Can somebody help me solve a weird BEC issue? - RC Groups
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Jun 11, 2012, 03:49 PM
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Piece's Avatar

Can somebody help me solve a weird BEC issue?

(edited to reflect new information and testing)

My new 60A LeaderHobby ESC finally showed up from China and I'm eagerly trying to get my little foamy pylon plane running again. The ESC has a LeaderHobby label on it, but it's definitely a HobbyWing device. It has an internal switching BEC.

Anywho, the BEC puts out a solid ~5.25V as measured by my wattmeter. The most current I could get the servos to draw was 1.09A by circling the stick very quickly (with no load on the surfaces), and the voltage dropped to 5.08V minimum during that test.

However, as soon as I touch the throttle to run up the motor, the BEC cuts out for just a split second which causes the receiver to go to fail-safe mode and reset itself. The power is off and back instantly; my wattmeter backlight doesn't even turn off since it happens so fast but the meter does reset. I can see no obvious drop in BEC output voltage when running up the throttle.

If I'm very careful with the stick, I can get the motor running and then it's just fine. No throttle change seems to affect the BEC output once the motor is running; it's just the transition from stop to go.

What's going on here, and how do I fix it?
Last edited by Piece; Jun 11, 2012 at 05:24 PM. Reason: New information, change of plans.
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Jun 11, 2012, 04:19 PM
Yes, yes I am.
cjbucher's Avatar
I take it you are using 72 Mhz transmitter/receiver?

If so, you need to find a way to get the ESC and the receiver as far apart from each other as possible.

If it's not 72 Mhz - you might have another problem.
Jun 11, 2012, 04:32 PM
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Piece's Avatar
It's 2.4GHz (Spektrum DX6, the original DSM one). Now that I think about it, though, it's really acting more like it's losing the signal altogether than just normal, garden-variety glitching. The ESC went into a cutoff mode that I later learned is a result of a lost throttle signal. When I start putting the pieces together in my head, the servos are all jumping specifically to their failsafe positions and not just moving randomly as I thought earlier.


I'm definitely gonna look into other possibilities. I suppose this means I can't avoid tearing the fuselage open... again... to get the ESC out and do some more tests Could be a bad BEC, I suppose.
Jun 11, 2012, 05:25 PM
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Piece's Avatar
I edited the first post; it's definitely not RF noise as I originally said.

I suppose an external BEC would solve the problem, but I feel like the "power blink" is so quick and so consistent that there must be some other way to get around it.
Jun 11, 2012, 05:29 PM
Lardog's Avatar
I've used a number of Hobbywing ESCs (both branded and OEM) with and without external BECs. I've never had one do this. I suspect you simply have a faulty unit.
Jun 11, 2012, 06:09 PM
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Piece's Avatar
Partially faulty, let's say. It's making me nervous.

I just pulled the ESC out of the plane and hooked it up to a much smaller motor. Same issue, but now only when the ESC applies the brake and the motor stops. I tried on a 2S pack as well, and power was rock-steady the whole time.

I shut the brake off and tried on 3S again with the little motor. No issues. Worked perfectly. Switched back to the big motor on 3S with no brake and the problem is gone.

I'll test it more extensively in a few minutes. I'm not sure what'll happen when I try hitting it with more current; all tests so far have been with the motor unloaded.

I'll probably still run an external BEC instead just for peace of mind, but I'd like to know what's going on
Jun 11, 2012, 06:41 PM
Senile Member
Lnagel's Avatar
After reading all of your posts describing your problem I strongly suspect that your problem is caused by a loose, intermittent connection at one of the connectors or a broken wire making intermittent connection. This is reinforced by the fact that the symptoms randomly change after components are switched out which makes and breaks connections and flexes wires.

Jun 11, 2012, 07:22 PM
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Bruce Abbott's Avatar
Originally Posted by C₄H₁₀
The power is off and back instantly; my wattmeter backlight doesn't even turn off since it happens so fast but the meter does reset.
Either the ESC is putting a momentary dead short across the battery, or you have a bad battery connector.

I tried on a 2S pack as well, and power was rock-steady the whole time.
So it's OK with a different battery. Do you have another 3S battery to try?
Jun 11, 2012, 07:35 PM
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Piece's Avatar
Thanks guys. I'll check through the connections and probably resolder them just for giggles. Ordinarily my soldering is pretty solid, but mistakes certainly happen. I guess it could also be a loose factory joint in the ESC, though, and I used leaded solder on the pre-tinned leads. If the factory used lead-free then I might have five bad connections straight off. Clip, re-tin, no problem.

Bruce, I've got plenty of other packs to try but I'm 99% sure that the one I'm using isn't the problem. I'll try a few others just for the sake of completeness.
Jun 11, 2012, 08:51 PM
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Piece's Avatar
Went through my connections. Nothing's wrong. I even resoldered the battery connections just to be sure, and I clipped the tinned portions off and used all leaded solder on clean wire so I'd be positive of good joints. Prettiest damn soldering ya ever seen.

I'm now rather convinced that it's related to the brake setting or, more precisely, the braking itself. With the brake enabled, power to the receiver cuts out when the motor runs up hard or stops. With the brake disabled, everything works normally. I just tried three motors and everything is still consistent with my earlier findings.

The level of consistency and reproducibility of the problem sort of makes me doubt that it's an intermittent connection. I would think a connection issue doesn't know what ESC settings are enabled
Jun 12, 2012, 10:25 AM
Yes, yes I am.
cjbucher's Avatar
Well, there ya go. Looks like the Braking feature might be defective on your ESC (or the circuitry related to it). Or it could still be the BEC being a little on the weak side and when braking does it's job, it somehow affects the BEC to the point where it fails.

In either case, the ESC does sound a little flakey. If you can make it work without the brake then go for it but just be aware that there is something flakey about that ESC.
Jun 12, 2012, 12:12 PM
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Piece's Avatar
I think I'll just run it with a separate BEC. The ESC itself is rock-solid and it's just the BEC that cuts out. I tried with external receiver power, internal BEC disabled, and everything's fine. Worse case, radio power is guaranteed no matter what the ESC does.
Jun 13, 2012, 01:43 AM
F3A Team Finland
Finnspeed's Avatar
It could be conducting interference from the ESC/BEC also that causes the RX to hiccup. Is the ferrite in place in the RX wire? Braking and starting the motor cause large current spikes inside the ESC and these could partially conduct towards the RX.

Have you tried another (newer) RX? If it indeed is a short voltage dip of the BEC, connecting an electrolytic capacitor directly to the RX +5V and GND may be enough to filter them. As you probably know these are readily available with servo connectors attached.

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