Re: Gecko G201 and Drive Current ?

Hans,

Are you sure your power supply is doing its job?

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Hans Wedemeyer <xyz@h...>
wrote:

> Jon,
> The clamp-on amp meter is DC only, range FSD 0-1mA(one milliamp)

through 0-10Amps

> The old HP 428 is one of the few oldies (tubes) I keep around

because it is so handy.

> Calibration is easy to check and it is good.
> Here's one for sale on eBay http://cgi.ebay.com/ws/eBayISAPI.dll?

ViewItem&item=3308854547&category=4678

>
> I did the current shunt, simply placed it in the 0V return total

power supply. As the resistor is

> very low in value 0.027 Ohm I figured it would not influence the

overall performance that much, and the results are the same

> resisitor in circuit or not.
> My first measurement was wrong (posted earlier results) as the

signal across the 0.027 Ohms is so low

> and there is a lot of switching noise, I missed what appears to be

steps in the wave form.

> The new reading appears to be about 0.1V pp which would indicate a

total circuit current of about 3.7 Amps.

> I suspect the 3.7 Amps total should be divided by 2 (two windings

being driven) which would make the per winding current

> about 1.6 Amps.
>
> I have a 15,000uF Cap. at the Power input of the Gecko (6 inches

from it), total power lead length is 3 feet. Power unit is regulated
36 Volts 9Amp.

>
> The motor specs. are Current/Phase 5.6 Amps, Phase resistance

0.39, Inductance 4.1mH

>
> All measurements are taken with motor running. When the motor is

OFF the disable feature is active and winding current is reduced.

>
> One last thing that may shed some light on what's going on.
> I have zero experience with the Gecko modules, and based upon all

the massive heat sinks everybody seems to be selling for them, I
assumed at 5 Amps the Gecko Module should at least be warm... well

> it's cool to the touch and I only have a small 6" x 6" x 0.065"

heat sink during this initial testing phase.

>
> As my tests are under my control, I'm able to ensure there is no

over heating. I wish there was some heat ...that would indicate some
Amps are flowing..!

>
> I this ever works, final heat sink will be the case of the device

which is 0.375" think and has a surface area of over 4 square feet !
That should be enough to keep the Gecko cool....

>
> Any more suggestions would be welcome. In the mean time I'll work

on measuring AC current in a winding.

> Best regards
> Hans W
>
>
> Jon Elson wrote:
>
> > 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
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
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