Help newly installed BMS

[martinev]

Hi can someone give me where to check next please
I've just replaced our original Bms for this new BMS but battery positive meter probe and meter probe to negative connection it shows 76v .
Then probe on battery positive red and probe to Bms B- shows 72v but probe to positive red and probe to C- is 6.2v ? Thanks

 

[999zip999]

Okay tell us more about this pack that you're working on did you make it did you get it what type of cells how many in series how many in parallel what brand name what model number of cells and probably a link to your BMS would help that you bought

 

[martinev]

hi ,
no i didnt build it
bms 72v -80am
battery 72v 45ah
20s
18650
15 in each cell
more details of bms is on the photo

 

[docw009]

First thing I would do is take off the BMS balance connector, Then connect the black probe of your meter to the most negative terminal. Then, using a suitable tip on the red probe, measure the other 20 pins on the balance connector in sequence. Write them down,

-You want to see the voltage increase steadily as you walk up the pins toward the end, where it will be 76 volts, This tells you the ibattery builder wired the balance wires correctly in order.
-You want each voltage delta to be over 3 volts as you change pins. If it's under 2.9 volts, a working BMS will not allow any voltage at the output.

If both are true, then there's no reason for the BMS to not output voltage and it's probably at fault, IF either are not true, then you have to fix a wiring error or examine the low voltage banks.

 

[lnanek]

Worth pointing out some BMS don't turn on after installation until they've been connected to a charger at least once. Also some don't turn on the MOSFETs in both directions until they sense current. There's voltage drop before that.

 

[martinev]

Hi Inanek . I had read that so when I plug the chased in it just stays on green ( fully charged) . Here is a small test I have just done. See what you think 
I can't upload video it's to big. Dam

 

[martinev]

First thing I would do is take off the BMS balance connector, Then connect the black probe of your meter to the most negative terminal. Then, using a suitable tip on the red probe, measure the other 20 pins on the balance connector in sequence. Write them down,

-You want to see the voltage increase steadily as you walk up the pins toward the end, where it will be 76 volts, This tells you the ibattery builder wired the balance wires correctly in order.
-You want each voltage delta to be over 3 volts as you change pins. If it's under 2.9 volts, a working BMS will not allow any voltage at the output.

If both are true, then there's no reason for the BMS to not output voltage and it's probably at fault, IF either are not true, then you have to fix a wiring error or examine the low voltage banks.

Thanks brilliant. I've I have just done what you said but I can post video it's a big file. annoying

 

[docw009]

Don't need to post a video. Just check if the voltages increase on the banks in a steady fashion, and if the difference between adjacent pins, which is the bank voltage, is in the safe zone. Lithium cells operate between 2.5V at discharge to 4.2V at max charge, However, a BMS is usually set with these limits between 3.0 and 4.2V for extra safety and better cell longevity,

If you understand how cells are wired, you can do this directly by measuring the opposite sides of each cell bank. Twenty banks for 20S. They all have to be 3.0-4.2V. FOr a healthy battery, they should all be the same, within .1 volt of each other, and around 3.8V if you're measuring 76 volts,

 

[martinev]

hi docw009
i have done the measuring by removing the 2 plugs with sensing wires and using probe in the wires ,
76.9
72.8
68.8
64.7
60.6
56.6
52.5
48.5
44.4
40.3
36.3
32.3
28.2
24.2
20.1
16.1
12.1
8.09
4.05

thanks

 

[docw009]

That's 19 banks, all averaging 4.04 volts, which is good. You're missing the 20th bank. The connector shows B20-B1 and B-. Maybe you missed the B1 to B- voltage, You should meausre it just to make sure it's also 4 volts,

I see a thermocouple in the controller picture. Make sure its leads aren't frayed. Sometiomes you have to reseat the balance connector to start a BMS, and sometimes you need to connect the charger for a second.

Is this a bluetooth BMS?

