Top balancing taking forever

[blutow]

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

If your power supply is really set on 3.65v and 10a and it's showing 3.64 and .4a, the cell should be done unless you have a connection issue or the power supply has a problem. What voltage does the cell read if you put a multimeter on it? Also, does your power supply have an indicator whether it's in CC or CV? I assume it's in CV based on what you are describing.

 

[Hedges]

0.3A

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

0.1022V/0.3A = 0.34 ohms.

Too much resistance. Get a thicker wire, at least 12 awg, and put a ring terminal on it. Ring under battery nut, and other end in binding post on supply. Same for both positive and negative.

Make sure all battery nuts are snug.

(possibly, scrubbing aluminum terminals and busbars to remove oxide would help.)

 

[Hedges]

If your power supply is really set on 3.65v and 10a and it's showing 3.64 and .4a, the cell should be done unless you have a connection issue or the power supply has a problem. What voltage does the cell read if you put a multimeter on it? Also, does your power supply have an indicator whether it's in CC or CV? I assume it's in CV based on what you are describing.

0.1V drop from supply to battery. Probably another 0.1V back on negative.
He has 1.65V at the supply and 1.45V at the battery, and it's taking 0.3A

 

[sonny93]

0.1022V/0.3A = 0.34 ohms.

Too much resistance. Get a thicker wire, at least 12 awg, and put a ring terminal on it. Ring under battery nut, and other end in binding post on supply. Same for both positive and negative.

Make sure all battery nuts are snug.

(possibly, scrubbing aluminum terminals and busbars to remove oxide would help.)

Your quick maths is greatly appreciated! By the sounds of things the next step is to make some quality cables. I will report back with an update once I've tested this out.

 

[charly]

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.

What charger did you use initially?

 

[sonny93]

Team, this really SUCKS. I am pretty frustrated. Does anyone else have these issues? Still testing trying to charge one lifepo4 battery up to 3.4V
I swapped the wires for a thicker one and added ring terminals. I reduced the voltage drop between the positive of the PSU and the positive on the battery far closer to 0.

Here are some tests. At first I thought things were going to work, but I woke up to find the battery had reduced in voltage since I began charging again.

3.355V on battery @1:22pm 2/03/2021

attached terminals, PSU reads
3.41V
AMPS is jumping around but is now averanging readings such as 1.97, 2.0, 1.6, 1.7, 1.85

Time @ 7:27PM 2/03/2021
PSU reads
3.4V but is ocassionaly dropping to 3.39V
1.1-1.4A

Timw @2:02AM 03/03/2021
PSU 3.41V
1.35,1.57,1.59,1.43,1.49,1.63,1.58,1.54

Just woke up this morning to check to see how it's going
Time 10:39AM 3/03/2021
Wake up to see PSU is at 3.33
Amps at 0

Unplugged the terminals and measured the battery which reads 3.342V
So since yesterday at 1.22pm, it went from 3.355V down to 3.342V.

what.
Going to reset the PSU to 3.4V and see what happens this time.

 

[sonny93]

Ok so test #2 with the new cables.
PSU is at 3.42V, ocassionaly jumping to 3.43V
2.5,2.6,2.7A, jumping around

007.8mV between Positive PSU and positive battery terminal

 

[Hedges]

If PSU is set to 3.4V and 5.0A, then the 2.5 or so amps is what the battery wants.

You could disconnect supply, readjust it to 3.6A, reconnect supply. Then the battery might take more.

Or, so long as it is taking several amps, just be patient. Charging is happening.

 

[sonny93]

If PSU is set to 3.4V and 5.0A, then the 2.5 or so amps is what the battery wants.

You could disconnect supply, readjust it to 3.6A, reconnect supply. Then the battery might take more.

Or, so long as it is taking several amps, just be patient. Charging is happening.

Thnanks for your input Hedges. Ok, unplugged, I reset the PSU to 3.6V, turned it off, connected the terminals and switched the PSU back on.

PSU Currently reading 3.61-3.62V
Roughly 8 Amps.

 

[Bob B]

If the cell is at 3.42V and the power supply is set to 3.65 .... before connecting it ..... that is only .23V of differential. So, at Hedges say ..... probably just more patience required.

If you have a 1 ohm 50 Watt resistor, you could test the power supply. Set the output voltage to 5.0 volts and then connect it to the resistor and see if the power supply can push 5 amps.

 

[Bob B]

Thnanks for your input Hedges. Ok, unplugged, I reset the PSU to 3.6V, turned it off, connected the terminals and switched the PSU back on.

PSU Currently reading 3.61-3.62V
Roughly 8 Amps.

There you go

 

[sonny93]

Great news all. I arrived home at 2:40am to find the PSU was at 3.5V and the amps reading 0AMPS

Unplugged the terminals from the battery and the battery read 3.508V!! Woohoo. I'm going to update my opening post with the solution once I successfully charge the 4 batteries together in parallel. Thanks Hedges for your assistance.

Conclusion: The skinny alligator wires provided with cheap PSUs are too thin and create too much resistance to supply current to the batteries while top balancing. Get a thicker wire, at least 12 awg, and put a ring terminal on it. Ring under battery nut, and other end in binding post on supply. Same for both positive and negative.

 

[sonny93]

Oh no! Looks like it worked too well. It charged one battery to 3.72V, one battery to 3.66V
How do I discharge these to avoid further damage sitting at that voltage?

