GotWay charging questions

[SirGeraint]

I know the battery packs continue to charge for a 'little' while after the Charger LED turns green but should it continue for 3 hours after (and still going)?  If not, what would cause it to do this?

Also, do the small components (the 16 rows of transistors, resistors, etc) on the BMS normally get too hot to touch?  If not, what would cause it to do this?

Does GotWay use the same values for all of the components on the BMS for the 170Wh pack (16SP1) as they do on the 340Wh pack (16SP2)?

Here's the results from the Charge Doctor:

  9:37     66.7V    0.54A     0.0Wh
  9:45     67.4V   0.44A    5.0Wh
  9:53    67.5V     0.38A     8.7Wh
 10:01    67.5V    0.33A    11.9Wh
 10:09    67.5V    0.27A    14.8Wh
 10:15    67.5V    0.26A    16.5Wh   LED on Charger turns green
 10:19    67.5V    0.25A    17.6Wh
 10:27    67.5V    0.24A    19.6Wh
 10:36    67.5V    0.22A    22.0Wh
 10:44  67.5V    0.21A    23.9Wh
 10:53  67.5V    0.20A    26.0Wh
 11:02    67.6V    0.20A    28.1Wh
 11:10     67.5V   0.19A    29.9Wh
 11:17    67.6V    0.19A    31.3Wh
 11:24    67.5V    0.19A    32.8Wh
 ....
 11:56    67.5V    0.17A    39.4Wh
 ....
 12:13  67.6V     0.17A    42.5Wh
 12:21    67.6V    0.17A    44.1Wh
 12:29    67.6V    0.17A    45.5Wh
 12:39    67.6V    0.17A    47.6Wh
 12:47  67.6V    0.17A    49.0Wh
 12:56  67.6V    0.17A    50.8Wh
 13:04    67.6V    0.17A    52.3Wh
 13:15  67.6V    0.17A    54.4Wh
 13:24    67.6V    0.17A    56.1Wh

 

Thanks

[zlymex]

Yes, battery packs continue to "charge" for as long as the charger is in power. In another world, the charging current will be approach to a small but none zero value. The reason for this is the BMS balancing circuit which consume certain amount of current at charge end. It is my suggestion to charge this way(continue to charge 3 hours after the Charger LED turns green) once every week so that the batteries remain balanced.

Those small components (the 16 rows of transistors/MOSFETs, resistors, etc) are main part of the balancing circuit and consume this amount of current.
The main component of a typical charge balancing circuit for a cell is the charge balancing IC represented by HY2213-BB3A
I cannot find the data sheet in English so I just explain a little.

The IC itself consumes very little current(3.5uA max) and monitors the cell voltage continuously. Once it reaches 4.200V it will turn on the MOSFET and bypass certain amount of current from the cell.
The amount of current bypassed depends on the resistor Rbn and is 4.2V/Rbn (neglect the on resistor of the MOSFET).
For Gotway MSuper2(I had dissembled the battery pack), the resistor value is 75 ohms(two 151 in parallel) making the balance current of 4.2/75=56mA. Therefore, the total power consumption of a battery pack is 16*4.2*4.2/75=3.76Watts. This will make the pack very warm if you continue to charge for several hours after the light turns green.

I don't have a 170Wh battery pack from Gotway and I haven't seen any inside photo. I guess the balancing circuit for 170Wh is the same as that of a 340Wh. I have several other BMS boards or BMS photos and they look very similar except the value of the bypass resistors may be different.

As for the remaining 0.17A current, it's quite normal for a 850Wh Gotway owning to there are three packs and each pack consumes 0.056A.
However, if the EU is a 680Wh, it's a little higher than normal. The reasons might be:
--- error reading by Charge doctor
--- the current consume by Charge doctor also counted in
--- faulty BMS
--- EU leakage current
--- battery leakage

BTW, IPS adopts different balancing circuit(MAX14921).

Edit: Add a photo showing balancing circuit of a BMS board. The balancing current would be 4.2/68=0.062A.

[SirGeraint]

Thanks a bunch, @zlymex.  That helped a lot.  I knew you would know this. 

[SlowMo]

14 hours ago, zlymex said:

Yes, battery packs continue to "charge" for as long as the charger is in power. In another world, the charging current will be approach to a small but none zero value. The reason for this is the BMS balancing circuit which consume certain amount of current at charge end. It is my suggestion to charge this way(continue to charge 3 hours after the Charger LED turns green) once every week so that the batteries remain balanced.

I am afraid to let my charger stay after the light turns green after hearing these news about exploding hoverboards while charging. How do we keep an eye to prevent this from happening?

[zlymex]

32 minutes ago, SlowMo said:

I am afraid to let my charger stay after the light turns green after hearing these news about exploding hoverboards while charging. How do we keep an eye to prevent this from happening?

There are reasons why battery exploding, namely following three points must be met at the same time.

1. Overcharge or excessive discharge(including short circuit).
Overcharge may result from faulty BMS and/or faulty charger. Excessive discharge may result from faulty BMS or faulty EU(if no output protection on BMS).

2. There is no safety switch in the cell or faulty switch
Every normal 18650 cell has a built-in safety switch and will switch the cell off when over temperature to prevent further charge/discharge.

3. There is no safety vent in the cell or faulty vent.
Every normal 18650 cell has a built-in vent and will open when internal pressure is too large to prevent explosion.

Therefore, good battery, good BMS and good charger are the three basic elements for safety. Good EU manufactures have invested a lot on these safety aspects so there is no need to worry about when charging. Having said that, my advise are put the EU and charger away from flammable materials and better not leave them unattended while charging.

[SlowMo]

Very good explanation! Thanks @zlymex! I would suggest these post be pinned for all to understand.

[playdad]

Well at least it now seems like Water can be used to put out Lithium Ion fires? Seems like they previously said water wouldn't work but that may only be the case for Lithium metal.