Inmotion V12 MOSFET board replacement - Walkthrough & lessons learned.

[Richardo]

Overview

After my low speed cutout ewheels offered to ship a replacement board if I preferred, and because this was before much was known about the issue, and because I had no idea what I was getting into, I said yes. Also I didn't know our first baby would do her jailbreak while I was doing this thing. It was a lot of work and even though I'm 'handy' it would have been a better decision to mail the wheel back for repair. I'll go into more detail below.

 

Other Resources

 

Going into it, here was the documentation I had available:
* https://youtu.be/Lromtvbd0VA Inmotion's video of the replacement
* https://youtu.be/rzdvh_1zRLg Wrong way's teardown
* https://youtu.be/86LHfrcoXPE Inmo's fast forward factory teardown
* ecodrift. ( thx @Chriull)

Tools Needed

* 2mm hex
* 2.5mm hex
* 3mm hex
* 4mm hex
* phillips driver
* long-ass thin screwdriver for tapping out pedal axle, or vise grips for pulling it out.
* non-conductive thermal paste
* ideally you will have new, thick thermal pads. I don't know the dimensions, but some very thick like 5mm and some very thin possibly sub-1mm. If anyone knows the actual size of the thermal pads used, dm me and I'll update this post.
* masking tape or some way to label every screw hole and cable you disconnect. plus something to write with.
* a tiny, tiny pry thing like flathead screwdriver smaller than would be in a glasses repair kit. Two would be even better if you had a helper
* needle nose pliers or something to manipulate tiny cable connectors where fingers don't fit
* maybe some glue to repair broken connectors. I used superglue
* a way to organize all the screws you remove. I used 8 different plastic baggies

If I saw someone write all these requirements for organization, I might think "I don't NEED that I can remember it or figure it out" - boy that would have added a lot of time and frustration to the reassembly. Even doing it a second time, I would still make myself organize and label everything.

 

The Process

0. Note: I labeled the screw holes with a number, and each number associates with the type of screw that goes in that hole. The types are pictured at the very end of this section 

1. First, loosen the 4mm set screw holding the pedal axle in place.👇

 

2. Then tap your pedal axle out👇

 

3. when my tapping' screwdriver wouldn't send the axle out far enough, I grabbed it with a vise grips and tapped the grips 👇

 

4. pop your pads off at a corner, and then unclip them the rest of the way. make sure you're lifting the rigid plastic underneath the foam.👇

 

5. label and unscrew all the screws on the perimeter of the side case. No pic here my bad. Check the first inmotion video in 'other resources' section

6. Label where all the screws from under the pad go- for this round. there are more, later! 👇

 

7. rear bumper- screws in green, and after they're removed from both sides of the board, unclip the clips (orange tape)👇

 

8. front bumper. screws on the left and right side marked with green tape, and the clips are the orange tape 👇

 

9. recessed screws to get the trolley handle assembly off. 3mm and include a washer/spacer thing 👇

 

10. more screws (green) and clips (orange to remove trolley handle👇

 

11. Led board thing from the 2nd batch of wheels👇

 

12. lots of cables to match up on this board, label the wires & connectors. Hope you don't end up with a side led control switched with a front/back strip.👇

 

13. speaker connector removal- the socket part didn't seem attached to the board at all, and pulled away from the pins. When I reassembled it, I put a drop of cyanoacrilic glue on the socket, pushed the socket over the pins (noting orientation on the board silkscreening) and waited for it to dry. Afterwards I reattached the cable to the now-glued socket. Not sure if this was a great idea, because the non-conductive glue might interfere with the pin connection. Seems to have worked though. This is where you'd want to use a tiny pry thing to pop the very-fragile clip on the socket and release the plug. Also might need needle nose pliers to glue it onto the board or push the cable back in. And maybe you could avoid this whole thing by leaving the little LED daughter board attached? I just though of this now and don't know if it'd work. 👇

 

14. these deeply recessed screws to attach the controller heatsink to the rest of the wheel seem like they'll stay in place, till they fall out and hide from you under your washing machine. for an hour! 👇 

 

15. load of cables to keep organized, though they can be mostly 'reasoned' out during reassembly.
NB the LED wires connect to that little controller board when you reassemble- even though they fit directly in connectors on the main board. Don't forget about the daughter board.
NB the Hall effect wire connector is sort of hidden under the blue/green/yellow motor phase wires. 
NB the silicon housing for the phase wires can be inverted/turned inside out to give you access to that area without breaking the glue seal around the wires. Also, you can pull on the colored heatsink to get the phase wires out of their sockets— but the Hall effect connector needs careful treatment and delicate connector-prying 👇 

 

16. good to keep everything labeled! can you imagine how annoying it would be to reinstall the old, busted board? 👇 

 

17. photo of broken board. Note the capacitors on it- the model and physical size (but not the electrical figures) changed on the replacement board 👇 

 

18. video of the broken board connected like inmotion asks👇 

 

19.  new board. the mosfets were bent in shipping which I pray didn't put micro fractures in the wires. Here is also where I realized I'd need thermal paste to complete this. Add another delay.

