"Simple" solution for Lithium charging

[emilevirus]

Firmware has a few bugs which I reported and supposedly working on it. Fans are loud. I wouldn't sleep near it.

[Burgerman]

Anything that can do 600 watts at 90% efficiency is goung to need to move enough air to dump 60 watts. Or 20 watts at 200w output. So a compact unit isnt going to be quiet if its going to cool well. My laptop supply is dell 90 watts no fan. Too hot to hold if charging...

[emilevirus]

Your laptop CPU dumps more watt than that and fan isn't loud. Good quality fans don't whine. They just whoosh.

[Superchunk]

Your laptop CPU dumps more watt than that and fan isn't loud. Good quality fans don't whine. They just whoosh.

yeah i replaced my icharger fan cause it annoyed me. Got this instead https://www.noctua.at/en/products/nf-a4x10-5v

[Superchunk]

He wants a type-C PD as well.

would I be able to just put 48V@5a usb c to JK BMS? Will it charge or just cut off high voltage? If the latter, Can I not just add a buck converter then plug into bms by xt60?

[shirley_hkg]

Chair's electronics are connected. I won't apply 48v to it.

What are you aiming at, other than plug and charge by carer?

[Superchunk]

Chair's electronics are connected. I won't apply 48v to it.

What are you aiming at, other than plug and charge by carer?

ideally, plug, charge and balance by carer with usb c.

[Burgerman]

would I be able to just put 48V@5a usb c to JK BMS? Will it charge or just cut off high voltage? If the latter, Can I not just add a buck converter then plug into bms by xt60?

You would have a large impedance mismatch. The battery voltage will control the charge voltage. So it will "pull down" the 48V to thenominal 24v level and may damage the 45v supply or cause it to shut down as if it was short circuted. If it doesent do any of that then your supply that was 200 watts at its 48V is now 100 watts to the battery and the rest is wasted. So you may as well use a 24v nominal system like a laptop charger.

You can safely charge a AA cell directly from the wall AC with a simple diode and a resistor. Its the same thing. But more than 99% of the energy goes to waste as heat in the resistor. In your case half the power is wasted as heat in the inverter. Which it may sense and shut off. Or overheat.

[Superchunk]

would I be able to just put 48V@5a usb c to JK BMS? Will it charge or just cut off high voltage? If the latter, Can I not just add a buck converter then plug into bms by xt60?

You would have a large impedance mismatch. The battery voltage will control the charge voltage. So it will "pull down" the 48V to thenominal 24v level and may damage the 45v supply or cause it to shut down as if it was short circuted. If it doesent do any of that then your supply that was 200 watts at its 48V is now 100 watts to the battery and the rest is wasted. So you may as well use a 24v nominal system like a laptop charger.

You can safely charge a AA cell directly from the wall AC with a simple diode and a resistor. Its the same thing. But more than 99% of the energy goes to waste as heat in the resistor. In your case half the power is wasted as heat in the inverter. Which it may sense and shut off. Or overheat.

Well that sucks, it seems that every approach I can think of is flawed in some way. What approach would you suggest to achieve the following constraints: 20-48v@5a usbc charging/balancing that is plug and play?

[emilevirus]

There's that: https://www.toolkitrc.com/m8dac/
No BMS needed and can charge as fast as ZXD.

[Burgerman]

In order to have 240 watts with a small supply like the USB PD you need 48V. All the components and wires would need to be double the size to do it at 24v.
But your battery is 24v. So now you would need another inverter and lose another inverter to go from 48 to 24 and lose another 10 to 15% in order to reduce voltage and double the current. Which is as big as your 240w PD box... Then you need to feed that to the BMS in order to balance etc which is physically big again. You end up with something as big as that charger above or the ZXD+BMS or a hobby charger like I already linked to.

So not really sure what you want. I think this fixation on a 48v PD thing is your problem. Its not useful.

[Superchunk]

In order to have 240 watts with a small supply like the USB PD you need 48V. All the components and wires would need to be double the size to do it at 24v.
But your battery is 24v. So now you would need another inverter and lose another inverter to go from 48 to 24 and lose another 10 to 15% in order to reduce voltage and double the current. Which is as big as your 240w PD box... Then you need to feed that to the BMS in order to balance etc which is physically big again. You end up with something as big as that charger above or the ZXD+BMS or a hobby charger like I already linked to.

