Top balancing, a more practical method?

[Castaway Camper]

Good Afternoon & Merry Christmas

I'm building a 16S battery using EVE 304 Ah prismatic cells attached to the Overkill Solar 16S 100Ah BMS. Question I have is, does it make any sense to go ahead and build the battery with BMS all connected then slowly charge with my 60V-5amp Bench power supply, allowing the BMS to make balancing corrections as voltage ramps up. If the BMS falls a little behind, I can burn off the additional power from individual cell(s) as needed with a light bulb for instance. The BMS interface provides the cell voltages in real time providing me with what I believe is all the information needed to confirm that I have successfully top balanced. This to me just feels most efficient.

 

[Ampster]

It will depend on how well the cells are balanced. There is no good way to know until you start charging them. I have done both processes and they both worked. My latest 3S16P pack I parallel top balanced to 3.55 per cell then assembled them into the pack and attached an active balancer to fine tune them at 2 Amps because my BMS can only do less than 0.5 Amp balancing.

 

[FilterGuy]

Good Afternoon & Merry Christmas

I'm building a 16S battery using EVE 304 Ah prismatic cells attached to the Overkill Solar 16S 100Ah BMS. Question I have is, does it make any sense to go ahead and build the battery with BMS all connected then slowly charge with my 60V-5amp Bench power supply, allowing the BMS to make balancing corrections as voltage ramps up. If the BMS falls a little behind, I can burn off the additional power from individual cell(s) as needed with a light bulb for instance. The BMS interface provides the cell voltages in real time providing me with what I believe is all the information needed to confirm that I have successfully top balanced. This to me just feels most efficient.

The process you described can work but..... Keep in mind that the Overkill has a very small balance current. (I think it is something like 200mA).
So... if you are charging at 1 amp there is no way for the balancer to stay ahead of a cell that is 'running away'. Consequently, you will need to be very vigilant in in using the light bulb to 'burn off excess'

Also, I like to top balance to a voltage that is slightly higher than what my normal operating voltage will be. Consequently, while doing what you describe, I would set the cell cut-off voltage in the BMS to a higher voltage than what the normal operating voltage will be.

 

[wholybee]

The BMS won't keep up. It could take weeks or more
However, you can do as you say, then once it starts balancing, take it apart, connect in parallel, and balance with a power supply the normal way. Saves a lot of time.

 

[Castaway Camper]

OK I understand what you guys are saying about the week balancing ability of the BMS, If the battery cells are of similar IR & voltage (matched & Batch) as they say, and that I hope to get. It may not be a very significant balancing demand out of the box?

 

[FilterGuy]

OK I understand what you guys are saying about the week balancing ability of the BMS, If the battery cells are of similar IR & voltage (matched & Batch) as they say, and that I hope to get. It may not be a very significant balancing demand out of the box?

Correct. In some of the recent videos from @Will Prowse, he states that he builds his batteries and capacity tests them without top balancing. Only if the capacity test fails will he back up and do the top balance.

I suppose you don't even have to do the capacity test to decide if top balance is needed. Just watch the individual cell voltage and see if they stay close to each other as the charge completes. If they all stay close.... no balance is needed. If one cell is slightly off you might be able to bleed it off with a light-bulb rather than doing a whole top balance.

 

[John Frum]

Depends on the quality of the cells.

I suggest to charge in series and then discharge/charge individually once you see the delta situation when the bms invariably trips on cell over-voltage.

To clarify, you can charge/discharge cells individually while the cells are in serial configuration.

 

[Castaway Camper]

Good advice, I'll proceed based on your notes above. Thanks.

 

[noenegdod]

I just cut and pasted this from another thread I posted it in this morning:

I am honestly completely sick of the whole top balancing topic. After having done the whole parallel top balancing thing I have come to the conclusion it is a stupid waste of time and mental energy unless you dont have the money to buy this. If you dont then yes, you must parallel top balance but if you can afford the $100 dont waste the time. Install the balancer, charge the pack until the BMS stops charging, stick a bench top power supply on set to 3.65v X the number of cells in series you are charging and walk away. I have done this a couple times now and it is so easy and fool proof. No taking the battery apart and putting it back together and because it is balancing at 4 amps it is super fast.

 

[Bob B]

Good Afternoon & Merry Christmas

I'm building a 16S battery using EVE 304 Ah prismatic cells attached to the Overkill Solar 16S 100Ah BMS. Question I have is, does it make any sense to go ahead and build the battery with BMS all connected then slowly charge with my 60V-5amp Bench power supply, allowing the BMS to make balancing corrections as voltage ramps up. If the BMS falls a little behind, I can burn off the additional power from individual cell(s) as needed with a light bulb for instance. The BMS interface provides the cell voltages in real time providing me with what I believe is all the information needed to confirm that I have successfully top balanced. This to me just feels most efficient.

I balance my pack that way ..... but, my BMS has 1.2A of balance current .... and my cells seem to be very well matched.
I personally would give it a try .... and use manual balancing if necessary.

 

[Ampster]

After having done the whole parallel top balancing thing I have come to the conclusion it is a stupid waste of time and mental energy unless you dont have the money to buy this.

Earlier I posted a similar process using a Heltec 2Amp active balancer on a 3P16S pack.

