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Old Jun 17, 2005, 03:50 PM
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radfordc's Avatar
Lansing, KS, USA
Joined Jan 2002
1,453 Posts
Answers to BEC overload problems.

Of late there have been several reports of CC controllers shutting down in flight with 3S batteries and three or four servos. The linear regulator on the P-10 and P-25 isn't designed to dissipate more than 5 watts and a fully charged 3S battery will start to overload the BEC at about .65 amps.

Dimension Engineering has developed two new products that are worth looking at. First is the ServoSense: http://www.dimensionengineering.com/ServoSense.htm
The servosense is an inflight current logger for radio gear. It is designed for use with regulated sources such as a BEC. ServoSense measures the following:
Max current that occurs during flight
Maximum average current during any 15 second interval
Average current over whole flight

The other neat product is the Park BEC: http://www.dimensionengineering.com/ParkBEC.htm
The ParkBEC is the smallest and lightest switch-mode BEC on the market. It weighs only 6.2g (4.1g without wires) and is specially designed for running parkflyer type aircraft with pack voltages up to 33.6V and as many as six sub-micro servos without worrying about an overheating BEC.

The beta testers for these products have been raving about their performance:
http://www.rcgroups.com/forums/showthread.php?t=373286
http://www.rcgroups.com/forums/showthread.php?t=367978

I've ordered one of each.

Charlie
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Old Jun 24, 2005, 05:56 PM
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kallend's Avatar
United States, IL, Chicago
Joined Sep 2004
3,568 Posts
I just got one of each in the mail. I was curious about the servo draw and the BEC in my Phx 25 running a Hitec Electron Rx, CSM gyro and 4 Futaba S133s.

Max current draw I could produce = 1.1A (while giving the tail a good work out with some pirouettes). This gives about 6.6 watts dissipated in the BEC regulator in my system.

Avg. current = 0.25A (or about 1.5W dissipated in the BEC)
Max while in a fairly steady hover = 0.4A, or 2.4 W dissipated.

Anyhow (and I know it's been posted before but I couldn't find it in a quick search) what is the max current and watts that the Phx25 BEC can reliably supply/dissipate?
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Last edited by kallend; Jun 24, 2005 at 09:57 PM.
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Old Jun 24, 2005, 06:15 PM
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radfordc's Avatar
Lansing, KS, USA
Joined Jan 2002
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I've read that 5 watts is about the max that the BEC can safely dissapate.

I checked my P-25 in a Formosa with 3 servos and 3S battery and saw peak current of .6 amp and 15 second max average of .2 amps.

Charlie
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Old Jun 24, 2005, 07:38 PM
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tadawson's Avatar
Lewisville, TX
Joined Dec 2003
836 Posts
Keep in mind that the 5 watts is a long term dissipation. For short bursts, even on 3S, the BEC can tolerate more. Keep in mind that these are SHORT bursts due to the low thermal mass involved due to the lack of a heatsink!

Having said that, I just flew my micro heli - 3xHS56 ,1Xhs50 and a CSM200 gyro on a PHX25 for about 15 minuted, and the entire controller stayed barely warm to the touch. Oh, motor is a JGF 400DH, ran at about 70 throttle most of the time . . . .

- Tim
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Old Jun 24, 2005, 08:29 PM
Dimension Engineering
Akron, Ohio
Joined Jan 2002
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Depends a lot on cooling airflow. I'd say even two to three watts on the P25 inside a non ducted fuse is asking for trouble.

Of course, if some Castle guys wanted to jump in here with the real power/temperature curves (at varying airflows even) that'd be better.
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Old Jun 24, 2005, 09:56 PM
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United States, IL, Chicago
Joined Sep 2004
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Agreed. I've been getting 15 minute flights on my heli with 4 servos+gyro and a 3s LiPo using the Phx25 BEC, with no problems.

Now, when my previous gyro went bad, I did have BEC cut-out, but no damage ensued since I was landing anyway and only about 6" off the deck.

It would indeed be nice to have the exact specs from CC.
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