3rd Prong on DC supply and electrostatic table conundrum?

[David New Jersey]

I have a 24V 1.5A DC supply that went south. It's like a laptop style, rectangular box supply, with the 2 prong, IEC-60320-C7 AC connector going into it.

So, it's a 2 prong AC input, with the 3 DC output pins, in a little metal barrel sheath which are:
+24
-24
gnd

It's easy to find 24V supplies that have the +24 and the -24, but not the third gnd pin. I think the 3rd pin is important because the machine being supplied has an electrostatic platform which "sucks" paper down against it, and I'm guessing that third ground pin might have something to do with that?

Opening up the broken supply the 3rd pin traces back to the power supply board trace ground.

If I buy a 2 pin 24V supply to replace it, using the 3 pin connector from the broken supply, should it be similar if I just run that 3rd pin to the ground trace of my new supply without the 3rd pin? Or, might there be special circuitry to manage events on that 3rd pin ground that might relate to the electrostatic table (wouldn't that be high voltage, and when I turn off the electrostatic table via it's toggle button and the static goes away, is it draining back via that 3rd pin to the PS ground trace)?

 

[(*steve*)]

You need to find a +/- 24V power supply. They'll be less common than you think.

When you say others have + and - 24, if they only have 2 connections, that means they are the negative and positive of the 24V output.

What yours has is a total of 48V output. with 24V between 0V (gnd) and +24V, and another 24V (with the polarity reversed) between 0V (gnd) and -24V

You can't just run another lead to do this. You *might* be able to get away with two of these power supplies, but that also depends on where and how the supplies are grounded (it may be to their -ve rail).

 

[shrtrnd]

I work pretty regularly on old Hewlett Packard x-y table plotter type recorders.
The electrostatic table has it's own separate power circuit, it uses 400VAC to energize the table. That's not going to have anything to do with your 24VDC issue. It will be it's own High Voltage circuit.
Your ground output SHOULD be the ground for your +/- 24VDC output. But you haven't told us the make or model of your equipment, so I don't know if it might be some special purpose Earth Ground for your device.
(I doubt that, but who knows).
SO. In answer to your last question. Your electostatic table power circuit is going to be separate from your DC 'Ground' issue.
Without a make and model, we can only speculate about the rest of your issue.

 

[David New Jersey]

Thank you for responding, sorry for not providing model info, I though it might be too proprietary and obscure a technology and couldn't google data sheets pertaining to it, but here it is:

Xrite (previously Gretag Macbeth) i1iO Robotic Color Patch Reading System.
http://www.xrite.com/product_overview.aspx?ID=754

Power Supply label/specs are (also in photo of label attached):
Mfgr: HITONG
P/N:ADP42ABC
MODEL: HTSW-ADP42ABC
INPUT: 100v-240v, 50/60hz 1A
OUTPUT: +24V 1.5A
Center Pin = +

UPDATE:
Seems like I just found the "approval" document for the same model power supply from the Chinese mfgr, but this doesn't have the 3rd ground pin (closest model to mine I can find online), but it keeps that question lingering, why the ground pin?

http://www.dianyuan.com/bbs/u/30/1120098520.pdf

Thanks all, the machine manufacturer using the supply (actually, Xrite, who monopolized the market by buying up Pantone and Gretag and others) extorts ridiculous "Flat Rate" boated repair fees for any repair work. They made me so mad when they did this that I started doing small repairs for people in the business in NY for free a few years back just to fight that kind of dirty business practice. Unfortunately, aside from easy PS repairs like voltage regulators and obviously blown components, I'm not experienced enough to sort out this little PS on my own. If anything, repairing or replacing this without Xrite's profiting is an exercise in keeping monopolistic practices in check...

Thanks so far!
David

 

[shrtrnd]

From what you told us, just make sure the replacement power supply is wired-in the same as the original. If it's a ground connection on the new supply, the wire to the DC ground plane sounds right.
I was just letting you know that your electostatic table is going to run off HV AC, and a separate circuit from the DC output.
Good luck.

 

[David New Jersey]

Ah ha, ok, well that makes sense if it's running on an AC circuit, so I'll run that ground line back to the DC ground plane, thanks for the advice and hope for the best!
David

 

[(*steve*)]

Is that images of the dead power supply?

If so, then is looks like the DC output is floating from ground (not uncommon) and that a separate ground connection is also supplied.

If you want to fix that power supply, I'd look at replacing those output caps.