 

[FilterGuy]

I just cut and pasted this from another thread I posted it in this morning:

I am honestly completely sick of the whole top balancing topic. After having done the whole parallel top balancing thing I have come to the conclusion it is a stupid waste of time and mental energy unless you dont have the money to buy this. If you dont then yes, you must parallel top balance but if you can afford the $100 dont waste the time. Install the balancer, charge the pack until the BMS stops charging, stick a bench top power supply on set to 3.65v X the number of cells in series you are charging and walk away. I have done this a couple times now and it is so easy and fool proof. No taking the battery apart and putting it back together and because it is balancing at 4 amps it is super fast.

That is fine if you are in a position to build multiple batteries. However, for the DIYer that may only be building a single battery, they may not want to shell out for the tool you linked to. It comes down to cost vs convenience.

 

[codfish]

So... If you are in a situation where you could shallow cycle the battery more or less daily ( solar). Then one could just-
0/ set BMS disconnect to 3.65+ per cell
1/ charge up to the BMS disconnect (3.65+ on any one cell) - Once - note the pack voltage
2/ set the daily pack voltage to a bit less than that
3/ proceed and utilize the pack daily however you intend (since you haven't completely top balanced you shouldn't expect full AmpH)
4/ move up the pack charge voltage on a weekly? basis to slowly creep up on "fully" top balanced
5/ Eventually when you are satisfied the balance is OK, then back down the charge voltage to your long term plan ( not maximum charge for most cycles presumably)

 

[noenegdod]

That is fine if you are in a position to build multiple batteries. However, for the DIYer that may only be building a single battery, they may not want to shell out for the tool you linked to. It comes down to cost vs convenience.

That is true which is why I said "if you can afford it". I am a DIYer and have only built a couple batteries. Doing 16 cells with a bench top power supply takes forever and is a PITA. Even if you only build one I think it is worth having, again, if you can afford it. It certainly is not a critical component, just a really nice to have one.

The BMS I am using has the ability to stop the charge and discharge at preset SOC I dont know if others do that or not). I intend to have my battery live in the 20-80% SOC so there is the possibility it will eventually drift out of balance. Every so often I plan to take it right up to 100% and make sure the cells are in balance so the balancer will have use beyond the initial top balance.

 

[time2roll]

Why even do the initial test charge? Just build and put the battery in service. I would initially limit charging to 27.2 to 27.6 volts and see what goes. Yes you can bleed off power if you do find a couple cells had an initial higher state of charge. Or slap an active balancer on and let it roll.

 

[Gazoo]

OK I understand what you guys are saying about the week balancing ability of the BMS, If the battery cells are of similar IR & voltage (matched & Batch) as they say, and that I hope to get. It may not be a very significant balancing demand out of the box?

I believe cells could have the same IR and voltage and still not be capacity matched. I have learned a lot about having non capacity matched cells and if I ever buy cells again I will make sure they are capacity matched. If the cells come capacity matched meaning the capacity of the cells are within a few amps of each other, then IMO there is no need to parallel top balance.

 

[curiouscarbon]

Good Afternoon & Merry Christmas

I'm building a 16S battery using EVE 304 Ah prismatic cells attached to the Overkill Solar 16S 100Ah BMS. Question I have is, does it make any sense to go ahead and build the battery with BMS all connected then slowly charge with my 60V-5amp Bench power supply, allowing the BMS to make balancing corrections as voltage ramps up. If the BMS falls a little behind, I can burn off the additional power from individual cell(s) as needed with a light bulb for instance. The BMS interface provides the cell voltages in real time providing me with what I believe is all the information needed to confirm that I have successfully top balanced. This to me just feels most efficient.

Hello!

If the bench power supply is connected to the P- and *not* the B-/battery negative terminal, then the BMS will be able to interrupt the bench power supply charging when needed for safety.

It sounds like you have a pretty good plan already.

Gently to recommend rely on BMS to interrupt charge, not self. Attention finite, life happens

Nice selection on BMS, the overkill/JBD BMS is the best value for the money that I know of out there.

Good luck!

 

[biisty]

I just cut and pasted this from another thread I posted it in this morning:

I am honestly completely sick of the whole top balancing topic. After having done the whole parallel top balancing thing I have come to the conclusion it is a stupid waste of time and mental energy unless you dont have the money to buy this. If you dont then yes, you must parallel top balance but if you can afford the $100 dont waste the time. Install the balancer, charge the pack until the BMS stops charging, stick a bench top power supply on set to 3.65v X the number of cells in series you are charging and walk away. I have done this a couple times now and it is so easy and fool proof. No taking the battery apart and putting it back together and because it is balancing at 4 amps it is super fast.

Will this do the job?

 

[87 Dream]

Many many ways to skin the cat. Doing an initial charge helps gets the SoC levels up. All depends on how wack out of balance the 15 or 16 amigos are. But I think this is a smart way to see what you are dealing with. Beats waiting 10days with a 5A bench power supply and waiting for better days.

We need to work smarter not harder...We are in the world of efficiency aren't we??

87

 

[toms]

Slowly but surely the youtube fad of parallel top balancing is dying out.

It was only ever useful for people that had no understanding of what they were trying to achieve.

Build your battery pack in its final configuration, charge with your normal charge controller, adjust SOC of individual cells if/when required.

There are many ways of doing this, and the best way for you will depend on how aggressive your capacity requirements are, and what equipment you have available.