Converting my Omega D-2 enlarger to LED illumination

[Larry Gebhardt]

That is true, but ASA1000 already has the LEDs and the driver. For my latest head I went with blue and green LEDs, which I don't think you can get in a COB format. Have you tried one of the 50W or higher for an enlarger?

[domaz]

That is true, but ASA1000 already has the LEDs and the driver. For my latest head I went with blue and green LEDs, which I don't think you can get in a COB format. Have you tried one of the 50W or higher for an enlarger?

I haven't but look at this video as food for thought. He was able to achieve alt process prints on a conventional enlarger with a 100W UV LED. Perhaps a 50W or 100W RGB COB LED might be the way to go for a Silver Gelatin. Although, I think 100W would be way overkill if this modified enlarger can actually expose Cyanotypes (although it takes a while).

[Larry Gebhardt]

I've had reasonable success with a single 3W white LED as a point source in a Durst 138. I suspect the 50W COB would be way too bright for point source enlarging. But I see there are now Royal Blue and Green 50W COB LEDs, so those could be ideal for getting more power into my VC condenser light source. Thanks for the link.

[ASA1000]

The LEDs and driver ASA1000 has could be wired all in series or in a mix of series and parallel strings. The Meanwell driver he's using puts out a constant current of 1.05A and it will increase the voltage up to 60V to push that much current through. At 1.05A the forward voltage of the LEDs are just under 3V, so it is possible to put 20 of those LEDs in series and still be within the design parameters of the power supply and LEDs (based on the voltage vs current graph in the spec sheet). If you run two strings of 6 in parallel each LED would be driven with ~0.5025A and produce less light and heat and last much longer, but 12 in series will produce more light and still be well within the 1.5A limit specified by the LEDs and under the 60V limit of the driver.

The spec sheet for the driver is here, https://www.meanwell-web.com/content...PC-60-spec.pdf and from it we can see the driver has a "SETUP, RISE TIME = 500ms, 120ms / 230VAC 500ms, 120ms / 115VAC at full load". In my experience with that same driver it didn't seem that long.

For reference the LED spec sheet is at https://www.ledsupply.com/content/pd...umentation.pdf Based on the Relative Spectral Power Distribution of the 3000K LED I'd expect softer results. The neutral white has much more blue light, and it looks more balanced compared to the green.

16 is the max with the driver I'm using, but I dont like maxing stuff out. If I add any more light I'll probably switch to the 100-1050 driver. Drivers aren't that expensive ($15 - $20). Im thinking, if the corners of the frame are a bit dim, I might add one more led at each corner and then one on the outside of each 'run'. But it's all 'thinking' until I do some paper tests, which will be next week, if UPS does their part!

[Bernice Loui]

From that data sheet:


Observe the min output voltage spec and max output voltage spec. Lower the output voltage demands from the power unit higher the power dissipation (heat and more), stress on the internal devices in the power unit. This is due to the powered unit being a constant current device, not a constant voltage device..

If the LEDs are wired in parallel, light output variations will be greater due to the variations of LED forward voltage and thermal effects. On top of that, there will be light output variations with each individual LED due to production variations.. All this needs to be accounted for in the design to achieve good results.


Bernice

16 is the max with the driver I'm using, but I dont like maxing stuff out. If I add any more light I'll probably switch to the 100-1050 driver. Drivers aren't that expensive ($15 - $20). Im thinking, if the corners of the frame are a bit dim, I might add one more led at each corner and then one on the outside of each 'run'. But it's all 'thinking' until I do some paper tests, which will be next week, if UPS does their part!

[stevea]

I didn't notice that they had started selling coloured COBs. Has anyone looked at simply replacing the halogen/dichroic-filter pairs in a Ilford multigrade head? Means all the controllers, etc, will still work (although they'd likely require recalibration)...

cheers,
-steve

[ASA1000]

Heat rises, better cooling would be achieved by reversing the flow of the fan from blowing on the LED array to pulling the hot air up and out of the top.

Another way would be to figure out what light wave length(s) variable contrast paper is most sensitive to, then pick LEDs that best match the VC paper sensitivity range, apply a light output controller to each color LED (wavelength of light), put the LED's light output into an integrating sphere with the light output of this sphere into the enlarger (similar to a single light bulb). This results in a variable contrast paper light source that is more efficient with a very high degree of VC paper contrast control.

Not a simple project any more,
Bernice

Ive been thinking about your suggestion of reversing the airflow, but I dont see how that would work. This is a solid piece of 1/2 inch aluminum. if I reverse the flow there is nothing to keep the air on the surface. I'd have to have holes in the plate or something, otherwise the air would come in the 'vents' and be drawn to their fan without ever passing over the surface. If you have another way, please share that with me. And thanks again for the input!!