Making new selenium photocells

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spektro

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Mar 30, 2020
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Hi guys!
I found a recipe for a selenium photocell. Only one ingredient is needed: selenium rectifier plate. Recipe requires 40x40mm square or 50mm circle plate, but I'm pretty sure, that smaller one will work as good.
Below is machine translated quote from a polish book.
Maybe someone will be able to produce new selenium meter.:D
How to make a selenium photoelectric cell? For this purpose, we take a single plate of an ordinary selenium rectifier, even if damaged, with dimensions of at least 40X40 mm or a diameter of 50 mm. First, we remove the white, shiny, metallic layer. After gripping with universal tweezers about 0.5 cm² the surface of the plate at its edges, heat the lower (iron) side of the element over a soldering iron or electric stove. When the top layer has melted, as can be seen from the sudden increase in gloss, rub the alloy with quick movements of a clean and hard brush until a gray mat surface appears. If this layer turns out to be shiny or there is a celery smell - the tile is damaged, eg overheated. After cooling, we solder the copper wire with one drop of tin to the remaining layer in the place where we held the pliers. Lead the second wire from the bottom of the plate (from the iron layer). For the tests, we connect the element to the terminals of the microammeter or milli-voltmeter. When a cell is illuminated, e.g. by sunlight, the meter needle must deflect. By illuminating the cell with a 100 W bulb from a distance of 0.4 m, we should obtain a voltage of 100 ... 110 mV (10 k ohm load) and the current of 30 ... 41 mA (load 50 k ohm). With 2k ohm load the voltage should be in the range of 45 ... 50mV
Click to expand...
 
I see many brand new photovoltaic cells currently listed for sale on eBay.
Perhaps one of the smaller models could be used in a camera light meter.

Chris
 
I just found 2 big selenium rectifiers (apparently no one cleaned electrics workshop in my work since the fifties). I'll give it a go then. If it works, then I'll try to get Leningrad or other dirt cheap selenium meter to experiment.

ChrisPlatt said:
I see many brand new photovoltaic cells currently listed for sale on eBay.
Perhaps one of the smaller models could be used in a camera light meter.
Click to expand...

As far as I know silicon cells aren't linearly sensitive to visible light. They are much more sensitive to red, so you'd need to block red light slightly with green-blue filter. Then, if voltage isn't too low, simple resistor voltage divider (potentiometer) should be enough to calibrate new cell.
 
I would love to see the workshop!

Good luck, I hope this works.

spektro said:
I just found 2 big selenium rectifiers (apparently no one cleaned electrics workshop in my work since the fifties). I'll give it a go then. If it works, then I'll try to get Leningrad or other dirt cheap selenium meter to experiment.

As far as I know silicon cells aren't linearly sensitive to visible light. They are much more sensitive to red, so you'd need to block red light slightly with green-blue filter. Then, if voltage isn't too low, simple resistor voltage divider (potentiometer) should be enough to calibrate new cell.
Click to expand...
 
It's also true that CdS cells (rarely used now, but once the norm) are also non-linear, with a higher red sensitivity as well. This is born out by my experience with the Leica M5, which gives me an overexposure of 1 stop, compared to my M6 and several hand meters, when used with a 25A red filter. No filter, it's dead accurate.
 
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