Finding and Replacing Blown Motor Controller Mosfets

Finding and Replacing Blown Motor Controller Mosfets

In this video Phil illustrates the process he uses at Grin for identifying and replacing shorted mosfets in an ebike motor controller.

Mosfet usually fail when they have to deal with sustained high amperage that generates more heat than they can dissipate. They can also fail from exposure to excessive voltages on the wrong pins or electrostatic discharge.

A well engineered controller will use temperature sensors to limit the current through a mosfet if as it overheats to prevent a catastrophic failure in use, but many systems don’t have this intrinsic protection and instead on the motor and bike parameters to generally not overstress the component in normal use. As a result, it’s not uncommon for people who push their ebike systems to the limit to find themselves dealing with mosfet repairs in the process.

When they fail it is almost always in a short circuit. On a bike with a direct drive hub motor this results in a heavy cogging and chugging whenever the wheel is turned.

Fortunately a repair is often possible as Phil shows. If it is only one mosfet that is blown, the odds are good that a mosfet replacement alone will fix things. But if both the high and low side mosfets of a motor phase our blown, then that usually indicates damage that has also propagated down to the mosfet drivers and other components, and the odds are lower that a mosfet replacement alone will fix the controller.

There is more ebike troubleshooting information available here

Readers Comments (50)

  1. Darrell Whiteman April 4, 2021 @ 11:36 pm

    what does the letters and numbers refer too on the solder side of the controller

  2. Can anyone please help me with a faulty e scooter? Every time I go to charge it up it shorts out the battery charger. The battery is actually fully charged, I disconnected the battery from the control unit. Every time I go to connect it back up it blows the battery connectors to bits

  3. What’s the cost for you to repair?

  4. Thank you!

  5. Excellent educational video but would have liked to see the heatsink compound replaced.

  6. Can blown capacitors from over-voltage equal a blown mosfet? thanks for the video

  7. my battery cable fell of so the kers burned anything on my controller.
    sadly i dont think that replacing mosfets will help if the esc just does nothing anymore, even the scooter doesnt turn on anymore.
    I have a functioning replacement controller but it’s from a german 20 kmh m365 clone, and just the tail light flashes … so i have to replayce broken parts but what for parts?

  8. Awesome Education my Brother wish I had the funds to drop ship you at non conductive Vise
    Made from my own Recycled plastics , with some cool Hemp plastic 3D printing.
    Lord Jesus please Bless this Man and His Family

  9. Eddie Buckelew April 4, 2021 @ 11:43 pm

    Thanks for this. Helped me diagnose a bad mosfet in my daughter’s hoverboard. Unfortunately, I’m unable to identify the mosfet, so I can’t get a suitable replacement. Either way, now I know what the problem is!

  10. great post thankyou for that the share!

  11. elestirmen elestiri April 4, 2021 @ 11:43 pm

    think you

  12. hannes dobbelaere April 4, 2021 @ 11:45 pm

    i only have 5 mosfets on my controller, of wich 2 have continuity with ground wire (on the top aluminum part of the mosfet)
    how do i determine wich one is faulty. the way i measured as in the vid, i have no ground connection on either colors measured on the print board?

  13. Can’t find my controller to buy baught 2 not working how to find model cant see any number on the board

  14. Xhon Hidershaj April 4, 2021 @ 11:47 pm

    Hi. I was wondering if you could fix mine. I can’t do it myself cause I don’t have any tools.. please lmk if that would be possible. I can send it to you and you can charge me

  15. now how do you check a brushed controller

  16. Are mosfets all the same ?

  17. Does this go for brushed controllers also?

  18. The pedal assist wiring shows positive +5V and signal wire + 4.6V. Please any help. What can I replace? The throttle works fine. Except the pedal assist not working. Please advice.

  19. Giuseppe Richiusa April 4, 2021 @ 11:55 pm

    sorry mate i dont have reading on any phase with positive conector, any idea?

  20. Hi I am after some mosfets ru6888r
    There is also other numbers on it .
    89 p1926
    Do these numbers matter or is it just the first one ?
    Kind regards daniel

  21. Can you do this with the mosfets on the bms aswell, I’m assuming you can?

  22. Why do say Sodder when there’s an L in solder pronounced Sol der

  23. Gerhard Malberg April 5, 2021 @ 12:02 am

    Only LOW side mosfets can short to ground when fail and are thereby detected by measuring between GND – DRAIN (body of mosfet)
    HIGH side mosfets can short to PHASE when fail and are thereby detected by measuring DRAIN (body of mosfet) – PHASE (one of the three phase wires)

  24. Great video, very well explained. Here’s what happened last week, after a heavy rain my ebike died, the display doesn’t turn on anymore, so I decided to check the controller. Doing a resistance test I connected each phase wire with the negative probe while alternating the positive probe with the positive and negative of the power inlet. From each phase wire the negative gives 0 while the positive gives 18, should I conclude that all negative mosfets are blown? Please help 🙁

  25. Great. Thanks! Maybee A stupid question: Does it still make sense to adjust the 2 shunt sensors, i mean by soldering make it wider, bridging. You sure know what I mean. I have an escooter with 2x 45A controllers (1 controller per wheel) and the BMS also offers 90 or 100A. The BMS circuit board on the battery pack can only spend as much as it says, no more?! I hope someone can tell me whether that still makes sense or not. Thank you all 😊

  26. I have an ebike just come in been standing in his shed 6 months, has no light on display, battery is good fully charged all wiring and connections are controller connections all good bike is only 18 months old , any pointers please ???
    could be controller but all looks new condition

  27. Thanks Phil for the video. I have identified several blown Mosfets after seeing your video. I have a chinese controller with 12 Mosfets. No markings to identify them. Can you tell me what Mosfets I need, and where to get them? I have a 48V, 26amp controller.

