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Top balancing taking forever

sonny93

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Dec 17, 2020
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I'm having trouble getting my batteries past the 3.35V mark. 4 x 3.23V 272aH LoFePo4 Cells in parallel.
Today I changed my method to the incremental top balance (@3.4, then put psu to 3.5, then to 3.6 etc.) after waiting maybe 4-6 days setting the benchtop powersupply to 3.6V without the batteries moving up.
I came back home tonight to find that the PSU voltage had drifted from 3.4V to 3.35V, so sadly another day wasted where the batteries couldn't creep to balance

I'm growing frustrated and impatient. I hear it is meant to take a long time, but I would like to at least do a capacity test on 4 of the 12 batteries I purchased.
Is there something else I could do? Maybe charge the cells individually to 3.5V and then in parallel?
 
It can be painfully slow depending on amperage. The main voltage curve is 3.000-3.400 and between those voltages it is Sllllooooowwwwwww. but once cells reach 3.400 they can get to 3.65 quite quickly and that is when you really have to Guard Dog the charger to ensure it does NOT cross 3.650V while allowing the Amps taken to drop to below 1.0A so the cells saturate fully. Once all the cells have saturated AND settled, then top balancing them at 3.65 and again allowed to saturate until they take less than 1A as a set you'll be done. LFP will settle from 3.65 to 3.500 +/- 0.050V within 12 hours which is normal.

The only way to Speed up the process is by using higher amperage.
Charging individual cells "Top Charging" then independently is faster than doing sets of 4,8 or 16.
Then once Top Charged, doing the final Top Balancing will go quicker.
272AH cells can take up 136A charge rate (0.5C)

I did my last batch of 280's. They took 14 hours to go from 2.83V to 3.65V starting with 40A CC and ending at 1.0A being taken. This was after a full capacity discharge test. That would have taken 28 hours @ 20A or 56 hours @ 10A. PER CELL ! I use a TekPower TP1540E Benchtop Power Supply.
 
As Steve indicated, you want to get the current as high as you can with your power supply. Most of these type power supplies come with poor cables and junky alligator clips which limit the current ..... it would be a good idea to fabricate your own or at least cut off the alligator clips and put on ring terminals.

Just make sure you don't increase the current by setting the voltage too high .... always adjust the voltage with the leads disconnected.
 
I just woke up this morning to check to see if it adjusted at all. The PSU voltage dropped back down to 3.36 overnight... is this normal? I havent seen any mention of this in any of the resources or in Will's video on top balancing. What the heck is going on here?
Look at it from the bright side: the fact that it takes so long is a testament to how much energy you're really storing in the system.
How many amps are you pushing? What is your power supply capable of?
I guess that's one way looking at it, but I will also likely be drawing more than 30 watts at a time! The PSU is new and is a:

300W PS-3010DF 110V/220V 30V 10A

Really not sure what to do. If the PSU voltage keeps going down, I'm kinda stumped.


As Steve indicated, you want to get the current as high as you can with your power supply. Most of these type power supplies come with poor cables and junky alligator clips which limit the current ..... it would be a good idea to fabricate your own or at least cut off the alligator clips and put on ring terminals.

Just make sure you don't increase the current by setting the voltage too high .... always adjust the voltage with the leads disconnected.

This sounds like a good suggestion. The current is being limited by the resistance of the crappy alligator clips? Could that have something to do with the PSU voltage decreasing?
 
The PSU voltage will reduce to the level of the battery charge ..... that is normal. Those alligator clips are definitely limiting your current.
 
I don't think you have reported how many amps is actually being delivered by the power supply.

I just did the math for someone else and came up with 4x 280Ah cells assuming 50% SoC, with 4A charge rate, would take 3 days.
If you've been delivering 10A for 6 days, I'd look for a puddle of electrons on the floor. If there isn't one, I doubt current is flowing.

Once you figure out these first four, you have 8 more to go. If you have a 4s BMS with overvoltage disconnect, you can follow the instructions to first charge them in series; that will be done in 1/4 the time.
 
I don't think you have reported how many amps is actually being delivered by the power supply.

I just did the math for someone else and came up with 4x 280Ah cells assuming 50% SoC, with 4A charge rate, would take 3 days.
If you've been delivering 10A for 6 days, I'd look for a puddle of electrons on the floor. If there isn't one, I doubt current is flowing.

