Batrium balancing issue

batteryshed77

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Hi all, I'm new here and have joined due to the wealth of expertise you seem to have in your ranks. I also intend to be building batteries for a while so look forward to helping out too. But for now, I'm having some issues during the commissioning of my project..

I have purchased and installeda Batrium WatchmonPLUS (WM5), been through all the guides and confident I have it set up correctly. I have a 12S cell configuration, the cell voltages of which can be seen in the images attached. Also attached is the cell telemetry - from both images you can see there is a 0.19 difference between min and max cell voltage - so I've sent the bypass voltage to 4.12 to start to reduce this differential and the red bar above cell 7 indicates this cell is discharging.


image_txvtoi.jpg



image_ekdans.jpg


It's clear that the Watchmon *thinks* it is balancing cell 7, however after many days of operation with no change to the cell voltage - it's crystal clear that it in fact is not balancing this cell.

Does anybody have any ideas what might be happening here? I'm talking with Batrium support however the time difference between us means I'm effectively getting one message per day each way so it's slow progress - and I don't feel like they really grasp the issue.

I suspect a faulty board, I hope not but can't see any other outcome at this stage.
 

HughF

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I don't see the problem here? It looks like your pack is pretty seriously mismatched and cell 7 is hitting it's upper voltage ceiling long before the rest of your cells are.

You have a couple of options:

Manually balance the pack then let the WM5 take over
Put a cooling fan on the WM5 and then leave it to get on with it (don't try this without a fan)
Rebuild your pack with better matched cells

Can you provide more information about the cells you are using, the charger you are using (whether it is in communication with the WM5 over CanBus) and other system components.
 

batteryshed77

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HughF said:
I don't see the problem here? It looks like your pack is pretty seriously mismatched and cell 7 is hitting it's upper voltage ceiling long before the rest of your cells are.

You have a couple of options:

Manually balance the pack then let the WM5 take over
Put a cooling fan on the WM5 and then leave it to get on with it (don't try this without a fan)
Rebuild your pack with better matched cells

Can you provide more information about the cells you are using, the charger you are using (whether it is in communication with the WM5 over CanBus) and other system components.

Thanks for the response HughF

I agree the pack is mismatched, the issue is that cell 7 is not actually being discharged - the watchmon thinks it has been discharging this cell for days now (at least 40ah supposedly balanced off, from a 100ah pack and it's still at 4.15V!)

It does a great job of balancing all the other cells if I lower the balance set-point, it's just this one cell that it won't discharge.

For the options you suggest (for which I am grateful)
> I don't see how manually intervening will help given that it's clear cell 7 balance circuitry is not working.
> This is my current status, I'm letting it get on with it however the heatsink doesn't heat up due to the balance issue. (it does heat up if I balance other cells too)
> I believe the cells are actually well matched, I had a discharge issue on a couple of cells (6 & 9)which is now fixed (before I got the Batrium) and the Batrium has balanced every other cell down (except 7) very effectively. To begin with cell 1 was highest, for example. (I didn't balance all the way down to where 6 & 9 are as it feels a bit wasteful, so plan to manually charge these up)

I'm usingLG 2170 5ah cells and a Victron Multiplus which communicates to the BMS via a Venus GX, the connection works fine and I'm able to charge the pack according to the Batrium set limits without an issue.
 

HughF

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So, to understand your problem fully - you charge the pack and it balances when charging? You can bring all cells to 4.15v ok?

As soon as you start to discharge the pack, cell 7 doesn't sag much and all the other cells drop from 4.15v very fast?
 

batteryshed77

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Yes that's correct, it balances while charging.

However because cell 7 isn't balancing, I can't bring all cells up to 4.15V. The voltage differential between the cell with Vmax and cell with Vmin will remain the same (which in my case is a large 0.19V)

Currently I have a Vmax configured of 4.15V, so it charges until cell 7 hits this value then stops.