  28. Nice. Tiny comment. spinning motor doesn’t QUITE prove you have good phase signals. I’d grab it with the glove and convince myself the torque is good.

  29. Chennai Tamizhan Arun April 5, 2021 @ 12:10 am

    What will be the result if I replace 85v 150A mosfet ( k150e09ne- 18 nos) & 63v caps with 100v 200a (SSF1006 mosfet) & 100v Caps.

    Controller is 48v 45a…

  30. stacy collinsworth April 5, 2021 @ 12:10 am

    how I tell what kind of electric scooter I have when it’s not identified on the frame

  31. Im trying to diagnose my nanobot d4+ 2.0 scooter. This problem does not happen in the cold morning on my first ride but happens in middle of day when it is warmer. Im in NM. What happens is both motors cut out when I’m in dual mode and when i go full throttle, and also sometimes when i try to just accelerate quickly. when it cuts out i does not come back alive by simply backing off a little on the throttle but i have to totally go back to 0 or no throttle and then the motors start if i re-engage the throttle more gently incrementing the speed. It does not happen in single mode when in just rear hub drive. When in single mode i can press the throttle fully and as quickly as I like. If I think of the thumb throttle as a clock that goes clockwise from 12 to 6. it is at the 5 when the motors cut out. It also happens if i got from 12 to 3 very very quickly. I’m pretty techy and i can replace of fix most anything but I like to diagnose first. I did have an extra thumb throttle speed controller so i did decide to replace that (because a year ago i brew out its usb power port when making a dual charger for a camera i have) but changing that speed controller had no change in the symptoms. Do you think there is a short somewhere in the system on full power or is it a hall sensor. Is it overheating and the bms cutting out? There are two controllers in the scooter with a communication wire between them, could one of the controllers be off. Both motors shut off when this happens. What tests should i run to see where the problem is? I have opened up the scooter before because I silicone sealed everything to protect from water. but actually moved to NM where there is little rain and I do not ride it in mud or water anyway. Any help appreciated.

  32. CHIEF IBBREDE Chukwu-emeke Oghene-Lukome April 5, 2021 @ 12:11 am

    No No leaning not from the video absolutely rubbish

  33. Nathan Andrews April 5, 2021 @ 12:12 am

    Great video!! Question: I have a 1000 watt Ecotric Hammer, 48 Volt, I want to use a 52 volt battery with. Is there any reason why the 48 volt controller would be damaged by this? My 48 volt battery puts out 51+ volts when it is fully charged… Why such a gray area? I don’t see any 52 volt controllers for sale, but everyone is upgrading to widely available 52 volt batteries. What do you think? Thanks.

  34. Hey good video can you advise on whats best i recently have a fault with my scooter it powers on ok, the issue is that it won’t accelerate and the brake light stays on, i have checked everything cables, battery charges ok the only thing is the controller or the motor hub i followed your video checking the misfets and can seem to find the problem ive checked the internet for a replacement but they all have different end connectors to mine are these controllers standard ? can i replace the end connectors.

  35. I have a Charly scooter which is made in Germany, although I have the less common 110 V US version, And appears that the controller box is fried. Is this something that you might be able to repair? The LED display does show a problem with the controller, and there is resistance when I try to turn the wheel by hand. Further, the motor does still work when I power it directly.

  36. My 3 speed settings wont work how do i go about diagnosing that? Ive tried jumping it with a wire. It went out after my charge port shorted but everything else seems to work fine

  37. your work bench is making me claustrophobic man!

  38. Good finding them!!! If thick of my phase wires that comes from the MXUS 350 watt 36V motor is = 1.5mm diametr (1.77mm2), can I change my 13A 36V controller to another one 18A 36V? Will my motor be warm or not? Now it is cold. Thank you.

  39. Can you get away with just replacing the blown mosfets or do they all need replacing with the same batch ?

  40. What if you put a 48v on a 36v controller what would burn out thanks

  41. Need a microphone

  42. mason appalachiantrail April 5, 2021 @ 12:26 am

    Define mosfet?

  43. My scooter shuts down and have a Undervoltage protection error, Any advise what causes this? thanks!

  44. Thank you.

  45. Hi. Can you please mention if a brushless motor controller matches any hub motor. Are there any specific hall sensors which must match the motor controller.

  46. Sehr gutes Video!

  47. Thanks for this great guide, the biggest problem to find the right china mosfet, in my case it is a brainpower control. DC52V (the scooter is a Speedway 4 clone + no dualtron 1x800w motor) the mosfets(to 220) have the designation:
    K M
    ..9Y ……. 19x
    2452 ….. L12
    …. K3475N ..
    Unfortunately I could not find a data sheet to find comparable replacement mosfets. does someone have a tip?

  48. AJI KATAKUSA KITCHEN April 5, 2021 @ 12:36 am

    Thanks for your tutorial lesson

  49. stacy collinsworth April 5, 2021 @ 12:36 am

    How can I find out what kind of electric scooter I have would it not be in marked on the scooter or the blame it all

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