I'm using an Arduino Mega with the official Ethernet Shield 2 (non-POE) and a 12V servo (RDS51150, 5V PWM signal).
I use a common 5A 12V power supply for Servo and Arduino (via the VIN pin)
I have an optocoupler between the PWM Pin and the Servo (Sparkfun BOB-09118: ILD213T and transistor). However, the high side of the optocoupler is using the Arduino 5V pin
The whole setup runs at 40°C environmental temperature inside a casing (not completely closed, but temp definitely goes up inside)
The 3m SFTP cable runs a short distance along other data and DC cables (for motors)
The setup was running without issues for a couple of days. Last night something fried the Arduino and the Ethernet shield but not the Optocoupler and Servo. The power supply and Ethernet switch are fine as well.
Here some pictures of the damage on the Ethernet Shield (and a undamaged board for reference). The parts in the damaged area read "TR3GB" and "UY2nA".
It appears it got your camera or the room is filled with smoke. I think the problem is you overheated something. All electronics have a max operating ambient temperature, exceeding that can fry them. You need to consider the power being dissipated by the internal chips and there temperature rise in your ambient. I would expect the first thing to fry would be the voltage regulator. Post an annotated schematic showing exactly how you have wired this, be sure to show all connections, power, ground and note any leads over 10"/25cm.
Not a good idea. Electrical noise and/or high voltage spikes from the servo and associated power wiring likely destroyed the voltage regulator on the MCU board.
Avoid that by using separate power supplies, but connect the grounds.
By the way, 12V/5A is probably not sufficient for that servo. The power supply must be able to handle the stall current, which the servo briefly draws every time it starts moving.
Hi @jremington, thanks for your input.
It seems the voltage regulator on the Mega is still working, LEDs light up at least. Also the LED on the Ethernet Shield lights up. But only dim. I currently cannot access the Mega itself, will look into it in more depth once Im able to access it.
Would the situation improve if I add a DC/DC converter (VIN up to 36V) between the common 12V supply and power the Arduino via its 5V pin (or still via the Arduinos VIN pin with >7V to keep the onboard regulator and the protection on the board in the loop)?
Regarding the Servo: I'm using it way below its specs regarding the force. During normal operation its not using more than 1.2A, why I even installed a thermomagnetic 2A circuit breaker before the common power supply to actually "detect" a case where it stalls and could damage the mechanic setup. The circuit breaker never triggered.
That doesn't matter. All brushed DC motors briefly draw the stall current every time they start moving. The surge typically lasts around 10 milliseconds.
If the shaft is not rotating, it is by definition stalled.
It seems the voltage regulator on the Mega is still working, LEDs light up at least.
That is not a valid check. The board is obviously damaged beyond repair. If you insist on using Vin with the new board, keep the input voltage between 7 and 9V, from a power supply that is not shared with the high power servo.
Thanks a lot @jremington.
I assume the following would be the safest approach:
12V supply A: Arduino
12V supply B: Motor and additional DC/DC for generating the 5V (servo side) for the optocoupler isolating the PWM signal. The optocoupler also isolates the ground of both systems, to avoid loops.
Regarding connecting both grounds: 12V supply B (motor) is a simple, standalone power supply. Supply A (Arduino) however, would be a industrial grade supply inside another control box shared with other equipment like ethernet switches. I'm afraid that I could create a situation in this case that could impact the other equipment. What do you think?
7 to 9 V is better. You can use the Arduino 5V output for the optocoupler.
Common ground is not required if optocouplers are used for all signals. Ethernet signals are magnetically isolated, so common ground is not required there either.
If this is an industrial setup, you should consult a professional engineer with training in industrial installations.
Understood, as the on-board linear regulator will cause a lot of heat otherwise I assume.
What would be the downside of keeping the 5A supply? So far it did not have any issues with the servo movements itself even running the system for weeks.
