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18v25 controller has low 5v fail


i have several (5+) 18v25 motor controllers and have discovered they are not very good about regulating the 5v BEC rail. wellthey are good at regulating it, but they all regulate it to 4.5v instead of 5v, and i am suspecious this is leading to issues with my rc reciever being spotty at times.

anyone else have this issue? whats up with that? are there schematics avail online anywhere so i can see if there is just an error, was an adjustable linear reg used and the wrong value stuffed? im running off a 16v supply fwiw.



Do you have anything else connected to your receiver or powered from the 5V BEC rail on the Simple Motor Controller? Can you try measuring the voltage on the 5V BEC rail with everything disconnected from it?



yeah, even on a brand new one with nothing connected to the 5v rail i get 4.5. a schematic or copper file would be a big help so i can probe out the issues myself.


We do not release the schematic for the board, but it is normal for that BEC rail to be around 4.5V. We have not heard of any problems with it not powering RC receivers in the past, although I suspect some RC receivers are intended to work with closer to 6V. Also, if you are powering other devices with that pin (such as servos), it might not be able to handle the current demands of your system. You might try powering your RC receiver from a separate supply to see if the issues go away. If they do, you could consider using a step-down voltage regulator to power your RC receiver (and other peripherals connected to it).



ok so i am now trying to use it in the cold (50 deg f) and therail has dropped to a meager 3.9 volts. there is nothing else on the rail except a spectrum rx module, so excessive load can’t be blamed. this is kind of absurd. 3.9v is not 5v. i have several hundred dollars worth of these things here in front of me, i shouldnt have to buy even more hardware to get it to work.


is there a zener generating this rail or something?


The relevant circuit is just a 5V regulator with a diode after it (which is there for dealing with USB power). That accounts for the voltage being around 4.5 volts, but 3.9 volts sounds really low. What voltage do you get with your receiver disconnected, and how much current does the receiver draw?



im using the same 18v15 simple controller and tried to power a arduino yun but the wifi is not starting to work .
just sometimes and in long interwalls i get a blink from wifi and lan port …i mean the power supply 5v does not a good job . and now im using a other bec 5v and it works .



As stated in the “Logic Power” heading of the “Connecting Power and a Motor” section of the Simple Motor Controller’s user’s guide, the 5V output on this board can supply approximately 150mA (in addition to the powering the board). Since the Arduino Yun can potentially draw upwards of twice that amount, it would not be appropriate for powering the Yun.