# measure average current consumption

#### bug13

Joined Feb 13, 2012
2,002
Hi guys

How do I measure the average current consumption of a servo motor, so that I can calculate how many cycle my circuit can run for a known battery.

After receiving a signal from a user, the servo will go to position A, then wait for 4 seconds, then go back to the original position B.

How do I work out the average current consumption?

Thanks

#### WBahn

Joined Mar 31, 2012
26,398
Measure the current over one or more cycles and average it. How you do that depends on what measurement capabilities you have access to, which of course we can't even begin to guess at.

#### crutschow

Joined Mar 14, 2008
28,529
You can integrate the current with either a A/D converter and a microprocessor or an analog integrator with a long time-constant.

If the servo current is relatively constant when it's ON then you just multiply that current by the duty cycle (ratio of the ON to OFF time).

#### KMoffett

Joined Dec 19, 2007
2,918
I would think that in one position or the other, if the servo is always powered, the current would be pretty constant. The only variation would be during the brief period when it's moving from one position to the other. How often is it moved from A to B? Just measure the hold current and the move current. Calculate you average from that. If the difference between hold and move currents isn't great and the time between moves is long, then just consider the hold current.

Ken

#### THE_RB

Joined Feb 11, 2008
5,438
I use a 'scope and a series resistor on the power wire. You can move the servo through the required pattern, and the scope shows current at all points in time. Then a few calcs will give you a pretty good idea.

A digital 'scope or PC based 'scope is best as it can record slowly and gives you time to analyse the current waveform.