Are these values normal?

[Iridetheshortbus]

Cell #4 is high but the voltage didn't run away and trigger an over voltage alarm which is a more serious situation so I wouldn't recommend getting a separate power supply. A separate active balancer is the way to go because it will keep things in line at every charge cycle.

Is important to select a model with a Voltage based trigger that can be set at 3.4V. The balancer should only be active when the first cell hits 3.4V.

I'm using a JK-BMS brand active Bluetooth balancer but it doesn't have the above feature. Maybe the new models do? Funny thing is their BMS's with balancing built-in does have the feature.

Andy at Off-Grid Garage has posted MANY BMS and balancer YT videos if want to do some research. If the newer JK brand 2A balancer doesn't have the feature maybe try Neey. Sorry, I'm not up to date on all the choices at the moment.

Thanks for the information, just to clarify I meant getting a power supply to perform a top balancing.

 

[BentleyJ]

Yes, I was just making the point that a bench top power supply is a manual process where its connected once every few months to top balance then removed. An active balancer is installed permanently, much less trouble.

 

[Iridetheshortbus]

Yes, I was just making the point that a bench top power supply is a manual process where its connected once every few months to top balance then removed. An active balancer is installed permanently, much less trouble.

People top balance more than once? I should mention I didn’t top balance when I originally got my battery’s they seemed close enough. My bms (overkill solar) performs some balancing but I’m assuming an active balancer does more?

 

[BentleyJ]

I believe Overkill uses Passive balancing which means resistors are used to reduce the voltage of high cell(s). Basically wasting energy as heat so the amount of current has to be very low, Like 100 to 200mA. Would take a long time to balance the cells.

Active balancing removes energy from the high cell, either with capacitors or inductors, then injects the energy into the low cell. This type can be 1A to 15A. Much more efficient and doesn't produce excess heat. (although that would be desirable in a cold climate) Recommended at least 1A of balancing current for each 100Ah of battery capacity.

 

[mikefitz]

charging fully today these are my values. Should the cell voltage be higher?

Looks normal, the battery is still accepting a small charge current.

if I’m pushing 30amps into the battery

30 amps into a 300Ah battery , (charging at 0.1 C), will have achieved full charge by the time the battery reaches 14.0 volts. Note the graph shows cell volts under charge , with a low charge current full charge is reached as the cell approaches 3.5 volts, 14.0 for a 4 cell battery. Once the charge voltage is removed the battery volts will be in the region of 13.4 volts at rest.

assume I’d attached the shunt between the battery positive and positive bus bar?

No, the shunt connects between battery negative and negative buss bar, recommend Victron Smart shunt, or the Victron BMV712.

my cells is off from the others. Should I look into do a top balancing?

The battery reached 13.97 volts and all the cells exceeded 3.4 volts, that's a full battery. If you lower the charge voltage to 13.90 volts or slightly lower, with a long absorbtion period, the cells will better balance over time with the BMS balancer. It's not critical, so carry on using the battery as normal.

a notification when I reach a certain percentage or amp/hrs remaining

The Victron BMV712 shunt with programmable internal relay could activate an alarm at a SOC or voltage level.

didn’t top balance when I originally got my battery’s they seemed close enough. My bms (overkill solar) performs some balancing but I’m assuming an active balancer does more?

Personally I am not a fan of active balance circuits but if added should perform better than the BMS. Your battery inbalance is not too serious and is typical of ready built battery, (I know yours is diy). With suitable charge voltages and extended absorbtion, your BMS should have an effect. It's worth trying for a few weeks before taking alternative action.

I think you have a Renogy Rover solar controller, its default setting for lithium is not ideal. I suggest user setting a charge and float voltage of 13.8 volts, try this for a week or two and see if the balance improves.

Mike

 

[time2roll]

So I currently don’t have a power supply so would you suggest getting one to top balance or would the active balance be the better route?

I went with an active balancer. Still a bit slow but it works around the clock so I can generally ignore it. Money well spent.

Keep the top charging voltage limited to 14.000 volts or just enough to avoid over volt protection until it gets sorted out.

 

[Iridetheshortbus]

Looks normal, the battery is still accepting a small charge current.

30 amps into a 300Ah battery , (charging at 0.1 C), will have achieved full charge by the time the battery reaches 14.0 volts. Note the graph shows cell volts under charge , with a low charge current full charge is reached as the cell approaches 3.5 volts, 14.0 for a 4 cell battery. Once the charge voltage is removed the battery volts will be in the region of 13.4 volts at rest.


