Well, this is an interesting little conundrum...

[TimothyMoulder]

Good morning everyone,

I've got 2 servo driven axes that each use a Heidenhain glass slide to the motion controller for position and velocity. Drives are set to torque control.

The glass slides draw a ridiculous amount of power to operate, about 1.5 amps each. Since the motion controller cannot provide that much amperage, I've got a 5VDC power supply (PSP05-020S) feeding both of them. The power supply is rated for 4 amps.

This arrangement has run for several years without issue. A couple weeks ago, I noticed the mounting bracket for the power supply had broken, leaving it hanging in the cabinet by the wiring. No big deal, order another and swap it out.

Now, to be clear, this is the exact same model of power supply, from the exact same supplier. This is a like-for-like replacement.

So I swap it out, and suddenly, the glass slide for the first axis stops working. It jumps when I attempt to jog it, and trips for following error. The position display does not show anything, staying at "0.000" regardless of position. The second axis is unaffected and operates normally.

All the voltages are correct, so I swap the old power supply back in - normal operation on both axes.

Today I tried a second new power supply - same thing. Then, reasoning I may be drawing more amps than the single power supply can reliable source, I connected both new supplies in parallel - same thing. Put the old original supply back in, back to working normally.

Well, now I'm stumped. Unless I got two defective power supplies in my order, I have no good explanation for what is happening here.

Any thoughts?

Thanks!

Tim Moulder

 

[JesperMP]

Measure voltage, measure amps.

Connecting PSUs in parallel may or may not be possible, depending on the type of PSU.

 

[drforsythe]

I agree with Jesper. Measure the voltage and current of both the old and the new power supplies. Measure the voltage of each power supply prior to connection of the scales and after and compare the voltage drop (if any). It could be possible that the problem scale is failing and requires a slightly higher voltage than on the label. The old supply could be riding the high side of the spec and the new supply may not be able to hold the voltage high enough when connected.

 

[ndzied1]

Does the power supply have an adjustment for output voltage like this one?

Perhaps it is set lower than the scales need.

 

[PiperJohn]

Just because you install another of the same doesn't always mean its good. I've seen bad batches of new components come in.

Older power supplies used to be linear whereas newer power supplies are switching type.
Switching (SMPS) are less expensive to make but can be noisy if not filtered well.

It's difficult to know without a scope to monitor the output ripple.

I'd verify voltage, then...

Try a better quality PS or perhaps add a LC filter to mitigate noise.