Once you figure out these first four, you have 8 more to go. If you have a 4s BMS with overvoltage disconnect, you can follow the instructions to first charge them in series; that will be done in 1/4 the time.
I listed the PSU above. The PSU is only capable of delivery a maximum of 10A. I have the dial set all the way to the right so Im assuming that is so how much is set.

I'm curious about the 4 series+BMS pre charge method. Do I just set my PSU to 12V and the amps to maximum?
 
I don't think you have reported how many amps is actually being delivered by the power supply.

I just did the math for someone else and came up with 4x 280Ah cells assuming 50% SoC, with 4A charge rate, would take 3 days.
If you've been delivering 10A for 6 days, I'd look for a puddle of electrons on the floor. If there isn't one, I doubt current is flowing.

Once you figure out these first four, you have 8 more to go. If you have a 4s BMS with overvoltage disconnect, you can follow the instructions to first charge them in series; that will be done in 1/4 the time.
Also, you address my core frustration with this process: I have no tools or understanding of how I can measure if something is actually happening. How do I measure if current is flowing into the batteries asides from using a multimeter to check the voltage on the batteries every couple of hours? I seem to be the only person having issue with no current actually going into the battery.
 
Also, you address my core frustration with this process: I have no tools or understanding of how I can measure if something is actually happening. How do I measure if current is flowing into the batteries asides from using a multimeter to check the voltage on the batteries every couple of hours? I seem to be the only person having issue with no current actually going into the battery.
May be you should invest in DCA Clamp on meter.
 
I listed the PSU above. The PSU is only capable of delivery a maximum of 10A. I have the dial set all the way to the right so Im assuming that is so how much is set.

Presumably you set voltage to desired level such as 3.65V while nothing connected to the supply. The display would show that voltage.

You set amperage all the way right, which probably is maximum or 10A. If supply was not connected (battery not attached yet) and you shorted the supply terminals with a wire, I would expect display to show that amperage.

Having set target voltage and current, if you connected supply to battery it would then show voltage and current at the moment.
What does it show now?

Typically, it might show 3.5V and 10A while in CC mode, later 3.65V and 7A in CV mode, later 3.65V and 1A in CV mode.

Some people have said you shouldn't run an inexpensive supply at its maximum current, because if not well designed it might fail. One guy suggested 80% which would be 8A.
 
I'm curious about the 4 series+BMS pre charge method. Do I just set my PSU to 12V and the amps to maximum?

For that to be safe (not wreck your batteries), you need to have a BMS wired to all the cells, and it needs to have something like relay or FETs that let BMS disconnect the supply. People have said to wait until all wires are hooked up before plugging the harness into BMS because otherwise they killed it.

With BMS protecting the battery, power supply voltage wouldn't be 12V (3V per cell), but rather 4x individual cell voltage, for instance 14V if you want to charge to 3.5V per cell.

Because the cells aren't balanced, one of them will exceed 3.5V before pack reaches 14V. Whatever setting the BMS has (perhaps 3.65V? You may have to program it; I've never used one) will lead to disconnect. At that point you reassemble in parallel to finish top balance.

There is an instruction on how to do this in the forum resources.
 
Also, you address my core frustration with this process: I have no tools or understanding of how I can measure if something is actually happening. How do I measure if current is flowing into the batteries asides from using a multimeter to check the voltage on the batteries every couple of hours? I seem to be the only person having issue with no current actually going into the battery.

The display on the supply should show current and voltage.

Some that I've used more recently at work (models from HP/Agilent/Keysight) have a mode where display shows voltage and current setting vs. voltage and current at he moment.

Most of the supplies just show voltage on terminals and current flowing through terminals. So we set them for voltage with open circuit and set the for current with short circuit.

The instructions I've read for some power supplies (not specialized battery charger/testers) has said that if used to charge batteries a diode is required to prevent battery from backfeeding into the supply. When those supplies are turned off they pull their output down to zero volts, and any battery with it (which can kill the supply.)

Do you have a DMM? If so, disconnect supply from batteries and measure supply output voltage. See if you can adjust it and set it to desired voltage.
If you don't have a DMM, do you have a lightbulb of 30V or less? If so, try to light it.

