Re: [CAD_CAM_EDM_DRO] A3977 Calculating ITrip

ghidera2000 wrote:

>I'm missing a vital bit of information about setting up an A3977
>based unit. The A3977 explains how to set ITrip (the current at
>which you want to cut off the motor supply) but I can't seem to find
>anything that specifically says how to determine what ITrip value
>you'd want to use.
>
>Lets say I use a 5V 1A motors. I'm going to be supplying them with
>20 volts which means the maximum current I want to allow is .25A.
>Is .25A where I want to set ITrip? Seems a tad high, supplying
>maximum current all the time...
>
>

No. You want to set it for 1 A. 0.20 A is roughly the average
current the
driver will draw from the power supply (for each phase). But, the motor
current should be 1 A. It will only connect to the power supply 20%
of the time, therefore the draw from the power supply will be 1/5th of
that, or .20 A.

>Is there a formula to determine the ideal current or even just
>a "increase until X happens" method?
>
>

Sure. Turn it up until the motor burns out, then run the next motor no
higher than 80% of that! Otherwise, use the manufacturer's data plate
rating.

Jon