NB- pay attention to where the thermal pads are when you transfer them to the new board- it doesn't come with them, and I had to guess for the tiny one in the lower left. Pay particular attention to how close the long pad is to the mosfets, when I reassembled it mine squeezed out to touch the MOSFET pins. Or almost touch them. It's silicone and nonconductive but still makes me feel a sense of foreboding 👇 

 

20. the shield for the board/heatsink assembly is fragile. Don't torque these screws too much!👇 

 

20.5. Spaghetti!

 

21. replacement board already had thermal paste on the sides of the mosfets somehow? maybe a factory test.👇 

 

22. the insulator between mosfets and the heatsink. a very important piece of plastic!👇 

 

23. These motherfuckers didn't line up exactly, but it wasn't a struggle to screw them back down. 
NB the insulating washer on the MOSFET screws is fragile and can crack easily👇 

 

24. insulating washer on MOSFET screw 👇 

 

25. fastened mosfets
NB - after replacing then, use a continuity tester or the diode testing mode on a multimeter to check for continuity between the heat sink of the MOSFET and the black screw. I think the wheel will break if current can flow between the two.
NB - while testing, avoid touching the gate lead (center) of  the MOSFET. That's sensitive to current and I believe even static electricity can be enough to damage it.👇 

 

26. hard to see rating of the new capacitors, but appears to be the same. The numeral you can hardly see due to my photography is a '6' not a '5' 👇 

 

27. video of replacement board in inmotion test. 👇 

28. Check your pedal hangers while you have your tools out.. Despite the thread locker, mine were loose enough to move with my fingers- and there are  reports on the forum from other people with loose hangers, too. 👇 

 

29. Here is one example of why it's worth labeling every screw on every part- there are through-holes that are indistinguishable from the places you should actually put a screw. If you screwed the front bumper on using this hole then you'd be blocked from putting the side panel on. 👇 

 

30. Here are the screw groupings I made:

 

 

Outcome

 

Concluding thoughts

As you may be able to imagine, my brain isn't think good right now to summarize anything. Let me know if you find any errors or have suggestions. I haven't ridden it yet (snowy outside) or done the 'stress test'. Here is a pic of our dog meeting our daughter for the first time!  He's quite solicitous and waits by her crib to let us know whenever she makes a sound. Hope this post helps some of you.!

 

Edited January 21, 2022 by Richardo

[Tawpie]

Nicely presented, and congratulations on the family addition!

Do you dare stress test the replacement board?

And yes, MOSFETs are static sensitive and can be damaged if they're zotted. It doesn't take an actual ZAP with spark to do them in, a discharge that you wouldn't ever notice can be sufficient. It's highly recommended to always wear a static protection wrist band when working with them (a real one, with the in line safety resistor, they aren't that expensive).

[RArtem]

Actually, you can easily screw off pedals with hangers with 4mm ballhead hex wrench. No need to remove axle.

[Chriull]

6 hours ago, Richardo said:

* that Russian site's post if I googled. 

Just for completenes the link for the v12 articles there: https://ecodrift.ru/tag/inmotion-v12/

6 hours ago, Richardo said:

non-conductive thermal paste
* ideally you will have new, thick thermal pads. I don't know the dimensions, but some very thick like 5mm and some very thin possibly sub-1mm. If anyone knows the actual size of the thermal pads used, dm me and I'll update this post.

For thermal pads no thermal paste is needed - in contrary it's counterproductive. As in the link of the thermal pad you provided is written "Ideal Gap Filler"

Thermal paste is just needed to fill the "micro gaps" by the roughness of hard surfaces like metal and cermics/mica. And for this only in a minimal dose - every bit of thermal paste separating the metal and ceramics/mica decreases thermal conductivity!

6 hours ago, Richardo said:

21. replacement board already had thermal paste on the sides of the mosfets somehow? maybe a factory test.👇 

If it was already hard/dry then it sould be scraped/grinded/polished off!

Thermal paste just has a better thermal conductivity than air to fill out these micro gaps! But compared to the metal pieces the thermal conductivity is almost like a thermal insulator.

6 hours ago, Richardo said:

22. the insulator between mosfets and the heatsink. a very important piece of plastic!👇 

That's the "important real thermal pad". Unfortionately here (?all/most?) manufacturers combine thermal pads and thermal paste.

Best solution here would be an ceramic insulator (some kind of special ?Aluminium oxide?) followed by mica. For both of this thermal paste is needed. There afaik exist also very nice thermal pads (coming up to mica?)- which could be a nice upgrade.

Unfortionately there also exist many real bad thermal pads...  Like hopefully here no "piece of plastic" was used to just insulate!

6 hours ago, Richardo said:

NB - after replacing then, use a continuity tester or the diode testing mode on a multimeter to check for continuity between the heat sink of the MOSFET and the black screw. I think the wheel will break if current can flow between the two.

Exactly!

Edited January 18, 2022 by Chriull