I hate to be the bearer of bad news (well, sometimes I enjoy it but not right now), but there is a possibility the supply got killed by the battery and that would explain no charging. It happened to another guy because he connected backwards, but it can also happen due to backfeed. If this is the case you may want to replace it with a specialized charger.
 
The display on the supply should show current and voltage.

Some that I've used more recently at work (models from HP/Agilent/Keysight) have a mode where display shows voltage and current setting vs. voltage and current at he moment.

Most of the supplies just show voltage on terminals and current flowing through terminals. So we set them for voltage with open circuit and set the for current with short circuit.

The instructions I've read for some power supplies (not specialized battery charger/testers) has said that if used to charge batteries a diode is required to prevent battery from backfeeding into the supply. When those supplies are turned off they pull their output down to zero volts, and any battery with it (which can kill the supply.)

Do you have a DMM? If so, disconnect supply from batteries and measure supply output voltage. See if you can adjust it and set it to desired voltage.
If you don't have a DMM, do you have a lightbulb of 30V or less? If so, try to light it.


I hate to be the bearer of bad news (well, sometimes I enjoy it but not right now), but there is a possibility the supply got killed by the battery and that would explain no charging. It happened to another guy because he connected backwards, but it can also happen due to backfeed. If this is the case you may want to replace it with a specialized charger.
So I tried this, and the voltage reads 3.4ish Volts when the PSU is set to 3.4V

Really don't know what's going on. I've just unpacked them from parallel and now trying to charge an individual cell @ 3.4V. The PSU is displaying the following right now:

3.41V
0.2A
0.6ish Watts
 
Presumably you set voltage to desired level such as 3.65V while nothing connected to the supply. The display would show that voltage.

You set amperage all the way right, which probably is maximum or 10A. If supply was not connected (battery not attached yet) and you shorted the supply terminals with a wire, I would expect display to show that amperage.

Having set target voltage and current, if you connected supply to battery it would then show voltage and current at the moment.
What does it show now?

Typically, it might show 3.5V and 10A while in CC mode, later 3.65V and 7A in CV mode, later 3.65V and 1A in CV mode.

Some people have said you shouldn't run an inexpensive supply at its maximum current, because if not well designed it might fail. One guy suggested 80% which would be 8A.
I completely missed this post I am very sorry Hedges. Has been so long since I've been on a forum.
I can confirm that when I short the positive and negative leads with the batteries not attached, I have the following readings when the PSU is set to 3.4V before shorting

PSU changes to CC LED
0.5V
10.42A
7.919W
 
OK, supply delivers 10A into a short.

Into battery set to 3.4V, supply is at 3.4V (CV) and current is 0.2A
That is OK, just slow to charge a 280 Ah battery.
3.4V is low, battery probably doesn't accept much current.
There is probably voltage drop across skinny wire, even at 0.2A

I would disconnect supply, turn it up to target voltage (might be 3.65V), reconnect and see what happens.
Probably a few amps, maybe 10A.
Then I would measure voltage from supply positive terminal to battery positive terminal. That should be close to zero.
If much voltage drop, use thicker wire, under ring terminal and clamped in supply terminal.
 
Ok, batterty disconnected - 3.65V set on PSU - reconnect positive and negative to single cell battery,
Reading as below
3.65V (PSU is jumping between 3.65 and 3.65 and 3.66V)
0.3A
1.092W

So I measure the voltage from supply positive terminal to battery positive terminal = approximately 102.2mV (varying)

Any further thoughts?

EDIT: Now reading on PSU
3.64V
0.4A
1.492W
 
As others have stated, if you are using the supplied alligator clips with little wires, you should switch them out for bigger wire with ring terminals. My cheapo power supply was flaky pushing any amps until I did that.

Also, are you positive you have the settings right on the power supply? You should be setting the max voltage and max amps. Mine shows settings clearly as I adjust the dials and then it jumps back to the real-time output when I stop adjusting.

Finally, do you have your BMS and the charger that you are planning to use for your battery? As others have mentioned, you can just do a quick build on the battery in series with the BMS and then charge with a real charger to push some serious amps in. I just got 16 lishen 272's yesterday and I did the initial charge with the pack in series with BMS. It charged for a couple hours at ~75a before getting close to bms cutoff. Then I put them in parallel and top balanced them this morning at 7 amps on my cheap power supply. Took about an hour to get them to 3.64.
 
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