Need help with this blown KT controller

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kdog
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Need help with this blown KT controller

Post by kdog » Nov 05, 2017 6:12 am

Hi all
A friend has asked for some help with his ebike (cause I put it together for him) it's a 500w DD hubby with a KT controller and LCD display. I built the battery for him which is a 13s6p.
All pretty standard, it's been going well for 3500 k's but he's had a series of failures in a week (which I'm suspicious are related).
I got it going for him and he took it out for a ride, started off ok, then he did some heavy regen braking down our hill. Then no power and cogging. Damn it!
Motor's fine no shorts.. But all phases cog when connected to controller
Taking the controller out it seems that all phases are shorted. I'm familiar ( but lack indepth knowledge )with testing fets.
Testing with my DMM I got this:
Battery + to all phases 0.00ohm
Battery - to all phases Aprox .45v drop
so am I correct in thinking...
That all fets are shorted but have intact body diodes, seems unusual to do ALL fets. The fets all look fine, there is no visual damage to the controller at all.
Is there some other process that could produce this result?
The controller still works in all other respects.
Cheers

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Re: Need help with this blown KT controller

Post by amberwolf » Nov 05, 2017 4:36 pm

When you say the
kdog wrote:The controller still works in all other respects.
exactly what do you mean?

Do you mean it still drives the motor normally? If so, the controller is not damaged (at least, not FETs/gates/etc) but could be receiving a wrong signal from outside controls (such that when throttle is not applied, brake is enabled, like slip regen).

If it does not drive the motor anymore, then usually if it cogs when connected to controller, but not when it doesn't, then at least the FETs are blown in the controller, and possibly the gate drivers or other associated parts.


Otherwise, if it does not drive the motor anymore, but FETs/etc are not damaged, then an ebrake/regen signal is probably still being enabled on it, braking the motor.


I'm not sure I understand your getting a voltage reading during the FET testing. What setting were you using?

If volts, the controller must be powered on (and to get any voltage you must also engage the throttle and if it is not sensorless must also have correct hall signals coming into the controller from the motor).

If ohms, the controller must be powered off.

casainho
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Re: Need help with this blown KT controller

Post by casainho » Nov 05, 2017 5:31 pm

kdog wrote: That all fets are shorted but have intact body diodes, seems unusual to do ALL fets. The fets all look fine, there is no visual damage to the controller at all.

The controller still works in all other respects.
I am being developing our OpenSource firmware for BMSBattery S / Kunteng controllers. With the development and test I did burn already some mosfets on S06S (6 mosfets controller) and S12S (12 mosfets controller) and did the replacement of mosfets.

If helps you, grab here the schematic of the controller: https://opensourceebikefirmware.bitbuck ... _S06S.html

Yes, I had some shorted fets and the controller would work like sending the information to the LCD but would fail as soon I increased throttle (down mosfets negative were shorted).

Sometimes more than 1 fet shorts, maybe you are in a situation were all fets from the 3 phases did short...
Developer of OpenSource firmware for EBike BMSBattery S/Kunteng KT motor controllers: https://opensourceebikefirmware.bitbucket.io/

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fechter
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Re: Need help with this blown KT controller

Post by fechter » Nov 05, 2017 6:05 pm

If the FET measures like a diode then it's not shorted. Your measurement of the high side looks like they're shorted.
"One test is worth a thousand opinions"

kdog
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Re: Need help with this blown KT controller

Post by kdog » Nov 05, 2017 9:40 pm

I'll try to elaborate/ clarify ( but bear with me- it's not my strong point)
the controller seems to be shorted in all phases- there is cogging in all combos of phase wires. There is no ebrake signal on LCD ( and this does work when I engage brake) an the controller communicates with the LCD (responds to throttle/pas ebrakes on the screen but comes up with the error code for internal short)
There is no drive of the motor.
I think I did half the reading on diode and half on Ohms function cause I got distracted for a while between them. But redoing it in diode mode I get
0v btwn pos and all phases (shorted?-should be open?)
~.45v btwn neg and all phases.
I guess I'm looking for confirmation that all the fets are shorted. It seems unusual to have all fets blow simultaneously ( and that I'm not missing something)
Casainho- thanks for that info- It seems similar to your failure.

