60ah ADD ON build with Pictures

[Burgerman]

And me.

[expresso]

Yes. 45 is ok, provided you could find good stuff .

That's my problem. I need recommendations on a reliable supplier. Anybody ???

I emailed my last seller i purchased from. if he has something in the size your looking for etc, - i will then forward it to you to look it over. his prices are fair and his shipping is alot better then most i found before.

[greybeard]

I emailed my last seller i purchased from. if he has something in the size your looking for etc, - i will then forward it to you to look it over. his prices are fair and his shipping is alot better then most i found before.

Thanks Expresso.

[foghornleghorn]

grp 24 will not fit in either of my chairs

I thought the Puma 40 came with a one size battery box that fitted everything 78Ah downwards by adding internal padding pieces to fit the smaller batteries snugly so they don't move around. Are you sure group 24 won't fit?

[greybeard]

They do, but the previous owner had dropped the adjustable base height to its lowest setting and I am not fit enough to lift the chair off the base to raise it again. Not only that, after buying new grip 34s that will fit, I can't afford a new set of grip 24s. I self financed everything I needed since becoming disabled. Luckily I had the funds to do it at the time, but not any more.

[Burgerman]

I am living on the same benefits as you.
Tell me, why not WCS for a chair? Or the WCB that I am now on, then they will give you a cheque. That way you can buy a chair, or lithium for the one you have, or a used backup chair, or whatever?

[LROBBINS]

John, Do remember that the system Shirley has proposed to me includes a DC-DC converter, so you're not using the "raw" voltage of either the lead or the Li. Seems rather like a "low power" version of powering the PL8 from a battery.

[greybeard]

I am living on the same benefits as you.
Tell me, why not WCS for a chair? Or the WCB that I am now on, then they will give you a cheque. That way you can buy a chair, or lithium for the one you have, or a used backup chair, or whatever?

WCB - wheelchair budget?

[Burgerman]

Yes. But it will be disconnected from the lead battery. So it is running from the lithium battery? So if that lithium has 7 less than full cells, and one that is full, (3.600V? It suddenly jumps up from 3.3V right at the end. It becomes full as suddenly as flipping a switch) then total battery voltage does not matter It will already be less than 8x 3.600V (28.80V). Because 7 cells will be 3.3x or at best 3.4x volts most likely.

Since the device is RUNNING on the very lithium it is attempting to balance, the high volt cell will fall, and the others will rise. Till all are the same. Total voltage will be well below the 8X 3.600V per cell since you added no more energy. It cant take out power to charge the other 7 cells, and put more back! Remember that between 3.5V and 3.6V on a lifepo4 is the ONLY place you can actually balance the cells. If total battery voltage falls below 28.00V (3.5v x8) then you cannot and should not be attempting to balance. Below 3.4V is definitely going to cause problems. Because not only will it not work, it can do the exact opposite for many hours. State of charge is more temperature dependent than voltage dependant at that voltage or lower. And if a balancer is just 2 or 3mV out of accuracy (or a few cells are warmer/cooler) then it will spend hours UN balancing. Remember that the battery voltage of all cells is almost identical across almost all of the charge. Try balancing at say 50$% charge, and you will make the pack very unbalanced! The last 1% it shoots up from 3.35 approx to 3.6 or higher if allowed suddenly when full. So much less than 1% of that charge right at the end is "allowed" to balance. They all pop up high, one after another once full. Its not a slop, its a spike.

I agree it could balance the cells IF its charger was running while balancing. But a charger typically ends and/or fall to float level or stops altogether at around 1 to 2A CV. That way before any low cells are pulled up higher to 3.600V. Which is why a power supply is the only way that will work. Or possibly that shirly one you already have, set to say .2A and then it will continue to provide power untill the balance ends. But mobility chargers or your other charger will not do that.

[Burgerman]

I think that all this is not relevant though. In shirleys last post he says to do this ONLY ONCE initially. So it could be powered externally, from the lead, or a power supply. He intends it only for initial balance as it can do 2A, so balance much faster than the normal BMS typically a hopeless 100mA or less... On OFF At the wrong voltages.

But these normal BMS cannot balance a new or stored pack unless all cells are very close. Because a stupid 100mA current will take say 30 hours to balance a cell if its just 3Ah different from its neibour. So what happens if you have a cell thats full, and a few that are at say 30%? On a 100Ah battery that means the typical BMS will take 66Ah to top up. At 100mA! Thats 660 hours or a full month. The 2 Amp initial balancer, as a ONE OFF, will balance them in 33 hours. Thats a long time, 2 and a half days. But better than 660! Which wont ever happen, because the mobility charger will turn off or go to float at 2 amps... Can you see why BMS packs are not simple? Many potential issues, no means of knowing whats going on, and all the extra wiring. At least this one does not try to control discharge and keep cutting off the power till reset every time you climb a curb or turn on the grass.

