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Old 03-10-2012, 03:41 PM   #1
Glacier Girl
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Default Something else to check, your bec!

Rebuilding a trash can retrieved CAP 230, and found an interesting problem. Used an Hobby King 7.5 amp bec for it.

Plug in the pack to bind the receiver, rx lights up, but won't bind.
OK at less then 10 bucks, I guess I was due for a bad HK/Spektrum rx.

Toss it, install a second one. This one flashes for a split second then nothing.

Call me stupid, but I did this twice more, last one being a known good one. Same results.

Finally dawns on me to do some checking.
Check the output voltage on the bec and get 14.8 volts!!!

WTH! double check and I have matching voltages on both sides of the bec.

Pull the bec and remove the cover. Guess the poor joker on the assembly line that day couldn't read English. Printed right on the circuit board are the locations for power in and power out. And yep, they were wired backwards.

Backwards, there is nothing to stop or regulate voltage through the bec, so as assembled the rx's all got straight pack voltage.

I unsoldered and resoldered the leads on the bec and it now works like it should. Just wish I could say the same for the receivers.


So anywho, something else to check when building a bird. Check the bec output BEFORE connecting it to anything.

When I die, I want to go like my Grandfather did, in his sleep...... Not screaming like the passengers in his plane.
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Old 03-10-2012, 05:04 PM   #2
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That's good sleuthing.
Gotta love that kind of QA on parts.

fly
If you're going to learn to fly them, you have to learn to fix them.
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Old 03-10-2012, 09:10 PM   #3
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With how important a BEC is, and how inexpensively you can get a programmable Castle Creations on for ($22), it's one thing I have always felt was just worth buying name brand. This has definitely reinforced my thinking on this! Sorry about your RX's, that sucks!
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Old 03-10-2012, 10:20 PM   #4
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That's a real pain. Chinese quality control often isn't what it might be that's for sure.

Steve
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Old 03-11-2012, 12:18 AM   #5
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Originally Posted by JetPlaneFlyer View Post
That's a real pain. Chinese quality control often isn't what it might be that's for sure.

Steve
Exactly, as to the poor quality control, especially with discount brands.
I would rather push a proven linear BEC chip, than use an unreliable UBEC. In concept, they are not the best way to go about voltage regulation, but at least they work reliably withing their range. One thing people don't pay much attention to, is that most linear BEC failures happen with ESCs using 1-2A linear BEC chips, and not the 3A chip. Weak linear BEC chips on earlier Eflite ESCs caused a number of Eflite airliners to go down, which is completely irresponsible for a top dollar vendor. Pay attention to the linear BEC ratings, and only buy brands that are not penny cheap and use low rated linear BEC chips. I've pushed the heck out of 3A linear BECs on 3s and never had a failure, even with poor cooling. My one linear BEC failure: You guessed it, a twin EDF with 20A Eflite ESCs.

Another thing is that you don't need a 1million amp UBEC. Most importantly as noted in this thread, is that you need one that actually works. Consider that I've ran 5 sub-micro servos on 3s lipo with 3A linear BECs and never had a failure. With the 3s derating, the BEC was likely only supplying 1.5A if even that, dissipating the remainder of the potential energy in heat. That said, a 1.25A quality Dimension Engineering Park BEC has proven adequate for 5 and 6 sub-micro servos on 3s with several planes that I have.
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Old 03-11-2012, 01:18 AM   #6
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Originally Posted by NFA Fabrication View Post
With how important a BEC is, and how inexpensively you can get a programmable Castle Creations on for ($22), it's one thing I have always felt was just worth buying name brand. This has definitely reinforced my thinking on this! Sorry about your RX's, that sucks!
I've had a couple of CC ESC's a few years back where the servo connector wires were not properly crimped into the pins. The wires came out by applying a few ounces of force on the leadwires. It was obvious the assembler used the wrong size crimper die on the terminals.

Good thing the models were using an external 10 Amp CC uBEC. I've got 8 of the CC and Common Sense uBEC's, have tested them at 10 Amps plus, and other than the connector issue, had zero problems with them over the past five years.

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Old 03-11-2012, 01:26 AM   #7
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Originally Posted by Bill G View Post
Exactly, as to the poor quality control, especially with discount brands.
I would rather push a proven linear BEC chip, than use an unreliable UBEC. In concept, they are not the best way to go about voltage regulation, but at least they work reliably withing their range. One thing people don't pay much attention to, is that most linear BEC failures happen with ESCs using 1-2A linear BEC chips, and not the 3A chip. Weak linear BEC chips on earlier Eflite ESCs caused a number of Eflite airliners to go down, which is completely irresponsible for a top dollar vendor. .
Just a note:
The current ratings on those linear voltage regulators are only valid when the regulator has a BIG heat sink on it. If you look at the linear regulators on the typical ESC, these regulators do not have any heat sink.

The only way a linear 1.5 Amp voltage regulator will be able to handle 1.5 Amps continuously on a 3 cell LiPo battery, is if its bolted to an finned aluminum heat sink twice the size of the entire ESC. Same for the 3 Amp chips. Take a look:
http://www.wattflyer.com/forums/showthread.php?t=63779

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