MM Pro BEC updated? - RC-Monster Forums

SpEEdyBL · **MM Pro BEC updated? -** 05.10.2010, 03:26 AM

My current MM Pro that I bought a couple of weeks after the release date seems to have what I would describe as a weak BEC. When using it to power my JR9100s servo, the LED on my AMB transponder flickers when the servo is moving and shuts off completely with additional load. I put a Novak 25v 2700uF power capacitor across the battery slot of the Rx. It reduced some of the flickering, but that's about it. I've set the BEC at 5.0, 5.5 and 6.0v using 2s and 4s packs for the main power with the same results. My MMM never had this problem. And for the info, the esc only rarely shuts off for a split second at most.

My question is, has the MM pro bec been improved or is it still the luck of the draw if I buy another MM pro? I know other people do not have this problem with the exact same setup.

BrianG · 05.10.2010, 09:52 AM

Not sure if the BEC was updated, but all four of my "first batch" MMPros have BECs with similar results; the BEC in all of them will "shutdown" if the current exceeds somewhere around 2A. As a result, I only use this ESC with the BEC enabled in lighter vehicles (Slash 2wd, CRT.5, etc) where steering load is not very high.

ravin · 05.10.2010, 12:26 PM

I'm having the same problem with a brand new one.It's in a stampede with the stock servo(I also tried 3 other servos).

simplechamp · 05.10.2010, 01:01 PM

http://www.rc-monster.com/forum/showthread.php?t=26856

See that thread, both of us are having almost the exact same problem. We both added capacitors to the RX and it fixed the problem, no more glitching or shutting down. I'm starting to believe it might be the RX causing the issue. We were both using SR300's.

BrianG · 05.10.2010, 01:20 PM

I have noticed that Spektrum receivers are quite sensitive to ANY voltage dips and noise on the BEC line. So, it makes sense that the cap helps.

ravin · 05.10.2010, 07:37 PM

I put a novak cap on it and the problem is gone.

jhautz · 05.10.2010, 07:54 PM

I think its luck of the draw. I run mine in a 1/8 buggy with a 200oz digital servo and have no issues. A buddy of mine has one that worked great for a while then started having the weak BEC issues after running it for a few months. Another friend of mine has issues with it in his Hyper 10sc. Was stuttering when he gave it throttle.

Not sure what the answer is except make sure you have your endpoints set correctly and everything moves freely in the steering system to reduce the load as much as possible. Also, not a good ESC for servo overkill from what I can tell. Sounds like its designed right at the edge for any kind of heavy servo load. Also keeping any other "extra" components that arent needed like extra fans and such will also help minimuze the load on the bec.

BrianG · 09:19 PM

From lots of research and experimenting with switching BEC circuits, I've found that heavy loads (and/or shorted) on the output is VERY hard on the Schottky diode, and can also saturate the BEC coil. Not to mention if the main switching FET goes bad. Do that enough and I can definitely see it weakening or even failing.

A cap definitely helps supply a little extra current boost when needed, which makes the BEC "see" a more steady current flow. I would say anything around 1000-2200uF would be ideal. However, too much capacitance can cause issues on initial hookup when the caps charges. Of course, a cap won't help a BEC that has already been weakened, so don't wait to install one if you are using the MMPro in a heavier vehicle and/or powerful servo.

Obviously, a low ESR cap would be better, but regular 85*C caps are still better than nothing. It's really a simple matter to either buy a pre-made cap/connector or solder a servo connector to a cap, so there's no excuse not to run one.