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msx pro, bricked M50 packs and fried controller


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got the wheel for a really deal , i could tell the mosfets were blown from the resistance but wasnt expecting the batteries to be at 0 volts. i still got it for a good price though















going to see if i can bring these cells back to life

think these are the packs that burn down houses and have wanted to get my hands on one, now ive got 2 to play with :D

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Wow thats great info I believe. You might be the first person who can provide a link to the 900Wh pack fires! I'm not entirely sure what the link is personally, but I'm sure some of the gurus on here can piece together something. To get this evidence prior to a total meltdown and losing the source of the problem is gold dust information!

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B12 looks like... rust? (could have rusted after it nearly caught fire though)

You know, after the BMS is disconnected, the cells might be ok! Although, I have no idea what B12 is for and what happens if that connection open circuits.

Edited by Tawpie
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pack 2 got interesting








when pulling the nickel it started sparking on my pliers, grabbed the voltmeter






grabbed that other burnt cell and its at 3.77v


im going to go and strip the cells down


what do you think, bms shorted out ????

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55 minutes ago, Tawpie said:

Although, I have no idea what B12 is for and what happens if that connection open circuits.

B12 is just a connection point for a group of cells, and a tap for a BMS signal.

There has to be something specific with this B12 junction, given both packs have exactly the same issue. I don't think is the board per se, it's the same design as many other BMS's from GW. I still have an old 84v one at home. I must admit, the rust smacks of water damage...is it at the top or bottom of the pack? But again that could be another red herring...why don't other types of GW pack have the same problem? The plot thickens..

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theyre LG cells Paul.


12 is the series connection

if that is nickelstrip it can only handle 7.5 amps, all the amps go through that 1 piece of nickel. 100v wheel, if you pull 2000 watts thats a bare minimum of 20 amps, its also a pressure point and rusted, probably got cherry red.

inside of wheel is spotless

rest of the cells are at 0.1 volts

weird that the burnt cell group has 3.78v and the others 0.1v

going to grab a 12v bulb to make sure my voltmeter isnt acting up

ill look to see if the bat +/- is double nickel strip

2 packs would split the amps down to 10/pack

Edited by goatman
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10 minutes ago, goatman said:

if that is nickelstrip it can only handle 7.5 amps

Maybe GW changed the spec/supplier of the strip on the 900Wh packs, that double folded connection to a single point at B12 is exactly the same format as many other GW's, and is in fact the same as the Sherman too as I changed a BMS on one.

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just looking at the dividers, you can see where the nickel gets hot at batt +/- and 12s/13s , soldering will get it hot also but





out of all the batteries

7 are reverse polarity

6 are 0.00v

all the rest are around 0.1v except for 4 cells 

this is what makes no sense to me 

the 13s cells are 3.78v

both packs fried at B 12 on both packs

and the 2p cells at 13s are at 3.78v on both packs

the negative of 13s p-groups were not attached to the bms

the nickel was blown and burned the shrink, foam, cell holders and separator

do you think the bms sucked all the other p-groups down zero???

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Reverse polarity? SO you had batteries with negative charge, in with others of a positive charge? Could the gross imbalance have caused a rush of electrons to flow and pop that nickel? Apologies if that is a dumb question, I don't know much about packs.

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I have no idea if this in anyway is possible but these are my thoughts.  The mosfets blow and the wheel becomes hard to turn because some power is flowing to the magnets.  This drains the batteries. Leaving the batteries connected will completely drain the batteries. The batteries that did not drain were out of connection to the pack.  I think if you disconnect the batteries they quit draining and the wheel can then be turned normally.  I have no idea if any of this in true it is just my thoughts.   I would think it would be a good idea to disconnect batteries any time you have a blown board.

Edited by Paradox
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the current would have to flow through the bms balance leads because the circuit was severed, no?

the guy said he fell over, when he picked it up, didnt have the button depressed, the wheel free spinned and blew

blew 3 caps and 2 mosfets

it seems like the B12's were compromised from getting too hot and condensing then rusting, so when 1-B12 blew the other B-12 took all the amps and blew. how would that take out the caps and mosfets

what would have blown in the bms to drain down all the cell groups  through the balance circuit


how can all that happen in one event?

anyone that has these packs can easily check to see if the B12 has burned through, just pull the foam back a little and you  can see the hole from the outside without taking out the battery



Edited by goatman
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made up 4-1s18p packs with tinfoil and magnets



using the ebc-a20 tester started the charging process, curve looks fine, nothings getting warm




charged that first pack to 3.3v it took 5293mah and put it to the side to sit while i charge the other 3 packs to 3.3v

2nd pack is charged to 3.3v it took 5537mah

3rd pack started charging, its 1s19p

Edited by goatman
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5 minutes ago, supercurio said:

@RagingGrandpa have you seen this thread?

I'm guessing he's already on a plane to YVR so he can get up close and personal... :rolleyes: (2 meters away of course, masked, and outdoors... this is all done outdoors with a 55 gallon drum of water just out of camera view, right?)

Edited by Tawpie
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Thx for the shoutout @supercurio, indeed I hadn't noticed this topic yet, fun stuff.

Love BC, fond memories.

21 hours ago, goatman said:

both packs almost caught fire at same spot


Nah, they just blew their "fuses" ;)

... the same as mine did: 


On 12/30/2021 at 3:19 PM, RagingGrandpa said:
The pack is a fuse.
Currents >140A will quickly melt the strips and disconnect the pack.
(This 'strip fuse' melted in about 700ms with 150A, so perhaps consider an equivalence to a ~60A label rating.)
But are cells instantly damaged from this? No immediate ill effect was seen, but long-term monitoring was not done.

(If there is a severe fault at the control board, a low-resistance short-circuit, the strips in the packs will melt during the massive current that flows.)

Sorry to hear some cells died during storage, some time after the strip blew... but once the strip blows, you have to replace or rebuild the pack, so the dead cells seem not to matter at that point. 

And yes, nickel-plated steel. But it works, and it's good that it melts- it prevented fires from starting if the massive discharge would have continued.

So you're left with a good shell, motor, rim, and all the minor accessories... and then a dead controller and 96 cells to dispose of (since they have seen a 60A discharge).


Edited by RagingGrandpa
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it was the motor that i was interested in

all this testing is the bonus:D

do you think that bms is still good, it drained the cells that were attached to it

Edited by goatman
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13 minutes ago, goatman said:

do you think that bms is still good

It probably is still good, because it doesn't participate in the short-circuit current. And luckily there is no "smart" / latching logic to worry about resetting.

If you salvage it, be sure to test the balancing resistor activation for each cell group, which should activate at 4.2V and cease at 4.19V. Also check that the charger interruption kicks in when a cell gets above 4.25.

Which replacement cells will you use?


Edited by RagingGrandpa
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