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diy solar

Top Balancing "How to"

On page 3, heading 4 Top Balancing your cells, see bullet point four.
I read the answer directly on the forum thread and the author says that ultimately it doesn't matter. I also read that there could be a difference of between the DC power supply and the actual value but in this case what should I do? Take the next step towards the 3.65v target? Thank you for taking the time to answer me. As I said above, I am French and there may be difficulties reading me ...
 
I read the answer directly on the forum thread and the author says that ultimately it doesn't matter.

Please provide a link to that. You may be taking something out of context.


I also read that there could be a difference of between the DC power supply and the actual value but in this case what should I do? Take the next step towards the 3.65v target? Thank you for taking the time to answer me. As I said above, I am French and there may be difficulties reading me ...

New leads that don't allow for so much voltage drop should help. A difference of .17v is quite a lot. If you're using the alligator clips, that could be part of the problem.
 
I can tell you from personal experience, they do ship at different state of charge. Always verify.

I had multiple cells arrive above 95% SOC, and others at 50%.

I also think that sometimes the balance is counterproductive on a BMS, but don't have enough experience to say conclusively.
I know the Daly BMS does 35 milliamps of resistive balancing, and then doesn't do it continuously. It could easily take a year to balance cells like that (or even more, depends on how often it gets above 3.4v where I set the balance to start).

A top balance is just a sure way to get the SOC in cells quickly in sync. You are welcome to do as you wish with your cells, but I recommend it.
Not from what I've seen thus far with Daly, they seem to draw the 35ma off the top cells while the other cells continue charging. That doubles the balance rate actually.
 
Yes unfortunately the cables are thin!

But why does my DC power supply mark me 3.50v if in reality the cell pack is at 3.33v ??

The missing 0.17V is somewhere.
Voltage in a loop always adds up to zero (if you keep track of polarity), or voltage across battery plus voltage across positive wire plus voltage across negative wire adds up to 3.5V

First use DMM to read voltage across terminals of supply. That may be less than 3.5V because some voltage drop is inside the supply.
You've read voltage across batteries already. Now read voltage from one end of negative wire to other end of negative wire. Do same with positive wire.
Because the wires are thin, some voltage is dropped across them.
This only happens while current is flowing through the wire. As battery (slowly) charges up and its voltage increases, current will begin to decrease and voltage drop across wires will decrease. Eventually battery and supply will be same voltage. It just takes Loooonger.

I read the answer directly on the forum thread and the author says that ultimately it doesn't matter.

Drop across wires ultimately doesn't matter because it will decrease to zero. But takes longer - what does supply say for amps? If half what supply is rated for, takes twice as long.

I also read that there could be a difference of between the DC power supply and the actual value but in this case what should I do?

If due to current flow and voltage drop inside the supply wires, just wait.

BEFORE connecting supply, measure voltage of its terminals with no load. That is what voltage the battery will reach eventually.
 
Les fils aux extrémités opposées garantissent que toutes les cellules ont le même accès à la charge.

Veuillez fournir un lien vers cela. Vous prenez peut-être quelque chose hors de son contexte.
I didn't quote the right sentence, sorry.

New leads that don't allow for so much voltage drop should help. A difference of .17v is quite a lot. If you're using the alligator clips, that could be part of the problem.
IMG_20210314_160257.jpg
No alligator clip, I screwed the lugs directly onto the aluminum strip. For info I set 3.3A with 0.75mm² cables.
 
I read the answer directly on the forum thread and the author says that ultimately it doesn't matter. I also read that there could be a difference of between the DC power supply and the actual value but in this case what should I do? Take the next step towards the 3.65v target? Thank you for taking the time to answer me. As I said above, I am French and there may be difficulties reading me ...
If you are using the original leads supplied with the power supply then you will see a large voltage drop. What you are seeing is that VD, get larger leads. Keep your voltage set at 3.65 but source larger leads and you can even stack them to lessen VD.
 
Hello, I'm still calling on you! My power has reached its target of 3.50v yet when I test the cells individually they are at 3.33v ... is this normal? thank you,
Normal due to the voltage drop of your leads. Eventually the cells will test 3.65v just like your power supply. Amps will drop in the process.
 
