A question about servo power draw

c2tb34

I am posting this question in Propeller forum because the project I am working on is using a propeller.
If this should be in the Sandbox section, I apologize [noparse]:([/noparse]

TLDR below wall of text.

The project I am working on requires 11 servos and 11 RC time inputs. Each servo has its own
potentiometer, and a change in the potentiometer's rotation corresponds to a proportional change
in the servo's rotation. I have a wall power adapter which I will use to power the propeller and its
RC time circuits, and I have a second wall adapter which I am planning on using to drive the servos.
In research for this project, I could not find much explicit or straightforward data regarding the current
draw of servos. As I understand it, their current draw is rather variable and is related to the load and
movement status of the servo. The servos are rated to operate with 3.5-7.5 volts. The adapter I
plan to use to drive them with outputs 5 volts at 1 amp. Should I be running into any current issues?
Or is there not any way to tell?

TLDR: Will a 5 volt/1 amp power supply be enough to power 11 servos?

I will post updates on my project as I have time. And as a hint to what it is I am building...
it is quite handy [noparse]:D[/noparse]

Mike Green

A single servo can draw peak currents on the order of 1A when it's starting to move against heavy mechanical load. When in motion under light load, it might draw on the order of 150 to 250mA. When idle (not moving) a servo might draw perhaps 20-50mA. With the power source you've mentioned (1A), you could power one servo under heavy load, maybe 4 to 6 servos under light load, or all 11 servos if they're all idle. There's no way you could power any combination of these situations with the power supply you've mentioned. How big your power supply has to be depends on the details of how you plan to use your 11 servos. If you're only going to move one at a time, you might manage with a 2A or greater power supply. If you could use all at the same time, but mostly lightly loaded, you might manage with 4-5A. It all depends.

CannibalRobotics

Holding current can become an issue too if a servo is pushing against a load to hold it in place.
Timing on movement can help. If you don't have much holding torque then stagger the others so you are only moving one at a time or as few as possible at once.

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Dr_Acula

It might be quite difficult to find a power supply capable of running 11 servos all at once. As Mike Green says, up to 11 amps. That is a big wallwart.

I'm thinking a hacked PC power supply could do that. They need a dummy load, and I've used a stripped down motherboard (no ram no CPU) as a dummy load. Or power resistors on the 12V and 5V lines. Then you would have a high amp power supply.

Alternatively, four nicads and keep them topped up with a constant charge (that you turn off if over charged) and monitor for over and undervoltage and shut it off if one cell goes flat etc.

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c2tb34

Thank you guys for the quick and informative responses.
Most of the servos will be under a load during operation. The rest will be under a light load during operation.

Knowing that each servo could draw up to 1 amp (although unlikely to happen), and finding a single 11 amp
power supply would be relatively difficult, would it be overly shameful to use multiple 3 amp power supplies?

w8an

Whatever works! I would not be shamed by ingenuity and cost cutting measures.