SOK "open-circuit current" for Victron battery balancer wire sizing

[jessicadavis]

Hi everyone ~

I've been experiencing some trouble with my solar system shutting off in the evenings despite very few loads and lots of charging. Long story short, I got SOK on the line and they confidently suggested my batteries are out of balance and that I purchase Victron's battery balancer to remedy the issue.

According to the manual for the balancer:
In case of series-parallel connection, the midpoint interconnecting cables must be sized to at least carry the current that arises when one battery becomes open-circuited. -
In case of 2 parallel strings: cross section 50% of the series interconnecting cables.

I have 4 SOK 12v 100Ah batteries wired in 2S2P and I'm trying to figure out what the "current that arises when one battery becomes open-circuited" is in order to properly size the wires and fuses. Right now I'm thinking 16awg with 10A inline fuses. Can anyone verify this is all good with the batteries?

Also, would it be ok to only add inline fuses to the 24V & Common wires and leave the ground fuseless?

Thanks in advance

 

[sunshine_eggo]

I worship at the alter of BLUE, but their balancers are anemic, and I would NEVER own them unless I didn't need them, and they were free. They are good for MAINTAINING balance, but not fixing it. IMHO, you would be MUCH better served with 2X HC01 balancers:

https://www.amazon.com/Display-Battery-Equalizer-Voltage-Balancer/dp/B09GLMCNXK

And avoid the parallel interconnects.

It may be time to take the bank down, wire in parallel and charge to full as 12V.

 

[jessicadavis]

I worship at the alter of BLUE, but their balancers are anemic, and I would NEVER own them unless I didn't need them, and they were free. They are good for MAINTAINING balance, but not fixing it. IMHO, you would be MUCH better served with 2X HC01 balancers:

https://www.amazon.com/Display-Battery-Equalizer-Voltage-Balancer/dp/B09GLMCNXK

And avoid the parallel interconnects.

It may be time to take the bank down, wire in parallel and charge to full as 12V.

Please say it ain't so!!! I'm so exhausted by all the varying products people recommend. SOK insisted it would be a good fix - and I specifically asked whether it would be necessary to charge individually to 12V once detached (I don't have a good way of doing so, totally off-grid) and they said no, just to reconnect with the balancer involved and it would fix it over time.

I haven't tested the voltages detached, but in the system they're all the same, sometimes with a .1 difference as series pairs - so I guess that's a good thing. He said the voltage variations wouldn't be explicitly noticeable until they were detached and the multimeter was being used on them as individual 12V units

 

[sunshine_eggo]

Please say it ain't so!!! I'm so exhausted by all the varying products people recommend. SOK insisted it would be a good fix - and I specifically asked whether it would be necessary to charge individually to 12V once detached (I don't have a good way of doing so, totally off-grid) and they said no, just to reconnect with the balancer involved and it would fix it over time.

I haven't tested the voltages detached, but in the system they're all the same, sometimes with a .1 difference as series pairs - so I guess that's a good thing. He said the voltage variations wouldn't be explicitly noticeable until they were detached and the multimeter was being used on them as individual 12V units

If it's a pain skip it. You may also be dealing with imbalance within one or more individual batteries even under normal voltage.

Please provide:

bulk/boost/absorption voltage (3 names for the same thing)?
bulk/boost/absorption duration?
Float voltage?

 

[jessicadavis]

absorption - 28.8
absorption duration - fixed, 15 min (never changed from setting)
float - 27

 

[jessicadavis]

If it's a pain skip it. You may also be dealing with imbalance within one or more individual batteries even under normal voltage.

Please provide:

bulk/boost/absorption voltage (3 names for the same thing)?
bulk/boost/absorption duration?
Float voltage?

absorption - 28.8
absorption duration - fixed, 15 min (never changed from setting)
float - 27

 

[sunshine_eggo]

absorption - 28.8
absorption duration - fixed, 15 min (never changed from setting)
float - 27

Lower absorption to 27.6
Increase duration to 3 hours
float is good.

The idea is to hold the battery at an elevated voltage for an extended period to give them more time for each BMS to balance internally.

 

[jessicadavis]

Lower absorption to 27.6
Increase duration to 3 hours
float is good.

The idea is to hold the battery at an elevated voltage for an extended period to give them more time for each BMS to balance internally.

Done ~
in the history section of the app bulk, abs, and float are three different shades of blue within the columns. most days its mostly in bulk, and historically when its switched to abs its there for about 1 to 2 hours despite it previously being on 15 minutes in the settings. can you explain whats going on here?

 

[sunshine_eggo]

Done ~
in the history section of the app bulk, abs, and float are three different shades of blue within the columns. most days its mostly in bulk, and historically when its switched to abs its there for about 1 to 2 hours despite it previously being on 15 minutes in the settings. can you explain whats going on here?

Screenshot?

If you have marginal or variable solar, the count can restart.

Also, set your tail current to something really low like 1A.

 

[jessicadavis]

Screenshot?

If you have marginal or variable solar, the count can restart.

Also, set your tail current to something really low like 1A.

