Why would I want an external BEC when my ESC has one?

[JEB123]

Why am I hearing all this about running an external BEC so your motor and ESC run cooler? To my knowledge, a BEC allows you to power your Rx from your main battery, thus "eliminating" the additional Rx battery. It cuts your motor power to whatever you set, shutdown, 50% power, whatever, while still maintaining enough power to the Rx and servos to land the aircraft before losing control. I have the Scorpion 45A ESC which has a built in BEC. Except for maybe running a better BEC, why would I want an external BEC? Are these folks thinking of a voltage regulator? Is there something I am missing here? :confused:

[JEB123]

Anyone still awake out there?

[ginnz]

i think an external bec is only needed when you use an esc that doesnt have the bec..... as far as i know.

[JEB123]

Allright! Now I don't feel so stupid for asking. That's what I thought too, but let me not speak too soon, lots of people are asleep and I know I'll likely get ragged on soon ( I hope not, hehehehehe). Didn't misspell anything, did I? Hey, it's a tough room, no respect at all.
Thanks ginnz!

[TheBum]

I hate to burst your bubble, but that's not entirely true. From what I've seen, most ESCs in smaller helis have linear voltage regulators in their BECs, so if the current drain is high enough, they can overheat. An external BEC typically is a switching power supply, which doesn't bleed off excess voltage drop-related current in the form of heat like a linear regulator does.

[JEB123]

Okay! No bubble here, that's why I'm asking. Thanks for replying "TheBum". Well, I was right about the fact that I was missing something. I see the difference. I believe the Scorpion has a linear reg. in it. I just ordered 2 sport BEC's from dimension engineering, One for each TRex. Better safe than sorry. So much for my clean wiring job. Gotta give credit where it's due, you were right flexbs. And there you have it Rick, time to pull out the ol' wallet again! Ouch! Double ouch for me! Sorry, you too ginnz! :shock:
Flexbs tells me this is the best deal:
Here's the link:
http://www.dimensionengineering.com/SportBEC.htm

[Vulcan Grey]

I had to get an external BEC beacuse the BEC that was built into my ESC was only rated at 2A.

3 Hitec HS-65MG, 1 Hitec HS-81, and a Futaba GY-401 were too much for a 2A BEC.

The BEC I use now is a Castle Creations 10A max BEC.

My speed control is much cooler now.

[JEB123]

I had to get an external BEC beacuse the BEC that was built into my ESC was only rated at 2A.

3 Hitec HS-65MG, 1 Hitec HS-81, and a Futaba GY-401 were too much for a 2A BEC.

The BEC I use now is a Castle Creations 10A max BEC.

My speed control is much cooler now.
Yeah, you were pretty close to being maxed out. The Sport BEC's I ordered are only 3.5A and the spec says they will handle approximately 8 standard or 4 to 6 digital servos. That menas they're allowing a little less than 0.5A per servo. At that rate your 3 standards alone would use up 1.5A and the digital draws more. The GY401 only requires 50mA to operate, but I'd say you made a wise decision. Thanks for your input!

[JEB123]

I received this PM from a fellow HF with regard to the necessity of external bec's. "fyi: i just spoke to lucien miller who is the rep for scorpion and he said the builtin bec on our esc's have 5amp ratings which is more than enough and equal or better than the average external bec amp ratings, and he said they have not had any issues." Any responses from all you HF's to send back to him? I can read your minds...karnak say :bs

[Smiley]

BEC's not only help cut down on the heat generated by your ESC but also help cut down on any drop in voltage throughout the flight. The linear BEC's built into most ESC can drop their output voltage to the electronic under high loads. If this happens when all your digital servos want power then you can sag the power even lower. Get to low and your sensitive receiver (spectrum) might stop working. Putting a simple cheap BEC on a plane or heli is a nice way to help guarantee that you wont have a problem with power to the electrical system.

I use 2 amp BEC's in both of my flying wings just to be sure. The ESC's are buried in the wings and I don't want them to heat up. I don't always use BECs either. I have never used them on any of my heli's and simply use the phoenix series of ESC's which seem to do great in that application.

Smiley

[JEB123]

Thanks for your input Smiley, I bought 2 of Dimension Engineering's 3.5A SportBEC's for each of my TRex's. I'm sure they're well worth it even at $30 bucks each. :thumbup: Check it out: http://www.dimensionengineering.com/SportBEC.htm

[Lplate]

Am i weird for using both my Jeti Spin's internal BEC (which is a switching one) and an external Turnigy 3A-5A BEC simultaneously? This was based on my friend's suggestion. And I thought it was a pretty innovative idea. Hope there isn't any negative effect doing it this way.

How I did it...

My receiver and gyro/tail servo are powered by my internal BEC...
My Cyclic servos (inolab digital servos) are powered by my external BEC.

Weird right? Heheh.

[Lplate]

So in my receiver, you'll see the three cyclic channels with only a single wire in each.
And I used two pairs of male & female JR plugs to separate the three red wires from the three black wires. Did this so I didn't have to solder the wires/tabs together so i can still sell the servos by plugging them back into the original servo plugs.

[JEB123]

So in my receiver, you'll see the three cyclic channels with only a single wire in each.
And I used two pairs of male & female JR plugs to separate the three red wires from the three black wires. Did this so I didn't have to solder the wires/tabs together so i can still sell the servos by plugging them back into the original servo plugs.

Explain again what you did with the power wires? Can you draw a schematic, or take a picture? It sounds like it should work ok.