Why does Analog Multimeter need AAA Batery

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"Dick" <LeadWinger> wrote in message wrote:

Actually I think the OP probably had a cheap instrument and never gave us a make/model....so hard to say how it would react to rechargeables but if the meter was cheap....it shouldn't make much difference since accuracy would not be an issue with such an instrument.... :>) Ross
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"Dick" <LeadWinger> wrote in message wrote:

Very possible...I will check the site myself....might be one of those situations where we are both correct by situation....not particularly important as long as our fine meters get the job done...and fine they are...take care Dick, Ross
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wrote:

I have a number of portable scopes and meters and have always used rechargeables with no problems and that was on meters I used to calibrate to .001 volts....I'm with you...they work just fine...Ross
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On Sat, 26 Feb 2005 17:46:33 -0500, "Ross Mac"

You're right. It would just be an unnecessary expense.
Dick
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On Sat, 26 Feb 2005 17:50:16 -0500, "Ross Mac"

Agreed. The Fluke 87 is one of the best investments in test gear that I ever made.
Dick
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"Dick" <LeadWinger> wrote in message wrote:

safely
my
with
Ross
I have an old led display Fluke (Model 8030A) that uses 4 NiCads. You leave it plugged in when in when possible.
http://www.tucker.com/java/jsp/doorway_partnoFLU8030A_invid9533.htm
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Yes, but you are talking about a bench instrument, not a portable, hand-held like the OP was asking about.
Dick
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"Dick" <LeadWinger> wrote in message wrote:

leave
It is portable. It came with a carrying case and all. Just that when on the bench you can keep it plugged in to keep the batteries charged. But those LED displays draw a lot of current.
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In alt.home.repair on Sat, 26 Feb 2005 17:46:33 -0500 "Ross Mac"

I believe accuracy should be independent of whether the battery is fully charged or not. They set it up so the measurement is in proportion to a known resistance, so it should read correctly at any battery voltage. (although eventually the battery is too weak to move the needle or power the lcd's.)
BTW, everyone mentions alkaline batteries, but one of my digital meters requires a 9-volt carbon zinc battery. An alkaline battery won't fit in the space provided. (Unlike C, D, AA, and AAA batteries, 9 volt batteries are different in size between carbon-zinc and alkaline.)
Meirman -- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.
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Well, that way you need two batteries and a charger, and rechargable batteries are more expensive than plain carbon zinc, and the meter may not work well on 1.2 vs 1.5 V, and this arrangement won't monitor house voltage, and it takes more human attention, and it's less fun.

More like 1 mA, altho that's too much for an Eveready 1212 AAA with a 540 mAh capacity that loses 10% of its energy over a year. That only needs 0.10x540 = 54 mAh over a year, or about 6 microamps on a continuous basis, if the meter is never used for anything else, but the movement might require another 100 microamps. And why waste power in that resistor, vs a charge pump like this, viewed in a fixed font? - C | \ | | | 1.5 V ------------------| |--------------->|--------------------> . | | | | | 120V . --- --- . ^ - ------------ | | | | | | / | | | - --- --- --- - _ -
Q = 170C coulombs and I = 60Q = 106 x 10^-6 amps makes C = 0.01 microfarads. The battery would be a fine smoother and voltage regulator. Harbor Freight stores sell $2.99 digital multimeters. Maybe they need less than 100 uA.
My flashlight plugs into the wall. Very convenient, because I know where to find it and don't have to change batteries. My CO and barn heat detectors work that way too, by design, with audible and remote X10 alarms and "non- rechargable" batteries that rarely need changing. I hate changing batteries. I lose my cheap Casio watches with 7 year Li batteries before they go dead.
Nick
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Oops. Q = 340C makes C = 0.0047, or two 0.01s in series in case one shorts.
Or a 20 mW LimeLight, with less power. What does it take to power a 648A PIC?
Nick
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That might be an Insteon/X10 interface PIC...
The data sheet says it uses about 100 nanoamps at 3 V in sleep mode and 12 microamps at 32 kHz. If it's awake 1% of the time, say 1 second out of 100, when it talks to a central controller, it would need 0.99x0.1+0.01x12 = 0.22 microamps. Q = 340C coulombs and I = 60Q = 0.22x10^-6 amps makes C = 10 pF, theoretically-speaking :-)
If we needed more power and worried about overcharging the 2 AAAs, we might use the PIC to measure the voltage and only enable the charge pump as needed.
Nick
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wrote:

Absolutely incorrect. That is not how a meter works. And anyhow....a spare battery and a charger???....That is not expensive.... Not trying to fire ya up here but those are the facts.

My math error...E=IR 60PVDC/47Kohms = 1.2ma or so....The incorrect charging rate for a rechargeable.

Those batteries are normally referred to as "Puny Duty" and typically never make it to 10 recharges... I don't think this is a good recomendation to the NG....

I cannot make heads nor tales out of your schematic, fixed font or not, but it appears we now have a capacitor in the circuit...what happened to the "diode and resistor" and you still need a regulator since you still have 60 volts across a 1.5 volt battery. And please no, no....not that doorstop 3 buck meter...a good set of leads will cost you more than that thing. That meter is more likely to get you into more trouble than it ever gets you out of. That "THING" would only be good for very crude troubleshooting.
This post is beginning to smell of TROLL.....well maybe not....but the bait and switch characteristics are there!

