Luna Pro battery adapter $$$$

chip j · Feb 9, 2014

Why do these cost so much -$60@B&H? They're just a small metal sleeve w/a bump in them.

Tom1956 · Feb 9, 2014

If they are voltage regulators designed to use the 3v silver battery combos and regulate it to 2.7v, then the silver battery's ability to give flat response (output) over its lifespan; is enhanced to approach or rival mercury batteries. I'm not sure what they are--just heard of them. But if what I believe is so, then it is the best 60 you'll ever spend. If you have a luna-pro with its cell still running linear, then you have the best meter ever made.
A few years ago I researched this subject exhaustively. I found a man who actually had designed and had some prototype regulators made to his order. I bought one of the remaining prototypes after he got married and his priorities changed, and abandon the project. I wired in my little regulator into my luna-pro's power supply circuit, and it has performed beautifully. You get accurate readings till the batteries' last gasp of breath, then dies. Flat as a pancake is the resonse till that last gasp.
Or you can tinker around with hairbrain schemes and never have an accurate meter for more than a few days till the voltage curve changes. BTDT

Kawaiithulhu · Feb 9, 2014

The battery adapter isn't a regulator, just a precise voltage drop and form factor fix for silver oxide battery replacements. Silver oxide batteries have the same lifespan property of mercury, their voltage doesn't drop until the end and so the regulation isn't needed.

The cost comes from this: "high volume low cost or low volume high cost, pick one" It's a niche item with some tiny electronic bits and it's still cheaper than sending a Luna Pro out to the one or two shops that can modify the guts inside the case directly.

Tom1956 · Feb 9, 2014

I think you need to further study the voltage curves. Silvers are not flat but for their first 50% of their lifespan. From that point they become no better than alkalines. But the subject is now moot with your information that they are not true regulators. The prototype I bought was a true regulator, even with the ability to raise voltage when the 2.7v fall-off point had been reached. At least, within a reasonable timespan. But by then, the actual battery curve was so far along as to be near depletion, anyway.

Tom1956 · Feb 9, 2014

Modify the guts? Well, heck, I can do that with 2 shakes of a lambs tail. What's that going to do for the lousy curve of most batteries? Like I said--BTDT.

Tom1956 · Feb 9, 2014

See this link:
http://www.houseofbatteries.com/documents/357-303.pdf

Kawaiithulhu · Feb 10, 2014

Tom1956 said:
See this link:
http://www.houseofbatteries.com/documents/357-303.pdf

Awesome, thanks! I'll keep my batteries on a shortened replacement schedule now.

Eventually I'll replace my old Luna Pro that I've had since HS in the late 70's, but for now this is how I've kept it running.

Tom1956 · Feb 10, 2014

Sure, friend. But there's no reason to replace it. Keep an eye on lower end response for accuracy. That assured, your CdS cell linearity is still good and there's no reason to get rid of it.

AgX · Feb 10, 2014

Do it yourself, with the manual by de Gruijter:

http://www.buhla.de/Foto/batt-adapt-US.pdf

Xmas · Feb 10, 2014

google battery cell problem and as well try this link...
http://rick_oleson.tripod.com/index-111.html
but silver cells are close enough?

if you use the meter every day use a Zn air cell if infrequent use a silver cell and diode replace every 18m.

for an accurate light meter I use a Weston II or III

the local village electical shop still sells Shockety diodes (Maplins).

oops AgX posted the other link

Tom1956 · Feb 10, 2014

Speaking from my point of view, all these links are almost comedic. I've read 'em all. For a whole year I studied this problem from every point of view. But each time my studies ended up at the same conclusion. A silver battery is a fair performer compared to the mercury. But its failings still did not stack up. Schottkey diodes, adaptors, re-adjustment of sensitivity... you name it.
I guess I'm claiming to be a self-proclaimed expert on this particular subject. And there's not much in this world I can lay claim to such a level of knowledge and proficiency. A voltage regulator is the only answer, if you want a perfect result; which I actually finally achieved. OK. I'll shut my yap on this one, guys. The second best idea was one von Hoegh came up with on his Nikkormat. But I've only been here a year and didn't know about his wein idea

Xmas · Feb 10, 2014

HiTom

Sure a voltage regulator and a higher voltage battery would work but I've got a large number of cameras that would need one as well as two lunasix...

But ignoreing your expertise

Zinc air cells are so close to 1.3v, they are available as hearing aid or Wein and economic for a working pro who will use the meter regular they have limited life in service, ie once you remove the seal a few months... and may turn on slow...

The silver cell is ok if you discard early and fit a diode adapter. If you drop the adapter and it dissapears into a drain you are stuck. You can test the battery with multimeter & resistor before a shoot, they are on shelf life time with a Lunasix unless you clamp the rocker down discard after 18m

It is easy for me to add a Shockety diode internally and stick a label to remind me (use AgO). But is nice to use a K1000 and not have to worry about a shop open on Sunday... even silver buttons are difficult.

A Weston II/invercone is way cheaper than your regulator I always carry one as a backup.

Ian Grant · Feb 10, 2014

I bought an adapter off ebay for mine about 6 years ago, not expensive at all particularly as it included the batteries.

