At what voltage your pack reaches 100%

ESK8 Electronics
115

Yeah for LiPos that makes total sense! I missed that part when I read your post last night. I thought you were using liions.

Lipos have about 10% remaining after 3.5V and yes, the internal resistance has a big effect on how fast they drop off after. Whenever we buy LiPos we request the manufacturer to send us matched cells so we never fly packs with unmatched cells. We buy Lipos from thunderpower though and they are a bit pricey.

Liions hit the cliff at ~3.1V but that by itself is more tame than the lipo cliff, also using quality cells from the same batch usually means a lower spread in internal resistance and lastly we use several cells in parallel which helps out average the internal resistance in case there is a weak cell.

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116

Ok, so I charged my battery last night until the power supply output was down to around 50ma and the voltage meter on my board showed 42v, then immediately shut off and disconnected he bms to check cell voltages.

  1. 4.198
  2. 4.202
  3. 4.204
  4. 4.205
  5. 4.204
  6. 4.205
  7. 4.204
  8. 4.205
  9. 4.204
  10. 4.205 So then I plugged the bms back in and went to bed. Today when I got home from work, I turned the bms on for a few minutes and the total pack voltage was at 41.9v I turned the bms off and disconnected it to check cell voltages again and:
  11. 4.195
  12. 4.195
  13. 4.200
  14. 4.200
  15. 4.200
  16. 4.200
  17. 4.200
  18. 4.200
  19. 4.200
  20. 4.200 So it appears that the bms with its low balancing current needs ample time to balance the pack once its fully charged. I would have liked to leave it on the charger longer to see if it would balance while charging the low cells but it got too late and I work the early shift. It also appears that one of my packs may be a little slow though 5ma difference isn’t bad Imo. I have it back on the charger now receiving 42v at currently 50ma to see if the low cells will balance up and wondering if the 4.2v cells will hold. I will update on that later. Update: So I left the pack on trickle charge (50ma) for about 2 hours and now the low cells (1and2) are at a full 4.2v And now it’s time to go ride… P.S. I think the extra 2 hours of trickle charge is totally unnecessary. Simply charging down to 50ma the first time would have been plenty good enough.
2 Likes
117

How are you measuring those? 0.005V is likely within the acceptable error of your meter

Those are perfectly balanced as far as I’m concerned. 4.200 ± 0.005V all around

118

Checked cells with this:

IMG_7160.JPG.jpeg2250×3000 1.21 MB

119

Wow that’s a great finding!

I don’t understand what you mean by “then I plugged the BMS back and went to bed”

Were you charging with no BMS at the begining? Did you change the wiring and connected the BMS back in? I’m not following… Unplugging a BMS is not easy at all as you need to solder wiring

Did you measure the cell voltages before begining the charge cycle?

120

Check out my Lipo battery build, you will see that I have quick disconects on my balance wires for each 2s pack. The bms was connected while charging then I disconnected the balance wires so I could easily check individual cell voltages. Then I reconnected the balance wires and went to bed, it was late and I work the early shift. The next day the cells where all balanced. I guess the bms was balancing them even though it was turned off. I did measure the cell voltages before the charge cycle. those results where in an earlier post.

121

I went for a long ridde tonight anfd I ran my board with my unbalanced pack until it reached cutoff start voltage which is 30V

Before the ride, this were the voltages of each pack:

  1. 4.16
  2. 4.10
  3. 4.09
  4. 4.16
  5. 3.75
  6. 4.08
  7. 4.12
  8. 4.16
  9. 4.10
  10. 4.18

As you can see the pack #5 was unbalanced way below the others, unfortunately I don’t have any way to balance that pack until I receive my Korad power supply in 20 days. Nevetheless, I went and made the test even though I knew pack #5 had high risk of getting below 2.8v

After going all the way down to 17% SoC, I felt a big drop in power, I knew I had reached cutoff start 30V (VESC Setting), so I stopped and went home. After checking the log I saw I had gone from 33.8V until 28.5V of battery because of battery sag, I knew I had gone too far and the pack #5 could have suffered a low voltage hit.

436×1795

So, I opened up the enclosure to meassure voltage for each pack and found out the pack #5 had 1.74v (sh!t) the other nines were 3.5v.

  1. 3.56
  2. 3.53
  3. 3.53
  4. 3.56
  5. 1.74 (probable cell damage)
  6. 3.53
  7. 3.55
  8. 3.57
  9. 3.54
  10. 3.57

Pack five was signifcally hotter than the rest.

I connected my brick charger (that’s the only one I currently have) and waited to see what happened. To my surprise, pack #5 started to charge pretty quick, faster than the rest, and recovered in less than 10 minutes from 1.74 to 3.3v, the temperature of the pack lowered and evened at the same temperature of the other packs, at this point I don’t know if the cells from pack #5 are damaged or not.

