CC BEC ,design flaw.
 

So here's the story.I was running my Erevo last week and the steering stopped working.I took it in and checked it out,and the servos had just stopped.Checked everything out and it seemed alright.So I thought OK stock servos it happens.Tried a old spare and it seemed to work fine.Put in a Digital Futaba,tested it with a 2s lipo and all seemed fine.Got ready to run on 4s,turned it on and ....smoked it.So I said to myself,could be a bad bec, grabbed my other 1 that I had from my Maxx.(The last time I had drove it my MM smoked)So tried it all out again on 2s and all was fine.Put in my JR servo,loaded up 4s and turned her on....smoke.So now I'm a little upset,slap my Novak system in my Maxx,only to find that it's servo's had been fried when the MM went previously,or perhaps the bad BEC had something to do with it.So at this point I ask on the brushless forum and someone said that when a CC bec fails it can just pass the input voltage stright through.So I finally got around to testing them today and that exactly what happened.Green light still on showing all is good,but they are putting out the same voltage thats going into them.I believe this is messed up.Why put out a product like this with no built in failsafe.I'm out a couple hundred in servos,all over something that IMO should not be able to happen.

this very subject has been discussed before and for this reason I will never use a CC BEC...here are a couple of links to good BECs....I run the Western Robotics High Voltage model

http://www.helidirect.com/product_in...oducts_id=4667

and the Koolflight is a good one also

http://www.hobby-lobby.com/ubec.htm

http://www.helidirect.com/product_in...oducts_id=4667

:oh: ^^^ That is a serious BEC!!!!

I've been running 2 CC BECs since they first came out with no issues on 4 and 5S lipos. I don't remember seeing any of those threads on problems, but I'm a bit concerned now, not so much about the servos but blowing my Nomadio React receivers which have become pretty rare and scarce to get for decent $$ w/o getting gouged on e-bay. I could easily see a fully charged 5S blow a receiver putting >20v through it.

If you are electronically inclined, a voltage sensing switch can be added to the output of the CCBEC so if the output goes above a set value (~6.5v should be good), the circuit simply cuts power. Basically just an op-amp with the CCBEC output voltage fed to the + input of the diff amp, and create a reference voltage (6.5v) using a zener and resistor on the - input of the diff amp. The output of the op amp can be a PNP transistor (probably a darlington) or a FET that actually does the switching. Should be simple enough.

I will never put another in my vehicles.These are both pretty new,probably neither ran 30 times.Pissed me off so much I put my Novak system in my Erevo just So I wouldn't even have to think about it.Not to mention not being able to get my MM replaced.I thought I was inclined,but you lost me. :) IMO that should be included with it.

My 2nd CC BEC crapped out on me this weekend.

Wow that bites asheck.

I'm not out to slam CC here but I did have a CCBEC fail with no use, after thoroughly checking and re-checking, my rx & servos were spared cuz it was running off 2S, (under the max for Spektrum) but for some reason the insulation on the rx lead of my (then) brand new MM almost completely melted off, I had no choice but to resolder a new lead on the PCB, which is not something I want to do again.

But....... those of you not racing- weight be damned- run an rx pack!

I really do not understand how weight is such an issue for plain bashing.

Just my 3 cents.

If i get some time this weekend, I'll throw together a prototype circuit and post the schematic. There's enough of these out there that some protection would be nice. I probably should go out and get a FET, but I'll most likely use a darlington transistor simply because I can make that out of the discrete transistors...

Well,can't help but grin here,Now that I have an open sevo spot that might be just the place to put a receiver pack. Brian I won't be using another 1 of these,but it sure sounds like it's needed,and you have me quite curious as to what it would take to make these safe.

That's a logical and pretty simple design, but it's been a long time since I etched a circuit and would have to spend as much on chemicals and supplies as buying one of those linked ones. Also - wouldn't the transistor have to support the full battery voltage so that it doesn't burn out just from overvoltage across terminals?

i have a dumb question for you guys, the MMM bec doesnt happen to have the same problem with passing input voltage through when it fails as does the cc bec?

I may be barking up the wrong tree, but is there any way a fuse of some sort could be added to the output? If it blows then the ccbec is toast anyway. I have played with the small buss fuses (slow blow) in my Cerwin Vega tower speakers... would something like that work? I know that fuses are usually used for over current purposes, any chance they could be used for over voltage?

I only ask as I have about 10 of the ccbecs, and all run $50+ receivers and $110+ servos. I can only imagine the flame that I would produce if one of them cooked either component.

I am a die hard cc user, but may have to move these becs along if they are questionable.

yeah, etching is a PITA if you don't have the stuff already. I would just breadboard it with the pre-clad PCB found at radioshack. There is a minimum amount of components so it should be clean. If you start adding things like status LEDs, and other fancy stuff, the circuit gets bigger. Enclose the whole thing (except the switching transistor/FET) in epoxy or something for protection.

And yes, the output transistor/FET would have to be rated for the battery voltage you plan to use and the max current you plan to draw. The good news is that ratings for 40v+ and ~10A are not difficult to come by.

It would depend on the design. IIRC, the MMMBEC also uses a discrete BEC design (as opposed to a BEC circuit IC like most BECs use). Patrick has said that ANY BEC that utilizes a discrete switching FET is subject to this type of failure. So, I would say that it is a possibility. However, we don't know exactly how the CCBEC fails to make it do that, so it's difficult to know if the same thing would happen to the MMM BEC.

A fuse is for over-current protection. We need over-voltage protection. The only way the fuse would help is if the CCBEC failed, sent full B voltage to the devices, and those devices pulled a lot more current. But, if that happens, the damage is already done. Many devices are voltage sensitive with little or no actual current flow. The only way I see to protect your expensive receivers/servos is to use an external voltage-sensing switch.

Oh this is nice to read about.
Anyone wanna buy my brand new and never used CC BEC?

Chances are nothing will go wrong. I've been using one in my Hyper8 with no issues. And I'm sure there are lots of them out there being used with no problems as well. It just seems bad because most people don't make new threads saying "my stuff works" - they just post when it doesn't.