"Simple" solution for Lithium charging

[ex-Gooserider]

My experience w/ the PL8 feeding it from a typical fixed voltage 'shoebox' supply is that the supply maintains a constant voltage (combination of the rated voltage and the setting of the 'trimmer' adjust pot, I find will get about 27V from a 24V rated unit) and varies the current from Zero to it's rated value (likely higher would be possible, but risks shutdown or smoke escape...)

A server supply should do similarly, remember you can control voltage OR current, but NEVER both at the same time (a law written by some dude named Ohm...) and if it's putting out a fixed voltage it MUST be able to vary the current output...

Is there any reason one can't use the JKBMS or similar unit the same way one uses the PL8, namely attaching it to the power supply and making a connecting cable to the chair with power and balance wires? It seems like this might make a good 'travel / portable' unit as it is seemingly smaller and possibly lighter than a PL8... I could easily see a smallish box with the BMS and a shoebox supply as opposed to the big box I have with the same supply, a PL-8, and a laptop along with it's charger... All of which takes a good bit of setup and table space, as opposed to possibly a smaller box with an AC cord coming out one end and a charge / balance cable the other...

I've also been talking about my lithium conversion w/ the local WC support group, and see a distinct possibility that they will want me to make conversion packs for them - in which case I will need to make a low-effort easy to use way to charge the pack as well - since our supply of PL8's is limited at best, so this would be a good way to handle it...

ex-Gooserider

[shirley_hkg]

Does it easy enough ?

https://www.wheelchairdriver.com/board/ ... =2&t=12583

[Burgerman]

My experience w/ the PL8 feeding it from a typical fixed voltage 'shoebox' supply is that the supply maintains a constant voltage (combination of the rated voltage and the setting of the 'trimmer' adjust pot, I find will get about 27V from a 24V rated unit) and varies the current from Zero to it's rated value (likely higher would be possible, but risks shutdown or smoke escape...)

A server supply should do similarly, remember you can control voltage OR current, but NEVER both at the same time (a law written by some dude named Ohm...) and if it's putting out a fixed voltage it MUST be able to vary the current output...

Is there any reason one can't use the JKBMS or similar unit the same way one uses the PL8, namely attaching it to the power supply and making a connecting cable to the chair with power and balance wires?

Yes read from here on:
https://www.wheelchairdriver.com/board/ ... 30#p213933

But one main reason is that the PL8 has a setting that limits INPUT current as you charge. And output charge rate current.
Which you can set to say 18A, for a 20A capable supply. If it didnt have this, like on a BMS, then charge current input is limited only by the difference between battery voltage and power supply voltage and the total resistance of the BMS/BATTERY/Power supply/wiring. Ohms law...
Which means the supply will either smoke up, or if its equipped it will shut down due to severe overload.

It seems like this might make a good 'travel / portable' unit as it is seemingly smaller and possibly lighter than a PL8... I could easily see a smallish box with the BMS and a shoebox supply as opposed to the big box I have with the same supply, a PL-8, and a laptop along with it's charger... All of which takes a good bit of setup and table space, as opposed to possibly a smaller box with an AC cord coming out one end and a charge / balance cable the other...

Looking at the smaller BMS in my hand its about the same as a PL8 but thinner. Longer and shorter (W/L) so very little to be gained. Weight is the same.
The BMS cannot be set to limit input current though, so cut out or smoke.

I've also been talking about my lithium conversion w/ the local WC support group, and see a distinct possibility that they will want me to make conversion packs for them - in which case I will need to make a low-effort easy to use way to charge the pack as well - since our supply of PL8's is limited at best, so this would be a good way to handle it...

Suggest you need a supply that can do current limiting.

You CAN set a JKBMS BMS to limit input current. Say 40A on a 50A supply. Or rather set max charge current. Be carefule as these are not always exactly the same thing. But that doesent do what you think. It CHOPS OFF power/charge completely - no control - if it exceeds your set value. So it will draw mega amps then after 30 full seconds will chop off the charger. And the chair. Ohms law will ensure that an almost unlimited current tries to flow (and it will)... So smoke! (Or cut out of supply if its capable). Then 30 seconds later it re-connects automatically. If it sees above your set Amp parameter it does the same again some 30 seconds later...
In other words unlike the PL8 or any CURRENT LIMITED charger like the ZXD or even a mobility charger, this current limit behaves like a slow acting breaker. Its NOT proportional. Its not intended as a charge rate control, but as a safety "fuse". Your uncontrolled server or shoebox supply will die or cut out.

Watch.
https://www.youtube.com/watch?v=xTKiOvJ_ejg


youtu.be/xTKiOvJ_ejg

Also his 3.65 is too high.
His comments on balance do not mention that balancing below 3.45 UNBALANCES the pack either.