What SHOULD of coursebe happening is that this cell is then balanced off to say 4.13V (or whatever I set it to)and the whole pack charges a little bit more, closing that differential bit by bit.

This is certainly what the Watchmon THINKS it's doing - but in reality cell 7 voltage is not being reduced, resulting in the issue I have.

Under discharge there is no sag, cell 7 remains offset from Vmin by 0.19V the whole time.
 

Redpacket

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I think what HughF is hinting at is that it's not a problem with cell 7 but with cells 6 & 9 dropping faster under load.

Rather than cutting off charge when you reach your set voltage, you should hold it there until charge current has dropped away.
Doing this will hopefully allow cells 6 & 9 to "catch up" their SoC to the other cells - if that turns out the be the issue.
Obviously be careful doing this if the pack is unbalanced so cells don't go high.
You might also be able to carefully manually boost cells 6 & 9 with an isolated charger.
 

Wolf

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Thinking slightly out of the box I would just for sh*ts and grins move # 7 cellmonitor to a different location resync the Batrium and see if the issue follows the sensor or if it stays with cell 7.
Did you run a capacity test on each of the 12 packs before joining them all together?
Are they within ?5Ah of each other if you did?
Also did you manually check each pack voltage and compare it to what Batrium is telling you?

Wolf
 

daromer

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Cant move 7th on the WM5 since its static position but you can move the pack itself

Does the wm5 become hot when balancing on the cell 7? It should be hot if it actually balances.

It could be that balancer 7 is brooken perhaps? Or as suggested just other cells very bad?
 

HughF

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Redpacket said:
I think what HughF is hinting at is that it's not a problem with cell 7 but with cells 6 & 9 dropping faster under load.

Rather than cutting off charge when you reach your set voltage, you should hold it there until charge current has dropped away.
Doing this will hopefully allow cells 6 & 9 to "catch up" their SoC to the other cells - if that turns out the be the issue.
Obviously be careful doing this if the pack is unbalanced so cells don't go high.
You might also be able to carefully manually boost cells 6 & 9 with an isolated charger.
This ^^^

You might need close to an hour or perhaps 2 hours of absorption timer to get this pack balanced, possibly even more. To do that you will need to cool the WM5. And you will need to limit the current from the charger, luckily the WM5 can ask the Victron charger to go into limit mode.

You don't want to stop charging when cell 7 hits 4.15v, you want to drive them into balance until all the cells are bleeding off current.


batteryshed77 said:
Yes that's correct, it balances while charging.

However because cell 7 isn't balancing, I can't bring all cells up to 4.15V. The voltage differential between the cell with Vmax and cell with Vmin will remain the same (which in my case is a large 0.19V)

Currently I have a Vmax configured of 4.15V, so it charges until cell 7 hits this value then stops.

What SHOULD of coursebe happening is that this cell is then balanced off to say 4.13V (or whatever I set it to)and the whole pack charges a little bit more, closing that differential bit by bit.

This is certainly what the Watchmon THINKS it's doing - but in reality cell 7 voltage is not being reduced, resulting in the issue I have.

Under discharge there is no sag, cell 7 remains offset from Vmin by 0.19V the whole time.
Please let me know the settings you have for the absorption setpoint and timer from your Victron charger(s)
 

batteryshed77

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daromer said:
Cant move 7th on the WM5 since its static position but you can move the pack itself

Does the wm5 become hot when balancing on the cell 7? It should be hot if it actually balances.

It could be that balancer 7 is brooken perhaps? Or as suggested just other cells very bad?

I believe it to be exactly this - because the Watchmon stays cold while it believes to be balancing cell 7.

