LOOMO 2200wh MSX partial battery tear down

[Doug Hnut]

been riding this 2200wh 100v MSX  from loomo for 10,800 km in about 6 months and thought it was time to check on the battery health. with an estimated 120 cycles im still able to get 100-110km range at about 30 kph average(180lb rider) compared to 120km when new.  they supposedly used reclaimed tesla 21700 cells, but that could be new cells from a pack that didn't pass inspection. and i've seen some very questionable 1845wh 100v msx's  using a add-on pack with the BMS loosely mounted.

anyways i though i share what i found.

this is the day i got it. 24s5p with tesla cells.

this is where the BMS is

without the heat shrink wrap

       

smallest 24s BMS i have ever seen. charge only of course. there is a blank sheet of PCB separating the BMS from the cells, good!.  i would love to find a source for this tiny BMS.

from here i measured every P group voltage,  3.36V +/- 0.01v. i was impressed, especially because the pack was at gotway 5% SOC.

pic of the cell label. NCA21700T 3.7V nominal, 18.5Wh, 5000mah. which should technically make this pack 2220Wh

this is the only part i dont like, a single layer of 10mm wide nickle to pass all the current. not sure of the thickness, maybe 0.2mm?

but i guess if the pack lasted this many cycles without problems, should be ok .

since all the p group voltages were good, i decided not to tear into the rest of the pack as this is my only all purpose wheel.

 

[Mike Sacristan]

Awesome! Thanks for posting this.

Also... that is an impressive amount of riding you have done! 

[Staxkz5z6]

On 9/2/2020 at 12:16 AM, Doug Hnut said:

been riding this 2200wh 100v MSX  from loomo for 10,800 km in about 6 months and thought it was time to check on the battery health. with an estimated 120 cycles im still able to get 100-110km range at about 30 kph average(180lb rider) compared to 120km when new.  they supposedly used reclaimed tesla 21700 cells, but that could be new cells from a pack that didn't pass inspection. and i've seen some very questionable 1845wh 100v msx's  using a add-on pack with the BMS loosely mounted.

anyways i though i share what i found.

this is the day i got it. 24s5p with tesla cells.

this is where the BMS is

without the heat shrink wrap

       

smallest 24s BMS i have ever seen. charge only of course. there is a blank sheet of PCB separating the BMS from the cells, good!.  i would love to find a source for this tiny BMS.

from here i measured every P group voltage,  3.36V +/- 0.01v. i was impressed, especially because the pack was at gotway 5% SOC.

pic of the cell label. NCA21700T 3.7V nominal, 18.5Wh, 5000mah. which should technically make this pack 2220Wh

this is the only part i dont like, a single layer of 10mm wide nickle to pass all the current. not sure of the thickness, maybe 0.2mm?

but i guess if the pack lasted this many cycles without problems, should be ok .

since all the p group voltages were good, i decided not to tear into the rest of the pack as this is my only all purpose wheel.

 

Now this only bring that loose bms on the outside or are they any other bms's in the battery packs also ?

[Planemo]

Looks OK to me, nice one very similar to the Loomo add-on 18650 packs that they do/did for the 1230Wh 100v MSX to make it 1860Wh. After 10k+ km I reckon it has proved itself.

[Mantraguy]

I have a similar-looking 20S BMS on my Tesla 1500Wh that I have to replace soon (it's in the mail). Your BMS, despite being 24S, looks similar in its size to mine, but I haven't fully unwrapped mine. Yours has one set of battery connectors soldered directly to the BMS, and the other 'set' has a connector that snaps in place. I'm curious - did you follow the leads to determine which set goes to which battery pack?

 

[alcatraz]

What about the second pack on the opposite side? Are they both sharing the same one bms?

Yes 10x0.2mm of nickel is crazy. Your concern is warranted. Check the shrinkwrap in that spot if it's been overheated.

Sounds like you're riding this thing quite carefully if the power output is held down.

Thank you for sharing your findings. That's very interesting.

[Mantraguy]

I know on my Tesla V2 (the modded 1500Wh version), it is a shared BMS. There's only one BMS, and it's attached to the main (motor wire) side - it's VERY small (~3" x 1.5" or so?) and handles both packs. The second pack can be disconnected by way of a large (11-pin?) connector and, of course, the XT60.

 

[Doug Hnut]

On 2/9/2021 at 10:05 PM, alcatraz said:

What about the second pack on the opposite side? Are they both sharing the same one bms?

Yes 10x0.2mm of nickel is crazy. Your concern is warranted. Check the shrinkwrap in that spot if it's been overheated.

Sounds like you're riding this thing quite carefully if the power output is held down.

