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Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

mancoast

Oct 6, 2018
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Greetings,

I seek relevant forums and communities to document my issue and to formulate structured dialogs. With respect to the repair and restoration of a vintage DC power supply from the early 1980's, I need advice and direction. Majority of my experience exists on the computer designing systems, but this project sparks a new curiosity with vintage electronics restoration.

The Sorensen DCR 600-4.5B DC Power Supply, 0-600V, 0-4.5A, 2700W rests on my workbench with the system input voltage supplied from 208V 3-phase 20A because the Sorensen factory default M1 configuration needs 208 VAC for DCR-B series 2700-Watt models. The manual for this vintage Sorensen power supply exists on the internet (Document No. 165042 Rev F), however I am not sure if we can post external links here. Additionally, I have concurrently formed similar threads across a plurality of electronics forums, so know that there exists cross-posting.

When initially getting the device, the system's chassis fan activated with a flip of the main breaker, however little else occurred in the 7" high chassis. Troubleshooting at the component-level initialized by tracing the supply line voltages. The schematic reflects line voltage to a large transformer, so I verified voltage at those nodes. However, at this point I seek advice and directions. The service manual states, “DCR-B series supplies are phase controlled type with SCR's (Silicon Controlled Rectifiers) or Triacs at the input to the transformer, followed by a passive LC filter … Low dissipation transistors and diodes are located on a single printed circuit board while high dissipation devices are heat sinked to aluminum brackets and heatsinks.”

Replacement of the single printed circuit board (DCR control board P/N 586955-1) returned some progress. Now, the system generates variable voltage output when the main breaker activates, however I cannot reach the required 600V specified by the manual. What are your thoughts and advice?

Sincerely,
Mancoast
 

Nisar-von-Voltenbräackter

May 23, 2018
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May 23, 2018
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Polyphase Delta or Wye configuration? I anticipate in advance that a capacitor could had leaked or an SCR may had busted. Have you checked those components?
 

mancoast

Oct 6, 2018
6
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Oct 6, 2018
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Polyphase Delta or Wye configuration? I anticipate in advance that a capacitor could had leaked or an SCR may had busted. Have you checked those components?

Hello Nisar-von-Voltenbräackter,

To determine the configuration, should I report the transformer wiring in terms of M1, M2, or M3 for input voltage? (208, 220, or 230 Vac)

The PCB has already been replaced and the large capacitors in the chassis appear intact on visual inspection. None of the capacitors have any signs of leaking. Is there an easy way to test the large caps?

The SCR’s are buried in the chassis on the aluminum heat sinks. How do I test an SCR?

Thanks,
Mancoast
 

kellys_eye

Jun 25, 2010
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I am not sure if we can post external links here.
Relevant links are allowed and this site can support pdf uploads and/or images as required.

Post a schematic for the best response to your queries.
 

mancoast

Oct 6, 2018
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Oct 6, 2018
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Hello,

The service manual available here: https://www.ntecusa.com/docs/DCR80-33B_data.pdf
This manual lists the theory of operation, block diagram, and detailed schematics. Any suggestions or thoughts for how to proceed with the component level troubleshooting?

I started by tracing line voltage; is this a correct approach/process for fixing analog circuits like this device?

Thanks,
Mancoast
 

mancoast

Oct 6, 2018
6
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Hello,

The voltage will adjust down to zero and up to about 190V over the full range of the knob.
It does not suddenly drop to zero. This was verified using an external multi-meter.

What do you suggest to further troubleshoot?

Thanks,
Mancoast

Pictures:
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kellys_eye

Jun 25, 2010
4,880
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Do you have any experience working with such voltages?

Check the reference voltage first.
 

mancoast

Oct 6, 2018
6
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Oct 6, 2018
Messages
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Greetings,

Thank you very much for the pointers and direction. Reconfiguration of the resistors on the control PCB enabled an output voltage of 600V. This required removing the (4) 150k resistors from the old board and populating them on the "new" board.

Now I would like to perform a load test. Below are pictures of a very large 5.5 OHM resistor. What is the recommended procedure for load testing this PSU. What size wires are required from the terminal block to the resistor?

Thanks,
Coast

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kellys_eye

Jun 25, 2010
4,880
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600V into 5.5ohms is 100amps! The PSU would cut out (safety cutout, current overload) well before that was reached.
To load it to its maximum you would need to put the 600V across a 133ohm resistor.
 

mancoast

Oct 6, 2018
6
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I believe the fundamentals of Ohm’s law V=IR and the supplemental P=V*V/R. Does there exist 133 Ohm resistors that disapate 2700 watts without letting the smoke out?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
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I believe the fundamentals of Ohm’s law V=IR and the supplemental P=V*V/R. Does there exist 133 Ohm resistors that disapate 2700 watts without letting the smoke out?

Try some heating elements. You may have to place them in series/parallel.

At a pinch, get 13 or 14 10Ω 200W resistors and place them in series. They will also have to be mounted on a heatsink. Ensure they're rated for at least 1000V between the terminals and the case.

As a bit of a hint, you may find that 50W resistors are less than 25% of the cost of a 200W resistor, so it may make sense to connect more, lower power resistors together.

In a dummy-load I made for testing a power supply, I used 4 x 50W resistors in series/parallel because it was the cheapest option.
 

kellys_eye

Jun 25, 2010
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Does there exist 133 Ohm resistors that disapate 2700 watts without letting the smoke out?
Not directly..... Steve points you in the right direction though.

Getting a decent load for that unit at full power won't be easy nor will it be 'safe' unless you take adequate precautions. Fire is only ONE issue you're faced with.

A load of domestic filament light bulbs wired series/parallel might suffice and be easiest to assemble. Connect three 150W 240V lamps in series - make 6 like them and wire them all in parallel. Use standard light socket bases and 1000V rated hookup wire.

That'll make a load good for 720V and 2750 watts!

Wear sunglasses.
 
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