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I’m still charging at the moment, currently at 90% SoC but cell #5 still has a lower charge than the rest, the initial fast charging of pack 5 stopped at 30% and continued at the same level as the rest.

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As you can see pack #5 won’t reach 4.2v, it never did from day one.

My mistake was to not balance all packs before mounting the battery with nickel strips from the beggining, I though the BMS could take care of it but I was mistaken. I’m hopping I could fix it with my Korad charger otherwise if you have a better solution to balance the pack I’m open to ideas.

1000×1000

If I had the pack disassembled I could use the parallelling method described here, unfortunately the pack has already being soldered, so I’m looking for an alternate method.

1 Like
122

Keep close watch on pack #5.

123

Keep messing with it like that and sooner rather than later you’ll find yourself with a board on fire…

124

Has anyone tried charging or discharging on the individual balance leads to bring out of balance cells back in?

I haven’t had any issues with my packs but perhaps an option

125

That would be a good idea, but I guess you will need a 4.2v charger to balance the out of balance pack which I don’t have ATM.

I have these options:

  1. Disassemble the pack and use the parallelling method to get all them balanced, assemble them back again.
  2. Disassemble the pack and discharge the cells untill I get them atthe same SoC
  3. Wait until I get the Korad power supply

@PXSS I’m trying to fix this problem, I’m not sure how a cell with low capacity could potencialy lit my board on fire.

126

You could just make a simple discharge device to manually bring down the voltage of each cell. Basically you’d just attach a resistive load to the (+) and (-) terminals of one cell.

For a voltage range of 4.2V to 3.7V, a 2 Ohm resistor would give you about 2A discharge

The maximum power dissipated would be about 8.8W. Therefore you’d need to buy high wattage resistor, sometimes called a power resistor. 10W would do. 20W resistor would be better.

Something like this 20W resistor would work:

Or on Amazon Prime for USA guys: https://www.amazon.com/uxcell-Wire-Wound-Cement-Resistors/dp/B0087ZDDOU

FullSizeRender.jpg2090×3139 1.13 MB

The pins could just be breadboard jumpers. You would unplug your balance plug from the BMS, and then stick your two discharger terminals into two adjacent pins on the JST plug (corresponding to the cell you’re trying to discharge). Check the cell voltage with the DVM. Then activate the switch to apply a ~2A load to the 20W (2 Ohm) resistor. Continue draining the cell until it matches the voltage of your lowest cell (cell 5 for you @Eboosted). Turn off the switch to see resting voltage. Keep toggling back and forth until the resting voltages match.

Then do this for every cell, bringing down the voltage of each cell individually until they match your lagging cell. If done correctly, you’ve just manually balanced your pack without disassembling it. Your BMS should now be able to balance them since they are all roughly the same voltage

Note: Would be a good idea to include a fuse as well!!

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127

Charging a cell that has been over-discharged has higher chances of exploding or as manufacturers call it “venting flaming gases”. Manufacturers recommend any cell that has been discharged under 1.5V is disposed of. Who knows how many cycles you’ve over discharged your cells by now. You are playing with fire. Be careful

128

Did you get your power supply yet? I just tried to charge one of my boards with my Battery Supports 5a charger and when the battery got to 41.5v the charger switched to green light. So I disconnected that charger and plugged my power supply into the board and it resumed charging with 42v 3a output in CV mode. After about 10 min the power supply output is down to around 500ma and the battery is at 41.9 and still charging. About 1/2 hour later Now the output is at 53ma and battery is showing 42v I usually stop when the output drops to around 50ma

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129

I found that my 12S adjustable charger “cuts off” at around 0.48A (480mA). The light turns green, and the fan stops. However it is not done charging. It will continue supplying <0.5A current until reaching the set voltage. The current slowly drops off from ~450mA to 6mA over about 20 minutes, resulting in an additional ~5Wh. The battery pack then reaches within 0.01V of the no-load supply voltage

130

No. I’m still waiting for it, it might be here next weekend, so testing will have to wait a little bit.

I balanced the cells manually, lowering the higher packs until I reached the voltage of the lowest voltage pack, I used 4 parallel 12V car light bulbs connected from needles on the leads of the balancing plug.

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You can lower three consecutive packs at 12V, so the balancing process gets way faster.

4032×3024

1 Like
131

Would you mind posting picture of your charger?

132

@Namasaki if your charger stops at 41.5v I’m very convinced you have an unbalanced pack, one of them has 41.9v or 42.00v and BMS cuts the charging process leaving unbalanced cells semi empty, even though the full pack has not reached 42.00v.

You might be correcting the balancing with your lab power supply as you used it later that time.

133

IMG_3605.JPG4032×3024 1.78 MB

Power meter was not included, but I’d highly recommend one (especially if you use an adjustable charger)

Notice the green light, while it is outputting 400mA

2 Likes
134

Would you share where did you get it?