If the center red wire from the ESC is not connected to anything and you are not exercising the throttle channel, then no matter how much you exercise the servos, the ESC should not draw any more power. The only possible change the ESC might see would be electrical noise from the servo current on the battery or signal wires. I doubt the ESC or its on board BEC would see any significant power increase or heating from noise either on the battery or signal wires.

Are you sure the ESC gets warm only when exercising the servos? Depending on the ESC, it could still be switching the mosfets even when the throttle is full off so that might cause a little heating but should not be increased just by moving the servos.

Originally Posted by jeffs555

If the center red wire from the ESC is not connected to anything and you are not exercising the throttle channel, then no matter how much you exercise the servos, the ESC should not draw any more power. The only possible change the ESC might see would be electrical noise from the servo current on the battery or signal wires. I doubt the ESC or its on board BEC would see any significant power increase or heating from noise either on the battery or signal wires.

Are you sure the ESC gets warm only when exercising the servos? Depending on the ESC, it could still be switching the mosfets even when the throttle is full off so that might cause a little heating but should not be increased just by moving the servos.

I'll check to see of the ESC gets warm with no servo movement.

Thanks and will post results.

Frank

I posted this in the CC forum, but also wanted to follow up wth this in this thread since it applies here.

The connectors are inside the fuselage so I couldn't disconnect the motor. I measured the temp before connecting the battery and the ESC was at 91 degrees. I connected the battery and after 9 minutes the temp was at 104 degrees (measured in the same spot).

So it looks like the motor is drawing current for some reason which is causing the ESC to warm up. Interesting results. I guess this is normal ops but I never noticed that happening before.

Frank

Does a switching BEC or UBEC waste the power (convert that voltage drop between the battery voltage and the receiver voltage into heat), as does a linear BEC?

If I use a 3S 2000 mah 11.1 volt LIPO battery (about 22 watt-hours) will it last just about as long as a 2S 3000 mah 7.4 volt LIPO battery (also 22 watt-hours)?

Which is better for use as a LIPO 6v receiver/servo power pack? 2S or 3S?

My intuition tells me to use the lighter of the two batteries. Correct?

Instead of dissipating the power not used (as a non-switching BEC does when dropping the voltage) the UBEC's switch the battery power on and off very rapidly to maintain the reduced voltage. Correct?

Why this is a hard answer to find on these forums is hard for me to understand. When making a purchase for a LIPO receiver/servo pack, this is one of the first questions that comes uop - 2S or 3S!

An additional question - should a capacitor be placed across a switching UBEC's output to minimize ripple (small high frequency changes in output voltage)? If so, how big of a capacitor (in microfarads)?

Depending on the design, they tend to be approx constant power for the power/efficiency rating point. So, (watts in) * (efficiency factor at that power level) = watts out. Because the input current will be less than the output current when the input voltage is higher than the output voltage, you have less resistive loss on the input side. Generally, the wiring loss is minimal unless it is a long run, so I don’t think that makes a valid argument 2S vs 3S. If you are going RX pack, probably 2S makes more sense. If you have a 3S aircraft, then use the main pack and save the mass, etc.

Most BECs have lower current rating with higher input voltage, so you have to give the spec some consideration vs your requirement. That is a bigger concern in 6-12S helis with massive servo draw.

BECs should have a spec on output capacitance- as an out-of-tolerance value can cause them to become unstable. Because they adjust very rapidly to voltage drops (i.e. a few uS), and your RX has a local cap, etc, seems the upside is very limited.

Hi, interesting discussion on the use of BEC and UBEC.

I’m new at “electric power”. I just got a 80 amp ESC which has no BEC.
http://www.ebay.ca/itm/110412093166?...84.m1439.l2648

info says , “Important Note: this ESC is Opto, without BEC supplying power to your Receiver, you need extra power source for your receiver. You can use a UBEC, a voltage regulator, or extra batteries as the power source for your receiver. ”

I used my regular 4 cell nicad flight pack with the receiver and everything seems to work ok.

Can I use this safely, or should I buy a UBEC instead? Thanks

Originally Posted by JohnAV8R

Hi, interesting discussion on the use of BEC and UBEC.

I’m new at “electric power”. I just got a 80 amp ESC which has no BEC.
http://www.ebay.ca/itm/110412093166?...84.m1439.l2648

info says , “Important Note: this ESC is Opto, without BEC supplying power to your Receiver, you need extra power source for your receiver. You can use a UBEC, a voltage regulator, or extra batteries as the power source for your receiver. ”

I used my regular 4 cell nicad flight pack with the receiver and everything seems to work ok.

Can I use this safely, or should I buy a UBEC instead? Thanks

No reason you can't use a separate battery for the receiver, but it adds a lot of weight. A UBEC will provide a lot more available power for the receiver and servos, as it draws power from the larger Li-Po flight battery, and it's lighter than a Ni-Cad pack. Also, the ESC has a low-battery cutoff designed to keep you from running the motor after the battery gets too low to power the servos and receiver, so you can always get the plane back to the ground under control. If you use a separate Ni-Cad pack, you'll loose this function.

Thanks Dave, good points. I'll get a UBEC.
John

I've read this thread again and "I think" we have come to the conclusion that a 3A BEC with the CC T-Bird ESC was not good enough.

How about this ESC http://www.altitudehobbies.com/brush...djustable-sbec ? It is 6A and looks to have a switching BEC. Will that be good enough for use for my circumstances? My 10A BEC gave up the ghost I think and instead of getting another one for $25, I'd invest in another ESC with the higher rated SBEC.

Thanks for the help.

Frank

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Thanks again! You are busy. The previous poster was very adamant on using something more than the 3A stock BEC on the CC ESC. But I ordered the ZTW ESC so I should be golden with the 6A BEC on it.

Thanks,

Frank

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I was looking at this plane the other day that runs on a 4S LiPo. And it uses a 2.5 amp BEC.

http://www.horizonhobby.com/products...4-pnp-EFL10075

ESC; http://www.e-fliterc.com/Products/De...rodID=EFLA1060

That makes me wonder how are they getting away with using the 2.5 amp BEC?

Frank