Help Digital caliper Battery I need to know what battery

Chances are good that it uses a SR44 or equiv., most callipers do.

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

If you have a battery in it, the number can be cross refferenced to the other makers numbers.

Cheers Trevor Jones

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."

Go to a dollar store and get any battery that will fit as long as it is

Ted

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:

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.

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.

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

A good drug store has more batteries like that for cameras and medical stuff. THat is where I get mine.

Martin

The pharmacy in my favorite supermarket carries a good selection and at a damn site better price than Rat Shack. Gerry :-)} London, Canada

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.

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.

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 -

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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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.

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.

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.

Hatters used mercury nitrate, much more dangerous than metallic mercury.

Paul K. Dickman

I think some of the over-reaction is a result of the extreme toxicity of some mercury compounds. Dimethylmercury is very scary stuff... one drop on *gloved* skin means a prolonged painful death. Vastly different than metallic mercury or even most mercury salts.

Tim.