View attachment 192693


No, the shunt connects between battery negative and negative buss bar, recommend Victron Smart shunt, or the Victron BMV712.
View attachment 192697

The battery reached 13.97 volts and all the cells exceeded 3.4 volts, that's a full battery. If you lower the charge voltage to 13.90 volts or slightly lower, with a long absorbtion period, the cells will better balance over time with the BMS balancer. It's not critical, so carry on using the battery as normal.


The Victron BMV712 shunt with programmable internal relay could activate an alarm at a SOC or voltage level.
View attachment 192706

Personally I am not a fan of active balance circuits but if added should perform better than the BMS. Your battery inbalance is not too serious and is typical of ready built battery, (I know yours is diy). With suitable charge voltages and extended absorbtion, your BMS should have an effect. It's worth trying for a few weeks before taking alternative action.

I think you have a Renogy Rover solar controller, its default setting for lithium is not ideal. I suggest user setting a charge and float voltage of 13.8 volts, try this for a week or two and see if the balance improves.

Mike

Thanks a lot for the details, I’ll definitely look into that shunt,
The more I looked into active balancers the more I don’t like. At most I would use one to top balance than shut it off, but would rather have the passive balance work better.

Want to make sure I don’t input something wrong,
What setting should I have for the charge controller?
My battery currently keeps tripping over cell voltage.

 

[mikefitz]

Charge voltages,
Normal use when the cells are better balanced, 14.2 volts Equilisation, 14.2 volts Boost, ( this is the absorbtion value) , 13.5 volts float, absorbtion period 30 minutes.

With the existing slight inbalance situation you cannot charge over 13.97 without getting BMS protection. So the idea is to use.charge voltages below 13.97 for as long as possible.
So set, equilisation = Boost = float = 13.8 volts.
Every few days increase the volts by 0.1, if the BMS shuts the charge path, revert to the lower voltage for a bit longer.

All the values in the BMS are correct, no issues there.

You don't have a serious issue with the battery.

Don't worry that you didn't carry out a 'top balance', most off the shelf battery manufactures don't either.
It's a risk attempting cell top balance with the 'traditional method', its easy, without experience, to damage the cells.

 

[Iridetheshortbus]

Charge voltages,
Normal use when the cells are better balanced, 14.2 volts Equilisation, 14.2 volts Boost, ( this is the absorbtion value) , 13.5 volts float, absorbtion period 30 minutes.

With the existing slight inbalance situation you cannot charge over 13.97 without getting BMS protection. So the idea is to use.charge voltages below 13.97 for as long as possible.
So set, equilisation = Boost = float = 13.8 volts.
Every few days increase the volts by 0.1, if the BMS shuts the charge path, revert to the lower voltage for a bit longer.

All the values in the BMS are correct, no issues there.

You don't have a serious issue with the battery.

Don't worry that you didn't carry out a 'top balance', very few off the shelf battery manufactures don't either.
It's a risk attempting cell top balance with the 'traditional method', its easy, without experience, to damage the cells.

Thanks a lot, I like this approach and will apply it.

 

[mikefitz]

use one to top balance than shut it off

There is a technique to manually balance a set of cells, 4 cells is easy.
Get a 12v vehicle headlamp bulb, incandescent type around 50 watts. Add two leads to the bulb to act as probes.
Have the battery under charge and with the cell volts over 3.40. Identify the high cell and apply the probes across the cell for a few seconds whilst monitoring the cell volts via the app. With a little practice it's possible to estimate the duration for a required volt drop.
If things are changing too fast stop charging for a time. So play 'whack the mole' with the probes to bring down the high cell . Once you get to within 30 mV difference at around 3.50 volts per cell consider a sucessful balance. Then under normal use the BMS should finish off the process.

Mike

 

[time2roll]

The more I looked into active balancers the more I don’t like. At most I would use one to top balance than shut it off, but would rather have the passive balance work better.

Interesting because both the passive and active turn themselves off once the balance is complete.

 

[Iridetheshortbus]

Interesting because both the passive and active turn themselves off once the balance is complete.

I meant I wouldn’t want the active balance working all the time, the battery should stay pretty balanced once’s it’s balanced right?

 

[time2roll]

I meant I wouldn’t want the active balance working all the time, the battery should stay pretty balanced once’s it’s balanced right?

Yes once balanced, the cells should stay in line fairly well and the active or passive balance shuts down unless needed.