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Old Jun 05, 2012, 01:40 AM
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Melbourne, Australia
Joined Jul 2005
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I looked only at separate switched BECs initially then compared them to a couple of ESCs I have with "2A" integrated linear BECs. Typical HobbyKing/HobbyWing 30A ESCs.

The integrated BECs I have run VERY hot at the same current as a switched BEC.

It will obviously depend on your battery voltage as well as the current you are pulling - I tested these at 12V which is as high as I would want to use an integrated linear BEC.

In summary:

1) An external switched BEC will always run cooler than a linear BEC at any reasonable load.
2) A switched BEC will handle higher applied voltage than a linear BEC (normally limited to 3S) since the linear BEC dissipates ALL the unused power as heat.
3) Even the cheapest switched BEC I tested kept working at high temperatures.
4) Don't believe any label that says more than 3A on a cheap switched BEC unless you actually test it. I have a "5A" one which shuts down at bit over 3A
5) The advantage of a linear BEC is that it generates much less electrical noise than a switched one - didn't look at that this time around. That's why the designers have to put a big ferrite ring on the servo lead of the switched BEC because they did fairly poor job of minimising the electrical noise it generates.
6) The only advantage of a linear BEC integrated into an ESC I can see is convenience and minimum weight for small planes.
7) If your ESC craps itself there is a fair chance your inbuilt BEC will too and you are cactus. With an external BEC connected to the flight battery you have a fair (but not guaranteed) chance of retaining flight control even if your ESC fries or the LVC cuts in at a very low value.

When I say switched BEC I mean an separate external switch mode BEC - the sort of thing you can buy for $5-$10 from HK. Typical of what a Bixler/Skysurfer/Easystar would use. There are fancier high quality ones, high voltage ones and specialised fail safe versions.

All my integrated ESC BECs are linear as far as I can tell.

I haven't looked at separate external linear (which are less common but have a good rep if used within their specifications) or switched BECs integrated into an ESC.

FWIW, I wouldn't use an integrated linear BEC on anything but a weight critical or small plane any more.

aj, the answer to your question ,"My question was supposed to be -> If I had a heat problem with an external linear BEC, would an external sBEC minimize or stop the heat problem. If I am reading your post like you wrote it, it appears that the heat problem would still be present. Am I reading your post correctly?"

is that an external switched BEC will normally run cooler than a linear BEC at almost all voltages since it is more efficient at turning input power into output power. There are a few cases where the linear BEC might be better when the input/output voltage is small but in practice it would only happen on 2S batteries I'm guessing. Haven't done the calculations.

So in one word, yes.

John
Quote:
Originally Posted by Limited flyer View Post
So are you talking about just testing seperate bec's or ones that are built in as well? What about swtch mode?
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