> Nick
As for connectiong the active and passive circuits in the meter....I want to be there when you try to measure the 240vac coming into the house and you put 120pvdc across that battery with a camera to catch the absolute look of surprise......Ross
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Ross Mac wrote:

Freight
100 uA.

not, but

the
have 60

The "diode and resistor" have been replaced by a "charge pump" (you can google this) for the reason of "why waste power in that resistor." This is not a bait and switch, it is merely an improvement on an earlier proposal.
If you remove the battery from Nick's charge pump circuit proposal, you have what's commonly called a "voltage doubler" (you can google this) and the open-circuit output voltage will peak at twice the AC input amplitude, which would be 340V for "normal" 120VAC-RMS input. Limiting the size of the capacitor limits the current output capability. Placing a battery across the output limits the output voltage by shunting the current flowing through the capacitor. Also remember the current=C*dV/dt, and dV/dt peaks at 170volts/sec. So to reiterate, current and voltage have been limited: as long as the battery is there and can accept the current, you do not have 60V, 120V, 340V or whatever, you have 1.5V regulated by the battery and no additional regulator is necessary.
I would modify this design by replacing the diode whose anode connects to ground with a zener rated for 2.5 to 5 volts. That way, if the battery should open-circuit, the downstream components won't see the 370V spike, it having been shunted by the zener. Similar "transformerless stepdown" circuits are used to supply regulated 12VDC to motion detectors.
I think Nick was off in his original math because he may not have considered that the output diode (the one with the cathode connected to the battery) begins conducting roughly as the AC input wave rises from its -170V minimum, and continues to conduct roughly till the input reaches its 170V maximum (we're ignoring .6V and 1.5V voltage drops across diodes and batteries as insignificant compared to 170V). Therefore the total charge moved per cycle is Q=C*340volts over the full voltage swing of -170 to +170. (I now see and agree with his math ammended in a subsequent post.) Current in amps (coulombs per second) is Q*60 because there are 60 cycles per second. Substituting the suggested value of .0047 uF for C, and current comes out to be 96 microamps. This is not meant to recharge a battery that has been run flat, but rather to compensate for the self-discharge of the battery such that it does not discharge during storage.
The question of whether the negative terminal of the battery is connected to an identifiable "common" node in the VOM's internal circuit is left for further consideration.
%mod%
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Good idea. Two caps in series might also help with single point failures.

UL-approved, in plastic boxes. I've heard California is banning the transformer ilk because of the standby power.

That's only a problem for alt.home.repair nitwits, IMO :-)
Nick
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Huh?
Incorrect, eh? :-)

Who's talking about recharging?

Pity.
I just measured a Craftsman digital VOM... 9 V at 1.54 mA.

Pity. That's "tails," BTW.
Nick
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wrote:

Kind of the response I expected....no answers just juvenile quips......PLONK......
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On Sun, 27 Feb 2005 09:40:27 -0500, "Ross Mac"

The majority of analog multimeters only need the battery to use it as an ohm meter. If only reading voltage, unless it is a transistorized (extremely high impedence) unit the battery is not required.

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snipped-for-privacy@sny.der.on.ca wrote:

Very true. The really cheap meters will say something like 2 Kohm / volt or 3 K ohm / volt on the face. A better quality one will say something like 20K ohm / volt. These ratings are usually based on 1 milliamp giving full scale deflection of the needle. The batteries for resistance readings only.
It was a pain trying to measure voltages across very high resistances. The meter would be in parallel with the resistance and completely mess up the real values.
Getting my first Field Effect Transistor powered meter was a reall blessing. It had something like 2 MEG ohms / volt sensitivity. Most of the digital stuff now probably has 10 or 20 Meg ohms / volt. In some cases that's no good. With almost no loading on a circuit/wire you can get voltages seemingly appearing out of nowhere, giving rise to much head scratching.
mike
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On 2005-03-01 snipped-for-privacy@4ax.com said: >Newsgroups: alt.home.repair,alt.energy.homepower > snipped-for-privacy@sny.der.on.ca wrote: [snip] > ... The really cheap meters will say something like 2 Kohm / >volt or 3 K ohm / volt on the face. A better quality one will say >something like 20K ohm / volt. These ratings are usually based on 1 >milliamp giving full scale deflection of the needle. No, not 1 mA. 2 Kohm/volt = .5 mA 3 Kohm/volt = .33 mA 20 Kohm/volt = 50 microAmps
[snip] >Getting my first Field Effect Transistor powered meter was a reall >blessing. It had something like 2 MEG ohms / volt sensitivity. Most >of the digital stuff now probably has 10 or 20 Meg ohms / volt. No, not "per volt". That's the input resistance for DC measurements.
My Beckman 3020 DMM is 22 megohms input resistance.
Fluke 27 and 73 read 11 megs on the Beckman Fluke 36 DMM and clamp-on AC/DC ammeter reads 2 megs.
Tom Willmon near Mountainair, (mid) New Mexico, USA
Net-Tamer V 1.12.0 - Registered
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