjustable (25A@28.2V max 600W)
- adjustable low battery input volt protection
- adjustable STOP/FULL residue current
- adjustable re-start to charge voltage
- displays of V / A
- remote ON /OFF .

Meant to connect via XLR charge port , current will be 12A max .

Photo below is a 12V version

[c500user]

But how do you keep the cells balanced?

[Burgerman]

It will work for an average user, but 12A isnt really enough for someone like expresso as he keeps going all the time. It would keep the battery topped up to a degree though. Theres only a couple of things that would worry me.

Not least, lithium ion cells may be cheap and very compact, but unlike LiFePO4 that we are normally using they are not safe. I have had a bunch of them go off like a massive firework in hobby use (use to drive a charger) for no reason we could determined. Fortunately they were just sat on a grass field so no prob. I wouldn't want them fixed to my powerchair! But at least they could be attached in a way that allows them to be discarded fast in an emergency.

Also, they only have about a 500 cycle life in real terms, if discharged and charged heavily. The only reason companies like Tesla get extended service life from them is by utilizing only the centre 66% of the capacity. Meaning their custom software only charges to around 4.075V, and never discharges down to the lower voltages in normal use. It tells you its empty when theres still 20% remaining. So they are not going to last well.

The other thing already mentioned is that I am not sure 12A is enough if like expresso you drive continuously, or if like me you are aggressive and 1 can kill a lead battery in about half an hour clearing up the garden or driveway for eg. You will need to use more cells in series for a voltage regulator to work too?

And... You throw away another 15% due to the voltage reg inefficiency.

7S charge on lithium ion, at 4.2V is 29.4V so a little higher but not enough as it discharges to use a regulator.
8S is 33.60V charge, which the PL8 can do, but at say 3V x 8 discharged thats only 24V, and too low.

So you also have to use at least 10 cells, realistically and a BMS which compounds the fire issue, and does a crappy job of charging too. Although it means a dumb charger can be used. And it will balance the cells to answer c500users question. It will also shorten cell life even more.

The other thing is that theres a lot of waste charging LA. The charging below 12.9V is quite efficient. Above this, most of the lithium power will go to waste "topping off" at CV. Wasted as heat, gas recombination, etc. So for it to work, its probably better to use a low voltage like 26V and max 12A. so that most of the energy isn't wasted while sat at a restaurant for eg.

[shirley_hkg]

But how do you keep the cells balanced?

BMS , with cell cutoff voltage @4.2V , won't over charge . Unlike LiFePO4 , Li-ion cell volt is much equivalent, and easier to balance.
100mA balance current will do well up to 70Ah pack .
Also , cells of good quality from big brands like LG , SAMSUNG , HITACHI , TOSHIBA , CATL . . . are easy to find . They help balance .

I wouldn't want them fixed to my powerchair! But at least they could be attached in a way that allows them to be discarded fast in an emergency..

That's true , so it won't be a fix fitting .

The other thing already mentioned is that I am not sure 12A is enough if like expresso you drive continuously, or if like me you are aggressive and 1 can kill a lead battery in about half an hour clearing up the garden or driveway for eg.
.

It's meant for ad hoc situations or users . Active users have opted the fixed add-on, or even full lithium already. I used to run 40 miles per charge on a G24 Gel and a 40Ah add-on long time ago .

Although it means a dumb charger can be used. And it will balance the cells to answer c500users question.

You will need to use more cells in series for a voltage regulator to work too?
The other thing is that theres a lot of waste charging LA. The charging below 12.9V is quite efficient. Above this, most of the lithium power will go to waste "topping off" at CV. Wasted as heat, gas recombination, etc. So for it to work, its probably better to use a low voltage like 26V and max 12A. so that most of the energy isn't wasted while sat at a restaurant for eg.

This regulator will switch between StepUp / StepDown automatically , like the PL8 . That allows me to choose 7S , which will also eliminate acqusition of independent charger. It's one of the requirements.

