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Saw tooth UPS output

Saw tooth UPS output

Saw tooth UPS output

(OP)
I have a colleague who is working on a three phase UPS (MGE Comet). He attached his scope to the output and he is getting 480VAC phase to phase and a perfect sine wave which is as expected. He is reporting that when he goes from phase to neutral he gets a 277V saw-tooth. I do not have any pictures from his scope to post yet. This makes no sense to me as a PWM Inverter produces a PWM square wave which is then filtered to create a sine wave. If the sine wave is there for phase to phase then the PWM section of the UPS is working correctly. Any ideas?????

UPS Service Manager http://www.nolanpower.com

RE: Saw tooth UPS output

The voltage drop across the diodes in the mains rectifier adds to the sine. There is not much rationale doing that measurement. Especially not if you think that what you see is a problem. It is not.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Saw tooth UPS output

Gunnar, wasn't there a very similar question roughly a year ago? I've tried searching for it but can't find it. Perhaps my recollection is incorrect.

RE: Saw tooth UPS output

(OP)
VE1BLL

You have just confirmed that I am definately going senile! I just checked my threads and I did already post this problem last year. Everything blends into a blurr after a week or so!!!!!!

UPS Service Manager http://www.nolanpower.com

RE: Saw tooth UPS output

OK, remember that now. I misinterpreted the question this time. Thought you were talking about L-GND, but you say L-N.
So, it is probably third tone injection this time also. No need to worry, I would say.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Saw tooth UPS output

(OP)
IRstuff: Yes he should be using a 10x probe as that is the equipment that we gave him! Also- manufacturer very unhelpful as usual.
Gunnar: I was referring to L-GND as the output of this UPS should have the neutral grounded.

UPS Service Manager http://www.nolanpower.com

RE: Saw tooth UPS output

Obviously a 10:1 probe with ground clip to GND. No diff-probe and no Y1-Y2. The 480 V measurement sounds a bit dangerous without a diff-probe. But if battery-driven scope - OK.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Saw tooth UPS output

Quote (Postraithrovers1 )

he should be using a 10x probe as that is the equipment that we gave him

That is obvious, isn't it?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Saw tooth UPS output

Splitting hairs? Do we need to?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

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