Replacing an obsolete battery...?

[Martin Rosenfeld]

I have an old photographic light meter that needs a no longer made
Mallory battery that was about 3/4 inch long and produced 1.3 volts. I
doubt that the meter would pull more than about 100 milliamps. Can
anyone help me to choose a modern battery (1.5 or 1.55 volts?) and use
something like a diode to drop the voltage to about 1.3? I know just
enough about electronics to know that I need help here.

Martin Rosenfeld

 

[Al]

In article <SOKdnW8yI5s6Ad7fRVn-vg@comcast.com>,
Martin Rosenfeld <mjrosenfeld01@comcast.net> wrote:

I have an old photographic light meter that needs a no longer made
Mallory battery that was about 3/4 inch long and produced 1.3 volts. I
doubt that the meter would pull more than about 100 milliamps. Can
anyone help me to choose a modern battery (1.5 or 1.55 volts?) and use
something like a diode to drop the voltage to about 1.3? I know just
enough about electronics to know that I need help here.

Martin Rosenfeld

Did you try an N size battery? It's about half the length of a AA. Could
you get it to fit?

Al

 

[Martin Rosenfeld]

Al,

Thanks for the idea. The N batteries I could find are either 1.5 or 1.2
volt. whereas I need 1.3 volts. There are button shaped batteries at
1.35 volts. I could use one of these. How much voltage does a single
diode drop in a circuit?

Martin

Did you try an N size battery? It's about half the length of a AA. Could
you get it to fit?

Al

 

[Martin Rosenfeld]

Al,

Thanks for the idea. The N batteries I could find are either 1.5 or 1.2
volt. whereas I need 1.3 volts. There are button shaped batteries at
1.35 volts. I could use one of these. How much voltage does a single
diode drop in a circuit?

Martin

Did you try an N size battery? It's about half the length of a AA. Could
you get it to fit?

Al

 

[Rich Grise]

On Fri, 25 Mar 2005 10:13:33 -0800, Martin Rosenfeld top-posted

Al,

Thanks for the idea. The N batteries I could find are either 1.5 or 1.2
volt. whereas I need 1.3 volts. There are button shaped batteries at
1.35 volts. I could use one of these. How much voltage does a single
diode drop in a circuit?

I wouldn't worry too much about the diode. Try a 1.2V N cell. I seriously
doubt if the calibration of the meter depends on an exact battery voltage.
Can the meter be calibrated? What kind of accuracy do you need anyway? If
it's off, you could compensate by adjusting the F stop by hand - just
write the scale factor on a little label, and tape it to the meter.

Good Luck!
Rich

Martin

Did you try an N size battery? It's about half the length of a AA. Could
you get it to fit?

Al

 

[Al]

In article <42445490.3080708@comcast.net>,
Martin Rosenfeld <mjrosenfeld01@comcast.net> wrote:

Al,

Thanks for the idea. The N batteries I could find are either 1.5 or 1.2
volt. whereas I need 1.3 volts. There are button shaped batteries at
1.35 volts. I could use one of these. How much voltage does a single
diode drop in a circuit?

Martin

Did you try an N size battery? It's about half the length of a AA. Could
you get it to fit?

Al

If the voltage matters that much, take the N cell and discharge it until
the voltage is 1.3V. It still might be able to deliver all the power
that circuit needs.

Not knowing the discharge characteristics of your original cell and the
requirements of the meter makes it very difficult to propose a solution.

Al