Really confused about what the P- is for on JK BMS

[mufmur]

I've watched plenty of videos and read the manuals but I still don't have a clear understanding of where the P- is connected to. I have a JK B2A24S20P

 

[Rednecktek]

Battery goes to the B- port, and the power goes out the P- port to your loads/terminals/whatever.

 

[mufmur]

Battery goes to the B- port, and the power goes out the P- port to your loads/terminals/whatever.

So the attached wiring diagram is wrong right?

 

[lexio]

yes

 

[Rednecktek]

Yyeeaahh... those wires going from the P- to the battery Positive terminal makes it a dead short. Magic smoke, sparks, angry wife will occour.

 

[lexio]

you also have 2 fuses 1 on the positive and 1 on the negative
also take a look at the sensing leads.

 

[Samsonite801]

Think of the BMS like the drawbridge gate on a castle, the B- is the inside of the gate, P- is the outside of the gate.

The BMS does 5 things, of course one of those is cell-balancing, but on the other 4, they are conditions that will shut the drawbridge.

-Overvolt threshold
-Undervolt threshold
-High-temp threshold
-Low-temp threshold

Keep in mind the castle analogy is not directly synonymous. The BMS could block one way and allow the other way. Like it can block charging but allow discharging, or it can block discharging and allow charging, or it can block both charging or discharging in certain cases.

I have always inferred that B- means Battery negative (direct-connect to cell pack) while P- means Power negative (Power input/output).

So far we have only spoken of 'Same Port' BMS. There are also 'Separate Port' BMS, where they still have one B- for inside (connection to cell pack), but have separate ports for the outside connection to world (loads and charging), one outside port is for loads only (output), and one outside port is for charging only (input).

Also so far, we've been referring to BMSs which use internal method (FETs) for controlling the continuity between the B- and P- flow. There are also some BMS types which are designed to control a large relay to open or close the gate.

 

[mufmur]

Think of the BMS like the drawbridge gate on a castle, the B- is the inside of the gate, P- is the outside of the gate.

The BMS does 5 things, of course one of those is cell-balancing, but on the other 4, they are conditions that will shut the drawbridge.

-Overvolt threshold
-Undervolt threshold
-High-temp threshold
-Low-temp threshold

Keep in mind the castle analogy is not directly synonymous. The BMS could block one way and allow the other way. Like it can block charging but allow discharging, or it can block discharging and allow charging, or it can block both charging or discharging in certain cases.

I have always inferred that B- means Battery negative (direct-connect to cell pack) while P- means Power negative (Power input/output).

So far we have only spoken of 'Same Port' BMS. There are also 'Separate Port' BMS, where they still have one B- for inside (connection to cell pack), but have separate ports for the outside connection to world (loads and charging), one outside port is for loads only (output), and one outside port is for charging only (input).

Also so far, we've been referring to BMSs which use internal method (FETs) for controlling the continuity between the B- and P- flow. There are also some BMS types which are designed to control a large relay to open or close the gate.

Thanks for that analogy! So the P- would then be connected to the negative busbar?

 

[Samsonite801]

Thanks for that analogy! So the P- would then be connected to the negative busbar?

Sure no problem at all...

Roger that.

 

[mufmur]

you also have 2 fuses 1 on the positive and 1 on the negative
also take a look at the sensing leads.

So the fuse on the negative is not necessary?
What about the sensing leads?

 

[400bird]

You'd put the BMS in place of the fuse on the negative side.

Also, your cells are numbered backwards. Lowest number is the most negative. It should match the BMS numbering or your just going to confuse yourself later on.

 

[Samsonite801]

So the fuse on the negative is not necessary?
What about the sensing leads?

Do you have the manual for it?

Did you see this thread?

JK-B2A24S20P Manual Needed

Anyone know where to obtain a manual, in English, for the JK-B2A24S20P BMS ? Bought one based on favorable reports I saw here. Didn't realize a manual is not included. Newbie, so lost without a manual. QR code on product provides links to several docs, but only in Chinese. Hoping...

diysolarforum.com

This BMS looks like it does up to 24s, are you going to use it as a 16s?

I have a 24s JK active balancer, and I use it for 16s so there are some wires that don't get used.

Essentially, the first wire on right (black) goes to extreme negative of pack, then the wire (red) all the way at the left side of left connector goes to absolute positive (that is the main BMS power + wire).

Then wire from right to left going between each cell up to highest cell, then don't use the leftover wires, just coil them up. I wound up taking the extra wires I didn't need out of the white connector (left connector on mine only has 3 remaining wires on it after I removed the unused ones, since I don't need 24s)

 

[mufmur]

You'd put the BMS in place of the fuse on the negative side.

Also, your cells are numbered backwards. Lowest number is the most negative. It should match the BMS numbering or your just going to confuse yourself later on.

Oh right, I see that

 

[Samsonite801]

Here's another manual:

https://batteri-energi.dk/wp-content/uploads/2021/04/JK-BMS-bluetooth-Manual.pdf

My JK balancer is the same like this one, so see how the P2 connector only shows using B15, B16, and B+ (the far left red wire), so I removed all the other wires carefully from the white connector (with a tiny pick tool, released the little tabs that hold them in and pulled the unused wires out):

 

[mufmur]

Do you have the manual for it?

Did you see this thread?

JK-B2A24S20P Manual Needed

Anyone know where to obtain a manual, in English, for the JK-B2A24S20P BMS ? Bought one based on favorable reports I saw here. Didn't realize a manual is not included. Newbie, so lost without a manual. QR code on product provides links to several docs, but only in Chinese. Hoping...

diysolarforum.com

This BMS looks like it does up to 24s, are you going to use it as a 16s?

I have a 24s JK active balancer, and I use it for 16s so there are some wires that don't get used.

Essentially, the first wire on right (black) goes to extreme negative of pack, then the wire (red) all the way at the left side of left connector goes to absolute positive (that is the main BMS power + wire).

Then wire from right to left going between each cell up to highest cell, then don't use the leftover wires, just coil them up. I wound up taking the extra wires I didn't need out of the white connector (left connector on mine only has 3 remaining wires on it after I removed the unused ones, since I don't need 24s)

The supplier sent me a manual but its not very clear, I will check that one and refer to it.

Yes I'll be using it as a 16S.

Okay got it, cell 16 on the diagram should be cell one

 

[Samsonite801]

The supplier sent me a manual but its not very clear, I will check that one and refer to it.

Yes I'll be using it as a 16S.

Okay got it, cell 16 on the diagram should be cell one

Yeah, B16 (last of the row you will use for 16s), and B+ (the tiny B+ wire all the way to the left of the P2 connector), both go to absolute battery pack positive like the picture.

 

[Samsonite801]

Going off memory here, but if I recall right, I had to tell it in the bluetooth app, that my pack was 16s so it doesn't try to sense 24s...

 

[mufmur]

Going off memory here, but if I recall right, I had to tell it in the bluetooth app, that my pack was 16s so it doesn't try to sense 24s...

Yes, there are plenty of videos showing how to do the app settings for 16S