V11 repair (MosFETs, fuse)

[reach]

Hi there,

I'd like to describe how I fixed my dead V11 (at least for 50 meters - read on...).
Since the donor PCB had the exactly same error pattern, I'm confident that this might work also for others, hence I share the story:

Disclaimer: you should be familiar with soldering techniques and electronics in general!
Whenever I re-connected the 2 fat battery power plugs, I took the wheel outside for that. I don't know how big the chance of fire is, but I do not want a Li-Ion battery to burn in my basement.
 

My V11 died after riding up a short steep hill. It was just a few meters and I expected not to master it (because I'm a bad rider - for the wheel it was surely well within it's specs). As expected I unmounted after ~2 meters. The wheel fell gently over and powered off. After switching on again it made a snapping noise in the electronic box at that was the last life sign. 
When rolling the dead  wheel I also felt that the motor was shorted electrically.

My dealer allowed me to open the electronic box myself to inspect the parts. Only after taking it completely apart, I saw that one MosFET was physically cracked. See picture.   
 

 

Since the spare PCB wasn't on stock I asked my dealer if I can replace the FETs myself, but he was reluctant, because he didn't know if this wouldn't harm also the top-board.
After almost 2 months (China...) I got a bit impatient so he not only allowed me to replace the parts, but also sent me a broken donor PCB.
Interestingly also this has a cracked MosFET: 

I also took some measurements on the board and found that the adjacent MosFET was also broken: while looking ok, it produced a short on all 3 pins. Same phenomenon on the other board. 
It turned out that the cheap parts tester from Banggood can nicely measure these transistors, so I could ensure that on top of not producing a short, they also actually work. 

So I took 2 working ones from the donor board and soldered them into my board and... nothing. 

A few days passed. The spare part was still sitting in China, so I took anther look and when I lifted that cardboard-like piece under the 2 big capacitors, I noticed these burn-marks on the bottom side.

 

Turns out these were from those 2 fuses underneath. While optically looking good, it was quickly found that they were blown. Also when unsoldering them, they fell apart. Cracked in the middle. Again, exactly the same on the other board. 

Since I didn't have SMD fuses at home, I took a 10 plus a 30A car fuse and connected them via a cable (since there wasn't enough room for this on the original spot) 

 

So I plugged everything together, took it outside (see disclaimer), connected the battery and... voila!! I worked!!!

Well, at least for the first 50 meters: I gently rode it, then I accelerated and stopped more and more aggressively (still talking walking-pace! Lightyears away from it's capabilities) After braking to zero (luckily) it suddenly began to shake violently, even in idle. See the video.

I had and still have no clue what's the cause. The first logical thing was to clean up that improvised tinkering solution with the fuses on the cable. Since the local electronic store didn't have SMD fuses on stock, I replaced the two 30A fuses with one 60A screw-type fuse which I just cut in pieces and used the middle "fusing" part (not sure if this is 100% state of the art, but I have nothing to loose). Looks like this:

I also intensively checked the PCB for solder droplets (solder splashed around a little during un-soldering) with a very high magnification glass. Unfortunately all this didn't help, so this is the interim end of the story. I will wait for the spare part and hope that it works with that one. Worst case my repair attempt damaged also the upper PCB but since it worked for 50m I consider this rather unlikely. Of course I'll let you know at this place hopefully soon.

Sorry for being so verbose but maybe the entire story helps to better understand the context. Of course I could also write a

TLDR: 
- measured all MosFETs for shorts
- replaced broken MosFETs
- replaced fuses

 

Of course I'd be super happy to hear if this actually helped somebody. Let me know! 

 

Cheers,
reach 

 

 

 

Edited September 6, 2021 by reach
formatting

[Lucid]

I am not sure if this helps, but I had something similar happen to mine.  It turned out that the 4 screws holding the motor to the frame were loose.  this allowed a very small amount of slop which the gyro's then tried to compensate for.  I'm at work so don't have many details, but it's been talked about in these forums, so hopefully this will at least give you something to look at/try.

[Seba]

On 9/6/2021 at 8:03 PM, reach said:

Since I didn't have SMD fuses at home, I took a 10 plus a 30A car fuse and connected them via a cable (since there wasn't enough room for this on the original spot)

You can get 30 A SMD fuses at Farnell:

https://at.farnell.com/bel-fuse/0685h9300-01/fuse-smd-30a-fast-acting-1206/dp/2848603

[Chriull]

51 minutes ago, Seba said:

You can get 30 A SMD fuses at Farnell:

https://at.farnell.com/bel-fuse/0685h9300-01/fuse-smd-30a-fast-acting-1206/dp/2848603

Maybe not the fast acting one There are medium and slow fuses, too.

[Unventor]

I am not MOSFET expert, but something I would consider in my lag of better knowledge is if you have burned MOSFETs then how many didn't fail but got strained to maybe be a weaker link on the board. 

It seems it is always the weaker link that takes the heavy strain and fails next time. 

I know from waiting on a new drive board myself, for several weeks as one of the 2 spare I needed was faulty, sucks. But it should arrive at my door this Wednesday. Unless I now jinxed it. 🤥

In general MOSFETs are in short supply right now. It is hitting many type of products.

[Seba]

3 hours ago, Chriull said:

Maybe not the fast acting one There are medium and slow fuses, too.

Fast acting are required for MOSFET protection. Still, they are not that fast

[Chriull]

5 hours ago, Seba said:

Fast acting are required for MOSFET protection. Still, they are not that fast

Yep. They'll never save the mosfets, but the wires (and surroundings).

That's what's fuses are for normally...

Ps: but of course best to stay with the fuses used originally! They should (hopefully) be designed to perform - speculations and feelings have no real impact...

Edited September 27, 2021 by Chriull

[reach]

Hi. I promised an update...:

I couldn't get it to work, but the new mainboard arrived eventually and this worked without any issues.

(Well, not really: with the new mainboard the V11 is totally toast in first place. The dealer told me that, although it does absolutely nothing, it still listens to Bluetooth. And that's correct. The Inmotion app sees the wheel, connects and guides you through the steps to activate, update and calibrate the new board and after this, voila, it works.)
 

Meanwhile, several months later, it broke again. Exactly the same problem:

 

While waiting for another spare board, I have got myself a KingSong S18 from eunicycles.eu 
Hope with 3 wheels in the house there should always be at least one in working condition :-) 

[mhpr262]

I really hope that affects only a very few V11s... Inmotion used the have a very good reputation as a quality manufacturer. That has taken quite a couple of hits lately, last but not least with the V12HS disaster.