 

[Hedges]

Put a suitable resistor or lightbulb on it.
It should come down to safe voltage fairly quickly (you can calculate what to expect), then be stable in the middle. Disconnect long before it approaches low SoC.

But don't understand how you got 3.72V on a cell after applying a 3.5V supply.
Did you just connect in series with a BMS? Is the BMS reading bogus voltages that don't match DMM readings of cells?

 

[sonny93]

I woke up to find the PSU had jumped to 3.8V overnight.... I think it is due to the temperamental nature of these amazon things. I had a few other days where I had it set to 3.4V and it had jumped to 3.66V. Pretty annoying. Connected in parallel.

I'm thinking of assembling in series and discharging with an inverter (don't have, but going to go buy a 500W one now). Not sure if this will work though as the BMS will trip the disconnect.
What size ohm resistor would I apply for a 3.2V battery discharge?

 

[Hedges]

If you had 1 ohm 10 watt, that would draw 3A and burn 10W. Blow a fan over it.

120V 100W incandescent bulb is about 120 ohms or slightly higher when hot (to draw a bit under 1A) but cold is about 1/10th that resistance.
So around 10 ohms, will draw 1/3A or 1W. If you have a lamp with 3 bulbs or one 3-way bulb up to 300W, then you'd get 1A for 3W.
Alligator clips from power cord to cell?

Toaster or other heating appliance doesn't change in resistance as it heats up.
A 1200 heating device would draw 10A at 120V, 0.3A at from the cell.
Don't use one with a fan because the fan won't like DC.

 

[sonny93]

If you had 1 ohm 10 watt, that would draw 3A and burn 10W. Blow a fan over it.

120V 100W incandescent bulb is about 120 ohms or slightly higher when hot (to draw a bit under 1A) but cold is about 1/10th that resistance.
So around 10 ohms, will draw 1/3A or 1W. If you have a lamp with 3 bulbs or one 3-way bulb up to 300W, then you'd get 1A for 3W.
Alligator clips from power cord to cell?

Toaster or other heating appliance doesn't change in resistance as it heats up.
A 1200 heating device would draw 10A at 120V, 0.3A at from the cell.
Don't use one with a fan because the fan won't like DC.

Thanks Hedges, using the resistor brought down the voltage. I have cells close now at 3.592V and 3.570V, and another two
I'm going to top balance the other two which now sit at 3.342V and 3.338V. After all cells are close within range, I will set PSU to 3.65V and watch very closely ><

I believe my mistake was reconnecting all batteries in parallel and charging last night while 1 cell was already at 3.5V before the others. Other cells would have been at 3.3V, and due that magical SOC graph that I only intuitively understand, the higher charged cell would have charged more quickly?

As for the PSU jumping to 3.8V overnight, I'm not exactly sure. My explanation is that perhaps due to the lower quality of these benchtop supplies their voltages can jump over. Or perhaps it can be explained in the context of one cell charged higher than the others?

One thing to point out that I did notice last night was that when I attached the ring terminals at 3.65V on PSU, the power supply swapped over to CC instead of CV. I switched it off, disconnected and brought the PSU to 3.6V instead. Reconnected and returned it to CV. Wasn't sure if this was an issue, it was just something I hadn't encountered as of yet using these devices so wanted to be on the safe side.

 

[Bob B]

I woke up to find the PSU had jumped to 3.8V overnight.... I think it is due to the temperamental nature of these amazon things. I had a few other days where I had it set to 3.4V and it had jumped to 3.66V. Pretty annoying. Connected in parallel.

I'm thinking of assembling in series and discharging with an inverter (don't have, but going to go buy a 500W one now). Not sure if this will work though as the BMS will trip the disconnect.
What size ohm resistor would I apply for a 3.2V battery discharge?

Are you certain you always adjusted the voltage before connecting the leads .... then no changes to the power supply after connecting?

Sorry ... but had to ask. The mistake most people make is to make changes to the power supply after connecting it to the battery.

 

[Hedges]

Some supplies let you also set an over-voltage. Some let you lock the setting. I saw such features in the manual for one of the cheap supplies being used by a forum member. See if you've got that available. Blue tape if nothing else. And then check with a DMM. 3.6 and 3.8 look pretty similar on a 7-segment display.

 

[Zwy]

Thanks Hedges, using the resistor brought down the voltage. I have cells close now at 3.592V and 3.570V, and another two
I'm going to top balance the other two which now sit at 3.342V and 3.338V. After all cells are close within range, I will set PSU to 3.65V and watch very closely ><

I believe my mistake was reconnecting all batteries in parallel and charging last night while 1 cell was already at 3.5V before the others. Other cells would have been at 3.3V, and due that magical SOC graph that I only intuitively understand, the higher charged cell would have charged more quickly?

As for the PSU jumping to 3.8V overnight, I'm not exactly sure. My explanation is that perhaps due to the lower quality of these benchtop supplies their voltages can jump over. Or perhaps it can be explained in the context of one cell charged higher than the others?

One thing to point out that I did notice last night was that when I attached the ring terminals at 3.65V on PSU, the power supply swapped over to CC instead of CV. I switched it off, disconnected and brought the PSU to 3.6V instead. Reconnected and returned it to CV. Wasn't sure if this was an issue, it was just something I hadn't encountered as of yet using these devices so wanted to be on the safe side.

If you cells in parallel and connected with busbars and you had good clean connections, it is virtually impossible to charge over 3.65v if you had the PSU set to 3.65v on CV.