Re: [CAD_CAM_EDM_DRO] Gecko G201 and Drive Current ?

Hans Wedemeyer wrote:

>Here's my setup.
>Gecko G201 and PACSI H32 Series motor parallel wired to take 5.6 Amps.
>Gecko has a 120K Current set resistor this should be a 5 AMP setting.
>DC Supply 36 Volts able to supply Max 9 Amps.
>Length of cable from Supply to Motor 3 feet. 14 Gauge Wire .
>15000uF Cap. at the Gecko module.
>
>I did not get the power I expected. This motor is rate at 445oz-in and the project was calculated to
>need about 160oz-in.
>
>When it failed I started to investigate. First I used a clamp on Amp meter on the Plus Output lead of the PSU
>

Does this clamp-on meter read DC? Most don't. I suspect it is reading
the current peaks
of the chopping action.

>and started the motor. It read 1 Amp ! I know the reading is integrated, but I really did expect it to show at least 2-3 Amps.
>
>

Not necessarily. Your motor probably has a resistance of 2 Ohms or less
per winding.
5.6 A x 2 Ohms = 11.2 Watts per winding, or 22.4 W for both windings.
neglecting
switching and other losses in the Gecko, with a 36 V supply, you only
need I=P/V =
22.4/36 = .622 Amps when standing still! Do you have the local
capacitor that is
supposed to be placed at the power input terminals when the main
capacitor is several
feet away?

>This makes me suspect the Gecko.
>
>Does anyone have a good method to confirm the Gecko really is switching these windings at 5 Amps ?
>I have equipemnt to test... just tell me how to test this :-)
>
>

You need a low-inductance current shunt or a Hall effect clamp-on
current probe to measure
pulsed currents like this. a low-inductance current shunt can be made
from 10 1 Ohm 1/2 Watt
resistors in parallel. This will have a resistance of .1 Ohm at 5
watts. You can use this with
a DVM, or better with an oscilloscope. But, with the scope, you need
isolation, as the
motor outputs of the Gecko are not referenced to ground.

Jon