Help newly installed BMS

[martinev]

Okay. This is your work. I've numbered the cell pins with the right B labels. B0 should be the black wire on the BMS cable. I don't understand your voltage data.

Put the black probe on your meter on B0. This is what you should get, B2 will be 4V, B4 will be 12 V, B6 will be 20v. etc, all these even pins increasing 8V per pin. B20 to B0 is the full battery voltage of 80V.

View attachment 335532


And the other side should be wired like this, If you keep the black probe of your meter on B0, B1 will be 4 volts and as you move left to B19, B3 will be 12 volts and the others will increase about 8volts per pin.

View attachment 335535

If you wish to see individual group voltages, and this should be obvious, you probe the opposite sides of the battery. For example, the first group #1 is checked at B1 and B0, Group 2 checked at B2 and B1. Do all 20 groups.

Don't have to remind you to be careful, All of the banks are at full charge, and there's 80-84 volts sitting here, Make sure no metal can touch those exposed nickel ends.

hi when you say B0 do you mean B- (negative black )

 

[lnanek]

Yeah, B0 and B- are the same thing. The first negative terminal of the first p-group is also the main negative terminal of the battery, which is just a bunch of p-groups in series. You should have two cables coming off it since your BMS has a main B- terminal and also a B- on your balance wire connector which then proceeds to B1, B2, etc..

 

[martinev]

hi Inanek
yes there are 2 x earth cables they are on the C- they are for the motor feed and charging input,
B-1 has the main black (neg ) which is from the battery .

Thanks

 

[lnanek]

Doesn't sound like you have it wired correctly then. My reading of the labels is that both B- on the balance connector and the main B- terminal need to have the main black negative from the battery:



B1 should be the positive side of the first p-group, so the other side of that first bank of cells that has the main black negative.

Most BMS manufacturers include, or provide when asked, a wiring diagram, so you could check that. Not all BMS require a B0 wire on the balance connector since obviously the BMS has that wired in elsewhere as well, but some do for whatever reason. Easier PCB routing or whatever.

 

[martinev]

Okay. This is your work. I've numbered the cell pins with the right B labels. B0 should be the black wire on the BMS cable. I don't understand your voltage data.

Put the black probe on your meter on B0. This is what you should get, B2 will be 4V, B4 will be 12 V, B6 will be 20v. etc, all these even pins increasing 8V per pin. B20 to B0 is the full battery voltage of 80V.

View attachment 335532


And the other side should be wired like this, If you keep the black probe of your meter on B0, B1 will be 4 volts and as you move left to B19, B3 will be 12 volts and the others will increase about 8volts per pin.

View attachment 335535

If you wish to see individual group voltages, and this should be obvious, you probe the opposite sides of the battery. For example, the first group #1 is checked at B1 and B0, Group 2 checked at B2 and B1. Do all 20 groups.

Don't have to remind you to be careful, All of the banks are at full charge, and there's 80-84 volts sitting here, Make sure no metal can touch those exposed nickel ends.

Hi I have tested as suggested and the even numbered side
all
2-4-6-8-10-12-14 -16-18-20 and 14 only measures at 52.5v and i think multiples of 8 it should be 60v
I also have 22 pins not 20 on my BMS plug,

 

[lnanek]

The bolt together battery guy had a good explanation of what it means when a BMS has one extra pin in case that helps you understand better:

Installing the balance wires​

Next, I like to add my balance wires. These are the thin wires with the white connector. Your BMS will either have the same number of balance wires as series cells in your battery, or one more. Our BMSs sold in our shop have one more wire than the number of cells in series. If your BMS has one more wire than the number of cells in series, then all the balance wires will connect to the positive ends of the parallel cell groups except for the very first one which will connect to the negative end of the first parallel cell group. If your BMS has the same number of balances wires as series cells, then each balance wire will connect to the positive end of each cell group only.

For our BMSs, you’ll start with the thin black wire, which connects to the negative end of the first cell group (the same place where the thick B- wire connected). But if you have a BMS with the same number of balance wires as series cells, you’ll start on the positive end of the first cell group, which is the opposite side of the first cell group from where the thick B- wire was connected.

It is best to connect the thin balance wires by removing the nut on one cell in the group, lifting the bus bar and then wrapping the wire around the threaded post. Then place the bus bar back on top of the cell, ensuring that it contacts the balance wire, and finally replace the nut and tighten everything down. This will clamp the balance wire between the busbar and the plastic cap. You could also clamp the balance wire between the busbar and the nut, but this would add some resistance to the flow of electricity through the battery, as the electrons flow through the threaded post, into the nut and then into the busbar. By placing the balance wire below the busbar instead of between the busbar and the nut, you allow the main flow of electricity to bypass the sense wire during pack discharge, while still allowing it to remain in electrical connection. Essentially, you’re wiring the balance wire in parallel to the flow of electricity and not in series.

Alternatively, you can also solder the balance wires directly onto the busbars. That way you don’t have to worry about making a clamped connection. Either way works just fine.

Continue with each successive balance wire by connecting it to the positive end of each successive cell. For our BMSs, the second balance wire (the first thin red wire) will be connected to the positive terminal of the first cell group. Then the third balance wire connects to the positive terminal of the second cell group, and so on. The last balance wire should connect to the positive terminal of your last cell group.

How To Install A BMS – VRUZEND DIY Battery Kit

vruzend.com

There's also cases where they just have an unused one on the connector as well. E.g. if they need 21 wires, the closest size connectors they might have are for 22 pins, or a 10 and a 12, etc.. There's also BMS that can take a variable number of p-groups, like 7 through 13s, which often require wiring the next to last p-group to multiple pins when used with a smaller battery in the supported range.

 

[martinev]

Hi.
Yes this one has 22 pins and wires..
My voltage on 14 is not good 52v .. Would that be one of the cells? Thanks

 

[lnanek]

You could always self balance the battery. Measure each p-group individually, with voltage probe on positive and negative end. Find the one that's low voltage vs. the rest, then stick an old 1S cell phone charger on it. If the BMS is wired correctly, it will start working again once all the cells are balanced. There's also cell meters that will do a balancing discharge for you, and hobby chargers that can do 1S through 8S blocks at a time.

If that p-group doesn't hold charge, or continuously goes out of balance, there's likely a short or bad cell in it, yes. Difficult to tell electrically because all the cells of a p-group are welded together in parallel, but sometimes you can find the bad cell by visual inspection.

 

[martinev]

Hi Inanek thanks I'll take a look.
Well I have had measured all p groups with 30 cells in each all between 4.3v and 4.7 v ???? I just don't understand this

 

[docw009]

Replace the battery in the voltmeter. As they wear out, the readings go up. Unless you hav been doing charging, there is no reason the voltages, which were originally 4.0-4.1V a few weeks ago should now read 4.3-4.7V.

If they really are that high, the cells are overcharged, which is dangerous, You would have to put that battery outside and figure out how to safely lower the voltage.

 

[lnanek]

Yeah, last lithium ion BMS I put in, any p-groups being over 4.25V means the BMS cuts out allowing charging and won't turn on again until all are under 4.15V for 1 second minimum. So 4.7V only reachable via charging without a BMS, or volt meter low on batteries, or shorts/miswiring.

Or a separate port BMS instead of a common port one combined with excessive regen braking while the battery is already full, I suppose. That would bypass protections.

That range of values between the p-groups is also too high. The setting on my BMS was any difference more than 0.15V means BMS off as well. Depends on the BMS data sheet, though, or for modern Bluetooth BMS, whatever you've plugged into the settings app.