EEVblog #814 - Keysight N8762A 600V 5100W PSU Teardown

[EEVblog]

A look inside a dumpster Keysight/Agilent N8762A 600V 8A System DC power supply.
Where did the magic smoke escape from?
PCB spark gap video:

[gerrysweeney]

Dave,

Not sure how you would feed your single phase supply into "All three phases" as you stated because in three-phase there is no "common", what you would need to do is feed your single phase supply into L1 and L2 (or L2 and L3, or L1 and L3), any combination should work fine.

Gerry

[c4757p]

I do hope he didn't have the fourth (earth) terminal in mind when he said that.

[EEVblog]

Not sure how you would feed your single phase supply into "All three phases" as you stated because in three-phase there is no "common", what you would need to do is feed your single phase supply into L1 and L2 (or L2 and L3, or L1 and L3), any combination should work fine.

Yes, correct. I should have looked and thought harder before blabbing. Yes this is not a common earth supply, so have to hook up one phase to 240V only.
The earth is only a safety earth.
This has already been corrected on the annotation.

[EEVblog]

Actually, come to think of it, the small three phase wires (near the MOV's) going over to the smaller PSU board looks suspicious. No reason to do that really unless that board is doing some sort of phase presence detection. In that case I'm likely out of luck and the thing won't power up with a single phase hooked up. Murphy might ensure that.

[Yansi]

The phase-loss detection(protection) circuit is quite probable to be there. It does make sense, because if losing one of the phases, you will overload the remaining powered part of the three-phase bridge rectifier.

[Phoenix]

Actually, come to think of it, the small three phase wires (near the MOV's) going over to the smaller PSU board looks suspicious. No reason to do that really unless that board is doing some sort of phase presence detection. In that case I'm likely out of luck and the thing won't power up with a single phase hooked up. Murphy might ensure that.

I've seen similar (Magna Power) units with phase loss detection, these things would be pretty smart inside.

What you might find is that the big relays only close once the system is up and running and you've enabled the power output; and that the power circuitry and those big capacitors havn't been stressed at all. Only need to follow that low power/signal path with the blown MOV, input bridge rectifier and whatever that goes to.

[RobB]

Take a good look at the remaining Fuse specs Dave. Being a switcher it will probably require a set of fast blow fuses.
Apologies if this is a grandma and egg tale.

[MartinX]

Some three phase supplies like that can be fed by a single phase, you would have to look in the manual so see if it is possible. A certain input would have to be used like L1-L2 and some dip switch or jumper be set in the correct position, I have come across some Sorensen supplies like that. As I understand it in the US there are single phase 120-0-120 outlets that can deliver much more than 10A.

[crispy_tofu]

Hehe, you have 247V in the lab, I have 250V!  (probably because I live close to a substation)
According to this document, the absolute maximum in NSW is 264V, with a notification for adjustment at 253V. 

[EEVblog]

Some three phase supplies like that can be fed by a single phase, you would have to look in the manual so see if it is possible. A certain input would have to be used like L1-L2 and some dip switch or jumper be set in the correct position, I have come across some Sorensen supplies like that. As I understand it in the US there are single phase 120-0-120 outlets that can deliver much more than 10A.

Yes, good read of the manual required first.

[gardner]

There are many VFDs available that are designed to run three-phase industrial equipment (pumps, saws, mills etc) from single/split phase supplies.  I believe you will find something from China that is designed for 120V that can generate three-phase 208V at 0-300Hz for $150 or so.

Edit:

Here's a nice one:
http://www.ebay.ca/itm/110V-3KW-4HP-13A-VARIABLE-FREQUENCY-DRIVE-INVERTER-VFD-HY-FOR-CNC-SPEED-CONTROL-/281385471151?hash=item4183e18caf:g:cwQAAOSwsB9WAAB2

[rs20]

There are many VFDs available that are designed to run three-phase industrial equipment (pumps, saws, mills etc) from single/split phase supplies.  I believe you will find something from China that is designed for 120V that can generate three-phase 208V at 0-300Hz for $150 or so.

