Dshot reliability and wraith32 v2 ESC fire

Hey friends! I’d like to use Wraith32 35a v2 ESC on my 18" quad. In my previous tests I draw about 60a total on full throttle, so I thought they’d be plenty. When I test hovered it, it started with a yaw shake that you can see in the vibrations. I went to land immediately but a single ESC popped before I could get it down. Everything went super smooth in the motor test. Any ideas what’s up? Any help is much appreciated!

Arduplotter IMU graph

2018-06-01 15-45-13.log (916.2 KB)

Update, it popped both clockwise motor’s ESC.

I think the problem is in combination of 30V MOSFET`s (QN3109), 6S battery and low-Kv motors. In situation with static thrust (on stand) all works perfect, but when you try sharp acceleration- deceleration commands, voltage spikes may be very high. I have registered spikes up to 36V using 35A Bumpbee-s and 300 Kv motor until magic smoke came down. Adding additional low-ESR caps and maybe TVS diodes should solve the problem, but further testing needed.

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How long the wires are between the battery and ESC? Inductance in the leads from the battery to the ESC might cause voltage spikes that can kill an ESC.

Probably about 15cm. Too long?

I tried the Wraith32 Metal v2 today. Did fine in a 5 minute position hold test on a windy day.

I wouldn’t fly any of these modern ESCs without an electrolytic cap added on the inputs.

Alex, can you point me to a 3109 datasheet, pls ?

I’ve got the 50A Wraith_32 Plus with 400kV, 15 inch and 6S, with 1000uF caps added, and they work smooth and are just slightly warm to the touch after a flight.

QN3109 datasheet:
QN3109.pdf (238.7 KB)

I made some measurements on Wrath32 Metal V2 (T-Motor 4006 KV380, max. current about 17A):

  1. 30cm long Battery to ESC wires (sharp acceleration):

  2. 5cm long wires (sharp acceleration):

The voltage peaks are still high. These spikes make large changes in voltage potential between ESCs and flight controller. I’m worried about the processor pins on dshot and telemetry link.

Next weekend I will try to add an electrolytic capacitor and/or a TVS diode.


I love it when people go professional and start o-scoping problems. Speaks volumes for dedication.
Can’t wait a full week for the next results, tho’ :smiley:

@havran, can you explain a bit more about your test setup? Where are you measuring the voltage?

I assume you would be putting the cap on the power input to the ESC, close to the ESC?

Hi @tridge, a picture is worth a thousand words :slight_smile::

I also plan to measure the voltage drops/spikes on the groud cable (blue line) as a simulation of the cable length between ESC and PDB. This voltage will be reflected on the PWM and Telemetry lines.

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Here are the measurement results with and without the added capacitors.
Capacitors are Panasonic FR 470uF/35V (30mΩ) two in parallel.

  1. 30cm long wires without the added capacitor:

  2. 30cm long wires with the added capacitors (scale changed on channel 2):

  3. 15cm long wires without the added capacitor:

  4. 15cm long wires with the added capacitors:

  5. 5cm long wires without the added capacitor:

  6. 5cm long wires with the added capacitors:

So it is clear that ceramic capacitors are absolutely insufficient. Maybe a small capacitance?
Although they have 2200uF, the capacitance varies greatly with DC bias voltage:

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Them bumpbee esc are not reliable, in less than a week two gave up on 4S. Also the first ver waith were the same, not sure about v2.

If you don’t need telemetry, higher than 4S or 30A, i highly recommend these, RS30A V2, they are ~$12, pretty small and I have ~11K flights without any desync with 1950d/s rates and aggressive los freestyle, zero failures even when the motor failed causing a short, these esc just kept going. My quad pulls 130A (~1900W) on punch out, so ~32A each, and I have double heat shrink (one on the esc and one over the arm for orientation)

Glad to see this once again. You made it very clear with the scope, thanks! (although keeping the scale the same for each measurement would make for a more intuative picture)

Ever since this topic it’s gotten my attention: https://www.rcgroups.com/forums/showthread.php?952523-too-long-battery-wires-will-kill-ESC-over-time-precautions-solutions-workarounds

The only reason the small race-quads can survive with the original smd caps is because of the very short wires + small motor (despite the large current) and very high C-rated battery’s. If you change one of these things you need to add a capacitor imo. (it’s never a bad thing to add one)