blown mosfet on 35a infineon controller?

[jansevr]

i have this controller here:

it was being run with a crystalyte hs3540 on 50v lipo at 40 amp limit (the shunt was modified to achieve this)

i believe that the mosfet has been blown. i have no idea what happened. my roommate and his friend had taken the bikes out the previous day and i hadn't used it until this morning. when i plugged up and started moving, the controller instantly started smoking - i immediately turned it off and unplugged. the friend said that there was no problems the previous day. what could have happened? also i don't currently have a fuse on the bike at all - would this have prevented the problem?

where can i buy the mosfets to replace the two blown ones?
also is it a fairly easy piece to replace?

would it be possible or make more sense to change the mosfets (i understand i would have to change them all)


thanks in advance!

 

[amberwolf]

You may be able to buy them from http://ebikes.ca, but if not, Mouser or Digikey or other places like that should carry the same type. Just make sure it is the same p/n as marked on the face of the other FETs.

As for why it might've smoked, it's quite possible the last user damaged the wires sticking out of the axle, even unknowingly, and they are shorted together. This could cause FETs to blow.

If the motor is not secured properly with torque arms or nuts are not tight, it is also possible the wheel could have spun the axle and twisted wires together, breaking insulation and shorting stuff together.

IT is also a known issue with the Crystalyte HS/HT series that at least the early ones had potential for wires to be cut or shorted in the channel in the axle. There are threads documenting how to modify the motor to prevent or fix this.


Depending on the cause of the problem and type/rating of fuse, the fuse *might* blow fast enough to prevent it, but FETs go really quick when they go, so my guess is that with the average fuse, it would first have shorted and THEN the fuse would have blown.

 

[knoxie]

Yes you would have to fit semiconductor fuses for it to catch it as the fet would blow well before the fuse, however a system fuse is a very good idea as a rule anyway. All points by amberwolf are spot on, you may also have to swap out gate resistors on the board too, check them with a DVM before you power up with the new fet.

Good luck

 

[jansevr]

the wires coming out of the motor aren't out of place or damaged in any way. the torque arm is still securely holding the axle in place, and the nuts are tight. if there is something wrong inside the axle, how would this have happened? also is there any way to test this before replacing the mosfets...and do i risk blowing any again if there is a problem?

 

[knoxie]

Its hard to check it out, there may not be anything wrong with the motor however these motors are notorious for the axle cutting in to the phase wires, this can be fixed of course but its not something that you should attempt unless you are sure what you are doing and yes if there is a problem it might blow the controller again.

If I were you I would at least try changing the fets, its pretty easy to do and wont cost a lot to do, try it and see if it works

 

[jansevr]

i just got the mosfets today. before i was able to install them however, i saw that the packaging notes that the mosfets are electrostatic sensitive devices. it also says to not open or handle except at a static free workstation. how big of a concern is this? or maybe the better question is what do i need to do exactly? my soldering iron is also only a 2 prong...will this not be properly grounded and ruin the mosfets? also do i need to purchase a wrist strap to prevent the electrostatic shock? should this always be worn while working on the controller?

 

[fechter]

It depends a lot on your humidity. In very low humidity conditions, static is an issue. Around here, I don't worry about it. If you always touch the case of the controller before touching anything else, there is little risk of blowing anything. Just don't walk across a rug and touch the gate lead of the FET. If you're really worried about it, you can lay out a sheet of aluminum foil and put everything on top of it while working. Take away the foil before powering anything.

When a FET blows like that, sometimes it takes out the gate driver too. You should check these, but it may not be easy. Visually trace the gate lead traces back to the next component, which is usually a resistor. Measure the resistor and compare to a good one. If it's blown, they usually go open like a fuse (and often look crispy). If resistors are good, try measuring from the gate trace to battery negative with a diode check meter (or ohmmeter). Blown ones frequently short to ground. Again, compare to a good one on another phase.

