Controller troubleshooting - motor turning resistance

[Allex]

Sorry is this has been answered before
Tried to search but did not find any direct information.

Have a hubbie which works fine with another controller.

How It started:
Tested the wheel in the air with a Lyen 9FET. Everything worked fine when applying full throttle and so on.
Then, when the wheel was still spinning I released the throttle and turned the ignition off, the wheel stopped very quickly, like it was ebraking.
After that it was dead, no response from the throttle. I can still flash the board and the board itself looks fine.
Now, when the phase wires are connected to motor I feel great resistance when trying to spin the wheel. The motor is OK - wheel spins freely and works fine when disconnecting and using another controller.

So what could have got wrong here I how to fix this? Blown FETs?

 

[dogman dan]

Classic symptoms of a blown fet on the controller.

 

[dnmun]

yep, you can test the mosfets without opening the controller with the diode tester on your voltmeter if you know what to do.

 

[Allex]

Could some one point me to a "how to guide", I would like to find the faulty ones and replace them. I am a noob in electronics
I can open the controller up no problem, but do not want to desolder every one of them for test.
Appreciate all the help guys!

 

[dnmun]

why would you desolder them to test? you can test them without opening the controller. the mosfets always have the drain at the higher voltage so it is easy to figure out how to test them.

use the diode tester on your voltmeter, measure the source drain body diode of the hiside by putting the voltmeter probes on the red wire into the controller and each of the phase wires, 6 measurements forward and reversed. then measure the loside by putting the probes on the black, ground, lead form the controller and each of the phase wires.

total of 12 measurements. there should be about 470mV forward bias when the red voltmeter probe is on the source and the black is on the drain, and when the red probe is on the drain and the black on the source then it should read open circuit.

 

[Allex]

Thank you I will try that, although I am not sure what you mean by "measurements forward and reversed" I would love to find explanation for dummies :]

 

[dnmun]

forward biased is when the voltmeter probes of the diode tester have the higher voltage, from the red probe, on the source leg of the mosfet and the black probe is on the drain. the body diode of the mosfet will conduct in this direction so it is forward biased, just as a diode is forward biased. it should have about 470mV of voltage drop which you read on the meter.

then reversed is when the red probe is on the drain and the black probe is on the source so the body diode is reverse biased and should not conduct. the meter will then read open circuit.

most will tell you just to measure with the ohmeter but i prefer to test the body diode to see if the mosfet is damaged. the forward bias should be identical for all of them.

 

[Allex]

Great thank you!
I found this helpful thread about testing:
http://endless-sphere.com/forums/viewtopic.php?f=16&t=8969&start=25

Also replaysing FET may be not the only thing...
fechter says:
When the FETs blow, it almost always takes out the gate resistors. The gate resistors are tiny little 10 ohm chip resistors. They act as fuses when the FETs blow, protecting some of the downstream circuitry (sometimes).

If the gate resistors blew, there's a 50% or so chance that the gate driver chip or the two transistors on the high side drive also blew. These are difficult to test without connecting a motor.

 

[dnmun]

be advised that a mosfet with the body diode forward biased will appear shorted to the ohmeter. i tried to explain. sorry it is not enuff for you.

 

[Allex]

Thanks!
I managed to find one faulty bank/phase.
Now, before I go and buy those expensive 4110.
I have another 36V controller with noname FETs on. Can I solder them on to my faulty Lyen just to test if motor start to spin? If it does then it is good news and only FETs are damaged and nothing else so I can proceed to buy three 4110 and solder them on.

 

[Allex]

Yup, that worked, swapped one irfb4110 with a different mosfet and the motor is good to go!