And his charger (a solar one) is set to 13.8V so that if all cells are balanced thats 3.45V per cell I suggest that is a fraction low as true cell balance is not apparent until 3.50 or 3.55V anyway. So he may get away with that in a solar system. But not advised.

[shirley_hkg]

JK-BMS + ZXD psu. Current will drop as battery voltage approaches CV.

Together with the shutdown timer and residual current, we could set termination current (to some extent) as a good balance charger.

[Burgerman]

How can the ZXD know that balance is achieved before it switches off at your choosen current?

[shirley_hkg]

When cells are not balanced, pack voltage will still be a bit away from CV. Charge current will be big. BMS will just chop it off. However, it will restart in a minute or 2, as the highest cell will be discharged.
Repeatedly, current will subside as cells are close to balance.

[Burgerman]

When that termination current kicks in, charger stops. Voltage at the battery drops. Now balancing is inaccurate or very slow because volts are too low to balance. Especially over time. How does the charger know to restart? Or do you mean to just leave it on?

With a lot of messing around with the BMS settings and charger settings you can arrive at a sort of balance that works OK.

[shirley_hkg]

Set timer 25 mins.

Its still 10 minutes to shut down.

May have to reduce timer to 15 mins.

[Superchunk]

I ended up making this little contraption for 48v@5a usb c charging, (excuse the mess this was the initial prototype lol)

Essentially it is:
1x icharger x8
1x custom esp32s3 board with 70v voltage regulator for MODBUS HID control
1x delay relay board
1x 12 AWG xt60 splitter to power both icharger+esp32s3
1x usb pd3.1 48v trigger board with xt60 + usbc female cable
1x 240w usb charger (external)

3d printed a box for all the stuff (you can see its base in the image) and mounted on the chair, icharger always wired in to the battery, routed usb cable/port to joystick, under the xlr port. Just plug any 100w-240w usb charger to charge, esp32 auto starts icharger program and can monitor it/stop it via wifi.

Feel free to roast this abomination and tell me what's wrong with it.

[emilevirus]

But it already exists... On Aliexpress USB C to XT60 240W.
Ah I guess it doesn't autostart though.

[Superchunk]

But it already exists... On Aliexpress USB C to XT60 240W.
Ah I guess it doesn't autostart though.

I could only find usb c to xt60 140w max on aliexpress. Can you link a 240w version? Would be cleaner.

And yes, the esp32 is for autostarting and wireless monitoring/control

[Burgerman]

Is there any point when the chargers output is linked to the battery and the charger isnt powered?

Because most hobby chargers have a warning inc iCharger to always connect the input power before the battery to the output. Or (looking for pic of a mushroom cloud icon)...

[Superchunk]

Because most hobby chargers have a warning inc iCharger to always connect the input power before the battery to the output. Or (looking for pic of a mushroom cloud icon)...

wait, why is it a problem to wire battery to charger before input power?

[Burgerman]

Because on odd occasions the mosfets will go bang.
Theres no control on them until the charger is powered up. They can switch at random and boom. You will be OK 99% of the time. Then when you least expect it... It just happens out of the blue.

The order that you connect or disconnect matters. The idea is that you never have a battery connected without a ready to go powered up charger.

Heres an example in a random iChargers chinglish manual...

Connecting method:

1. Connect iCharger's input power supply, and turn on it.
2. Connect Li batteries' balance port
3. Connect the main charging port's positive pole to cells' positive pole, and then connect negative pole to
cells' negative pole (this will avoid striking fire while connecting Li cells).
4. Start charging and discharging...
5. After finishing charging and discharging, pls disconnect the cell and charger, and then turn off the charger's
power supply.

https://www.icharger.pl/manuals/106B_en.pdf
Plenty of info about this on hobby forums.

I blew up 2 different hobby chargers in a very exiting way by ignoring this over the years. They suddenly go short circuit and have about 1000 batt amps go through them! Loud. Seen it happen many times at my local flying site. Along with very puzzled looks. Some were iChargers.

The PL8 is uniquely protected against this to a degree according to its designer. But again dont count on it. Even with that one its best to stick to good practices.

