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I must have Vendor #5, which draws twice as much as vendor #4. 
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Mr. P.V.'d
formerly Droll Troll
"Jeff Wisnia" wrote in message
...
Gunner wrote:
On Sun, 24 Jul 2005 12:50:09 GMT, Philip Freidin
wrote:
On Tue, 12 Jul 2005 09:40:22 -0400, "Proctologically Violated©®"
wrote:
Awl--
Anyone use these? Black, two buttons, mm/in, and zero? $20-30?
Anyone get the sense that they burn thru batteries like wildfire?
Mitutoyo's seem to last 1/2 of ferever, but these goddamm cheapies...
Which is surprising, cuz they have an auto-off feature, that my Mits
don't have!!
OOOhhh, OOOhhh, OOOhhh,
(visual: me at the back of the class room, jumping up and down because at
long last there is a question I know the answer to :-)
So it turns out that for the last 3 months, almost all my free time
has been spent studying the power consumption characteristics of
electronic calipers and micrometers.
First off, here is a surprise for you. When the chinese calipers are
off, they draw the same power as when they are on. The Mitutoyo draws
about half as much power as when it is on. Don't believe me??? Try
this:
Turn on your chinese caliper, close the jaws, press the zero button,
open it to 2 inches, turn it off, press the zero button, move it to
3 inches and turn it back on.
It was making measurements, and taking notice of the zero button while
it was "off". Actally, all it was doing was disabling the display,
which does not save any significant power. Even the SPC output is
active when it is "off".
The Mitutoyo caliper draws about 1/4 the power of the chinese caliper
when on, and about 1/8 the power when off.
... bunch of question about battery numbers ...
The two common cells for calipers are the LR44 and the SR44. Calipers
are usually shipped with the cheaper LR44.
LR44 is a Zinc + Manganese Dioxide chemistry
SR44 is a Zinc + Silver Oxide chemistry
LR44 starting voltage is about 1.500 Volts
SR44 starting voltage is about 1.550 Volts
Both are rated as 150 mA hours, but the discharge curves give very
different operational life depending on the required voltage for the
application. The LR44 voltage drops over the duration of usage. The
SR44 remains flat (and above 1.5V) for most of its useful life. The
calipers need at least 1.25 to operate.
The LR44 drops below 1.3 Volts after about 50% usage
The SR44 drops below 1.5 Volts after about 95% usage.
So you only get about 50% of the 150 mA hours from an LR44.
The SR44 start at a slightly higher voltage, and their flat discharge
curve makes them far superior for low power, long operational life
applications, like a caliper.
Jes tryna get more g-d bang fer my miserable buck.
Pick a Mitutoyo caliper, and run it with SR44 :-) You get what you
pay for.
Oh, oh, speaking of bang and bucks, I'm in 7th heaven:
*Finally* found these buttons at yer "better" 99c stores!!
Along w/ *16 packs* of AA and AAAs--yeah, 99c--plus NYC .0825.
Only thing is, you gotta scrape off the contacts on a wire wheel. No
foolin--they say so on the package.
All of these el-cheapo batteries come from manufacturers you have
never heard of ("sun-moon batteries", "rising star batteries", ...)
and although they say they are replacements for SR44 and LR44, they
are poor quality LR44 chemistry.
You can get the button cells for about 50c ea, mebbe less, in q's of
20-100, on the web.
The good news is that since you will be changing batteries often, you
will
get to use them all.
Here is the data I collected. Use a monospaced font to view properly
==========================================
All measurements are in microamps
Off On
Mitutoyo 500-171 2.0 4.0
Chinese Vendor 1 17.5 18.0
Chinese Vendor 2 17.5 18.5
Chinese Vendor 3 7.0 7.5
Chinese Vendor 4, #1 15.5 16.0
Chinese Vendor 4, #2 18.0 18.0
Chinese Vendor 4, #3 19.0 19.0
Chinese Vendor 4, #4 17.0 18.0
Chinese Vendor 4, #5 19.5 19.5
Chinese Vendor 4, #6 17.5 18.0
Chinese Vendor 4, #7 19.5 19.5
Chinese Vendor 4, #8 17.5 18.5
Chinese Vendor 4, #9 17.5 18.5
Chinese Vendor 4, #10 19.5 20.0
==========================================
Using an SR44:
So, for a Mitutoyo that is on for 1 hour per day the calculation is:
(1 hour * 4uA) + (23 hours * 2uA) = 50uAHour per day
SR44
(150 mA Hour) * 90% = 135mA Hour = 135000uAHour
Battery life is therefore 135000/50 = 2700 days = 7.39 years
The self discharge of the battery will probably make it
half this duration.
Here it is for the chinese calipers
(1 hour * 18uA) + (23 hours * 17.5uA) = 420.5uAHour per day
SR44
(150 mA Hour) * 90% = 135mA Hour = 135000uAHour
Battery life is therefore 135000/420.5 = 321days = .87 years
The self discharge of the battery will probably not be significant
You can do the math your self for the LR44 batteries. Remember to use
50% rather than 90%.
==========================================
For sale: 10 chinese calipers (vendor 4), $25 each + S&H .
Comes with a LR44 battery.
Philip Freidin
Crossposted into rec.crafts.metalworking for their edification.
Thanks for the marvelous workup Philip!
Gunner
"Considering the events of recent years, the world has a long way to go
to regain
its credibility and reputation with the US."
unknown
Real interesting to learn about that current draw when OFF. Who woulda
thunk that?
So.....I'm waiting for the smart folks here at rcm to come up with a neat
way to retrofit a battery disconnect switch which doesn't stick out like a
sore thumb. (No good just saying, "Take out the battery.")
YMMV but I've got a HF 6" Chinese caliper I bought about 4 years ago in
which an 357/SR44 cell keeps stays stiff for well over a year.
I assume it's Chinese, but I don't see a "made in" message anywhere on it,
though it does have a label with couple of tiny charts stuck on the
backside giving tap and clearance drill sizes for common sized metric and
Whitworth threads. (Why Whitworth??)
Before ending and hitting "send" I couldn't resist running downstairs and
using the 50 ua scale on my trusty Simpson 260 meter to measure my
calipers, which drew:
8.0 ua ON
7.5 ua OFF
I guess I had the luck to purchase ones made by "Chinese Vendor 3". Per
the math above I can expect better than two years life out of a battery.
That's the first time in a while I've been able to spell the word luck
with four letters. Usually It takes just three, b-a-d. G
Two years of battery life is good enough for me. At my age I'm already
getting hesitant about buying green bananas.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"Truth exists; only falsehood has to be invented."
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