I'm controlling a servo from a 5V Arduino (Pro Trinket). I'm supplying 5V to the entire system from a 3A bench supply. scope_0.jpg shows the supply output when the motor's idle. Scope_1.jpg shows the output when the motor is not quite stalled, at which point it's drawing about 800 mA. I have the current limited to 1.5A at the supply. Why is the voltage drooping so much, and why is the ripple so high? I would think a 3A supply should be able to handle this without breaking a sweat, but it's a Korad, not a Keysight, so maybe not. Other explanations/suggestions? Thanks for your help.

 

Include RC Servo in your title! There are many other kinds of servo's in the world!
Max.

 

I'm controlling a servo from a 5V Arduino (Pro Trinket). I'm supplying 5V to the entire system from a 3A bench supply. scope_0.jpg shows the supply output when the motor's idle. Scope_1.jpg shows the output when the motor is not quite stalled, at which point it's drawing about 800 mA. I have the current limited to 1.5A at the supply. Why is the voltage drooping so much, and why is the ripple so high? I would think a 3A supply should be able to handle this without breaking a sweat, but it's a Korad, not a Keysight, so maybe not. Other explanations/suggestions? Thanks for your help.

Try turning the current limit up and see what happens.

 

Include RC Servo in your title! There are many other kinds of servo's in the world!
Max.

Oops. Unable to edit it.

 

Try turning the current limit up and see what happens.

Bumped it to 3A; no change.

 

Bumped it to 3A; no change.

One more idea.
Try adding a large cap to the output of the supply. Maybe 1000 ufd or whatever you have handy.

 

I'm controlling a servo from a 5V Arduino (Pro Trinket). I'm supplying 5V to the entire system from a 3A bench supply. scope_0.jpg shows the supply output when the motor's idle. Scope_1.jpg shows the output when the motor is not quite stalled, at which point it's drawing about 800 mA. I have the current limited to 1.5A at the supply. Why is the voltage drooping so much, and why is the ripple so high? I would think a 3A supply should be able to handle this without breaking a sweat, but it's a Korad, not a Keysight, so maybe not. Other explanations/suggestions? Thanks for your help.

Sounds like it isn't a very good power supply. Do you have an alternative power source?

 

One more idea.
Try adding a large cap to the output of the supply. Maybe 1000 ufd or whatever you have handy.

Good idea, thanks. I'd tried .1 uF and 4.7 uF without any effect before posting here. Still, the biggest I have on hand is 2200 uF and, while it helps in the unloaded case (scope_2.jpg), it doesn't help with the voltage droop in the loaded case (scope_3.jpg), though it has a big effect on the ripple

 

Good idea, thanks. I'd tried .1 uF and 4.7 uF without any effect before posting here. Still, the biggest I have on hand is 2200 uF and, while it helps in the unloaded case (scope_2.jpg), it doesn't help with the voltage droop in the loaded case (scope_3.jpg), though it has a big effect on the ripple

Hmm, to bad.
Sounds like something is bad wrong with your supply. Do you have a schematic for it?

 

Hmm, to bad.
Sounds like something is bad wrong with your supply. Do you have a schematic for it?

No, it's a commercial bench supply (Korad KA3005D-3S), but I substituted a power supply harvested from somewhere that I had lying around and that solved the problem. Sounds like I need to ditch the Korad. Too bad. I really liked it until this.