Top balancing question

tsunami3775

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I originally started top balancing 2 days ago putting batteries In parallel with voltage set at 3.65 and got batteries from 3.2 to 3.3. Also the cells were balanced before starting and now they are not. I thought it was slow so I read more about it and say to start with a 3.4 charge then going higher and higher as it reached each baseline. But I’m thinking it has taken a long time and that something might be wrong? Should it take this long? Should I be doing something different?

You are correct from the pic that I used 8g wire on 2 of the batteries. Overkill solar told me I could do that since I was lacking bus bars.
 

sunshine_eggo

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Such a common problem.

You have 8 awg connections, but you've used thin wire and alligator clips from the power supply. You're trying to shove a waterfall through a drinking straw.

You need at least 10awg wire (8 if you still have it) and ring terminals. No temporary connections of any kind.

This is a perfect example of how critical quality connections are.
 

Sback

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Use a volt meter to set power supply to 3.65. Hook it back up to battery and let it run until amp drops to near 0. You may never actually hit 0 amps. As long as the battery reads 3.65 on each cell you should be good. It's also a good idea to make your own leads off of the box and get rid of the alligator clips.
 

tsunami3775

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Use a volt meter to set power supply to 3.65. Hook it back up to battery and let it run until amp drops to near 0. You may never actually hit 0 amps. As long as the battery reads 3.65 on each cell you should be good. It's also a good idea to make your own leads off of the box and get rid of the alligator clips.
Thank you
 

tsunami3775

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Such a common problem.

You have 8 awg connections, but you've used thin wire and alligator clips from the power supply. You're trying to shove a waterfall through a drinking straw.

You need at least 10awg wire (8 if you still have it) and ring terminals. No temporary connections of any kind.

This is a perfect example of how critical quality connections are.
Thanks will do
 

sunshine_eggo

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Use a volt meter to set power supply to 3.65. Hook it back up to battery and let it run until amp drops to near 0. You may never actually hit 0 amps. As long as the battery reads 3.65 on each cell you should be good. It's also a good idea to make your own leads off of the box and get rid of the alligator clips.

It's implicit, and it's stated in the guide I think the OP is using, but I'm going to reiterate that ALL voltage adjustments to the power supply MUST be made when the power supply is disconnected from the battery.
 

Dzl

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Also the cells were balanced before starting and now they are not.
Most likely not, this is a common misunderstanding. The cells probably were at or near the same resting voltage, but you received them partially charged in the middle of the voltage curve. Differences are not visible at this point, so what looks like balanced cells is just an inability to actually measure/observe whether cells are balanced or not. Its only really at very high or very low SOC that voltage differences between cells become pronounced.

I thought it was slow so I read more about it and say to start with a 3.4 charge then going higher and higher as it reached each baseline. But I’m thinking it has taken a long time and that something might be wrong? Should it take this long? Should I be doing something different?
It just takes a long time.
You've got 4 280Ah (I'm guessing) cells, that is 1120Ah in parallel, maybe they began at 30% or 50% so that means at 50% you need to add 560Ah to get them up to ~100%. It looks like you maybe have a 10A power supply, that means a theoretical minimum of 560Ah / 10A = 56hrs, but realistically you won't see the full 10A probably at all, and definitely not the entire time. From the picture it looks like current has dropped to under 1A. If you average 5A that is over 100hrs of charging. As sunshine mentioned, those little wires and alligator clips are not helping speed things along. But even with better connections/conductors, expect it to be a slow process.
 

tsunami3775

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Most likely not, this is a common misunderstanding. The cells probably were at or near the same resting voltage, but you received them partially charged in the middle of the voltage curve. Differences are not visible at this point, so what looks like balanced cells is just an inability to actually measure/observe whether cells are balanced or not. Its only really at very high or very low SOC that voltage differences between cells become pronounced.


It just takes a long time.
You've got 4 280Ah (I'm guessing) cells, that is 1120Ah in parallel, maybe they began at 30% or 50% so that means at 50% you need to add 560Ah to get them up to ~100%. It looks like you maybe have a 10A power supply, that means a theoretical minimum of 560Ah / 10A = 56hrs, but realistically you won't see the full 10A probably at all, and definitely not the entire time. From the picture it looks like current has dropped to under 1A. If you average 5A that is over 100hrs of charging. As sunshine mentioned, those little wires and alligator clips are not helping speed things along. But even with better connections/conductors, expect it to be a slow process.
Thank you! And if I add better connections like 8 or 10g wire do I put it inside here where the alligator clips came out of? I’m not sure how to make those connections.
 

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toms

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You have no idea on the SOC of a cell until it is taken to a voltage knee.

If your intention is to have the cells set up so you can reach the pack level high voltage (or “float”) voltage of your charge source without an individual cell exceeding its high voltage level then parallel top balancing is a very cumbersome way of achieving that goal.

Follow these steps instead:

1- assemble your system into its final configuration, including BMS.

2- connect your charge source, and charge the pack to its full voltage level.

3- If it reaches the full voltage without the BMS disconnecting, you don’t need to balance.

