You are here

Dead VESC. Power up when motor is spinning.

5 posts / 0 new
Last post
Bor Zabric
Offline
Last seen: 1 week 1 day ago
VESC Free
Joined: 2018-10-05 14:36
Posts: 2
Dead VESC. Power up when motor is spinning.

Hello.

I fried an focbox by pedaling my ebike @10 kmh and powering up the focbox.

It stuttered and started braking when I applied the throttle. On further inspection the high side mosfet on phase 2 was blown. Long story short gave it to a guy to fix who damaged the pcb gate got shorted to Vin and blew the dvr and I gave up.

Now I bought the VESC 6 from trampa boards. 

Is there a general problem powering up the VESC when the motor is spinning, does it have any protection ? Any way to prevent such things in the future. Im rebuilding the whole bike and intend to use an arduino betwen the throttle and vesc. The arduino would sense either the hall pins or the motor phases isolated optocouplers. If it detects the motor spining it would disable the throttle until it was rebooted. Would this be a good idea ?

Sincerely.

-Bor

frank
Offline
Last seen: 31 min 38 sec ago
VESC BronzeVESC GoldVESC OriginalVESC Silver
Joined: 2016-12-27 20:19
Posts: 216

Never power up the VESC with the motor when it is not connected to a battery and powered by the battery (and switched on). The motor is a generator as soon as you turn it and the energy needs to go somewhere (the battery). Without the battery attached you will cook the internal components. So always make sure the system is powered up and running before peddling.

Bor Zabric
Offline
Last seen: 1 week 1 day ago
VESC Free
Joined: 2018-10-05 14:36
Posts: 2

I understand that the motor spinning induces voltage in the motor windings that can damage the VESC. This would defiantly be a big problem if I were to take the bike down a steep hill with no battery. That is not what im trying to achieve.

I have taken the bike slowly down short paths (no more than 1800 rpm on 192 kv motor) many times. Im convinced plugging in the XT90S key and turning the throttle made the difference.

I would like to know if there is any way to make this "idiot proof" so that you can't damage it when you're in a hurry taking the bike outside and plugging it in at the same time.

Bor Zabric

Roger Wolff
Offline
Last seen: 3 days 20 hours ago
VESC Original
Joined: 2017-05-24 12:27
Posts: 198

NOW he tells me! I've been riding my bike like this for two weeks now! shit

Really.... It is not a problem. The BEMF of the motor will charge the capacitors to the level that they can power the VESC. So the vesc starts up and runs normally. The thing you MUST NOT do is try to brake. The voltage on the DC bus, now without battery will rise quickly only charging the capacitors, not the battery. This may happen so quickly that the VESC does not go into error mode before blowing something up. 

IF the vesc measures the DC voltage every 100 microseconds, and you configure the max voltage at say 25V we can tolerate an over-voltage of about 25V. So now we get the capacitor formula: I = C dV/dt = .002 * 25 / 10^-4 . This comes out to 500A: So IF the voltage is checked every 100microseconds, AND the capacitors are 2000 uF. you should be OK, even with a 2.5V voltage margin and a "max charging current" of 50A. Some more things to keep in mind: Don't go faster than you'd go with that max voltage, braking on the VESC simply won't work. 

Keep in mind that all this hinges on the VESC firmware checking the voltage on the DC bus every cycle. If that is only checked say every 2ms, things get worse rapidly. Also say a filter would make things much worse... 

striderkent
Offline
Last seen: 6 days 9 hours ago
VESC Free
Joined: 2018-12-17 22:56
Posts: 7

Bringing this up again...as I just did the same thing. Ran the bike around without the battery hooked up and had it programed with a bit of braking applied on "off throttle".

Any ideas as to which components would have fried?

Now VESC won't power up with battery applied. Any possibility it faulted and could be reset?

Thanks!