[Burgerman]

Do's and Don'ts for taking care of your charging equipment
https://www.electricwingman.com/guides/ ... rgers.aspx

If you take care of the circuits in your charger (and power supply) they will provide you with many hours of trouble-free operation. Over the years we have learned a good bit about dealing with these devices, in summary: -

SAFETY FIRST – ALWAYS be aware of your surroundings and your equipment. If in doubt, ask someone more experienced.
ALWAYS power up your charger BEFORE connecting a battery or batteries for charging
ALWAYS use good quality charge leads with no exposed contacts or breaks in the wire
ALWAYS connect the main battery pos/neg wires to your charger and then connect the balance connector to the balance board or appropriate socket on the charger
ALWAYS get into the habit of double-checking your battery cell voltages before and after a charge and before/after you fly
ALWAYS take care of your batteries, for example don't leave lithium polymer batteries fully charged as this has been shown to be detrimental to their useful lifespan
ALWAYS familiarise yourself with the safety features of your charger (e.g. capacity cut-off or maximum charge time cut-offs)
NEVER charge lithium batteries unattended
NEVER leave your charger powered up after use

[Superchunk]

well that sucks, shall I scrap this whole thing then?

[emilevirus]

You could just add a relay no?

[Superchunk]

You could just add a relay no?

that sounds simpler than it is given 30A 28V charging and for both the xt60 and the balance lead.

[shirley_hkg]

BMS is good enough for routine recharge.

Connect a Balance charger for maintenance from time to time.

[Superchunk]

BMS is good enough for routine recharge.

Connect a Balance charger for maintenance from time to time.

yeah think that's what I will do, maybe design another esp32 pcb with a relay later. Just thinking if I relay the balance lead, I can get away with just switching the negative wire right?

[Burgerman]

that sounds simpler than it is given 30A 28V charging and for both the xt60 and the balance lead.

Not sure I see what the aim is?

30A x 28V is 840 watts. Plus 10 or 15% losses in the conversion in the charger and the USB inverters seperately. Means 840 + say 20% minimum. So over 1000 watts.

Where is this coming from? Cant be from USB?

[Superchunk]

that sounds simpler than it is given 30A 28V charging and for both the xt60 and the balance lead.

Not sure I see what the aim is?

30A x 28V is 840 watts. Plus 10 or 15% losses in the conversion in the charger and the USB inverters seperately. Means 840 + say 20% minimum. So over 1000 watts.

Where is this coming from? Cant be from USB?

Good question. I have the option to use usb or just plug a zxd in directly and icharger auto-starts charging.

[Burgerman]

Or say 5 of these and a hobby charger!
https://www.anker.com/uk/products/a2345 ... ingleBox-1

Seems like a lot of complication.
Just use a small basic EXTERNAL BMS for balance only, taped to a couple of laptop 100w chargers...
Or a single 200w laptop supply. £24. And a tiny hobby charger.
https://www.ebay.co.uk/itm/186416057906
That will work for travel but be slow.

[Burgerman]

The real issue is how much to put back? And how long have you got?

Remember a full charge on a 244Ah lithium (the 230Ah cells) x about 26V is a huge 6,300 watt hours. So 6.6 hours inc balance at 1KW charge rate. Or 6.5 hours at 37 Amps...

Fortunately its infrequently that we have an actual empty battery.

At 5A charge, that will take err... Just over 49 hours. We get only 8 overnight!

[Superchunk]

The real issue is how much to put back? And how long have you got?

Remember a full charge on a 244Ah lithium (the 230Ah cells) x about 26V is a huge 6,300 watt hours. So 6.6 hours inc balance at 1KW charge rate. Or 6.5 hours at 37 Amps...

Fortunately its infrequently that we have an actual empty battery.

At 5A charge, that will take err... Just over 49 hours. We get only 8 overnight!

Yeah so worked this out already. The idea is when travelling I only want to carry 1 charger - a 240w usbc for my phone, laptop and chair. I pull about 50 Ah on average a day charging at 240w (so say a conservative 7A) will take 7-8 hours. If I am at home, I can fast-charge @30A with ZXD.

[emilevirus]

Why not just a BMS with a 10A lifepo4 charger. They're pretty small. https://www.aliexpress.com/item/1005009862077115.html?

[Superchunk]

Why not just a BMS with a 10A lifepo4 charger. They're pretty small. https://www.aliexpress.com/item/1005009862077115.html?

might as well just use my permobil charger then.

[emilevirus]

Why not just a BMS with a 10A lifepo4 charger. They're pretty small. https://www.aliexpress.com/item/1005009862077115.html?

might as well just use my permobil charger then.

With a BMS and only once in a while. It won't balance but it's fine if you only intend to use it every now and then.

[shirley_hkg]

He wants a type-C PD as well.

[Burgerman]

AC power, 8s and 1A balance on LiFePO4, 65w USBC etc for phones and laptops. Tiny and cute...
600w if DC powered. 200w output, if AC powered.

https://www.toolkitrc.com/m8ac/

https://download.toolkitrc.com/wp-conte ... l-V1.0.pdf



youtu.be/DcL62hj7OEg