Even if the other cells were 'bad' they would eventually close the cap to cell 7 (given it has been on charge /balance for days now)

unfortunately I can't move the pack around, but I can charge cells 6 & 9 up a bit with an external chargerto testmy theory at least
 

HughF

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You can always use a 12v car headlight bulb clipped across cell 7 to manually balance it, but to be honest it looks so close to the rest of the pack it looks more like cells 6 and 9 need a hard charge. You can start an absorption charge and then clip the bulb across the cell, watch what goes on with 6 and 9
 

batteryshed77

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[quote pid='69405' dateline='1605181156']
Please let me know the settings you have for the absorption setpoint and timer from your Victron charger(s)
[/quote]


The absorption set-point is 49.8V (4.15 x 12) and at present I have it on scheduled charge for 12 hours per day (purely to support this test/commissioning phase)

During the other 12 hours it discharges only a small amount as it's onlypowering the Watchmon and Venus


HughF said:
You can always use a 12v car headlight bulb clipped across cell 7 to manually balance it, but to be honest it looks so close to the rest of the pack it looks more like cells 6 and 9 need a hard charge. You can start an absorption charge and then clip the bulb across the cell, watch what goes on with 6 and 9

Good plan, I think I need to do this to prove the issue either way
 

HughF

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What's the absorption timer set to though?
 

daromer

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Try to change around if you can and test to see if any of the others get warm. You should easily feel it get hotter while balancing hard for a longer amount of time.
 

slimf

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This isnt a problem with 6 and 9.

If WM says its balancing cell 7 and it doesnt get warm, its stuffed.
 

batteryshed77

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slimf said:
This isnt a problem with 6 and 9.

If WM says its balancing cell 7 and it doesnt get warm, its stuffed.

This was precisely my thinking, however on further investigation I think I've got the answer.

While double checking the cell voltages with a multimeter so that I was applying a corrective charge to the correct cells, I noticed that while under balance, cell 6 was measuring 5V and cell 7 1.9V. Obviously something is seriously wrong there, so of course checked the multimeters accuracy on a bunch of other cells and it seemed fine.

While the watchmon was trying to balance cell 7;

Cell 6 was physically 3.96V (measured on cell) and was measured as 3.96V via the Watchmon - but actually had a voltage of 5.0Von the harness between battery and Watchmon

Cell 7 was physically 4.16V (measured on cell and was measured as 4.16V via the Watchmon - but actually had a voltage of 1.7V on the harness between battery and Watchmon.

After some head scratching, I realised it was a high resistance connection between Watchmon and cell 6. While no current was flowing, it measured the correct voltage - however when the watchmon attempted to balance cell 7, the voltage between Cell 6 + and cell 7 + collapses.

It just happens that the Watchmon must have some level of filtering in the measurements that it still broadcasts a measured voltage of 4.15V - and still tells me that it is balancing the cell - however due to the lack of the red LED and heatsink staying cold, it doesn't actually balance (because the voltage is being pulled down when it tries to).

Anyway, long story short, I re-did that connection and it's happily balancing away now. Still some time to go until everything is level but at least it's operating as expected. Thanks for the tips everyone, got me to the solution quicker than I expected!


image_kgplqi.jpg
 

HughF

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Well done for finding that, glad it is working for you now.
 

Eddy

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batteryshed77 said:
daromer said:
Cant move 7th on the WM5 since its static position but you can move the pack itself

Does the wm5 become hot when balancing on the cell 7? It should be hot if it actually balances.

It could be that balancer 7 is brooken perhaps? Or as suggested just other cells very bad?

I believe it to be exactly this - because the Watchmon stays cold while it believes to be balancing cell 7.

Even if the other cells were 'bad' they would eventually close the cap to cell 7 (given it has been on charge /balance for days now)

unfortunately I can't move the pack around, but I can charge cells 6 & 9 up a bit with an external chargerto testmy theory at least
Easy fix. Go to settings=> cellmon then check your bypass current 1.69A/temp 75c limits and bypass impedance1.7 Ohms. I screwed with this one time long ago and had thesame results.
 

daromer

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Eddy the problem was that it was not correctly wired from the start or atleast not good enough contacts.
 
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