I was thinking of suggesting the same thing; but do these VFDs output something close enough to a sine wave for the PSU to consider acceptable? These VFDs often assume an inductive load, right?

[ro_ss]

I would assume that the rest of the PSU is fine owing to the relays.
I'd say that they plugged in the PSU with the switch off thus the relays would be off and no power is applied to the PFC board and the rest of the PSU wouldn't have been damaged hence there isn't any  damage visible.

[maor]

So I was going through tdk-lambadas promotional video and guess what I saw?

[crispy_tofu]

Link?

[Huluvu]

Dave - I assume the mentioned gluing at 9:30 is defined by the result of S&V Test.
The glue will be placed on the components where the resonant testing showing any weakness.

Rgds

[bktemp]

What you might find is that the big relays only close once the system is up and running and you've enabled the power output; and that the power circuitry and those big capacitors havn't been stressed at all. Only need to follow that low power/signal path with the blown MOV, input bridge rectifier and whatever that goes to.

I was thinking the same when watching the video.
If Dave is lucky, the MOV or some other low power stuff blew/shorted before the two big relais enabled the high power stuff.
If there are no shorts at the DC rail going into the PFC, then all the high power stuff is most likely fine.


Why is there a spark gap on the pcb under the common mode choke at the output? I have seen this on many common mode chokes. Does anybody know?

[maor]

Link?

it's in hebrew...
http://www.tdk-lambda.co.il/about/local-video.aspx?pid=495

[Arjan Emm]

This power supply looks very similar to the genesys 2U series from TDK Lambda.
http://uk.tdk-lambda.com/products/product-details.aspx?cid=3&scid=273

[EEVblog]

Dave - I assume the mentioned gluing at 9:30 is defined by the result of S&V Test.
The glue will be placed on the components where the resonant testing showing any weakness.

Could be, but the exact same leaded parts don't have it elsewhere, so if so it wouldn't be (or shouldn't) because of an actual leaded component modal reason. So could be a PCB modal component involved. But I suspect the reason for the stuff is not nearly this complicated.

[EEVblog]

This power supply looks very similar to the genesys 2U series from TDK Lambda.
http://uk.tdk-lambda.com/products/product-details.aspx?cid=3&scid=273

Looks the same!
Schematics for that one I wonder?

[EEVblog]

I would assume that the rest of the PSU is fine owing to the relays.
I'd say that they plugged in the PSU with the switch off thus the relays would be off and no power is applied to the PFC board and the rest of the PSU wouldn't have been damaged hence there isn't any  damage visible.

Could very well be. And welcome to the forum!

[Huluvu]

Dave - I assume the mentioned gluing at 9:30 is defined by the result of S&V Test.
The glue will be placed on the components where the resonant testing showing any weakness.

Could be, but the exact same leaded parts don't have it elsewhere, so if so it wouldn't be (or shouldn't) because of an actual leaded component modal reason. So could be a PCB modal component involved. But I suspect the reason for the stuff is not nearly this complicated.

I know from our resonant testing lab that they put the whole unit on the shaker and vibrate it according special standards/requirements.
You always have some special resonant areas where the board or components became oscillating. (that's why they put glue on it)
Another reason might be some safety issue if the component get loosen.

[station240]

L1 Fuse blown
L2 MOV blown
L3 Fuse Blown
Seems to be some sort of pattern here. 

Both fuses blew instantly, the remaining Line was then shorted to earth by the MOV.
Never seen a ceramic fuse blow hard enough for the magic white dust to escape from inside.

I'd advise caution with using it over single phase.
As 5,100W over 240V is 22Amps, and the start up current could be higher, after all it does have 32 Amp fuses on all 3 phases (well did have).

The phase detection can be outwitted with this circuit, on the low voltage side of the sense resistors.
http://www.homemade-circuits.com/2013/09/three-phase-signal-generator-circuit.html