Author Topic: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown  (Read 27404 times)

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Offline AF6LJ

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #75 on: November 08, 2015, 05:06:45 pm »
Good Video..
Sue AF6LJ
Test Equipment Addict, And Proud Of It.
 

Online boffin

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #76 on: November 08, 2015, 08:22:01 pm »
I bet Dave has 3 phases distributed in his lab across different points of load. Extension cords and little bit of fiddling could do the job :-DMM  :-/O  >:D

I doubt it, it's a total waste of wire and effort running multiple phases to a small office like that.

In north American pretty much any building of more than about 1000 sqm would be three phase, so it wouldn't surprise me at all if Dave has 3 phase in his office, and dead easy to check.

Go to the main breaker and if it's a triple main breaker with breakers labeled ABCABCABC down the side it's three phase.  Each 'normal' circuit is one phase to Neutral.
Most houses are 2 phase 180 (at least in North America), double main breaker, and breakers labeled ABABABAB
 

Offline station240

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #77 on: November 09, 2015, 09:10:54 am »
It's been stated in several videos, The Lab does not have 3 phase, it's just a small breaker box on the wall. To get 3 phase would mean running a new cable downstairs to the main meterbox.
 

Offline Monkeh

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #78 on: November 09, 2015, 01:46:27 pm »
I bet Dave has 3 phases distributed in his lab across different points of load. Extension cords and little bit of fiddling could do the job :-DMM  :-/O  >:D

I doubt it, it's a total waste of wire and effort running multiple phases to a small office like that.

In north American pretty much any building of more than about 1000 sqm would be three phase, so it wouldn't surprise me at all if Dave has 3 phase in his office, and dead easy to check.

Go to the main breaker and if it's a triple main breaker with breakers labeled ABCABCABC down the side it's three phase.  Each 'normal' circuit is one phase to Neutral.
Most houses are 2 phase 180 (at least in North America), double main breaker, and breakers labeled ABABABAB

North America is not ROW.

Pretty much everyone else does things differently. And most of us do things much the same way.
 

Online Wolfram

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #79 on: November 09, 2015, 04:08:51 pm »
Incorrect, the three phase rectifier will always draw all current from the phase with the highest instantaneous voltage; which means a naive implementation of PFC after a three-phase rectifier will draw dramatically non-sinusoidal currents from each phase. Example:



Here we see a Y input going through a three-way rectifier, and then into R1, which is perfectly phase-correct by virtue of being a resistor (put another way, it implements your suggestion of keeping current in proportion to voltage). As you can see, the current waveform (red) is dramatically non-sinusoidal, as compared to the corresponding phase voltage waveform (green).

Ahh yes, I can see now where my naive picture went wrong. Thanks for the simulation  :-+
But I have to say, compared to a rectifier going straight into bulk capacitance, the above PF doesn't look that shabby to me. I guess around 0.85 maybe?
Can LTspice calculate the PF? Otherwise I'll see if I can take a shot at it, after I get some sleep.

Edit: I really should go to sleep. My sleepy state math gets me a PF of 0.83  :=\

Power factor is actually above 0.95, so it is not a bad solution at all. The first harmonic current is the fifth, at an amplitude of a fifth of the fundamental current.  It's a commonly used configuration, being significantly simpler and cheaper than a full 3 phase active PFC, while having very good power factor. One major advantage is that a simple off-the-shelf single-phase PFC controller can be used.
 

Offline max666

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #80 on: November 09, 2015, 11:07:24 pm »
Ah yes, thank you for correcting me, I should have just gone to bed.
Silly me calculated it by doing Fourier sine and cosine series and then managed to include both the sine and cosine series coefficients into the PF calculation 

Of course much quicker would have been to calculate it with PF = |P|/S ... meh.




With both methods I now get PF = 0.95577

Edit:
The first harmonic current is the fifth, at an amplitude of a fifth of the fundamental current.


So a low pass filter would be simple and effective, wouldn't it?
« Last Edit: November 10, 2015, 12:08:24 am by max666 »
 

Offline M4trix

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #81 on: November 09, 2015, 11:28:30 pm »
That's why I never liked maths. They say, gifted mathematicians are prone to schizophrenia!  :scared:  ;)
 

Offline max666

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #82 on: November 10, 2015, 12:02:43 am »
Me and myself can't agree to that, we both love maths 
 

Online Phoenix

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #83 on: November 10, 2015, 09:15:56 am »
So a low pass filter would be simple and effective, wouldn't it?

Would need a ginormous L and C to get the cutoff frequency into the baesbands. However, the PFC's have an LC filter (in some form) to attenuate the PWM frequencies, much much higher frequency than the fundamental and baseband harmonics though.
 

Offline max666

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #84 on: November 10, 2015, 11:46:45 am »
Oh right, we are talking ~250 Hz here.
 

Offline lm3baker

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Re: EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown
« Reply #85 on: December 07, 2015, 11:04:28 pm »
Dave, a good tear down.

Australia is NOT a 240V country. It is a 230V country. Vic and NSW still run 240V as nominal, but Australia as a country is officially classed as a 230V nominal voltage country. In any case, 247 V is nowhere near the "extreme limit of what is allow here". The limit is 264V in Vic and NSW. I get 255 volts here at the fuse box here but it is well within the maximum limit here in Victoria.

Nope. 253 Volts in Victoria. http://www.esc.vic.gov.au/getattachment/a6b85585-af03-4a2e-bb17-dfff74bbd886/Electricity-Distribution-Code-January-2011.pdf 255V is out-of-spec (but sadly not uncommon), and 264V would give a lot of modern equipment a short life.
 


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