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JK (JiKong) BMS - 4S

An 8s BMS expects to check the voltage of each cell by measuring the difference between consecutive balance leads. So if you have an 8s BMS is has 9 balance leads, and to check the voltage of cell 4 it will look at the difference between the B4+ lead and the B3+ lead. Now if you try to hook up to 2 separate 4S batteries, it will assume that the B5+ lead (the sixth of your nine balance leads) will indicate the voltage of the 5th cell, by comparing it to the B4+ lead. That won't work, and the BMS will try like hell to balance and it can't. Moreover, it will probably shut down with an under-voltage since it will look like cell 5 is something like -9V.

I watched the video you are talking about from Andy some time ago. I don't have time to watch it again right now, but as I recall the "trick" he did was to use an 8S BMS (or maybe it was 16S) on a 4S pack of cells. For some BMS's that will work, if you leave the unused balance leads unconnected to anything.
@Evan Bate
In Andy's video, he used his 24s JK to run a 4s configuration. The JK allows you to tell it how many cells are in the battery but it still has a minimum operating voltage. For the 24s that minimum voltage is around 44v minimum so the boost converter needs to be a 12v/48v. For the 8s the operating voltage is about 20v so to use it for a 12v battery you need a 12v/24v boost converter.
 
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.
Am I reading this correctly? Once you got the BMS to turn on you could reprogram it to run at 12v without the need for a boost converter?

Or is that just me being hopeful and reading what I want to hear?
 
Am I reading this correctly? Once you got the BMS to turn on you could reprogram it to run at 12v without the need for a boost converter?

Or is that just me being hopeful and reading what I want to hear?
What I ment to say was that I probably found the lower operating limit :)
A booster should provide any above this 18 volts.

The B+ and the Neg must get a voltage somewere above 18 volts; e.g. 24 VDC
(From a voltage booster or similar)
This will be the voltage you need to run the BMS.

And then the balance leads will provide the B1, B2, B3 and B4 cell voltage.
(B1=3,2 B2=6,4 B3=9,6 B4=12,8)

The B5... and upwards... will all be disabled in the APP.
 
I did buy the LCD
The LCD comes with a ring...

Since there is a picture of the LCD mounted on a bicycle,
I beleive the ring must be for mounting on a bicycle handle bar.

Could also be a ring transformer for measuring current?

Anyone?
 

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Not sure for what purpose this LCD would be for us...
The APP giving all kind of good info.

The only thing.... The LCD is colorful :)

Quick view of the battery status without having to pop your phone out. Usually I don't have my phone with me, or I have gloves, or my hands are dirty, or forgot the phone again.... I'll probably 3D print a custom enclosure for it and integrate it in my next box design.
 
Not sure for what purpose this LCD would be for us...
The APP giving all kind of good info.

The only thing.... The LCD is colorful :)
sometimes my phone run out of battery ?

while it charge from solar battery, LCD help me feel confident phone will charge and show battery status soon :)

have to be near LCD to see status, but it could stay awake for long time

phone can move around a lot and still see status no wire
 
Display might be nice, but as the digital mermaid discovered: The required connector has been added in a more recent hw version..

 
The main benifit that I hope to get from the digital display is the ability to start the JK without needing to break out a power supply or extra battery. It sounds like that function becomes the "push of a button". Looking forward to actual reviews.
 
The main benifit that I hope to get from the digital display is the ability to start the JK without needing to break out a power supply or extra battery. It sounds like that function becomes the "push of a button". Looking forward to actual reviews.
And I can confirm;
the bms do start up if you press that button on the side of that lcd.

And this fuction could be the reason enough for me
 
Display might be nice, but as the digital mermaid discovered: The required connector has been added in a more recent hw version..



I do understand buyers / users get some level of frustratio n…. but hey; it is Chinese way of doing business with foreigners

I did also order a largers size LCD
Just because it was in the same ad
When the box arrived this larger LCD was missing in the box…..

Since I paid for this lcd… I went back to the seller; the excuse was that «you dont need it, it will not fit your bms.»
Fine… but why did you still charge me for the item I did not need.

No harm done; I got my refund.

I also did order a adaptor.. not sure for what purpose it is made… but again.. in the ad.
I did receive the adaptor. Still dont know what it is for
 
I do understand buyers / users get some level of frustratio n…. but hey; it is Chinese way of doing business with foreigners

I did also order a largers size LCD
Just because it was in the same ad
When the box arrived this larger LCD was missing in the box…..

Since I paid for this lcd… I went back to the seller; the excuse was that «you dont need it, it will not fit your bms.»
Fine… but why did you still charge me for the item I did not need.

No harm done; I got my refund.

I also did order a adaptor.. not sure for what purpose it is made… but again.. in the ad.
I did receive the adaptor. Still dont know what it is for
I saw that adapter and wondered what it was for. hopefully someone knows. I was wondering if it might be to allow for permanent installation of the sense wires to the adapter and then seperate leads from there to each cell.
 
Another buy from same ad;
RS485 and CAN interface.

Probably another dust collector for me.
 

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If you don't want it, I'll take it.
Lets not jump to any conclusion.. not yet
I will finish my project (when my cells arrive)
Or finish sometime after arrival.

My idéa was to pick some values from the BMS and transfer those over to my Victron system.
Not sure how, but my initial reflex was I probably need one of them interfaces....

But my gut feeling is that I wont use them.
And then we can visit the post office :)
Finland? Looks like it then will be a pretty local postal shipment :)
 
My idéa was to pick some values from the BMS and transfer those over to my Victron system.
Not sure how, but my initial reflex was I probably need one of them interfaces....

Yes, that's what I do (and what you could do). The JK has a VenusOS driver.
Or you can have a Raspberry Pi as a command and control unit.

Finland? Looks like it then will be a pretty local postal shipment

Yeah, that's why I asked :)
 
Yes, that's what I do (and what you could do). The JK has a VenusOS driver.
Or you can have a Raspberry Pi as a command and control unit.



Yeah, that's why I asked :)

Yeah.. thats what I am doing in my motorhome;
A 4G router and a RaspPi with the LiFePo4, Victron MPPT and shunt.

My present project is a trailor with another RaspPi, solar, MPPT, inverter, 4x 320Ah cells and a JiKong JK 200A BMS. Should be possible to send some numbers over to a display in my motorhome. I would like to read some values from the BMS aswell ?
 
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