At what voltage your pack reaches 100%

ESK8 Electronics
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.

4032×3024

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.

1522×933

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!!

1 Like
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

1 Like
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.

4032×3024
4032×3024

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?

135

Somewhere in China from @PXSS 's group buy. There were 10S and 12S versions. It has a knob on the side to adjust the voltage; so for example, I can easily set it to storage voltage, max voltage, or anywhere in between. I usually only need to charge to 4.00V/cell

1 Like
136

Somewhere in China is accurate lol :joy:

2 Likes
137

You should do a new GB @PXSS

138

I don’t think that it’s the bms stopping the charger. I think the detection circuit in the charger is stopping the charger. I Think if the bms was stopping the charge process, it would stop the power supply as well. But, to be honest, I am just speculating at this point. I am sure of one thing. The power supply gave me a full charge and a friend and I went on a very long skate and my battery still had around 38v when we where done. I know, very long skate means nothing. Sorry I couldn’t get a good Satellite signal to track the ride.

139

@Eboosted You really need to fix your welding before we can help determine what if anything is wrong with your BMS/charger combo. I think all of your problems come from bad welds within your pack.

@Namasaki is correct. Your charger is stopping itself, not the BMS

140

After I manually balanced the pack of my Reaper it has been running perfect, battery goes all the way up to 42.1v consistently, yesterday I rode it and these were voltages:

  1. 4.00
  2. 4.00
  3. 4.00
  4. 4.00
  5. 3.99
  6. 4.00
  7. 4.00
  8. 3.99
  9. 4.00
  10. 4.00

I have a second build on a Loaded Vanguard with 10S4P, on that one I was getting ABS over current fault when I pulled the throttle from a dead stop, however during the last two days, I’ve not gotten that fault anymore.

Following @PXSS advice I pulled out the battery enclosure to check bad solder joints but all those were perfect, no bad welds at all, however unlike the Reaper this one has some sag even testing on the bench, just for a split second, it goes from 42v to 40.5v on full bench throttle, maybe it’s because I have a faster (higher sample rate) battery tester, but I don’t remember this sag when I first build it, hopefully this sag it’s perfectly normal or maybe the bullet connectors connecting each pack are not a very good idea, I’m not sure though, what do you guys think?

1912×1839

Another test I did was to check at what voltage the brick charger stopped charging. As soon as it got 41.4v charger stopped, I check the voltage of each pack and got these:

1 41.4 2 41.3 3 41.3 4 41.3 5 41.3 6 41.3 7 41.3 8 41.3 9 41.3 10 41.3

So, my assumptions from unbalanced pack on @Namasaki battery were wrong, the logic of the charger just works that way.

As soon as I receive my lab power supply I’ll do all kind of tests and will start charging my batteries at 40v and 42v only for ocassional long trips.

If you guys find a brick charger with adjustable cutoff end please post the link.