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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.

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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