DRV8302 Magic Smoke

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RSR
Posts: 10
Joined: 08 Mar 2016, 16:58

Re: DRV8302 Magic Smoke

Postby RSR » 07 Aug 2016, 13:43

Nichicon UHE1J561MHD -- a general purpose capacitor with reasonably low impedance

(but if I should order new with even lower impedance, then I would consider Rubycon 63ZLJ680MG412.5X35)

RSR
Posts: 10
Joined: 08 Mar 2016, 16:58

Re: DRV8302 Magic Smoke

Postby RSR » 07 Aug 2016, 14:54

rew wrote:The PVDD1 pin powers a (wimpy: 30mA max) linear 12V regulator. <snip>


... a tiny linear regulator generating 1.3W heat, or even more? (12 x 4.2 - 12)V x 34mA = 1.3W -- that is plenty for a small area in the chip.

The output of the regulator is mainly the gate drive, which can, according datasheet page 22, be roughly estimated as Qg * n_fet * f_pwm = 280nC x 6 x 20000 = 34mA, which is slightly above the specified max 30mA, however that estimate is not necessarily valid for so large gate capacitance -- it is an estimate for average (not RMS) current -- ripple currents can lead to RMS much larger than average.

The datasheet says this is just a rough estimate, therefore: use a safety factor of at least 2 !!! This means I should lower the PWM frequency during 12S and FOC to 8kHz, or not at all run combination of FOC and 12S on the VESC.

rew
Posts: 904
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: DRV8302 Magic Smoke

Postby rew » 07 Aug 2016, 20:40

Yeah, but with a guaranteed output current of 30mA, there is usually a "current limit" in the regulator, set for nominally 1.5 times that current. This should imho prevent the track from blowing up.....

I think the "rough estimate" is accurate to about 10%. The differences from the calcuated values come from the DRV's internal use and leakage in the mosfet gates. That leakage is "zero" to the closest approximation....

IceNine
Posts: 5
Joined: 24 Aug 2016, 15:13
Location: USA Southeast

Re: DRV8302 Magic Smoke

Postby IceNine » 24 Aug 2016, 19:52

Sorry to necro-post but I just burned up my Enertion VESC 4.10 in exactly the same way while configuring FOC on 12s. I have already ordered a replacement DRV8302 and capacitors for the C18 mod. Is there anything else that is likely to be burned out? The chip burned the instant I hit the throttle so there was little to no heat involved other than the brief melting of the DRV8302.

Also, should I switch my batteries from series to parallel and go 6s or would this simply require higher amperage and cause the same issue?

rew
Posts: 904
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: DRV8302 Magic Smoke

Postby rew » 25 Aug 2016, 21:56

Lower voltage means a lower max speed. If you max speed is adequate at 6S then by all means go for 6S....

(If you would change the gearing for 6s to get back that higher top speed, then the required AMPs for the same power would go up and you'd have to check if that stays within range. But I don't think you're planning on that. )

IceNine
Posts: 5
Joined: 24 Aug 2016, 15:13
Location: USA Southeast

Re: DRV8302 Magic Smoke

Postby IceNine » 26 Aug 2016, 18:13

rew wrote:Lower voltage means a lower max speed.


Would lowering voltage also reduce the torque? The board is already scary fast so I'm ok with lower speed but I'm a very large man so high torque is essential.

rew
Posts: 904
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: DRV8302 Magic Smoke

Postby rew » 27 Aug 2016, 05:02

Torque is directly proportional to current. If what you have now is adequate, then that's not going to change when you lower the voltage. Current is limited by what you enter in the software. (and if you enter too high numbers then you'll blow things up).

In the old days, a 12V, 12W motor would have a resistor builtin that would limit the current to its max current of 1A under (close to) worst-case conditions (i.e. a 12 Ohm resistance). Of course they build that resistance with the wire of the motor. Nowadays, my 50V, 50A motor has a resistance of 0.014 Ohm. so that would be 3.5kA at 50V, and 180kW max power... It is the motor controller that is tasked with a 50A current limit to keep things in one piece...

vyckakk
Posts: 5
Joined: 20 Oct 2016, 10:44

Re: DRV8302 Magic Smoke

Postby vyckakk » 04 Jan 2017, 15:09

Hello, I burned drv8302 on my vesc 4.11 . I tested motor without load with FOC and after 5 min. it burned. What problem it is with this FOC mode? I am using 12S batteries and 4000KW motor.

rew
Posts: 904
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: DRV8302 Magic Smoke

Postby rew » 05 Jan 2017, 08:04

The vesc is not suited to run half a train. 4000kW is just below half the motor power of a French high speed train (8800kW).

[edit] Looking for a link to back up my claim of the 8800kW, I found: http://www.khurramhashmi.org/crbasic_in ... s-ICE.html A German ICE has less power under the hood: 2x4800kW.

arvidb
Posts: 205
Joined: 26 Dec 2015, 14:38
Location: Sweden, Stockholm

Re: DRV8302 Magic Smoke

Postby arvidb » 05 Jan 2017, 10:46

vyckakk wrote:Hello, I burned drv8302 on my vesc 4.11 . I tested motor without load with FOC and after 5 min. it burned. What problem it is with this FOC mode? I am using 12S batteries and 4000KW motor.

You need to be careful with your units. Capital K means kelvin, capital W is watt. But I don't think you have a "4000 kelvin-watt" motor (nor a 4000 kW - kilowatt - motor as rew interpreted it), but rather that you have a motor whose motor constant KV is 4000 rpm/V. (You are somewhat excused by the fact that this is erroneously written as "4000 KV" pretty much everywhere. This is equivalent to writing a current as "10 I" or a time as "10 t", i.e. confusing the symbol with the unit. The correct thing to say is "4000 rpm/V".)

Sorry, I don't know why your DRV8302 burned.


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