VESC has died, need help to diagnose reasons

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buran
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VESC has died, need help to diagnose reasons

Postby buran » 02 Apr 2017, 08:49

Yesterday i have lost my VESC :`(
Now I need to understand was it an accident or it was expected behaviour in my setup

My setup was:
1) battery: 13s of 18650 (no load voltage at the moment of accident was about 52V)
2) geared hub-motor: freewheeled, i.e. there is no any valuable regen current by construction
3) I have missed phases when solder connector, it was waterproof 3phases+6signals connector, so i had no any chance to change phases without re-soldering connector to VESC. Result was: logical "forward" direction (BLDC-tools showed positive RPMs) caused motor rotates backward, i.e. motor rotated without rotating wheel (freewheel in an action), logical "reverse" direction(BLDC-tools showed negative RPMs) caused motor rotated together with wheel.
I decided to do quick test the setup without re-soldering. So I have enabled ADC, chose current+reverse button mode, and activated inverting of reverse button state. As a result it worked for me: pressing thumb throttle i accelerated motor in a "right" direction (together with wheel).

I was in BLDC-hybrid mode and started to test the setup with load (my weight) in the room(so distance to test was extremely short). After 3 or 4 "drag racing" for 10 meters controller has died. That means that even no LEDs flashes, programmer couldn't see stm32 too. As I understand something was wrong with power of CPU. I have measured voltage on VDD legs of stm32 it was -0.1V instead of 3.3V. There were no any traces of "magic smoke leaks" on board.

I understand that it is extremely difficult to make a diagnose "by a story", but I want to hear your opinions about causes of controller bricking:
1) it was bad idea to work with controller in "reversed" mode
2) it was bad idea to use it with 13s battery (I thought that freewheel will save me from regen-caused voltage spikes, i was wrong?)
3) ???

Thank you

artteth
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Re: VESC has died, need help to diagnose reasons

Postby artteth » 03 Apr 2017, 00:49

look at your vesc under microscope
if it too many garbage so that can be it(cheap chines vescs with too much garbage on it (i see it myself))
check 5v out and if it nothing you need to replace drv
if you have 5v so check all parts with your fingers to heat when vesc connected to power
if you do not have 5v so check all parts with your fingers to heat when vesc connected to power (some parts can heat up and suck all power)
if you have 5v and no heated parts so you need to check 3.3v converter
or simply if you can power 3.3v direct to 3.3v pin on the boar and if it will turn on then write if no then check heat parts and if you can check current in all steps

pf26
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Re: VESC has died, need help to diagnose reasons

Postby pf26 » 03 Apr 2017, 11:02

When braking a fast spinning motor, the motor inertia alone could regen enough power to increase the voltage to dangerous regions and kill DRV8302. chip. It is a good idea to first test a VESC using a current controlled power supply at moderate voltage - and to setup low current limits using bldctools.

buran
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Re: VESC has died, need help to diagnose reasons

Postby buran » 04 Apr 2017, 14:31

Last edited by buran on 04 Apr 2017, 14:46, edited 1 time in total.

buran
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Re: VESC has died, need help to diagnose reasons

Postby buran » 04 Apr 2017, 14:43


pf26
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Re: VESC has died, need help to diagnose reasons

Postby pf26 » 05 Apr 2017, 10:38

Yes, motor current limits.
As for voltage spikes, you better use a scope (preferably a fast one to see the short transients after FETs commutation)

rew
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Re: VESC has died, need help to diagnose reasons

Postby rew » 05 Apr 2017, 14:11

IMHO, the capacitors should catch the really fast transients before they do any harm.

What kills the DRV is when your battery has an internal resistance that is a bit high. Then regeneration will cause the voltage to rise to the batteryvoltage + I * Ri. where I is the regen current adn Ri is the internal resistance of the battery.

buran
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Joined: 28 Jan 2017, 18:02
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Re: VESC has died, need help to diagnose reasons

Postby buran » 08 Apr 2017, 19:09

Connected 3.3V from STM Nucleo board to 3.3 pin of dead VESC.
Result: voltage measured between ground and any contact on VESC's 3.3 line was 1.3-1.2V instead of 3.3, Nucleo's linear regulator(LD39050PU33R) was very hot, current was 0.2A.

I am a complete noob at electronics, but cannot understand how DC voltage could drop on 2V having current 0.2A if power supply (regulator) can do 0.5A at 3.3V according to datasheet?
May be there are some oscilatory things in action - unfortunately I have no any oscilloscope, only simple voltage-current tester.
Attempting to find hot element with my finger on board was not successful.

rew
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Re: VESC has died, need help to diagnose reasons

Postby rew » 10 Apr 2017, 06:15

Linear regulators usually have a "temperature shutdown" mode. When they get too hot, they will lower the output voltage in the hopes of getting less hot.

Your board has a semi-short, causing a current draw of > 0.2A at anything above the 2V you measured. The regulator, probably dropping the voltage from 5V now has 0.2A * 3V = 0.6W of heat to dissipate. In the current configuration that seems to be its limit. Datasheets can be misleading. They will mention "best case" numbers. So, when cooled even better than it is now, the regulator will be able to dissipate more heat than what it is doing now. And under those circumstances, (or a lower voltage drop) the regulator may be able to reach 0.5A....

buran
Posts: 12
Joined: 28 Jan 2017, 18:02
Location: Russia
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Re: VESC has died, need help to diagnose reasons

Postby buran » 11 Apr 2017, 11:25



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