BMS problems

PsychoticEpisode

Solar Addict
Joined
Nov 3, 2019
Messages
588
I have 3 overkill solar 24v BMS in my 280ah batters, and I'm having several problems. I sent an email to the company but only got an auto response on what they will respond to. Makes no cense I know but my problem is not on the list they sent.
Problem 1. All 3 BMS are locking when 1 cell gets to high in volt, wile locked they will not even allow discharging so its as if I don't even have the batteries.
Problem 2. I balanced the cells before I used them but after a few months the cells are way off balance now.
Problem 3. The BMS show 1 over all voltages of 27v but the main Bus bar they are all connected to and the shunt show 28.4v.
The only why have be able to unlock the BMS is to reset the capacity but then I do that the capacity drops for 100% to 60%.

What am I missing?
Screenshot_20211018-135825.pngScreenshot_20211018-135902.png

IMG_20211018_140105256.jpgScreenshot_20211018-135835.png
 

Ampster

Renewable Energy Hobbyist
Joined
May 3, 2020
Messages
4,366
Location
Sonoma, California
It has been a while since I used my Overkill BMS. I thought there was a button in the app that unlocked the discharge lock? Have you tried the discharge slider on the first screen?
 

MisterSandals

Participation Medalist
Joined
Nov 5, 2019
Messages
4,794
Location
Silicon Valley
Problem 2. I balanced the cells before I used them but after a few months the cells are way off balance now.
With your aggressive max charge voltage and what sounds like quite a few high voltage disconnects, your cells probably need top balancing again.

Looking at why you might be in this situation, I think your cells may not be perfectly matched, which would be necessary for such an aggressive (high) daily charge. Your cells, even as shown in your pics, are not equal at 3.55V per cell.

After top balancing, I would try a conservative 3.45V per cell (27.6V battery) and see how that works for you. That’s over 95% charge and below where cells tend to wildly diverge.

If that works well but you need more, you could creep the voltage up to BEFORE they significantly diverge (and possibly disconnect, and ruining your top balance).
 

mikefitz

Solar Addict
Joined
May 28, 2020
Messages
859
Its not clear exactly how your system is arranged, I will assume 3 batteries made up from 280 Ah cells each battery with its own BMS.
Problem 1. All 3 BMS are locking when 1 cell gets to high in volt
This is to be expected if one cell reaches cell high volt protection value or pack high voltage value is reached.
Your charge voltages may be too high, what are they?
The screen shot of switch settings does not look correct, only balance enable, charge balance and the temps for those provided ( not all of them), should be set 'on'.
Problem 2. I balanced the cells before I used them but after a few months the cells are way off balance now.
poor connections within the battery, bad poor quality cells, initial balance not implemented correctly. You don't need super accurate balance to get a usable battery. If its a worry, pull down the high cell with a suitable load (car headlight bulb). Apply across the high cell (cell 8) for several seconds whilst watching the voltage via the app, repeat as necessary.
Problem 3. The BMS show 1 over all voltages of 27v but the main Bus bar they are all connected to and the shunt show 28.4v.
This may be caused by the volt drop across the the 'closed' path
The only why have be able to unlock the BMS is to reset the capacity but then I do that the capacity drops for 100% to 60%.

set the charging and discharge switches to 'on' (green)

The BMS may loose capacity value when changes are made to the BMS, reset capacity will use pre set values in the BMS for the 20% to 80% cell volts settings (these will only be near accurate for a rested cell not under charge).

Mike
 

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,339
The picture you posted shows that charging is off and discharge is on.
 

PsychoticEpisode

Solar Addict
Joined
Nov 3, 2019
Messages
588
The picture you posted shows that charging is off and discharge is on.
The BMS is doing that on its own , once it get to high voltage it cut off the charging and will not let me turn it back on. Problem is that is is not discharging at all even with the slider on.
 

PsychoticEpisode

Solar Addict
Joined
Nov 3, 2019
Messages
588
With your aggressive max charge voltage and what sounds like quite a few high voltage disconnects, your cells probably need top balancing again.

Looking at why you might be in this situation, I think your cells may not be perfectly matched, which would be necessary for such an aggressive (high) daily charge. Your cells, even as shown in your pics, are not equal at 3.55V per cell.

After top balancing, I would try a conservative 3.45V per cell (27.6V battery) and see how that works for you. That’s over 95% charge and below where cells tend to wildly diverge.

If that works well but you need more, you could creep the voltage up to BEFORE they significantly diverge (and possibly disconnect, and ruining your top balance).
So top balance again and set the charge cut off to 3.45v to see if they get out of balance again.
 

Bob B

Photon Sorcerer
Joined
Sep 21, 2019
Messages
3,339
The BMS is doing that on its own , once it get to high voltage it cut off the charging and will not let me turn it back on. Problem is that is is not discharging at all even with the slider on.
In the parameters there is a trigger value and a release value. Once triggered, charging won't be re-enabled until the high cell drops below the release value.