Attached (most recent examples of abs & float)

I have tail current disabled as per current connected's setting recs:
https://www.currentconnected.com/product/sok-sk12v100/

 

[sunshine_eggo]

Attached (most recent examples of abs & float)

I have tail current disabled as per current connected's setting recs:
https://www.currentconnected.com/product/sok-sk12v100/

If you're not getting into float, you're not getting fully charged. Your images confirm my suspicion that you have inconsistent/inadequate solar, so your shutdowns may be more associated with using more energy than you are receiving.

It appears to me that you're picking and choosing which settings to implement.

After seeing your performance, recommend you revert to maximum speed charging:

29.6V absorption (CC)
27.6V float (CC)
Absorption: 30 minutes fixed (longer because you're rarely getting to absorption voltage)
Tail current: Disabled (CC)

Disabled temperature compensation if it's enabled.

 

[jessicadavis]

If you're not getting into float, you're not getting fully charged. Your images confirm my suspicion that you have inconsistent/inadequate solar, so your shutdowns may be more associated with using more energy than you are receiving.

It appears to me that you're picking and choosing which settings to implement.

After seeing your performance, recommend you revert to maximum speed charging:

29.6V absorption (CC)
27.6V float (CC)
Absorption: 30 minutes fixed (longer because you're rarely getting to absorption voltage)
Tail current: Disabled (CC)

Disabled temperature compensation if it's enabled.

That 29.6V absorption would surpass sok's recommended charge voltage of 14.4-14.6/ 28.8-29.2. woould you be able to explain the necessity of going beyond or ok to just set it to 29.2 which is max?
Changing float to 27.6

 

[sunshine_eggo]

That 29.6V absorption would surpass sok's recommended charge voltage of 14.4-14.6/ 28.8-29.2. woould you be able to explain the necessity of going beyond or ok to just set it to 29.2 which is max?
Changing float to 27.6

sorry. Math error. 29.2V max.

 

[inthewind]

Hi everyone ~

I've been experiencing some trouble with my solar system shutting off in the evenings despite very few loads and lots of charging. Long story short, I got SOK on the line and they confidently suggested my batteries are out of balance and that I purchase Victron's battery balancer to remedy the issue.

According to the manual for the balancer:
In case of series-parallel connection, the midpoint interconnecting cables must be sized to at least carry the current that arises when one battery becomes open-circuited. -
In case of 2 parallel strings: cross section 50% of the series interconnecting cables.

I have 4 SOK 12v 100Ah batteries wired in 2S2P and I'm trying to figure out what the "current that arises when one battery becomes open-circuited" is in order to properly size the wires and fuses. Right now I'm thinking 16awg with 10A inline fuses. Can anyone verify this is all good with the batteries?

Also, would it be ok to only add inline fuses to the 24V & Common wires and leave the ground fuseless?

Thanks in advance

Just wondering how everything has worked out. Did you end up installing the Victron Battery Balancer? I have one and am stuck at figuring out the wire and fuse size too.

 

[Minnichds]

Just wondering how everything has worked out. Did you end up installing the Victron Battery Balancer? I have one and am stuck at figuring out the wire and fuse size too.

It’s only an amp it says. You’re fine to use the recommended 18awg wires with 10A fuses. I may throw on 2.5A fuses though. NEC recommends fusing at 125% of expected max current and 18 AWG is suitable for 5A scenarios generally in automotive wire. The recommended 10 A fuse is likely them stating that the interior components are rated for 10A or slightly higher. You can use bigger wires but going smaller you run the risk of them melting and shorting.

 

[Minnichds]

Just want to state that I find the time series data in the trends tap to be crucial to successfully diagnosing any issues. I set it to voltage and current usually and then start zooming in on events or any anomalies and try to figure out why the data appears the way it does.

Today I fully charged my batteries to the recommended Voltage, going to play with my inverter settings one last time on charging profile, and then I tested some of my appliances just to get an idea on how much power they were drawing and to make sure the shunt was properly synchronized and zero current properly set.

I was also having some issues at the lower voltages but I didn’t have my solar array complete.



On my old 12V system, I had some similar issues with the absorption time on my Mppt. I set my absorption voltage time to 2 hours and that seemed to work the best. You can change this and see what works best, but too low of voltage settings is likely playing along with absorption to prematurely cease charging in your instance.

Lithium batteries generally only need 2 stages of charging. Bulk and absorption. I’ve read that float charging can be bad, however, I believe this to be float charging a battery not under constant load. Under constant load the voltage drops down and float charging may help keep the battery at 100 while under load, this should be set to the voltage at rest when it is fully charged.

Bulk charge is constant current charging and absorption is constant voltage charging. Boost charge I believe to be Renogy’s version of absorption charge, maybe others.

At bulk charge, your charger should charge at up to max current. Then switch over to constant voltage charge once a certain voltage is reached, this continues at a lower current until the batteries stop accepting current. This is your tail current. Setting this too high will cause the batteries to stop charging too soon. Setting too low and you risk overcharging the batteries. I see absolutely no reason to deviate outside the recommended settings for your batteries as you run the risk of damage and them being able to deny warranty service based on those settings.