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Old Jul 30, 2007, 04:23 PM
Valid8r
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Basics of BEC's External vs. ESC based? Education needed please!

So I'm trying to understand the basics of external (switching and without an external battery) BEC's and how they work with respect to the resistance based ESC in a speed controller.

One of my questions is simply related to the general laws of physics which would be conservation of energy. If a switching BEC is not generating as much heat (as the one built into my CC ESC for example), it should be using less energy and therefore my battery should therefore have more energy to fly my plane - right? If so, why doesn't everyone use one?

Thanks,
Jon
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Old Jul 30, 2007, 06:16 PM
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Staffs, UK
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Standard BECs are not "resistance based" and not all ESCs use linear regulator BECs. Some ESC have switching BECs anyway.

A switching BEC does save some power and you do have more to fly the plane...but the total power wasted in a standard BEC is only a tiny fraction of the amount used by the motor so you'll never notice the difference. Say a typical flight motor is using 100-250W. A typical linear BEC wastes on average about 2-3W so even if you could save all of with a switching BEC you'd only have around 1% extra for the motor. That might explain why not everyone thinks it's worth paying extra for .

Steve
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Old Jul 30, 2007, 08:55 PM
Dimension Engineering
Akron, Ohio
Joined Jan 2002
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Switching BECs aren't about longer runtime, they're about less heat generated. The 1-2% difference in runtime is trivial, but if you overheat the BEC, the 100% difference in flight time is rather important.

The circuitry to make a switching BEC is approximately 8x more expensive than to make a linear BEC. This, and the complexity inherent in doing one well (ultra low EMI, good transient response, wide input range), is why they're not built into all ESCs.

If you're getting one to get more flight time, spend the same 6 or 12 grams on a slightly bigger battery. If you're using a 6V one to get faster servo response, then that's valuable in some applications. If you're running anywhere near overheating the linear BEC, then they'll save your plane.

A foamy running three HS-55s from a 2s pack doesn't need a switching BEC. A 4s T-trex does.
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Old Jul 31, 2007, 01:16 AM
Valid8r
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Ok, thanks guys that's helpful information. If I may, another question.

I have read here (in other forums) that switching BEC's are "prone" to producing radio interference. Comatose, you reference EMI above, so is this a real problem for switching BEC's or is that a function of the design and if so, which switching BEC's are known to be 'good' from that perspective.

Also, can anyone tell me what type switching or other does CC use?

My questions are out of curiosity mainly. I have always used CC ESC's but recently someone suggested I may want to go to an independent BEC which I don't really understand, hence the questions. I wasn't necessarily trying to save power, just trying to understand the why's and why not's of using dedicated BEC's vs ESC BEC's and also relating all of this to the RX low voltage issues talked about with the Spectrum RX's.

Thanks again,
Jon
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Old Jul 31, 2007, 08:55 AM
AndyKunz's Avatar
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All the Castles I have seen have LDO regulators in them. Some have split supplies.

Andy
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Old Jul 31, 2007, 06:49 PM
Dimension Engineering
Akron, Ohio
Joined Jan 2002
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Quote:
Originally Posted by Valid8r
I have read here (in other forums) that switching BEC's are "prone" to producing radio interference. Comatose, you reference EMI above, so is this a real problem for switching BEC's or is that a function of the design and if so, which switching BEC's are known to be 'good' from that perspective.
Its a gigantic problem for switching BEC design - our requirements in terms of EMI are much much more stringent than most applications. Its overcomable by very careful design, but its extremely nontrivial to do. For example, ParkBEC has literally 500 hours of engineering time in it just tweaking the EMI ever lower. We've got half a dozen aborted designs that just couldn't be massaged low enough to be releasable. FWIW, the abandoned designs radiated less than some on the market, but I'm not naming names.

All switching BECs will generate some amount of EMI, just like all speed controls will. A really good one will be below the noise floor of the ambient environment and not reduce range. A really bad one can cut your range in half, or worse.

I'll let others chime in with which BECs they're had good success with, because I make a living making them so I'm ever so slightly biased.
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Old Jul 31, 2007, 06:52 PM
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Joined Mar 2005
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Hi Jon,
The amount of radio interference a switching BEC will produce is pretty much a function of how good a design it is. Any teenage undergraduate can throw together a switching BEC design in an afternoon that will power servos. To get a design that won't radiate takes months...

I can show you some $9.99 'UBEC' clones that put HORRIFIC amounts of radiation out, and will knock your range down to 10% of what it normally is. On the other hand, Kool Flight System's UBEC is a great product and it puts out almost zero interference.
All of Dimension Engineering's switching BECs put out almost zero interference and will not affect your range. Zero range reduction is the #1 design criteria in all DE BECs. (Keep in mind that I designed some of these, so I will inherently be biased.)

External switching BECs also generally have more output capacitance on them, which usually means they have better load transient response, which means they will be better at dealing with sudden servo load changes.

CC uses linear BECs on all of their speed controls at this time, which puts out zero interference. They will be coming out with an external switching BEC very soon I hear.

If you are running a Spektrum 2.4ghz radio system then the radio interference isn't a big deal. Just make sure that you have the latest firmware on your receiver and that is supposed to help the low voltage issue a lot.
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Old Aug 01, 2007, 03:42 AM
hul
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Switzerland
Joined Mar 2003
2,115 Posts
Quote:
Originally Posted by Comatose
I'll let others chime in with which BECs they're had good success with
I have used these:
SBEC (not available any more ?)
UBEC http://www.koolflightsystems.com/ultimatebec.htm
SportBec http://www.dimensionengineering.com/SportBEC.htm
Jazz 80-6-18 with switching BEC http://www.kontronik.com/index2e.htm

of these the SportBec and Kontronik are best, SBEC worst for EMI.
I'll get another SportBec when I need another BEC. Small, light, works well and cheap shipping even to Europe.

Hans
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Old Aug 08, 2007, 11:21 AM
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Joined Jan 2007
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How about the XBEC by common sense RC?

http://www.commonsenserc.com/product...roducts_id=323

Seems to have all the features, and only 19.99.

But I am getting some glitching, even with my DX6. Not exactly sure its the BEC as I having ruled anything out yet.

Anyone else have any experience with this BEC?
Could I be getting interfierence if the ESC im using has a BEC built in?
The reason I used it was cause my ESC couldnt handle the 5 servos I threw at it.

I also like being able to power up my reciever without the motor. This BEC runs off the balancing tap of my batts.
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Old Feb 10, 2009, 03:44 PM
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Erlanger, KY
Joined Nov 2006
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I've got a little bit of experience with it

You may experience some frequency interference if the XBEC is too close to the RX. Also, make sure that your Spektrum RX antenna are at 890 degree angles (perpendicular to each other).

You want it as far away from the RX as possible. I also try to isolate mine from the ESC just to make sure any possible feedback from the XBEC doesn't affect the timing.

Joe Curd
www.CommonSenseRC.com
http://www.youtube.com/user/CommonSenseRC
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