I have an old tutorial here: http://endless-sphere.com/forums/viewtopic.php?f=16&t=8969&start=45

 

[neptronix]

BTW, the original failure was most likely caused by the fact that you have shunt modded that controller past what it can really handle. Those AOT460 FETs in it are not all that great - double the rdsOn as the IRF ones used in most controllers, and half the amperage handling capability..

http://aosmd.com/pdfs/datasheet/AOT460.pdf

http://www.irf.com/product-info/datasheets/data/irfb3077pbf.pdf

You also have a motor with a high continuous amp draw as well.
It is my estimation that this controller could blow all over again.
I bet it got pretty damn hot during normal operation, and your friend tested it on some hills or stalled it, putting in the final stake.

p.s. what do you mean by 50v lipo? do you mean 50v nominal or 50v fully charged?

 

[cor]

Hi jansevr
You asked: would it be possible or make more sense to change the mosfets (i understand i would have to change them all)
As others have indicated - yes - changing all MOSFETs for higher current/lower resistance versions can improve the current handling and keep the controller cooler.
BTW, what is that blob of solder behind the black wire in the picture?
And why is there a cut lead lying next to the VR2- point at the bottom of the controller PCB?
If anything like that is rattling around in your controller, it can easily short and blow the transistors!
Cor.

 

[amberwolf]

The solder blob is his modded shunt.

I didn't notice that cut lead, but yeah, if there are others like that floating around in there already loose, they could've caused teh failure, and this one could cause a failure if it comes unstuck from where it is now.

 

[jansevr]

50v fully charged is what i meant. also, i have never noticed any heat from the outside of the controller. i don't know what you see cut either...the green wire next to the vr2 is connected to the on/off switch.

 

[jansevr]

so i got the fets installed and the controller back together. i plugged everything up and the cycle analyst powered up but the throttle didn't work. i tried moving the pedals with my hand and noticed that there was quite a bit more friction than there should be. i soon realized that this was caused by plugging in and unplugging the phase wires.

any suggestions on what the problem is/solutions?

thanks again for all your help

 

[cor]

Is there current flowing in *all* phase wires or only 2 of them?
If the MOSFET driver circuit was blown together with the MOSFET blowing, that would cause one phase to not have current and on only 2 phases the motor would not run, but will give higher resistance.
Another check is whether the hall sensor is connected properly or do you have a sensorless controller?
Cor.

 

[amberwolf]

i don't know what you see cut either...the green wire next to the vr2 is connected to the on/off switch.

i tried moving the pedals with my hand and noticed that there was quite a bit more friction than there should be. i soon realized that this was caused by plugging in and unplugging the phase wires.

If it was not that way before, then there is probably still something shorted in the controller. Does this happen when the controller is powered up, or when it is not? Or both?

 

[jansevr]

Ahh i do notice that when replacing the mofets...not sure what it was from but was just kind of hanging their so i removed it. the motor has the friction whenever the phase wires are plugged in regardless of whether the power is on

 

[dnmun]

did you check to see if the mosfets are shorted? did you replace all of the mosfets or just some of them? is there 5V on the hall sensor plug?

 

[fechter]

Ahh i do notice that when replacing the mofets...not sure what it was from but was just kind of hanging their so i removed it. the motor has the friction whenever the phase wires are plugged in regardless of whether the power is on

That indicates there is still a short in one or more of the FETs. You can measure resistance between each phase wire and battery neg, and again to battery positive to test each bank of FETs. A short will be obvious from the measurements and you can trace the wires back to the board to find the shorted parts.

 

[dnmun]

there is another guy with the same blown mosfets, i recommended you guys split the costs for buying them from digikey since shipping is so much.

http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=39500&p=578221#p578221

 

[jansevr]

what device do i need to use to measure the resistance? am i only testing each of the three phase wires with the battery neg? how am i supposed to find which of the 12 are shorted if there is only 3 wires to test?

also, i have already ordered and received the mosfets...hence me replacing the only two that i thought were blown only to find the controller still shorted.

 

[dnmun]

you use the ohmeter function built into the voltmeter. do you have digital voltmeter? how did you determine which mosfets to replace before?

 

[fechter]

what device do i need to use to measure the resistance? am i only testing each of the three phase wires with the battery neg? how am i supposed to find which of the 12 are shorted if there is only 3 wires to test?

There are 6 banks of FETs, each bank is a pair. Measuring each phase wire to battery negative will test the 3 low side banks. Measuring each phase wire to battery positive will test the 3 high side banks. Once you locate a shorted bank, there is no easy way to tell which one of the pair is shorted unless you remove one.