But it HAS got a normal low quality BMS complete with useless balance capability at the wrong voltage that turns off/on for hours if the charger stays on. And this is what he intends to use for normal charge and balance. 99% of the time. So the above post is not going to matter.

Yep, BMS makes it simple alright!

[rickystyx]

I'm in a similar position to greybeard in that I've been trying really hard to get my head around making an add on pack but it just makes my head explode trying to understand it all and I'm on a very limited budget - so please excuse my thickness and just very simply tell me if I'm being stupid. I'm thinking of getting one of these - https://www.dhgate.com/product/gtk-high ... 0282559664
Charging it seperately - in fact it would probably just sit on a float charge most days and be put onto the chair on days when I want to go any distance which may be three or four times a month sometimes in the same week if on holiday and use the lead bricks when just around the house and local to home.
I can't afford a powerlab 8 and seperate power supply and wouldn't have a clue how to use one if I could afford one, so I'd just use the charger that came with the pack to keep it charged and then plug it onto the chair when I wanted to go longer distances. The chair has new MK63Ah fitted but I just want to know that I have extra range if I need it to get me home.
I know there are issues with BMS etc but I really need to keep things very simple and wondered if this would work as a very simple add on?
Cheers
Richard

[shirley_hkg]

It is viable , provided you have the specifications of the BMS inside.


With that , members here could offer help , or even get you specific parts that you can plug in / bolt on.

[terry2]

Maybe you can use one of these https://www.ev-power.eu/Winston-40Ah-200Ah/?cur=1

And buy a simple charger from the same place?

I have no idea if 1 would work. But I don't see why not.

[rickystyx]

These are the specs that are listed but I have messaged them for detailed spacs for the BMS - Sadly I don't understand much about any of it but it does say that the output current can be changed - I'll see what I get back from them

Shenzhen Foxell Technologies Co., Ltd Battery Specification

Model:

C2440AH

Battery Type:

LiFePo4

Nominal Capacity:

40Ah

Nominal Voltage:

25.6V

Battery Dimension:

98x240x266mm, not final size
Battery Weight:

About 7.5KG

Internal Resistance:

less than 100 mohms

Cycle life:

More than 2000 times, DOD at 80%

Combination:

8S LiFEpo4 3.2v 32650

Input Charging Voltage

29.2v

Input Charging Current

Standard 5A, fast 10A

Continuous Discharging Current

45Amps( can customize)

Max Current Discharge

70Amps

Discharge cut-off Voltage

20v

Charging Temperature:

0~45Centigrade

Discharging temperature:

-20~60Centigrade

Storage temperature:

-20~45Centigrade

Widely Applications:

Electric vehicle, Electric Bicycle, Tricycle, scooter, golf trolley, cart, wheelchairs, Medical instrument, Solar supply system, , outdoor inverter, RV recreational vehicle, limo limousine motorhomes , solar panel, energy storage, electric tools, power tools, instruments, LED lighting devices,RC toys, inverter, household appliances and emergent device area, etc.

[Burgerman]

It will work. But its an oversized and overpriced way of adding 40Ah. Its also potentially unreliable and will have a shorter service life. And you will be in the dark about what is going on under the hood. But it is the only option if you really dont want to build a pack yourself. At least using a BMS pack as an addon will not leave you stopped dead at the side of the road.

[shirley_hkg]

I'd avoid these 32650 cells , notorious for leaking.

Pick something else .

[rickystyx]

Ok I'm going to try, I'll get my brother to help to build something for me - I found this pack on Ebay but haven't found anything other than this at a similar price - would this be a better buy?
https://www.ebay.co.uk/itm/8pcs-LIFEPO4 ... 1438.l2649
I have an Overlander RC-6S charger that will charge and ballance 4 cells so if I made them up as 12v packs then ballanced them before making them into a 24v pack would that work OK?
Then how could I charge them safely without spending lots on another charger?
Sorry for asking all these daft questions but I really am fairly clueless - I get my brother to do anything technical with me because I'm so clueless.
Cheers
Richard

[Burgerman]

If it allows you to set the termination current at the correct level, if it allows that capacity without errors, or timeout, if it starts balancing only above 3.45V, if it doesent have too short CV timeout, if it has adequate balance current for a large pack, and if it doesent error when theres more than 150mV difference between cells, and so on then it will charge 4S LiFePO4 properly..

[rickystyx]

This is why I needed a simple soloution - I'll start with building the pack then see if I can't blow it up once that's complete - I just don't know that I'll cope with all that spagetti
Cheers
Richard

[shirley_hkg]

Yes . It is useful for putting the pack together as an initial balance .

Get a BMS with same port for charging & discharging , and cell over-volt cutoff @3.65V max.

You'll then be able to charge both batteries as one as usual . May also need a few Schottky diodes to perfect it .

[rickystyx]

the only Schottky thing I understand comes in a bottle and makes me very happy - this on the other hand is a brown trouser job but I'll do a bit at a time and see what I can kill with it as I go along :0)