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Multimeter problem..

Community Veteran
Posts: 14,010
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Registered: 01-08-2007

Multimeter problem..

I've got a problem with a digital multimeter. It seems to be over reading voltages. 1 AA battery is supposed to be 1.5V.. 6 of mine are 1.6 and when measured in series they total up to 9.6V.
While I know there's usually a small tolerance this much can't be right? When trying to measure 3 of them (4.5V) I get over 5V. Obviously this isn't very constructive and is making some of my measurements a bit annoying.
At first I wondered if the battery was flat - IE maybe there could be a potential difference issue or a point of reference being out a bit but the low battery indicator hasn't  appeared so it can't be.
I've not got any other batteries to test it against.. only the car - which measures 13.2V.
It used to be very accurate many moons ago (I've had it 11 years).. maybe it just time to replace it but any ideas just in case?
I need a new signature... i'm bored of the old one!
14 REPLIES
198kHz
Seasoned Pro
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Re: Multimeter problem..

Are these alkaline or rechargeables? When I test an alkaline cell it generally reads about 1·6V open circuit.
More like 1·4 for a rechargeable just off charge, dropping to 1·3 after a few hours.
Not young enough to know everything
Community Veteran
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Re: Multimeter problem..

Hi
Yes, they're alkaline Energizers. That would explain it then.. maybe the meter is ok?
I was rather worried when I saw it reading 9.6V for all of them in series..
I need a new signature... i'm bored of the old one!
198kHz
Seasoned Pro
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Re: Multimeter problem..

Yup, sounds OK. Digital meters generally either work or they don't.  Wink
Not young enough to know everything
Community Veteran
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Re: Multimeter problem..

Ok thats brilliant - not bad for an 11 year old eh! At least I can factor those readings into my calculations then.
Cheers pal
I need a new signature... i'm bored of the old one!
198kHz
Seasoned Pro
Posts: 3,230
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Re: Multimeter problem..

Aye, it's nice when things keep working. I've got a BT badged Fluke which must be about 20 years old - good as new, and a Maplin one about 10.
If they've otherwise been well treated, it seems to be the LCD display which is most prone to failure. I suspect that otherwise the main reasons for early demise are rough handling or being dropped, frying by using the wrong range, or simply getting lost.
Not young enough to know everything
Moderator
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Re: Multimeter problem..

Fluke are the bee's knees but pricey. I have an ISO-Tech which serves well.

Customer and Forum Moderator.

pierre_pierre
Grafter
Posts: 19,757
Registered: 30-07-2007

Re: Multimeter problem..

try looking here for the Voltage characteristics of different type of Cels  http://www.powerstream.com/BatteryFAQ.html
look in this section, items 3 and 4
Table of Contents
  1. Definitions
  2. Battery Parameters
  3. Primary Batteries (disposable)
        1. Leclanché Cells
        2. Alkaline Cells
        3. Mercury Oxide Cells
        4. Zinc/Air Cells
        5. Aluminum/Air Cells
        6. Lithium Cells
        7. Lithium Iron Primary
        8. Magnesium-Copper Chloride Reserve
  4. Secondary Batteries (rechargable)
        1. Lead–Acid Cells
        2. Nickel/Hydrogen Cells
        3. Nickel/Cadmium Cells
        4. Nickel/Metal Hydride Cells
        5. Sodium/Sulfur Cells
        6. Nickel/Sodium Cells
        7. Lithium Ion Cells
        8. Manganese-Titanium (Lithium) Cells
        9. Rechargeable Alkaline Manganese Cells
       10. Nickel Zinc Cells
       11. Iron Nickel Cells
       12. Iron Air Cells
       13. Iron Silver Cells
       14. Redox (Liquid Electrode) Cells
itsme
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Re: Multimeter problem..

Quote from: 4C
Yup, sounds OK. Digital meters generally either work or they don't.   Wink

Not true they can still go out of calibration.
Quote from: 4C
I suspect that otherwise the main reasons for early demise are rough handling or being dropped, frying by using the wrong range

Not aware of any digital meter being fried by selecting the wrong range in more years than I care to remember working in electronics and telecommunications along side same pretty dumb technicians. Only fuses be blown when measuring high currents as the technicians have not used the correct inputs.
198kHz
Seasoned Pro
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Re: Multimeter problem..

Note the word 'generally'. Perhaps I should have said 'usually'.
Point taken re rarity of frying.
Not young enough to know everything
Community Veteran
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Re: Multimeter problem..

Digi Multimeters usually have a very high input resistance  when on Volts DC range therefore will not load a battery to any  significant degree. It does not need much of a load to bring them down to an operating level which is what one would expect. Although I do have a digi box I still have a Pullen series 100 multimeter of 1947 vintage and its 1.5 volt U2 battery for resistance measurement, price 4d still works!!
Community Veteran
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Re: Multimeter problem..

Quote from: colintivy
I still have a Pullen series 100 multimeter of 1947 vintage and its 1.5 volt U2 battery for resistance measurement, price 4d still works!!

Wow! Thats very impressive!
@pierre: Thanks for the link Wink
I need a new signature... i'm bored of the old one!
Denzil
Grafter
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Registered: 31-07-2007

Re: Multimeter problem..

Also, car batteries are only nominally 12V. The actual open circuit voltage varies with how much charge is in it. A fully charged healthy battery could well read about 13V.
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Re: Multimeter problem..

I usually get 14.2 off the car lol.
I need a new signature... i'm bored of the old one!
Denzil
Grafter
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Registered: 31-07-2007

Re: Multimeter problem..

With the engine running that is normal, because the output from the alternator has to be at a higher voltage than the battery in order to force the charge back in against the flow, so to speak.. With the engine running you should see somewhere between 14.0 and 14.5V. Turn the engine off and it should go down to somewhere between 12.8V and 13.2V if the battery is fully charged.