Battery Charging power supply - noob questions

Hello,

I plan to make my own 18640 cells battery. it should be a 6s 4p battery powering a couple of arduinos and raspberry pi's

V max = 6 * 4.2V = 25.2 V

Cmax = 4 * 2600mAh = 10 Ah

each cell has a C of 2600mAh (https://www.aliexpress.com/item/8pcs-lot-Li-ion-battery-18650-2600mAh-3-7v-Rechargeable-Li-ion-Battery-ICR18650-26F-26FM/32684559318.html?spm=2114.13010608.0.0.h42HLk)
[tested them with a nice Opus charger/tester ]

considering that from the 18650 specs, they can be charged up to 1C (lets take 2A to be safe and avoid overheating)

I want to use a 24V 2A power supply (https://www.aliexpress.com/item/dc-24v-2a-led-power-supply-constant-current-led-driver-48w-led-power-adapter-transformer-AC100/32679118502.html?spm=2114.13010208.99999999.262.KAWKAL)

I want to protect the battery with a BMS (**broken link removed**)


questions :
- it's my first diy battery so is this setup correct ?
- not sure about that BMS, it does not seem to have separate charge and discharge connections
- how can a BMS in general protect cells when they are connected in parallel anyway ?? having 4 cells linked to one sens BMS probe for isntance
- do I need to limit the power supply current since the BMS can allow up to 5A charging current
- do I need to limit the discharge current since the BMS can allow up to 60A
- if yes, how ?

thanks

Hi,

You correctely calculated your configuration total 10 Ah

Now with 1C charging this means 10A.

Klaus

KlausST said:

Hi,

You correctely calculated your configuration total 10 Ah

Now with 1C charging this means 10A.

Klaus

Click to expand...

so my power supply should be 24V 10A ?

did you check my other questions ?

Hi,

You already calculated 25.2V, therefore 24V will not be enough.

If you want to use any current regulating circuit, then it will need additional voltage.

Klaus

anyone else on these current limiting questions ?
thanks

Hi,

Shame the photo has "kiss-buy" plastered over the last letters/digits of the part number.

A cursory glance at the website for the purchase, no idea what a BMS is (in a sense), no datasheet to look at, the picture on the device of n batteries in series, the above remark that 24V isn't enough to begin with, let alone adding current regulation... I'm no expert, so I wonder if paralleling batteries for a series device makes any difference? Do you put sense wires on each battery with that, or one at the top and another at the bottom? The times I've pondered sensing current regulation in parallel LED strings, using one sensing device - I've always desisted as it seems a "might get away with it, or possibly won't" method...

Maybe that device is fine, if you can get a higher voltage version, but for that price, or maybe a little more, you can buy a plug-in smps and a battery charger/monitor IC + few components that I'm pretty certain will cover the design you wish to implement, with the advantage of design tools, app notes, and, I'll bet, adaptable reference designs.

To limit current, ignoring what Klaus has pointed out, you'd need a constant current source circuit to keep it to 2A, and evidently the discharge one also, unless you can know everything in advance that may ever happen . How - look for current limiting designs, from two BJTs (not the best method), to current sense amplifier + switch type device or op amp and mosfet/BJT current source/sink, then there are ICs that do all that.

I also recommend the (ubiquitous) fuses as protection in relevant places.

Probably there are other methods.

No idea of prices, by doing a bit of research you may find an equally-priced/ reasonably priced evaluation board for battery charging ICs that comes with plenty of documentation for what you intend, and is customisable, rather than something not so well documented from an online seller - see if you can get more info. from the seller about the BMS, anyway.

bms: battery management system, it's supposed to do ballanced charging by monitorin all series connections

yeah I was thinking about using 2 transistors or a lm317

24V psu should be enough to charge it since I really need 24 volts max for my motors anyway ( yes motors are involved too )

ok thanks