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Unread 11-01-2009, 22:29
writchie writchie is offline
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Re: Current Measurement

Quote:
Originally Posted by DeepWater View Post
I'm not sure why we would ever need more than 50A. We can't have any motor on a breaker greater than 40A so why wouldn't 50A be enough. Same with the 20A and 30A Phidgets on 20A or 30A breakers. Please explain further if I am missing something.
Motor currents can approach the stall current for short periods of time. You can have loads of 60 amps for 2 second and 100 amps for hundreds of ms without exceeding the capabilities of the battery, breakers, or speed controllers.

If you limit yourself to breaker amperage, your measurements will be clamped at 50 amps during these periods. This may or not matter to your application.

In this years game, friction may limit the maximum torques and consequent motor current for drives. But you could still have higher currents in your mechanism, especially shooters.

Also keep in mind that the speed controllers are PWM. Your current is pulsed (around 100hz for victors, 15kHz for jaquars). You need to integrate the current over time to have an meaningful values.