Did I blow a fet?

speedyebikenoob · Apr 21, 2021

I was riding my e bike today at about 35 mph up a slight hill (max it's capable of on a flat is 47 so I was pushing it a little bit) and felt the power decrease very suddenly and then the throttle became completely unresponsive. I shut the bike off and restarted it. The throttle worked for about five seconds and then became unresponsive again. Now it doesn't work at all.

The throttle did flake out on me earlier today also for about five seconds. Does this sound like a blown fet or is it something else?

markz · Apr 21, 2021

Is it a direct drive or geared motor?
*If its a dd, then you can just spin the motor unpowered and if you have a blown fet it will be more resistance then normal.

Could be a cooked motor, open the side covers and you'll smell if but do look at the windings. A dark color could mean its cooked.

To check mosfets - https://ebikes.ca/learn/troubleshooting.html

john61ct · Apr 21, 2021

Or the battery pack failed, if not the BMS (if any) then cells themselves

speedyebikenoob · Apr 21, 2021

markz said:
Is it a direct drive or geared motor?

Could be a cooked motor, open the side covers and you'll smell if but do look at the windings. A dark color could mean its cooked.

To check mosfets - https://ebikes.ca/learn/troubleshooting.html

I will definitely check the mosfets. The motor is a cyclone middrive, so geared. It looks hard to pull apart but I'll give it a shot. I doubt it's the issue though because I was watching the motor temperature and it didn't seem too high. I've definitely had it higher.

speedyebikenoob · Apr 21, 2021

john61ct said:
Or the battery pack failed, if not the BMS (if any) then cells themselves

I have a cycle analyst connected and the voltage read out, etc. looks normal. Just the throttle is unresponsive. I'm assuming if it's the bms, the battery wouldn't power anything at all including the cycle analyst?

thorlancaster328 · Apr 28, 2021

Take an ohmmeter and measure between each phase and battery +
Do the same thing between each phase and battery -

If any of the measurements are noticeably lower than the rest (often near zero), you most likely have a bad FET.

Based on your description of the problem I doubt that it's a blown FET. Blown FETs cause the motor to drag and vibrate (unless it's a geared motor w/ freewheel) and don't magically fix themselves for 5 seconds after a restart.

I'm pretty certain that it's either the battery or the BMS. A failing cell group in the battery would cause exactly the same problems you're having.

speedyebikenoob · Apr 28, 2021

thorlancaster328 said:
Take an ohmmeter and measure between each phase and battery +
Do the same thing between each phase and battery -

If any of the measurements are noticeably lower than the rest (often near zero), you most likely have a bad FET.

Based on your description of the problem I doubt that it's a blown FET. Blown FETs cause the motor to drag and vibrate (unless it's a geared motor w/ freewheel) and don't magically fix themselves for 5 seconds after a restart.

I'm pretty certain that it's either the battery or the BMS. A failing cell group in the battery would cause exactly the same problems you're having.

So looks like I don't have a motor controller issue, I verified today. I did pull the motor apart though and one of the phase wires had de soldered itself? So it looks like that was the issue, but I might have bigger problems cus looks like my motor is toast

One of the coils looks black

speedyebikenoob · Apr 28, 2021

A couple days ago the cyclone motor on my e bike just stopped working after I flogged it pretty hard up a hill. I just assumed it was a hall sensor, but I pulled it apart today and saw a phase wire had broken off. Giving it a closer look, I saw this. https://drive.google.com/file/d/19JBRKKLxnwkydDXQMCeAyKq2hxRZ1w00/view?usp=sharing

Two or three of the coils look darker than the other ones. It smells awful inside, like melted plastic. I reconnected the phase wire but the motor still wouldn't run. It would just make a whining sound a not move. Is this motor done?

thorlancaster328 · Apr 29, 2021

That's more burnt than my hubmotor was when it gave up the ghost. Given that a phase wire has come loose (melted off), the temperature inside the motor got at least hot enough to melt solder, likely higher.

Your motor is definitely toast.

speedyebikenoob · Apr 29, 2021

thorlancaster328 said:
That's more burnt than my hubmotor was when it gave up the ghost. Given that a phase wire has come loose (melted off), the temperature inside the motor got at least hot enough to melt solder, likely higher.

Your motor is definitely toast.

Aw that's too bad. Not surprised though as I was well above the power limit, running 4 kw bursts through a motor rated for 1680w, so I'm genuinely impressed it lasted this long. Guess it's time to actually upgrade to a motor that'll handle the power.

thorlancaster328 · May 5, 2021

speedyebikenoob said:
running 4 kw bursts through a motor rated for 1680w,

That's quite a lot of power. I burnt up a motor as well doing something similar, 150 phase amps into a motor only rated for ~40 continuous. By the end of a 15 minute ride it was smoking.

An alternative to upgrading to a beefier motor is to use a temperature sensor if your controller supports it. I'm still running 150 amps through a 40 amp motor but I have a temp sensor set to cut off power at 110c. Loses power after 5 minutes of hard riding but it's better than a burnt motor.

If you want to run POWER, get a low-turn QS205, put it in a small wheel, and prepare to triple the size of your battery.

speedyebikenoob · May 8, 2021

thorlancaster328 said:
speedyebikenoob said:

running 4 kw bursts through a motor rated for 1680w,

Click to expand...

That's quite a lot of power. I burnt up a motor as well doing something similar, 150 phase amps into a motor only rated for ~40 continuous. By the end of a 15 minute ride it was smoking.

An alternative to upgrading to a beefier motor is to use a temperature sensor if your controller supports it. I'm still running 150 amps through a 40 amp motor but I have a temp sensor set to cut off power at 110c. Loses power after 5 minutes of hard riding but it's better than a burnt motor.

If you want to run POWER, get a low-turn QS205, put it in a small wheel, and prepare to triple the size of your battery.

I think I love middrives a little too much to switch to a hub tho XD. My next motor will definitely have a temperature sensor I have a cycle analyst so it can ramp down the power anyways when it gets too hot. I'm considering the cyclone 4000, might be overkill because I'm only running 2400 watts continuous/ 4000 peak but in combination with a temp sensor it should be pretty bulletproof. I'm sick of my bike being unreliable lmao

Did I blow a fet?

speedyebikenoob

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markz

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