Thank you for sharing your findings. That's very interesting.

its shares one BMS. the shrink wrap shows no signs of overheating. i have taken this wheel to 75 kph(77 on euc world) and to the point of cutoff at high speeds where the pedal suddenly dips, but was able to save it. and have experienced it a few times, super scary!

ive recently checked the balance of the cells from the BMS at about 14k km and its still within +/- 0.01v. range has been much worse lately likely due to colder weather. now im at 15800 km

On 2/9/2021 at 12:07 PM, Mantraguy said:

I have a similar-looking 20S BMS on my Tesla 1500Wh that I have to replace soon (it's in the mail). Your BMS, despite being 24S, looks similar in its size to mine, but I haven't fully unwrapped mine. Yours has one set of battery connectors soldered directly to the BMS, and the other 'set' has a connector that snaps in place. I'm curious - did you follow the leads to determine which set goes to which battery pack?

 

may i ask where did you purchase your tiny BMS?

[alcatraz]

Steep climbing for a longer time is going to stress that nickel a bit more.

[Doug Hnut]

5 hours ago, alcatraz said:

Steep climbing for a longer time is going to stress that nickel a bit more.

 

does taking it to gravel mountain climbs to the point which the wheel started to tilt back due to overheating count? regardless, that single 10 x 0.2mm strip is holding up to a 175lb rider. i've read a few ampacity charts on nickel strips, and all the ratings are based off a one meter long strip. i guess the strips used on these batteries are so short the resistance is low enough to pass a large amount of current without melting anything

[Mantraguy]

On 2/12/2021 at 11:49 AM, Doug Hnut said:

may i ask where did you purchase your tiny BMS?

I have a problem with the charge circuit which I'm desperately hoping is the BMS. I think it's actually an error in the way the wheel is reporting battery voltage; it seems to read higher than actual, which seems to cut the charge circuit a bit early so I'm not fully charging to 84.0V (and therefore probably not balancing the cell groups). EUC world reads the voltage as 84.0 but multimeters and my charge doctor read it a bit lower. This started rather suddenly, and for a short time the wheel would not accept any charge through the charge lead (it has since fixed itself of that issue). All that to say that I'm getting a new BMS under warranty but I do have to replace it myself. They weren't excited at the prospect of sending a new battery (they may not have agreed to it), plus it would have to be shipped surface from China which would take 3 months. So, I opted for trying to replace the BMS myself. I think as long as I'm careful about it I should be ok; I expect I'll disconnect the leads from the batteries first, then reconnect everything to the new BMS before re-soldering the leads at the battery end. Then I'm not dealing with live connections on those tiny BMS pads. Hopefully it solves the issues I'm having. Thankfully I've been able to ride anyway, it seems to just cut the charge off by the time the charger dips down to around 1.0 amps. Previous to that it would follow a nice gradual charge curve and shut down at closer to 20-30mA.

[Doug Hnut]

5 minutes ago, Mantraguy said:

I have a problem with the charge circuit which I'm desperately hoping is the BMS. I think it's actually an error in the way the wheel is reporting battery voltage; it seems to read higher than actual, which seems to cut the charge circuit a bit early so I'm not fully charging to 84.0V (and therefore probably not balancing the cell groups). EUC world reads the voltage as 84.0 but multimeters and my charge doctor read it a bit lower. This started rather suddenly, and for a short time the wheel would not accept any charge through the charge lead (it has since fixed itself of that issue). All that to say that I'm getting a new BMS under warranty but I do have to replace it myself. They weren't excited at the prospect of sending a new battery (they may not have agreed to it), plus it would have to be shipped surface from China which would take 3 months. So, I opted for trying to replace the BMS myself. I think as long as I'm careful about it I should be ok; I expect I'll disconnect the leads from the batteries first, then reconnect everything to the new BMS before re-soldering the leads at the battery end. Then I'm not dealing with live connections on those tiny BMS pads. Hopefully it solves the issues I'm having. Thankfully I've been able to ride anyway, it seems to just cut the charge off by the time the charger dips down to around 1.0 amps. Previous to that it would follow a nice gradual charge curve and shut down at closer to 20-30mA.

did you check the output voltage of the charger while plugged in and charging? i recently diagnosed my friends MCM5 which was not charging to full. light on the charger would show green, but the voltage was 81.7v, i used my own 84v charger and it charged to 84V no problems. so he ordered himself a new charger. BTW most BMS will start to balance at 4.15V per cell. so if the voltage is at 83V or more it should start the balance process. either way good luck with the repair!

[Chriull]

5 hours ago, Mantraguy said:

I think it's actually an error in the way the wheel is reporting battery voltage; it seems to read higher than actual, which seems to cut the charge circuit a bit early so I'm not fully charging to 84.0V (and therefore probably not balancing the cell groups). EUC world reads the voltage as 84.0 but multimeters and my charge doctor read it a bit lower. This started rather suddenly

You are sure, that the volltage difference came suddenly?