I have no idea why there is no discharge current even when it is turned on.
 

chrisski

Photon Sorcerer
Joined
Aug 14, 2020
Messages
2,352
A screen shot of the Victron App showing the Battery set up could help also.

I have been using a 50 ah lithium pack and have just today hooked to charge my 280 ah Eve and am using the same charge parameters. I am using 27.5 VDC Absorption, with a 26.7 VDC float.

The only other thing I see on the Victron App that would stop charging is the temperature. Factory default seems to be 41 F, which is a bit high compared to what the batteries are rated.
 

MisterSandals

Participation Medalist
Joined
Nov 5, 2019
Messages
4,794
Location
Silicon Valley
So top balance again and set the charge cut off to 3.45v to see if they get out of balance again.
I would phrase it as top balance and apply conservative charge to 3.45V to see if you can keep cells from running away and hitting high voltage disconnect.

I am using 27.5 VDC Absorption, with a 26.7 VDC float.
3.4375V and float at 3.3375V. Looks great too.
 

PsychoticEpisode

Solar Addict
Joined
Nov 3, 2019
Messages
588
I am using 27.5 VDC Absorption, with a 26.7 VDC float.
What is Absorption because my MPPT don't have that in the settings, they have Boost, Float, Equalize, Charge limit.
I change my settings to this on the MPPT
Boost 27.6
Float 27.6
Equalize 27.6
Charge limit 27.8
If there is a better set up then this please let me know.
As for the battery cells I set them to the max charge is 3.45 per cell and 3.5 as over voltage.
Balance start set to 3.4 volts
 

chrisski

Photon Sorcerer
Joined
Aug 14, 2020
Messages
2,352
As for the battery cells I set them to the max charge is 3.45 per cell and 3.5 as over voltage.
Balance start set to 3.4 volts
I am not an expert on this and still learning my settings, but with the charge voltage set to 27.6, each cell would have to be perfectly balanced to be a cutoff of 3.45.

My guess is since all cells aren’t perfectly balanced, the Overkill BMS will turn off charging since one cell will exceed 3.45 before the average is 27.6. For my max voltage per cell, I set this to 3.55 with a release of 3.50. With this, the SCC should shut off charging at slightly less than 3.45 or cell. THe 3.55 is well under the 3.65 cutoff.

My max cell voltage of 3.55 may be way too high for an average of 3.45.
Float 27.6

With my small 50 ah lithium pack, I found that I can set float to the overnight resting voltage of the battery, 26.7 volts, and when I pull a load on the battery, the SCC will push those same amps back in. Once I start setting float less than that, more amps came out than were replaced which left me in the position of possibly being in a low SOC when the sun goes down.

I don’t know if Floating at the overnight resting voltage is a valid setting, but that is the minimum in my limited experience that worked.
What is Absorption because my MPPT don't have that in the settings, they have Boost, Float, Equalize, Charge limit.
I think its boost for you is my absorption. There are the settings for my VIctron. I’m not saying its perfect or even good. Looks like you have the VIctron software based off the pic of the phone. This is what my battery settings are.

95B42ABF-F39D-446A-A05B-0A6DA4486294.png
 

mikefitz

Solar Addict
Joined
May 28, 2020
Messages
859
As for the battery cells I set them to the max charge is 3.45 per cell and 3.5 as over voltage.
This is your problem.
The protection values in the BMS need setting higher, not at the same values as the charger. The BMS protection values are just that, protection against abnormal conditions, they are not intended to control the charge process.

Typically these will be,
cell over volts 3.65, release 3.50
battery over volts 29.2, release 28.0

There may be other values in the BMS that may not be correct. Using the values suggested in the Overkill manual or the default values in the supplied BMS would be a good starting point.
I change my settings to this on the MPPT
Boost 27.6
Float 27.6
Equalize 27.6
Charge limit 27.8
Boost is the same term as absorption.
Float should be set lower to 26 volts. ( the resting voltage of the battery_

You have additional settings, Boost duration, Equalisation duration, Boost reconnect.
Boost duration , zero or 30 mins
Equalisation duration , zero
Boost reconnect, 0.1 or 0.2 volts lower than float voltage.


Mike
 

PsychoticEpisode

Solar Addict
Joined
Nov 3, 2019
Messages
588
This is your problem.
The protection values in the BMS need setting higher, not at the same values as the charger. The BMS protection values are just that, protection against abnormal conditions, they are not intended to control the charge process.

Typically these will be,
cell over volts 3.65, release 3.50
battery over volts 29.2, release 28.0

There may be other values in the BMS that may not be correct. Using the values suggested in the Overkill manual or the default values in the supplied BMS would be a good starting point.

Boost is the same term as absorption.
Float should be set lower to 26 volts. ( the resting voltage of the battery_

You have additional settings, Boost duration, Equalisation duration, Boost reconnect.
Boost duration , zero or 30 mins
Equalisation duration , zero
Boost reconnect, 0.1 or 0.2 volts lower than float voltage.


Mike
Thank you Ill do that.
 
Top