If you are using the original leads supplied with the power supply then you will see a large voltage drop. What you are seeing is that VD, get larger leads. Keep your voltage set at 3.65 but source larger leads and you can even stack them to lessen VD.
OK, I'm installing bigger wires and keeping you posted.
 
Just tagging onto this thread - just received four new 3.2V 280ah Lishen cells that I will connecting series. Reading the pdf instructions for top-balancing, I'm wondering what's the definition of "mostly" charged, and if I need to follow that step before top balancing them. They are all at 3.22V. Is that "mostly" charged enough to go straight to step 4 and top balancing in parallel?
 
Just tagging onto this thread - just received four new 3.2V 280ah Lishen cells that I will connecting series. Reading the pdf instructions for top-balancing, I'm wondering what's the definition of "mostly" charged, and if I need to follow that step before top balancing them. They are all at 3.22V. Is that "mostly" charged enough to go straight to step 4 and top balancing in parallel?
You are in for a long wait. I very much recommend starting with series charging if you have a BMS. In series, they will literally charge 4 times as fast. 3.22v is not mostly charged.
 
Just tagging onto this thread - just received four new 3.2V 280ah Lishen cells that I will connecting series. Reading the pdf instructions for top-balancing, I'm wondering what's the definition of "mostly" charged, and if I need to follow that step before top balancing them. They are all at 3.22V. Is that "mostly" charged enough to go straight to step 4 and top balancing in parallel?

Don't think so. Check out a LiFePO4 curve, I think that is somewhere in the flat.
The idea is to get it part way up knee of the curve.
If you have patience (do the math to see what that means), you could parallel charge and top balance from where they are.
Alternatively, could build series pack with BMS and charge, then evaluate what to do next.
Maybe like Smooth Joey, top each cell of individually without disassembling the battery?
 
Don't think so. Check out a LiFePO4 curve, I think that is somewhere in the flat.
The idea is to get it part way up knee of the curve.
If you have patience (do the math to see what that means), you could parallel charge and top balance from where they are.
Alternatively, could build series pack with BMS and charge, then evaluate what to do next.
Maybe like Smooth Joey, top each cell of individually without disassembling the battery?
I think that is not a good idea for a user that is asking if 3.22 volts is mostly charged.
No offence @robpiero ☮️
 
I think that is not a good idea for a user that is asking if 3.22 volts is mostly charged.
No offence @robpiero ☮️
Hah, makes sense, I get my overkill solar BMS tomorrow, so I can do the series charging initially no big deal, nothings hooked up yet. Just wasn't sure where 3.22 was on the scale. Know I know! Thanks for the replies!
 
I think that is not a good idea for a user that is asking if 3.22 volts is mostly charged.
No offence @robpiero ☮️

Perhaps. But using a supply set no higher than 3.65V to top off individual cells by means of leads with alligator clips, seems pretty simple and safe to me. Assembling a pack with BMS and charging it once is something that has to be done anyway. Is the individual top balance approach more error prone than the usual approach of reassembling in parallel?
 
Perhaps. But using a supply set no higher than 3.65V to top off individual cells by means of leads with alligator clips, seems pretty simple and safe to me. Assembling a pack with BMS and charging it once is something that has to be done anyway. Is the individual top balance approach more error prone than the usual approach of reassembling in parallel?

One reason that could be suggested to top balance cells individually is that it avoids any connection issues. To be contrary, I would point out that it might be better to find a connection issue (uneven terminal, grit under a bus bar, etc) during parallel top balancing than once the battery is assembled in series.

For me personally, I would rather assemble the cells in parallel and commence top balancing right away. Connecting in series, then parallel, then back to series is more steps where the terminal threads could be at risk.
 
Perhaps. But using a supply set no higher than 3.65V to top off individual cells by means of leads with alligator clips, seems pretty simple and safe to me. Assembling a pack with BMS and charging it once is something that has to be done anyway. Is the individual top balance approach more error prone than the usual approach of reassembling in parallel?
The biggest real problem with charging up a single cell would be how out of balance the single cell would be when he does hook them up in series. Better to parallel charge them all until he gets his BMS, or just wait until he gets his BMS.
 
But using a supply set no higher than 3.65V to top off individual cells by means of leads with alligator clips, seems pretty simple and safe to me
Of course it does to you.
One potential problem for newbies is mixing up the polarity.
Probably won't hurt the cell much but the power supply may not like it.
 
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