Before posting I went to Radio Shack and tried all the cells they had
before it was time to leave. None fit, after I had the first caliper
working (using the sr44) I tried it to measure the opening on the side
of the second caliper. But none of the cells measured up.
Take the battery with you to the watch battery display at wal-mart or
wherever, You will find one there that fits. If you dont actually have
that battery (the dead one, that is) measure the space that it has to
fit into. You want the diameter in millimeters, and the thickness in
millimeters.
1.5 v is normal for a watch battery. In truth, any 1.5v battery can be
made to work this caliper, it just depends on how ugly you are willing
to get. :-) Lithium cells are usually 3v, and mercury cells are 1.3 or
1.2v (can't recall), so they are efectively ruled out.
If you have a battery in it, the number can be cross refferenced to the
other makers numbers.
Cheers
Trevor Jones
This is a common misunderstanding.
Digital calipers use a silver oxide button cell, typically the SR44 size,
aka 357, 11.6mm diameter by 5.4mm high.
VERY common today is the alkaline LR44, which is the same size button, and
same nominal voltage. This is put into toys, laser pointers, etc. and has
gotten very cheap because of the quantities from China and popularity.
BUT, alkaline buttons have much less mAh capacity, and droop voltage (non-
flat discharge curve) much sooner, than silver oxide, and thus don't run
calipers for very long.
Be careful, most retailers don't know the difference between LR44
(alkaline) and SR44 (silver oxide) and act like they are interchangeable,
when they aren't. It won't hurt your calipers to misuse an LR44 in your
calipers, but you'll only get hours of runtime from an LR44 instead of days
and days from an SR44.
Notorious for this error is Radio Shack. Radio Shack sells an alkaline
version of the silver oxide 357, which they call 357A. Ugh! No, it isn't
the same thing, and a waste of money in calipers!
You can buy Chinese button cells cheap on eBay, but the sellers typically
have no clue about alkaline vs silver-oxide non-interchangeability, and
claim their cheap alkalines are replacements for silver oxide.
See the excellent tutorials at:
http://data.energizer.com
Richard J Kinch
http://www.truetex.com/machinery.htm
What I was meaning, is that if need be, a regular alkaline battery
could be grafted in. That's what I was referring to when I said it
depends on how ugly you are willin to get.
Good info on the silver oxide vs. alkaline cells, though.
Cheers
Trevor Jones
Not always. I have an older digital caliper by B&S which uses
four 625 Mercury cells. Unfortunately, they seem to be made of
unobtanium these days. :-(
Otherwise, it is a nice caliper. I wonder if I can make a
replacement battery holder which will use some 3V Lithium cells (two of)
to get slightly more voltage than the four 1.35V mercury cells. IIRC,
all four are in series, with no taps other than the ends of the series
strings.
Enjoy,
DoN.
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On Thu, 06 Nov 2003 02:12:21 -0500, DoN. Nichols wrote:
You could try putting a silicon diode in series. That'll give you an
approximate 0.7 volt drop, giving roughly 5.3 volts. Not quite the 5.4
that the mercs would've given you, but a lot closer than 6.
If that doesn't get you close enough, you could try putting a couple of
germanium and/or Schottky diodes in series. Those have a smaller voltage drop,
about 0.25v for germanium, about 0.2-0.45 for Schottky. This varies somewhat
from diode to diode (even within the same type), so you may need to do
read some spec sheets and do some experimenting to find the right one. It
all depends on just how sensitive the caliper is to slight voltage
variations.
--
Tony Hursh
Need to find your home IP remotely? http://wheresmybox.com
A good thought. There should be room for several small diodes,
if needed.
Perhaps I should start out by powering it from a precision power
supply that I have -- switch selected voltages from 0 to 20V in 0.001V
steps (oven stabilized zener reference). It should work as it can
supply 500 mA, and I somehow doubt that the calipers draw that much. :-)
Thanks,
DoN.
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Just stop by a Radio Shack. They have a huge assortment of "button
cells". They are blister packed on little cards and you should be able
to spot one which matches the diameter of the battery holder in your
caliper.
If there's no indication in the caliper regarding which way to insert
the battery, take a guess and then turn it the other way around if the
first try doesn't work. There's very little likelyhood of damaging
modern low power electronics with a reversed battery.
Good luck,
Jeff (Who wishes he could sell things at the same margin as Rat Shack
does when they get $2.95 each for those little batteries!)
--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)
"If you can keep smiling when things go wrong, you've thought of someone
to place the blame on."
The SR44 is now called a No. 357. There are a bunch of 1.5 Volt
"button" batteries, just look for one that fits.
I had a Brown & Sharpe that used an obsolete battery, I made some
small aluminum spacers to that it could work with the No. 357. The
battery life sucked but it worked.
That must be the same one that I have. The one with the optical
scale buried at the bottom of the groove which would be for the rack
gear on a dial caliper.
They are no longer available, because they are mercury
batteries, and everyone *knows* that mercury is a dealy poison. :-)
Just ask the people at local school, where some kids stole a
bottle of mercury, and the school was shut down for a month to be
decontaminated. There was a big fuss over decontaminating the busses
the kids used, and some homes are still officially uninhabitable as a
result.
My primary question is "how come I'm not dead if it is so
dangerous?" (Given how much I played with it as a kid. :-)
Enjoy,
DoN.
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Don:
Same thing happened up here in Maine. They were only a bit more sensible - no
houses deemed unlivable, and the school ws closed for no more than a day, as I
recall. Greatest concern was the presence of lingering mercury vapor on the
buses. As if the air doesn't get changed every five minutes on a school bus.
Idiots everywhere, I guess.
As to your own health (and mine, for I also played with Hg as a kid, but not in
the last six months or so, but I may next week...), you do realize that long
term exposure will have mental effects before mortal ones....
John Martin
- Whose opinion should be disregarded, as exposure to mercury and other
dangerous substances obviously has made him mad as a hatter, about which he is
in denial -
Yep!
Understood. (Not sure how you would tell the difference in my
case. :-)
The ones who had serious problems, historically, were the makers
of felt hats (long term exposure, there), and somewhat later the early
photographers (since one of the processes -- Dageurotype, I think --
involved processing the plates in mercury vapor over boiling mercury.)
:-)
Enjoy,
DoN.
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Well - not dead. Just a tad bit warped anyway. I think
all that Hg is why you'r so involved with machinery, or
something like that.
The natural gas pressure regulators in the local area
homes had a mercury metal overpressure device built into
them - if the regulator seat failed open, it would
vent the outlet of the regulator to the outdoors by
blowing out a slug of mercury.
So the local utility decided to change them all, and
of course the guy who shows up to do it puts down an
absorber mat, and double bags all the parts and bits
of the vent line that come off.
I asked him how often he finds mercury in the vent line,
and he says around one in 20 or so. I asked what happens
if it gets loose and spills inside the house when he's
working?
"That's what *this* is for," he says, and points to a
cell phone that's perched on my dryer, next to where
he's working. "I make 'the call' and then the guys
show up in the bunny suits and do the full decontamination!'
Apparently the real driving force behind all this was
that somebody realized there was metalic mercury in the
regulators, deliberately spilled some inside their
house, and then sued the utility - and won.
Jim
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