So not really sure what you want. I think this fixation on a 48v PD thing is your problem. Its not useful.

ok but lets say I get 28V@5A PD, then I can charge through BMS with no additional hardware, just at 140w, correct? Won't I need a CC/CV device too?

[shirley_hkg]

Your device must be CC/CV capable, when it comes to charging battery.

[Superchunk]

Your device must be CC/CV capable, when it comes to charging battery.

Exactly, which takes us back to might as well just use the usb to power a smart charger like the icharger which is always plugged in to battery. Maybe a relay is the best option for this.

[shirley_hkg]

You have 2 main cables and 9 balance wires all connected to your X8.

Compact medical grade switching power supply + buck / boost conveter will it help ?

How do you find the result of JK BMS so far ?

[Superchunk]

You have 2 main cables and 9 balance wires all connected to your X8.

Compact medical grade switching power supply + buck / boost conveter will it help ?

How do you find the result of JK BMS so far ?

That's correct, but I will only need to relay 2 of the wires right? negative on the main and negative on the balance, that should suffice no?

I am not sure how this Compact medical grade switching power supply help me here?

[Burgerman]

All balance wires.

[shirley_hkg]

Bath it in 45℃ as well will increase efficiency.

[Superchunk]

All balance wires.

Bath it in 45℃ as well will increase efficiency.

Scrapping the balance charger idea then, what about something like this + bms?

https://www.aliexpress.com/item/1005010783842191.html

29.4V charge (bit high but BMS will handle it)
32-85V input isolated
8A output

Can just use usb pd as input right?

What's wrong with this setup?

[Burgerman]

I dont get this PD fixation.

You now need a PD device thats quite big. This new gadget. And a pretty large BMS... All to charge at 8A or a bit less.

What is the aim?

And...

29.4V charge (bit high but BMS will handle it)
32-85V input isolated
8A output

They do a 28V one. Which is a perfect 3.50V per cell. Then it wont do as much harm to the battery.

That tiny charger I linked above or something similar from the hobby world does all 3 of these things, in one box, and gives a USBC output to charge your gadgets. And will charge better and balance faster too.

[Superchunk]

I dont get this PD fixation.

You now need a PD device thats quite big. This new gadget. And a pretty large BMS... All to charge at 8A or a bit less.

What is the aim?

And...

29.4V charge (bit high but BMS will handle it)
32-85V input isolated
8A output

They do a 28V one. Which is a perfect 3.50V per cell. Then it wont do as much harm to the battery.

That tiny charger I linked above or something similar from the hobby world does all 3 of these things, in one box, and gives a USBC output to charge your gadgets. And will charge better and balance faster too.

The BMS + this charger can fit in the chair's battery box - the bms is already in there, so it would only be carrying 1 PD power supply for chair, phone and laptop @ 240w. The m8ac is only 65w on usb, which won't power my laptop.

So you'd recommend going for the 28V one instead then? Anything else I should be aware of before trying this setup?

[Burgerman]

Only reliability - have had several of those aliexpress chinese things fail. Get a couple!

[shirley_hkg]

It really doesn't matter NOT to be fully balanced, for a dozen cycles.

Your stock charger will be fine, if you are using it on vacation for a few weeks.

[Burgerman]

But the whole point is that he doesent want to take it.

[emilevirus]

My chair has an integrated charger. Only 5A but it gets the job done. Will charge a lifepo4 to 99% and doesn't balance. Fine when I go on a trip.

[Superchunk]

But the whole point is that he doesent want to take it.

Exactly.

Also 1 issue I just realised, is that the cc/cv charger will trip the ocp of the usb PD if 8A and I try to use it with say a 28V@5A PD supply instead of 48V@5A. So it won't work unless I only charge at say 3A even when I have a 240W PD. This kinda sucks.

[Superchunk]

My chair has an integrated charger. Only 5A but it gets the job done. Will charge a lifepo4 to 99% and doesn't balance. Fine when I go on a trip.

Which charger?

[Burgerman]

Why does your laptop need more than say 65watts?
What is it?

Cant it just run or charge from the chair?

[emilevirus]

My chair has an integrated charger. Only 5A but it gets the job done. Will charge a lifepo4 to 99% and doesn't balance. Fine when I go on a trip.

Which charger?

Stock lead mobility charger.

[Burgerman]

I think his chair has a "on board" stock charger for lead built in. That one.