18V7 + Serial Adapter

Hi, my name is Alberto, I’m writing from Italy. I apologise in advance for my poor/bad English (typical Italian :laughing: …).I bought a kit 18V7 and a serial adapter. I have to manage one motor (12VDC 50W) via RS232. The power source for 18V7 is a 12VDC or a 24 VDC stabilized (not battery), so I thought to take advantage of the pin BEC (set at 5V with jumper) and GND for RC power to supply the 3,3-5V serial adapter instead of using an external source, then connect only RX and TX to the 18V7. Can I do this?
I noticed that there is a voltage transient at the power up of 18V7 (from pins BEC 5V and GND) to 5,7VDC which then stabilizes around 4.7VDC. Is better to use source 3,3V to avoid level transient?

Thanks in advance.

Hello, Alberto.

Since your motor is 50 W, that means it would draw a current of 4.2 A (50 W / 12 V) during normal operation. The stall current will be much higher than that, which means the Simple Motor Controller 18v7 might not be a good choice for this application. If you encounter trouble, you should try to figure out what the stall current of your motor is and consider using a more powerful Simple Motor Controller. It is generally a good idea to pick a motor controller whose continuous current capability is higher than the stall current of your motor.

Your plan for powering the serial adapter from the 5 V line sounds fine, as long as the adapter doesn’t draw more current than the Simple Motor Controller’s regulator can handle. The 5.7 V transient you are seeing is most likely an artifact of how you are measuring the voltage; I would not worry about it.

–David