Constant charging volt and residuel current are adjustable to avoid waste on "topping off" . Alternatively , turn it OFF remotely .

Also, they only have about a 500 cycle life in real terms, if discharged and charged heavily. The only reason companies like Tesla get extended service life from them is by utilizing only the centre 66% of the capacity. Meaning their custom software only charges to around 4.075V, and never discharges down to the lower voltages in normal use. It tells you its empty when theres still 20% remaining. So they are not going to last well..

It's hard to see cells being used to end of their lifespan now.
Espresso is throwing away his healthy pack . Me too .

7 of this 50Ah cells are £85.00 here. Why bother much ? They are expendables .

[Burgerman]

Well then, try it. Buy a fire extinguisher!
Seems unwise on a wheelchair where we cant run away.

https://www.google.com/search?q=li+ion+ ... 80&bih=618

[Scooterman]

Would 14 x 70Ah li-ion version be a viable alternative to 16 x eve LF90s for a lithium conversion on a scooter?

Can the cells be connected and balanced with a pl8, just as you would with lifepo4, but obviously with different charging parameters.

I bow down to more knowledgable folk than me.

[Scooterman]

Well then, try it. Buy a fire extinguisher!
Seems unwise on a wheelchair where we cant run away.

https://www.google.com/search?q=li+ion+ ... 80&bih=618

https://www.ebay.co.uk/p/4754116-Alpine ... 1172916571

[Burgerman]

Will it work? Yes. Is it wise? No...

They have approx 500 cycles like lead. Unless you de-rate them and only use around 66% of their capacity. Then they last as long as LiFePO4. This is what Tesla does with very complex computer controlled cell charge and balance systems. Which pretty much removes the advantages in energy density they had to begin with. So yes you can do that. The cost advantage remains, but the fire problem also remains... Unwise in a mobility vehicle.

Can the cells be connected and balanced with a pl8, just as you would with lifepo4, but obviously with different charging parameters.

Yes.

[shirley_hkg]

. This is what Tesla does with very complex computer controlled cell charge and balance systems. Which pretty much removes the advantages in energy density they had to begin with. So yes you can do that. The cost advantage remains, but the fire problem also remains... Unwise in a mobility vehicle.
.

It has the same cell chemistry as that in our cell phone , usually plus another 100,000mA power bank , inside our pocket EVERYDAY .

This add-on will be recharged and discharged in a regulated 0.25C . Never has chance of undergoing abusive loads . It's not that scary .

[Burgerman]

Thats what Boeing thought! And apple. And Samsung. And hundreds of recalled camera batteries, and thousands of laptops, and there has been a few plane crashes too. And all those so called hover boards. And myself!

And these people: https://www.google.com/search?q=lithium ... 8&dpr=1.25

So I wish you all the best luck, but I wouldn't count on it being safe on a disabled device that we cannot get out of.

[Scooterman]

Just curious...

How does li-ion compare to lifepo4 £ per Ah (initial purchase price)

Then lifetime cost £ per Ah factoring in reduced cycle life.

Also are li-ion allowed in the cargo hold of aircraft. I.E. Going on holiday with wc or scooter?

[Burgerman]

Just curious...

How does li-ion compare to lifepo4 £ per Ah (initial purchase price)

Wild variation, but generally cheaper. Depends of how you buy, and there are vastly different quality lithium ion cells and wildly exadurated claims on many cells.

Then lifetime cost £ per Ah factoring in reduced cycle life.

If you buy 100Ah of lithium ion, and only USE 66% of that with care on upper and lower voltages lifespan can be 1000, to 2000 cycles depending on what you accept as end of life. But it defeats the price advantage. Unless you are tesla with a gigafactory.

Also are li-ion allowed in the cargo hold of aircraft. I.E. Going on holiday with wc or scooter?

Airlines do not differentiate between lithium ion (or lithium polymer) which are both dangerous, and safe lifepo4.