It is very normal that the wheel, multimeter and CD show different values (up to some 1V). In contrary i'd be a bit surprised if all three would show the same value...

5 hours ago, Mantraguy said:

and for a short time the wheel would not accept any charge through the charge lead (it has since fixed itself of that issue)

Single cell overvoltage disables the charge port until this cell is discharged again by the balancing resistor.

So such a behaviour after a full charge could be a sign of misbalanced cells.

5 hours ago, Mantraguy said:

it seems to just cut the charge off by the time the charger dips down to around 1.0 amps. Previous to that it would follow a nice gradual charge curve and shut down at closer to 20-30mA

That's exactly the charging behaviour of misbalanced cells - as written above one cell group reaches max voltage first and so charging is stopped by the BMS.

5 hours ago, Mantraguy said:

All that to say that I'm getting a new BMS under warranty but I do have to replace it myself

Imho this makes no sense with this symptoms. Especially soldering around the BMS! Sounds like some occupational therapy...

Especially in your case the BMS is accessible - one can measure everything easily!

You should measure the voltages of the 24 cell groups once charging stopped at about 1A.

And the 24 cells once the batttery is discharged? (The more, the better)

Chances are high that after such diagnosis you are back to battery replacement and can skip the BMS PCB exchange.

At least one should diagnose the problem before starting to solder around.

[Planemo]

Can you send a pic of the 1500wh pack setup please. Like @Chriull says, I am not convinced that this is a BMS issue, nor have I seen modded Gotway wheels without the extra packs not having their own BMS'.

[Mantraguy]

Hope I'm not hijacking this thread with all this! I have 3 chargers - the stock one, 1.5A, a cheap 'fast charger' that came with the wheel, which is supposed to output 5A but really just does about 2.0-2.6A. I bought a 5.0A charger recently. All output 83.8 - 84.2V (measured with no load). I have a charge doctor and can plot a graph of the charge progress (data point every 10 seconds, including voltage, amperage, and Wh since start). The cheap 2.5A charger (supposed to be 5.0A) outputs a highly variable current - it's constantly bouncing around from 2.0-2.6A. The new 5.0A charger outputs 84.2V at 4.7A and it's a nice flat output - no bouncing around at all.

The history of the issue is this: I was charging with the 2.5A charger, and wanted to speed it up a bit so I could get out for a ride. Since the charge doctor has two input ports (accepts 2 chargers up to 10A), I plugged in the 1.5A charger as well (as I had done a few times in the past), but I had forgotten to plug it into the mains first. So it was charging at ~2.5A but when I plugged in the 1.5A charger there was some arcing and both chargers went green -  charging stopped completely. I tried charging again but the battery would not take any current from either charger. Left it overnight, tried again in the morning, no luck. I tested the output of both chargers, they seemed fine (84V +/- a bit, with no load of course). I tested voltage of the wheel at the charge port and had voltage (don't remember exactly what but it was probably around 60% charged and the voltage matched the approximate % capacity). So, I took the wheel apart, looked at the connection from the charge port to the battery, everything looked fine (continuity and voltage etc). It still would not charge through the charge port, so I took a small risk and charged it (slowly, 1.5A) through the discharge port (disconnected from the main board). That seemed to work fine, I think it may have even followed the current decline that you'd expect to see while balancing, but I can't be sure of that (it was a while ago now). I went out for a ride, came back and it still refused to charge through the charge port so I once again took the side panel off, disconnected the main board and charged through that XT60 (discharge port). Once again, worked fine. Rode again, and somehow after that it would charge through the charge port - I hadn't done anything differently, it just suddenly worked for some reason. However, since then, it has not charged with that nice smooth drop off of input current that you expect to see when it's balancing cells.

When I had the wheel apart, I measured all the cells (4P) on the pack without the BMS (definitely only one has a BMS - sorry, don't have any photos but I'm 100% certain that only one has a BMS), which I did via the 11-pin connector that joins to the main pack (those wires go to the BMS of course). All were within .01V. I then removed the heat shrink from the main pack (the one with the BMS), and measured voltage of each cell from the tabs - again, all were within .01V of each other and of the cells in the other pack. The overall pack voltage at this time was around 70%, but everything was nicely balanced.

