I am tryng to power a servo (5V, high torque one) from an active POE (power over ethernet) splitter connected to a tp-link poe switch. The servo is controlled through an arduino.
The problem is that the splitter seems to blink, providing power to the servo only intermittently (for half a second or so, every two seconds or so).
Would anyone know of a way to solve this? I really need the power to come from my switch, which (rated at 190W total and 30W per channel) has more than enough power. Would you know if I was to buy an arduino servo driver shield whether this porblem would disapear?
It’s odd that the power does that. Are you sure there isn’t a problem with it?
What is the output voltage from the switch? It may be possible to add a simple rectifier diode and capacitor as sort of a local, but isolated, supply.
A servo controller won’t do any good.
So, the last time I had read up on PoE was 15+ years ago when it was first being developed – pre standardization. So I went and read up on it. I suspected there were some funky things going on in the background, and what I read backs that up.
The Wikipedia article has some good information, and this article explains what is probably going on.
First, the normal voltage sent over PoE is 48V, which is WAY too high for your Arduino and a servo.
Second, the powered device has to (normally) negotiate its power requirements with the power provider (switch.) When you mentioned the power switching off and on I suspected that was the case – that the switch was 'looking for" a proper PoE device and retrying. According to the link I provided that is indeed the case:
Once enabled, the PSE continues to monitor how much electrical current it is delivering to the PD, and will cut the power to the cable if too much, or not enough, power is drawn. This protects the PSE against overload, and ensures that POE is disconnected from the cable if the PD is unplugged.
It would help if you provided more details, such as the brand and model of equipment you are using as well as a schematic of how you are hooking up to it. A link to the switch’s manual would be much appreciated.
So the wirring is tp-link -> ethernet cable -> active poe splitter -> cables to the servo’s power (through a micro usb to 2.1 mm jack adaptor and a 2.1mm jack to screw terminal adaptor to get cables out of the micro usb of the poe splitter. I also wire the ground to the controlling arduino’s ground. Finally I wire an arduino pin to the servo’s signal line.
I was thinking that the switch might be turning power off if not enough current is being pulled but I can think of no way to remedy this.
As I mentioned, I’m not well versed in PoE. But I suspect you are right about the power. It appears to me you are doing everything else right.
What I would suggest is just adding some devices that draw constant power to create a permanent load. The servo only draws a minimal amount when not actually turning. I don’t know what the minimum load would be, but I would estimate something like 5 to 10 percent of the max. You might be able to reach that by adding some LEDs or maybe an incandescent bulb. Or simply a resistor. Something that draws 1 amp at 5V would draw 5 Watts, which would probably do the trick. A 5 ohm resistor would do that. Of course it would need to be rated at least 5 watts and ten is much better. Or a six volt light bulb that usually draws 5 to 10 watts would probably work fine on 5 volts. Or maybe attach something that actually serves some actual purpose.
Anyway, hope this helps.