[expresso]

This is scary - he just plugged it in to charge it and for no reason - bang -

https://www.youtube.com/watch?v=IAAxeXhmQuE

i love the idea that its only 15 pounds - thats great and small compact -

[Burgerman]

Those hover-boards only use a tiny 2 or 3Ah battery!

Imagine this event with a 30Ah (10x bigger) add-on! Theres no time to escape if disabled. The problem on those hover-boards was a BMS mosfet failing regularly. Not always when charging, but in use too. But the pack I had was with no BMS. It decided to go all fiery for reasons only it knew! It was made from lithium ion 18650 cells, 32 of them. Made a great firework! https://www.amazon.co.uk/Samsung-INR186 ... FWCH0475FF

I dont think that lithium ion cells and disability makes for a good or sensible match.

[flagman1776]

I can see the import of lightweight & energy density in hand held devises. Informed user should always prefer safer & longer lasting LiFePO4 (at this point in technological evolution) for sizeable packs. Where is this add on to be located? If it's seat back, like Espresso does, I don't see the need to go to LI cells.

[Burgerman]

I think he likes the greater energy density so it can be smaller and lighter. But by the time you lost efficiency with a voltage DC DC Inverter, and at only 12A I am not sure its worth the added dangers.

[c500user]

If you plan to use a DC DC converter anyway, why not use 3 or 4 x 176Ah LiFePo4 cells? The DC DC converter makes the voltage of the pack irrelevant.
You would need the DC DC converter during charging, but with 3 or 4 cells, it will be easier to keep balanced than with 8.

How about a 3.2V input, 28-ish V output DC DC converter during normal use.
A 28-ish V input to 3.5-ish V output DC DC converter for charging. That way there are no balancing issues.
Just a thought ...

[shirley_hkg]

BMS-wise , the smaller the Ah , the easier to balance .

One of my objective is the let user to recharge the add-on via his dump charger by himself .
Otherwise, I'd choose even higher voltage ; 36V / 48V . Then cheaper simpler smaller StepDown module will be OK .

[Burgerman]

28.2v div by 7 is 4.03V. About half capacity.
28.8v div by 7 is 4.1V about 80% capacity.

In both cases a stock bms wont balance at that voltage?

[snaker]

Shirley, can you post some reliable taobao links that are selling lithium ion cells and charging boxes? I need some cells and boxes for projects (not my chair ).

[shirley_hkg]

and charging boxes?

Don't get it .

[snaker]

I meant something like this.

[Burgerman]

Those are for 2 to 3Ah cells.

[snaker]

I found some 18650 cells of 8Ah. But not sure about their quality/safety, I dont like ... fire
https://item.taobao.com/item.htm?id=545670359170

[Burgerman]

Those are about 1.5Ah if lucky in reality, whats worse is that they are also very high impedance and rather cheap. So when I put them in my laser pen for eg its dull.

There are no cells in 18650 size that are even close to that claimed size!

Here is a list of decent ones. Remember that those claiming higher capacity deliver less current/greater voltage drop. And you are powering a chair so need high C rate.

Best 18650 Batteries of 2018 - Top 10 List

Sony VTC5A 2600mAh 25A.
Samsung 20S 2000mAh 30A.
Vapcell (VTC5D) 2800mAh 25A.
Panasonic NCR18650B 3400mAh 4.9A.
LG HG2 3000mAh 20A.
Samsung 25R 2500mAh 20A.
Samsung 30Q 3000mAh 15A.
Sony VTC4 2100mAh 30A.

This is a good page to read up on those cells.
https://www.18650batterystore.com/Best- ... -s/142.htm

[shirley_hkg]

remember : high C rate = low capacity .

So, choose either side to suit our application .

I bought a few 21700 @4000mAh .. US $3.00

[Burgerman]

Ultrafire 9.8Ah cells. Actual capacity .4xx Ah... Less than 1Ah.


youtu.be/yoCaWByTwUQ

[Burgerman]

More -- less than a single Ah.


youtu.be/W7-STZf8vog

[Burgerman]

And more... Be very careful what you buy.


youtu.be/eobzA1Jqgn4