So at this point, it would once again charge through the charge port. One thing I did notice though, is that in the past if I connected my charge doctor (essentially voltmeter) to the charge port, it read the battery voltage the same as what EUC world reports, and if I plugged in a charger at that time, the voltage stayed the same and it charged from that voltage. After the arcing incident however, if I connect the CD it shows a certain voltage, but the voltage suddenly jumps about a volt when I connect the charger. In other words, the voltage it reports under charge is about 1 to 1.2V higher than what the battery voltage measures when not charging (at rest). If it finishes charging now, with the charger connected it shows around 84.0V and EUC world app shows the same. If I disconnect the charger, the charge doctor voltage shows around 83.2V, although the EUC world app still shows near 100% (maybe 97-99) and close to 84.0V (83.8-84.0). So, I figured that when I got the arcing, perhaps I'd damaged something in the way that the BMS reports overall battery voltage so that it now reports the battery about 0.8 to 1V higher than it actually is (the charge doctor has always measured voltage about 0.2V higher than my voltmeter, and that hasn't changed since the incident so I don't think the CD is damaged). Does the BMS report voltage to the main board, or does the main board measure and report voltage directly? Like I said earlier, I don't believe it's completely balancing the cells based on the fact that it cuts voltage to zero from around 1.0 to 2.5a depending on the charger. If I use the 1.5A charger, it cuts at about 1.0A. If I use the 5.0A charger, it cuts off at about 2.5A. Battery shows 84.0 - 84.2V at that time, but then falls to about 83.2 when I disconnect the charger from the charge doctor.

It's a bit of a chore to measure cell voltage, but I can disassemble again and measure voltages before and after a full charge if you think that may help. I've been riding the wheel since then and with the exception of the charging issues, it rides fine - lots of power, the Wh I put back in seems to match what I'd expect from the length of the ride, and my range on a full charge doesn't seem any different (I usually get about 1km per %, or 15wh per km travelled).

Sorry for the long post - happy to hear any opinions!

 

[Mantraguy]

15 hours ago, Chriull said:

You should measure the voltages of the 24 cell groups once charging stopped at about 1A.

It's an 84V wheel, so only 20 cell groups.

[Chriull]

5 hours ago, Mantraguy said:

happy to hear any opinions!

This detailed descriprton now sounds more like the input protection of the bms is somehow damaged and the exchange hopefully solves the issue!

Charging "from the back" through the xt60 connector circumvents single cell overvoltage protection! So this should not be done on a regular basis - but since all of your cells where greatly balanced (hopefully) they are still and nothing happend. But you can check them once you swap the bms - you'll have to open the pack then anyhow?

 

[Meserias]

if you have time...and guts to do it.
unwrap all blue shrinking plastic and check if all cells are still soldered well at both ends.
vibrations could de-solder one or more of your cell...

[Mantraguy]

13 hours ago, Chriull said:

This detailed descriprton now sounds more like the input protection of the bms is somehow damaged and the exchange hopefully solves the issue!

Charging "from the back" through the xt60 connector circumvents single cell overvoltage protection! So this should not be done on a regular basis - but since all of your cells where greatly balanced (hopefully) they are still and nothing happend. But you can check them once you swap the bms - you'll have to open the pack then anyhow?

 

OK good - I'm happy to hear that the experts agree that the BMS may be faulty.

Yes I was aware that charging through the discharge port wasn't going to work as a longer-term solution, as it bypassed all of the protective circuitry that the BMS offers. Thankfully the charge port became 'active' again so I didn't have to do this more than twice. When the BMS comes in, I plan to test voltage of each cell group in a discharged state, then charge, and test again before I start the work of swapping out the BMS. If I find anything of concern (unbalanced cell groups etc.) I'll have to re-evaluate the overall health of the pack, but hopefully it won't come to that. 

I have a charger that can test the internal resistance of each cell group, but I'd have to do it one group at a time or in groups of no more than 3 or so at a time. Is there any advantage to doing that? It would be a little extra work but if there's a benefit to comparing IR of each group, it may be worthwhile.

7 hours ago, Meserias said:

if you have time...and guts to do it.
unwrap all blue shrinking plastic and check if all cells are still soldered well at both ends.
vibrations could de-solder one or more of your cell...

That's not a terrible idea either. Depending on how the balancing leads are soldered to the ends of the cells, just checking those may be adequate. I'll certainly have a good look at things and ensure all the connections are solid.

I don't have any of the really big heat-shrink they use on the packs, but I do have some bi-directional fibre tape that I could use. Does that sound adequate? It's similar to duct tape. I have cut the heat-shrink already; I did so carefully on a side and simply taped the two edges back together. It's obviously not as tight as it was before but at least protects the cell edges etc.

[Meserias]

that will do, one more thing.......that come in to my mind.
anyway, before take down that blue-wrap check on the internet nearby locations where you can re-solder (if case it's needed)
(it might not be necessary but at least you reduce opened time for that packs)

if you are reconnecting back (probably by re-welding) one cell make sure you don't get scared by spark because that cell could be totally empty.

 

[Torrez]

Is there anyway I can find this exact same bms .