Can top balancing be done this way?

[Bitbin]

As you guys can see the power supply shows 3.99 v but in reality its just under 3.5. The reason why i dont put the power supply on 3.65 it because current drops to 2 amps and the battery voltage barely moves. Im i doing something wrong or is the power supply bad? Could i charge the battery like this and just disconnect as soon as one of the cells reaches 3.65v?

Thanks.

 

[SeaGal]

Im i doing something wrong

PSU leads are not thick enough. You will also need to use proper ring connectors, not crocodile clips.

Do not set the voltage to above 3.65V

 

[S Davis]

Yep bigger wire and better connections, and don’t set above 3.65.

 

[SeaGal]

see also, @FilterGuy's excellent guide here..

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

 

[SeaGal]

Also, on closer look, unless I'm mistaken, you seem to have just wrapped a bit of wire around the other terminals and not clamped them down at all

 

[SeaGal]

Also, on closer look, unless I'm mistaken, you seem to have just wrapped a bit of wire around the other terminals and not clamped them down at all

Yikes, from your other thread I wasn't mistaken...

So, to answer your title question; that's a resounding "no".

 

[Bitbin]

Yikes, from your other thread I wasn't mistaken...

Yea it is a problem for top balancing? Saw a guy on youtube doing it. Lol

 

[Bitbin]

Yep bigger wire and better connections, and don’t set above 3.65.

Ok so my problem is the connection between the power supply and the batteries. Thanks

 

[SeaGal]

Yea it is a problem for top balancing?

Yes, a big problem. V=IR and as you have too much R, you don't have enough I for your given V

Saw a guy on youtube doing it

Don't believe everything (or anything solar related) that you see on youtube, unless he's called Will.

 

[Brett V]

Option 1:
Get proper bus bars and nuts on the batteries, all in parallel.
Use better wires between the power supply and the batteries.
Set the power supply UNLODED at 3.65 volts. Yes it will drop when you connect the batteries, that's because the batteries are taking a charge. Voltage will rise when they are approaching full charge.

Option 2:
Keep doing what you're doing and you will destroy your batteries.

 

[WrenchLight]

The cell datasheet should have the specs on what is fully charged. Usually it's something like 3.65V @ 0.05C rate. So 0.05C rate would be for example if you had a 100Ah cell, 0.05*100=5A. So in CVCC charge mode, after the cell is in constant voltage at 3.65V, once the cell current gets down to 5A, it's at 100% and then you need to stop charging. You can over-charge a cell even if the voltage doesn't exceed 3.65V.

If you swap the direction of every other cell, you can use busbars.

 

[time2roll]

As you guys can see the power supply shows 3.99 v but in reality its just under 3.5. The reason why i dont put the power supply on 3.65 it because current drops to 2 amps and the battery voltage barely moves. Im i doing something wrong or is the power supply bad? Could i charge the battery like this and just disconnect as soon as one of the cells reaches 3.65v?

Thanks.

Sure people do this all the time. And frequently miss the mark and the cells are at 3.8+ in the blink of an eye.
At 3.500 all is very close. Remove the power and set the voltage to 3.650. Then reconnect and wait. #10 wire and ring terminal would be faster.

With those flimsy cell to cell connections this is a good time to verify all cells are actually the same voltage. Or just tighten them down.

 

[Bitbin]

Thanks guys

 

[740GLE]

What BMS do you have?

I’m in the camp of skip top balance (that’s so 2018), assemble the battery with BMS providing balancing and over voltage protection, place it in service and let the balancer sort out the cells.

 

[Pierre]

What BMS do you have?

I’m in the camp of skip top balance (that’s so 2018), assemble the battery with BMS providing balancing and over voltage protection, place it in service and let the balancer sort out the cells.

I agree , but you need a decent balancer like a Heltec 5amp or so. Most bms’s only balance under 100mA.

 

[740GLE]

I agree , but you need a decent balancer like a Heltec 5amp or so. Most bms’s only balance under 100mA.

Drop the Daly and JBD, any JK with 2a balancer will get a 4s in tip top shape after a couple hours after cells crest 3.4v

Remember top balance only about shifting around that 1% or so of capacity.

To much can go wrong with feeble attempts in “top balancing like my grandfather used to do” as can be shown in the OP initial post.

IMO that top balance procedure should have a caveat that there are better ways than to follow these steps.

 

[Bitbin]

What BMS do you have?

I’m in the camp of skip top balance (that’s so 2018), assemble the battery with BMS providing balancing and over voltage protection, place it in service and let the balancer sort out the cells.

I have a tdt 8s 100ah with passive balancer. No jk bms where i live. I could connect a 2ah active balancer but havent. They seem to balance fine right now.

 

[S Davis]

Ok so my problem is the connection between the power supply and the batteries. Thanks

And to the cells, you need even charging to balance and with the wire wound around the posts like that you will not get it.

 

[740GLE]

I have a tdt 8s 100ah with passive balancer. No jk bms where i live. I could connect a 2ah active balancer but havent. They seem to balance fine right now.

That low a voltage you have zero visibility if the cells are balanced, one could be 10-20% difference in SOC.

From what I’ve seen from your too balancing configuration, I’d say your attempt at top balancing may have caused more unbalance that balancing.

Once cell voltages are above 3.4v then you’ll know what you have.

Also a low current balance BMS will still keep things in check, you just gotta give it time, lots and lots of time.