4- If the BMS disconnects, charge each cell one at a time to 3.65V. (watch the cell voltage - do not leave cells unattended unless using a high voltage disconnect)

When LiFePO4 cells leave the factory they are all at the same SOC - that is the nature of the process. If you are buying factory rejected cells (sold as A+++ on Ali ) the cells are likely to be at different SOC.

The difference may be less than 10%, and that will still not require balancing if you are charging your pack to 90% capacity.

Either way you won’t know until you have series assembled and charged your pack.

There are many ways to ensure your pack reaches full capacity - parallel top balancing is demonstrably the worst way.
 

time2roll

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Thank you! And if I add better connections like 8 or 10g wire do I put it inside here where the alligator clips came out of? I’m not sure how to make those connections.
Skip the banana plugs and use a spade or ring terminal to clamp to the power supply connector. Similar to that bar that bonds the ground and negative terminals.
 

S Davis

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My first top balance on a 12v 280ah pack took 72 hours with the 30v 10amp supply, the second was 76 hours. This is with a upgrade to 6ga wire and ring terminals.
 

tsunami3775

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My first top balance on a 12v 280ah pack took 72 hours with the 30v 10amp supply, the second was 76 hours. This is with a upgrade to 6ga wire and ring terminals.
Thanks for giving me some
You have no idea on the SOC of a cell until it is taken to a voltage knee.

If your intention is to have the cells set up so you can reach the pack level high voltage (or “float”) voltage of your charge source without an individual cell exceeding its high voltage level then parallel top balancing is a very cumbersome way of achieving that goal.

Follow these steps instead:

1- assemble your system into its final configuration, including BMS.

2- connect your charge source, and charge the pack to its full voltage level.

3- If it reaches the full voltage without the BMS disconnecting, you don’t need to balance.

4- If the BMS disconnects, charge each cell one at a time to 3.65V. (watch the cell voltage - do not leave cells unattended unless using a high voltage disconnect)

When LiFePO4 cells leave the factory they are all at the same SOC - that is the nature of the process. If you are buying factory rejected cells (sold as A+++ on Ali ) the cells are likely to be at different SOC.

The difference may be less than 10%, and that will still not require balancing if you are charging your pack to 90% capacity.

Either way you won’t know until you have series assembled and charged your pack.

There are many ways to ensure your pack reaches full capacity - parallel top balancing is demonstrably the worst way.
yah I tried the bms route but it was having problems mid charge. Started disconnecting.
 

tsunami3775

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Can you be more specific? It’s rare to have problems in the mid range.
Yah you actually helped me on another thread so I’m still working through those solutions. Now I connected the power supply to 8g wires and it won’t push out 3.65v anymore. It was with the alligator clips. Does that mean the wires too thick or the connections bad? Seems tight. Or do the wires on the power supply need to go inside the holes?
 

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sunshine_eggo

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Yah you actually helped me on another thread so I’m still working through those solutions. Now I connected the power supply to 8g wires and it won’t push out 3.65v anymore. It was with the alligator clips. Does that mean the wires too thick or the connections bad? Seems tight. Or do the wires on the power supply need to go inside the holes?

It isn't pushing out 3.65V because it can't; however, it is likely SET to provide 3.65V max. The battery is absorbing all the current. As the battery charges, you will see the voltage raise. Once the display reads 3.65V, the current will start dropping.

You are observing the desired behavior.

You should also take a moment to measure the battery directly - it should be lower than the 3.56V display.
 

tsunami3775

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It isn't pushing out 3.65V because it can't; however, it is likely SET to provide 3.65V max. The battery is absorbing all the current. As the battery charges, you will see the voltage raise. Once the display reads 3.65V, the current will start dropping.

You are observing the desired behavior.

You should also take a moment to measure the battery directly - it should be lower than the 3.56V display.
Ok thanks. Batteries before connected were 3.36
 

sunshine_eggo

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Ok thanks. Batteries before connected were 3.36

Not relevant. Battery voltage AT battery with a meter vs. what the power supply is the number you're looking for, i.e.,

With power supply connected and running, place voltmeter leads on a cell and measure voltage.

You will note the cell voltage is lower than the power supply voltage.
 

time2roll

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Yah you actually helped me on another thread so I’m still working through those solutions. Now I connected the power supply to 8g wires and it won’t push out 3.65v anymore. It was with the alligator clips. Does that mean the wires too thick or the connections bad? Seems tight. Or do the wires on the power supply need to go inside the holes?
The amps are over the PS rating so the voltage sags. This is normal and ordinary. Indicates the larger wire is working as designed.
As the cell voltages increase, the amps will taper and you will get full voltage as was set before connection was made.
 

Blackhat

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Now I connected the power supply to 8g wires and it won’t push out 3.65v anymore.

Just want to urgently reiterate something mentioned earlier, because it sounds like there may have been potential for a mistake amidst the confusion:

Set the power supply to 3.65V with the power supply DISCONNECTED from the batteries. Then connect it and DO NOT touch the voltage again.

If you adjust the voltage while the PS is pegged at 10A, you're increasing the max voltage the PS will provide but it won't show up on the screen and you have no way of knowing what it is. If it happens to exceed the max voltage of the cells, then when the cells get full the PS will just keep going and damage the cells.
 
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