Ian

AgX · Feb 10, 2014

Tom1956 said:
Speaking from my point of view, all these links are almost comedic. I've read 'em all. For a whole year I studied this problem from every point of view. But each time my studies ended up at the same conclusion.

Why do you not sum-up your findings and ideas and post them here?

In case a voltage regulater would be necessary, then a smd-circuit could still be tiny enough to be placed inside a camera- or meter-housing, for those who want to manipulate their gear. (On the assumption that the substituting cell still fits in the battery chamber.)

Those who have a U/I regulated power supply can mimic the different states of a cell and check what effect on metering/working of their meter/camera it has.

BrianShaw · Feb 10, 2014

Interesting. I've been assuming for many years that Gossen knew what they were doing.

pstake · Feb 10, 2014

BrianShaw said:
Interesting. I've been assuming for many years that Gossen knew what they were doing.

+1

My Luna Pro S has a voltage-dropping diode installed for modern batteries, and is recalibrated to work with those batteries.

It's darn near spot on with my Luna Pro SBC, from top to bottom.

benjiboy · Feb 10, 2014

Photography is an expensive hobby $60 isn't such a fortune in the scheme of things because Wein cell Zinc Air cells are expensive and don't last very long, in the long run the voltage reducing adaptor is probably the best option, and you know it will work correctly.

oldlincoln · Feb 10, 2014

Internal Battery conversion

I use a forward biased germanium diode like a 1N60 on single cell applications (OM1 et al) and sort through some regular silicon diodes (1N4007) for a .5 VDC forward drop for 2 cell applications like the Luna Pro. I use the PX625S silver oxide cells in mine they fit without a diameter adapter and last for years.

Tom1956 · Feb 10, 2014

AgX said:
Why do you not sum-up your findings and ideas and post them here?

In case a voltage regulater would be necessary, then a smd-circuit could still be tiny enough to be placed inside a camera- or meter-housing, for those who want to manipulate their gear. (On the assumption that the substituting cell still fits in the battery chamber.)

For a couple reasons--it's been a couple or 3 or 4 years ago, and I have only the recollection of having done it, but no notes I can gather. The years pass so fast now, what might have been 2 years ago could actually have been 4.
And for another reason. I don't want to come off as an overbearing know-it-all, daring anyone to challenge me.
It's enough for me to know I satisfied myself on the question of what would happen to the last roll of film before discovering the silver batteries had finally died. Because that roll would surely be over-exposed, for an occasional shooter such as myself. For those who shoot a lot, then that translates into several rolls overexposed because of the curve-falloff in battery output. To me, this was unacceptable. I continued on till I was happy even the last roll was shot with an accurate meter still running at 2.7v

BrianShaw · Feb 10, 2014

Tom1956 said:
... I don't want to come off as an overbearing know-it-all, daring anyone to challenge me...

Not to beat this dead horse even deader but publishing one's research, findings, and conclusions serve the communiy as a whole and does not do any of the things you think it may do. In fact, it does exactly the opposite and bolsters credibility. But this is a moot point since you no longer have notes or recollection.

Tom1956 · Feb 10, 2014

At that time I never knew of this board or what I was to later learn from my exposure to you folks. But allow me to once again give honorable mention to E von Hoegh's wein and Nikkormat idea about leaving air holes covered. Because I do know that if if duty time capacity of the battery per meter-reading meets his standard on a Nikkormat, then certainly it will work on the Luna Pro with its lower corrent draw. Though I cannot speak for its voltage curve.
Besides it is moot anyway because the inventor this little regulator only had several prototypes made before dropping the project due to marriage, and asked me to not pass on his name. Even sent me a photo of him and his bride. I remember it being a case of love is surely blind. But my best to him.

AgX · Feb 10, 2014

To my understandind the idea of E von Hoegh was the same as that of Wein: to reduce airflux to cell.
Wein did that by having custom produced zink-air cell with holes of smaller diameter and E von Hoegh hinted at using standard cells but covering a number of air holes instead.

BrianShaw · Feb 10, 2014

... but since EvH died before the zinc-air cell was first produced, he should be credited with thinking of the idea first.

miha · Feb 10, 2014

I can recommend this guy: http://www.butkus.org/chinon/batt-adapt-us.pdf

Tom1956 · Feb 10, 2014

miha said:
I can recommend this guy: http://www.butkus.org/chinon/batt-adapt-us.pdf

This was one of the ideas I rejected. Introduced too many contact surfaces and does nothing for the voltage output curve problem. The current draw of the meter is so low that extra contact surfaces introduced an intermittency problem. Think of the AAA's in your TV remote. How many times have you bought new batteries only to discover all you had to do was take thm off and wipe them off, or even revolve them in their compartment with your thumb? All this gimmick does ia suck the contents out of an egg and replacing them with something else so it would still look like an egg.
To sum up the problem the best course of action outside of regulation is to proceed with your favorite idea and test and/or replace the silver batteries regularly with a digital voltmeter, before your reach the end of the curve plateau. BTW--Family Dollar is now selling 357 silvers a lot cheaper than the drug stores or Wallyworld.

Luna Pro battery adapter $$$$

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