Hi Guys, I recently purchased a Gossen - Luna Pro lignt meter. I wasn't able to pick up a manual with the meter, so I went to Gossen's web site. I found the manual, but also found a note from the manufacturers of my meter that says I now need a battery adapter to make the meter work properly. Because mercury is no longer used to make batteries at 1.35 volts, I now need the adapter to step-down the newer silver oxide 1.5 volt batteries to the correct voltage. Do I ubderstand this correctly? I found the adaptor at B. & H. in New York but at $40 ( !!! ) I'm put off by the price. Do any of you have a suggestion? Alternative?
I believe the replacements are zinc-air batteries. The problem is you need to peel a cover off the air holes and let the battery sit (oxidize) so it comes up to power. The other problem is that once the cover is peeled, the batter will die in about 3 months whether it is used or not.
You could always solder a diode on line with the battery to drop the voltage as well. Don't ask me how, I went the zinc-air method, then went and bought a Sekonic L-358. My Gossen hasn'r seen daylight since.
The adapter is a long term fix, but make sure it will work. I have read in several places it may not work accurately.
You need a resistor, not a diode, and without knowing what the current draw of the meter is, it is hard to tell you which resistor you would need. You could also use a rheostat and vary the resistance until the circuit voltage is 1.35.
You would need to solder the resistor or rheo in-line between the battery terminal and the rest of the meter circuit. It is certainly do-able if you are willing to open up the case and are comfortable with a soldering iron.
PS I wouldn't go the mercury battery route as disposal is restricted by hazmat regulations.
I got the adaptor for my Luna Pro. Works fine. There are other options like the Wein cells (zinc air batteries), or I expect you could have the Luna Pro modified for the higher voltage. The adapter seemed like the least hassle to me.
Due to the trouble with battery I would do one of the following if I were you. 1. Not using the meter at all, just keep it for nostagia. 2. Try to find some mercury batteries although they are not legal. 3. Use an external battery pack that is regulated to a precise 1.35V. Something like 1AA pack with a regulator would do the job fine.