 

[martinev]

Hi docw009
Oh yes .
I'll double check thank you

 

[martinev]

Hi jasonwang3a
The battery voltage from battery positive and battery negative B1 is 76.2v
But measure from battery positive to BMS negative C1 ( motor and charging input ) it is only 6.2 v
something is wrong
Battery and cells seem to be
ok voltage spec.

 

[martinev]

Hi all
i have just run through the test again on the multi block plug
( plug 6 wires in one and and 15 wires in the other )
on testing from battery positive red to the pins again starting at 76.6 v
and i have on pin 14 and 13 i have 48.4v on both ,then on pin 12 is 44.2v
and on pin 15 is 52.5 v

How can I have 2 wires with same voltage 48v on wire 14 and 13

what do you think

thanks

 

[martinev]

That's 19 banks, all averaging 4.04 volts, which is good. You're missing the 20th bank. The connector shows B20-B1 and B-. Maybe you missed the B1 to B- voltage, You should meausre it just to make sure it's also 4 volts,

I see a thermocouple in the controller picture. Make sure its leads aren't frayed. Sometiomes you have to reseat the balance connector to start a BMS, and sometimes you need to connect the charger for a second.

Is this a bluetooth BMS?

hi yes if i had a BT adaper how can i have to cells the same voltage but still be in sinc 4 v etc wire 13/ 14 ?
thanks

 

[lnanek]

Maybe you've accidentally got two balance wires coming from the same p-group? Or one p-groups is dead and contributing zero volts to the series? Or there's a short in there somewhere. Happens pretty easily without cell spacers. Just takes some friction to rub through the cell heat shrink.

 

[docw009]

Hi all
i have just run through the test again on the multi block plug
( plug 6 wires in one and and 15 wires in the other )
on testing from battery positive red to the pins again starting at 76.6 v
and i have on pin 14 and 13 i have 48.4v on both ,then on pin 12 is 44.2v
and on pin 15 is 52.5 v

How can I have 2 wires with same voltage 48v on wire 14 and 13

what do you think

thanks

First cause is a dead cell bank. Go directly to the affected cell bank and measure the voltage of the cells.
Next cause is the 14th pin wire is miswired to the same place as the 13th wire.

Either way, that is why the BMS won't turn on,

 

[martinev]

Thanks.

 

[martinev]

Maybe you've accidentally got two balance wires coming from the same p-group? Or one p-groups is dead and contributing zero volts to the series? Or there's a short in there somewhere. Happens pretty easily without cell spacers. Just takes some friction to rub through the cell heat shrink.

Thank. You

 

[martinev]

Here are the wires 13/14 ( it was very tidy before I opened it up again)
I will have another look tonight. Thanks

 

[martinev]

Hi all.
I have done more voltage test down both sides all tests were done with the positive probe on the output positive red ( arrow) and I tested down one side then the other side. On the side with the positive red cables on the right it goes in 8v increments but one was reading 28v seams strange?

 

[lnanek]

Each of those double wide blocks is a pair of p-groups wired in series. That's why they go in 8v increments if each p-group is charged to 4v. So for the spot where the voltage jumps from 24v to 28V when moving two p-groups, something is wrong. Can measure each p-group group individually if you want.

 

[docw009]

Hi can someone give me where to check next please
I've just replaced our original Bms for this new BMS but battery positive meter probe and meter probe to negative connection it shows 76v .
Then probe on battery positive red and probe to Bms B- shows 72v but probe to positive red and probe to C- is 6.2v ? Thanks

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.




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.



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.

 

[martinev]

Well thank you so much. I live learning. Ok I'll do that tonight as per your instructions. Have a great day

 

[martinev]

Each of those double wide blocks is a pair of p-groups wired in series. That's why they go in 8v increments if each p-group is charged to 4v. So for the spot where the voltage jumps from 24v to 28V when moving two p-groups, something is wrong. Can measure each p-group group individually if you want.

Thank you again for helping me

 

[martinev]

This is the lambretta swing arm I have designed and built to accept a QS hub. Made from aircraft grade aluminum..