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Re: Need help with this blown KT controller

Post by fechter » Nov 06, 2017 9:17 am

Zero ohm reading between a phase wire and battery wire indicates a shorted FET. When measuring, reverse the probes to measure both ways.
A good FET will read like a diode. Blown ones almost always short.
"One test is worth a thousand opinions"

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Re: Need help with this blown KT controller

Post by kdog » Nov 09, 2017 1:14 am

I've got 15 fets on order.. Should be here in a day or two( 3spare). Hopefully that solves it, but I'm not overly hopeful, there's always something more. :(
Is there a way to test the gate drivers? or do I just try the new fets and see.

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Re: Need help with this blown KT controller

Post by fechter » Nov 09, 2017 9:07 am

kdog wrote:I've got 15 fets on order.. Should be here in a day or two( 3spare). Hopefully that solves it, but I'm not overly hopeful, there's always something more. :(
Is there a way to test the gate drivers? or do I just try the new fets and see.
Once you remove the old FETs, you can try measuring resistance from battery neg. to each of the gate leg traces. None of them should look shorted to ground. Also measure the resistance of the gate resistors. Beyond that, it's hard to test unless you have an oscilloscope and a way to simulate the hall signals.
"One test is worth a thousand opinions"

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Re: Need help with this blown KT controller

Post by casainho » Nov 09, 2017 9:20 am

kdog wrote:I've got 15 fets on order.. Should be here in a day or two( 3spare). Hopefully that solves it, but I'm not overly hopeful, there's always something more. :(
Is there a way to test the gate drivers? or do I just try the new fets and see.
Test by comparition. At least you can use the new one as comparition, on the signals. Look at the schematic and measure the signal output on microcontroller that goes to each driver. Than measure the driver output/gate of the power mosfet.
Developer of OpenSource firmware for EBike BMSBattery S/Kunteng KT motor controllers: https://opensourceebikefirmware.bitbucket.io/

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Re: Need help with this blown KT controller

Post by kdog » Nov 09, 2017 7:30 pm

Ok thanks fellas... I'll see how it goes in a day or two when the bits arrive
Cheers for the help.

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Re: Need help with this blown KT controller

Post by kdog » Nov 15, 2017 8:58 pm

Ok my replacement mosfets arrived so I got started on the repair. I broke out the old ones and desoldered the legs one by one, then I drilled out the solder in the hole. Is there a better way to do this? ..It worked fine though.
Annoyingly just one mosfet in each phase was blown, but I couldn't know this until they were separated.
I'm suspecting a high voltage event during regen. We did just turn the regen level up to full just prior to them blowing, so I'm going adj that back down.
Gate resisters all measure 51ohm ( as their marking suggests they should)
Gate to neg readings are all 27Mohm
So hopefully this will work.

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fechter
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Re: Need help with this blown KT controller

Post by fechter » Nov 15, 2017 9:15 pm

I use an industrial strength solder sucker, but for home use, doing the legs one at a time is a good method. I wouldn't drill out the holes, as they might be plated through. Solder wick or a wimpy solder sucker will clear the holes. Just make sure you get good solder flow on both sides of the board to reconnect things.

Even if only one FET blows, its good practice to replace all of them from a matched set.

Gate drivers sound hopeful.
"One test is worth a thousand opinions"

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Re: Need help with this blown KT controller

Post by kdog » Nov 15, 2017 9:47 pm

To late- I already did :? It was a tiny 1mm bit that fitted through an empty hole so hopefully it's ok.
We'll see...

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Re: Need help with this blown KT controller

Post by fechter » Nov 15, 2017 9:57 pm

As I said, just make sure the solder flows on both sides and it will be fine. Often times the through hole plating rips out when you remove the old FET anyway.
"One test is worth a thousand opinions"

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Re: Need help with this blown KT controller

Post by kdog » Nov 16, 2017 6:03 am

Yeha! She lives again... Hopefully for more than the first ride but so far so good.
Soldering all those little mosfet legs in is easier said than done... With all those smd parts right next door just waiting to float off or bridge to... Damn fiddly.
Thanks for the help everyone.

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