Cheap mid Voltage supply

[tedmich]

I just picked up a pretty good deal on a low line low voltage PS; a B&K Precision 9110 60VDC Out Single Output DC Power Supply new, open box for less than $150 delivered off Ebay. Its a nice little supply that lists for about $350 from Mouser or Digikey. Its nice but its not going to help me build my version of the Alembic F-2B preamp, which can need as much 320VDC so I kept my eye out for an affordable PS in the 500-600 VDC range. Enter the EC Apparatus Corp EC135

electrophoresis power supply, $60 delivered. These are all over the Ebay, big beefy, linear and capable of 550VDC at 250W, runs CC or CV.
These will kill careless kids in Biochem Labs so they have a variety of safety features, including zero output when it has too low a load; don't want someone to grab dangling bare leads that are LIVE!
As a result there are a number of funny Ebay listings with a Fluke plugged into the EC Apparatus PS outputs reading ~2.3VDC (LOL) because the DMM is too resistive to activate the output circuit...maybe its broke? "unable to test!"

It turns out theres a simple mod to bypass this feature

the output filter caps are actually 2 series 47uF/450V with no balance resistors (?) so 23.5uF good to ~800VDC. I think I'll replace these old Nichicon axials with couple of 470uF 315Volts snap in caps that are the same size and I'll include some 240k 5w balance resistors, we'll see what the ripple is then, as now its got 3.6VAC ripple on a 560VDC output.

[tedmich]

swapped in a pair of Epcos 380uF caps and AC at 560VDC is down to under 1 volt, probably good enough for rock and roll!

[Helmholtz]

swapped in a pair of Epcos 380uF caps and AC at 560VDC is down to under 1 volt, probably good enough for rock and roll!

At what load (current)?

[tedmich]

At what load (current)?

I'll dig out my 100w load and see!

heres the only high impedance output you can get without the mod above

[Helmholtz]

heres the only high impedance output you can get without the mod above

Sorry, don't understand. What is high impedance output with DC? Can't read your meter setting either.

What I meant is that the ripple voltage of a power supply always depends on load current. Without a load, ripple should be zero.
So to compare power supply ripple you need to specify the load current.

[tedmich]

Sorry, don't understand. What is high impedance output with DC? Can't read your meter setting either.

What I meant is that the ripple voltage of a power supply always depends on load current. Without a load, ripple should be zero.
So to compare power supply ripple you need to specify the load current.

Sorry if I was unclear; these PS have special circuitry to have near zero output (~3VDC at a few mA) if the load has "'too high" a resistance. For this application (usually polyacrylamide gel electrophoresis or PAGE) thats about 2k ohms; it won't put out anything at higher resistive loading (like a parallel DMM or human).

This extra safety circuitry may be why it has an appreciable VAC ripple with a typical MOhm DMM input impedance after the above mod. I'll see where its at pushing 100W at 500VDC, maybe with and without the mod (which is easily reversible if I ever want to run a couple PAGE gels at home with a novice technician!)