diy solar

diy solar

JK (JiKong) BMS - 4S

J

JanVJ

New Member
Joined
Dec 14, 2021
Messages
56
Location
Norway
At the moment I am collecting all the bits and pieces for a 12 Volt LiFePo4 battery bank.

My battery would be based on 4 pcs´s LiFePo4 320 Ah cells.
At this time I do already have a JK (JiKong) 200A BMS. (JK-B2A8S20P)
Would be easy to make my battery using this since already in my "workshop".
As many probably already figured out; its a 8S BMS and not a direct drop in to my 12 Volt battery bank.

There seems to be a quick fix to get around the 12 Volt;
I was looking at Youtuber Andy, Off Grid Garage, Australia;
In his videos he pointed at a 12 Volt solution;
Use of a voltage booster (in my case 12 Volt - 48 Volt) to make this work on a 12 volts battery bank.
Also pointed at a constant current draw in the 30+ mA range.


I still would like to use the JK BMS;
Many reasons;
Money saved since I already have the BMS.
Most important; For what I have seen the balancing function looks pretty good.
Also the APP looks to be a good one. Looks like there are functions to like..

Anyone out there tried this "12 Volt+booster" connection?
Any thoughts?

Any other 4s 200A BMS´s doing the same good balancing as the JK?
And also have the same APP?
 
Last edited:
Since you didn't link to it, I'm not going to waste my time trying to find the video.

To use an 8S BMS on a 4S battery, you must provide the BMS with voltage for the other 4 cells individually.

Based on your limited description, I don't see how Andy's "solution" would work for you.

IMHO, buy the right BMS and quit putting more effort into doing it wrong than doing it right.
 
The beauty of also trying what looks like stupid suggestions would be that one learn new stuff.
The horizon widens.

I did include the link to the video in my previous post.
 
Just because you had an idea, doesn't mean it was a good idea. LiFePO4 cells are expensive. I wouldn't risk them on an experiment like this. An 8s BMS wants to see eight cells. A 4s-8s BMS can be configured for a variable number of cells, but an 8s BMS cannot.
 
HRTKD said:
Just because you had an idea, doesn't mean it was a good idea. LiFePO4 cells are expensive. I wouldn't risk them on an experiment like this. An 8s BMS wants to see eight cells. A 4s-8s BMS can be configured for a variable number of cells, but an 8s BMS cannot.
Click to expand...
Hard to tell; if it was good or bad;

Often refered to as R&D, research and development

Turns out its already described in a manual,
How hard can it then be.
 
You posted a picture of the title page of the manual, not the whole manual, so I can't say for sure, but....

I'd be willing to bet the manual describes using a boost converter to power the BMS. Sure, that's fine. But I doubt the manual tells you how to use an 8S BMS for a 4S battery, like @HRTKD said.
 
Horsefly said:
You posted a picture of the title page of the manual, not the whole manual, so I can't say for sure, but....

I'd be willing to bet the manual describes using a boost converter to power the BMS. Sure, that's fine. But I doubt the manual tells you how to use an 8S BMS for a 4S battery, like @HRTKD said.
Click to expand...
I did post a DropBox link.
Under the link you will find a pdf.

And I just checked if the link was ok.
 
Last edited:
I tried for half an hour to download the manual from their site. It kept stalling and failing right at the end.

I didn't realize the JK was a "multi-cell" BMS, which is atypical of the majority of BMS in use. It does appear to be no issue to connect only 4S and then provide 24V to power the unit.
 
My BMS JK (JiKong) 200A BMS. (JK-B2A8S20P)
In other words a 8S BMS for my 4S battery bank.

My initial questions was;

Anyone out there tried this "12 Volt+booster" connection?
Any thoughts?

Any other 4s 200A BMS´s doing the same good balancing as the JK?
And also have the same APP?
 
The response to my post indicate nobody with similar project on the table. :)

I have tested the 8S BMS on the table without any battery cells,
only with my adjustable desk top PSU;

The BMS did not start at 12 VDC,
but at above approx. 18 VDC the BMS started when 5V applied over the B-P terminals.
(B 5VDC + positive and C/P 5VDC - negative)

After the initial startup I could lower the system voltage to 12 VDC.
The BMS stayed on.

I am confident that it will be ok using this BMS for a 4S 12VDC battery bank.

Hope this info would be useful for others.
 
I'm curious to know if you were able to connect the bluetooth to this model? I tried mine on Android and it located it but when I tried to connect it said "device is not supported"
 
ive used JBD 4S BMS with 3 serial LiFePO4 cells with no issues. in that case no boost converter was necessary

edit: it looked like this in the bluetooth app, again, not JK but an example of using a BMS with fewer cells than max allowed.

1641340496833.png

using a boost converter is less efficient but the consumption of the BMS is low so as long as there is occasional charging eg from solar it should be fine...

with 3S on a 4S BMS i did reprogram the parameters accordingly, including specifying 3 cell count. it works fine and shows all the voltages correctly (JBD not JK)
 
Last edited:
@JanVJ I am planning to do the same thing but have not yet ordered the parts. I look forward to your experience and insight.

I must say, Wow! I find it amazing that so many jumped on the OP with flames and arrows without any knowledge of the product in question (which per the documents he provided is suitable for 4S to 24S but need at least 36v across B- & B+). This in spite of his providing an excellent video of the system in operation on a test bench and providing the full manual.
 
I love that way this BMS does the 2A active balance as seen on Andy's vid. 30mA or 0.72 amps per day is a tiny price to pay for 2 amps of balance that only comes in above the knee and works with or without charging current.
 
Last edited:
hwse said:
I love that way this BMS does the 3A active balance as seen on Any's vid. 30mA or 0.72 amps per day is a tiny price to pay for 3 amps of balance that only comes in above the knee and works with or without charging current.
Click to expand...
I think it's 2A not 3A. Nonetheless it's a great BMS. I am also surprised dude got attacked out of the gate as I would also want to *try* this BMS if I was in his shoes. (I watched the same YouTube)

Mine is hooked up to my in-service 8s bank so I can't experiment with 4s but would like to know if OP has success!
 
hwse said:
@JanVJ I am planning to do the same thing but have not yet ordered the parts. I look forward to your experience and insight.

I must say, Wow! I find it amazing that so many jumped on the OP with flames and arrows without any knowledge of the product in question (which per the documents he provided is suitable for 4S to 24S but need at least 36v across B- & B+). This in spite of his providing an excellent video of the system in operation on a test bench and providing the full manual.
Click to expand...
using a boost converter and reprogramming for fewer cells makes total sense to me. in the end, the MOSFET drive current is small anyways so even with the boost conversion inefficiency it comes out on top of an equivalent resistive balancing BMS imo

does it add an additional point of failure? yes. maybe stock a spare boost converter?

currently i rely on JBD but it uses resistive balancing which is slow and throws the energy away instead of usefully redistributing it between cells

i think the idea has merit, and also would welcome any suggestions for reliable, programmable, high amp MOSFET BMS with active balancing.
 
You must log in or register to reply here.

Similar threads

kolek
JK-BMS or Daly BMS?
2
Replies
22
Views
1K
TimE
T
F
Single JK BMS Active Balance two 4S Packs
Replies
0
Views
138
fastknight
F
R
New BMS JK
Replies
4
Views
217
BentleyJ
B
R
JK BMS 8-17s 100amp won’t initialize
Replies
15
Views
286
timselectric
T
R
JK Inverter BMS & Victron
Replies
8
Views
370
robot_zombie
R
Back
Top