V8 BMS monitoring / wiring (?)

[null]

A guy over at French forum claims the BMS of the V8 reads voltage at a cell level, interrupting the charge when the first cell hits 4.21v (and thus not allowing balancing)

From the photos of V8 battery packs I've seen, the cells doesn't seem to have individual wiring. In a series Voltage adds up, and I dont see a way to read individual cells from that (our whole balancing problem). Besides I find it weird to have cell level monitoring but no balancing?

Anyone have some light here?
Do the V8 BMS know individual cell voltages (or the top one somehow), directly, indirectly or is it misinformation?

edit: original posts if anyone care.

Edited January 19, 2021 by null

[Chriull]

3 hours ago, null said:

A guy over at French forum claims the BMS of the V8 reads voltage at a cell level, interrupting the charge when the first cell hits 4.21v (and thus not allowing balancing)

I claim the same for the BMS of all EUC manufacturers!

3 hours ago, null said:

From the photos of V8 battery packs I've seen, the cells doesn't seem to have individual wiring.

The cell (group) voltage measurement happens on the PCB the cells are soldered to.

If one looks at the first picture of https://forum.electricunicycle.org/topic/18374-how-bms-works-gotway-pack-teardown/?tab=comments#comment-308452

one seed an "old" Gotway BMS with the solder pads for all the 16 cell groups. The "16 groups of electronic components arranged in stripes" are for measuring the single cell group voltages and depending on them enganging a balancing resistor or cutting the charge input off with the big mosfet on the left.

 

3 hours ago, null said:

edit: original posts if anyone care.

 

They do cut off at some higher 4.2x V - but most with some tolerance of +/- 0.05V .. so depending on the charge somewhere between 4.2 and 4.3V ?

Many Aliexpress BMS are specified for 4.28 +/- 0.05V...

And afaik inmotion BMS does balancing, too - but afair i've never seen the PCB from an Inmotion BMS, so i can't say. But i'd see absolutely no reason why they should not have this common and simple passive balancing!

[null]

I thought the series connection was done by the point soldered strips, is there a second set of cabling going between each cell and BMS then? How come we risk over voltage in case of a dead cell if charge is stopped by the highest Volt cell? I thought the added voltages of the series (lacking one cell) would make the remaining cells split the charger voltage (thus risk over voltage)

(I should read that thread rather than ask, sorry)

Edited January 19, 2021 by null

[Chriull]

7 minutes ago, null said:

I thought the series connection was done by the point soldered strips,

Yes. And additionally each paralleled cell groups welded strips go to the BMS PCB and is soldered there on the points B0 ... B16/B20 or B24. So the BMS board has for internal measurements the single paralleled cell group voltages.

7 minutes ago, null said:

is there a second set of cabling going to the BMS then? How come we risk over voltage in case of a dead cell if charge is stopped by the highest Volt cell?

We do not risk cell overvoltage. The dead cell is just more and more stressed with every charge and discharge. Here are only reports of battery pack undervoltage - no one reported overvoltage till now (beside measurement and adjustment inaccuracies)

7 minutes ago, null said:

I thought the added voltages of the series (lacking one cell) would make the remaining cells split the charger voltage (thus risk over voltage)

(I should read that thread rather than ask, sorry)

This is exactly one way how to detect cell misbalance - if the BMS stops charging prematurely!

Could be seen/checked with a HS110 and EUC World charge logs - https://forum.electricunicycle.org/topic/18317-battery-faq/?do=findComment&comment=307641

 

[null]

Thanks for the reply much appreciated.

I was under the impression the cells where in (1P) series, outputting total voltage (with no finer reading), then grouped as parallel. But looking at the pack photos they did seem grouped in parallel clusters who are I suppose then in series.

So the parallel groups are monitored for voltage, and it is the highest voltage that is appears. (?)

I'll have to ponder the thing with a new perspective, as well as do more reading then  

Edited January 19, 2021 by null

[OneLeg]

When we rebuild a V8 pack we hook it to an external battery balancer, and leave it for few hours then until all the voltages are aligned...

When you make a pack batteries voltages after testing each cell may be all over so balancing is a pretty good idea....

If you V8 becomes so unbalance all the red lights will light up on it...

At least the V8 battery is easy to access and deal with....you can just get a normally intelligent charger, some crocodile clips and charge each battery up to max....

[jaiong]

I'm encountering several v8 bms that doesn't switch off controller, after turning off set. You can tell when the bluetooth is permanently active after set is off.. (A typical V8 cuts the voltage output to zero upon turning off). 

This leads to battery draining 2-3v every day when left idle, uncharged, effectively draining the battery to death/zero voltage after 1-2 weeks.

Anyone with same issues?

Edited August 29, 2022 by jaiong