What is A Volt?

1 volt is the potential difference through which 1 coulomb must be raised to need energy 1 joule. BTW 1 joule = 10⁷ erg, 1 newton = 10⁵ dyne.

Just because kg, m and s are in the formula doesn't mean you can do it by measuring those parameters. There's A in there as well, which you might also measure with the multimeter.

If you have no other reference voltages, as a rough check you could use mains electric, which should be about 240 VAC, and car battery, about 14 VDC when the engine is running and battery well charged. That's a modern car with an alternator.

Well a battery is part of a system, if the system is working then everything is fine....in other words you measure the total output of the system, if it meets specs, then you know everything is as it should be....and your reading was correct....

Volt is an ampere in an ohm, watt per ampere . it could be other units as well.

In order to get an accurate assessment of charge level, depending on what type of battery, you may have to load it or check specific gravity.

It's an electric vehicle made by General Motors.

Hopefully it is not an "Electric Cavalier".

If you want a practical solution, you can use a precision zener diode in series with a current limiting resistor.

http://en.wikipedia.org/wiki/Voltage_reference

Or a voltage reference diode. They are pretty cheap.

https://www.google.com/search?q=voltage+reference+diode&rls=com.microsoft:en-us:IE-SearchBox&prmd=ivns&source=univ&tbm=shop&tbo=u&sa=X&ei=IFrJVN-KCtHkgwSN4IHQAQ&ved=0CBIQsxg

As for using the definition, you still have to count electrons to measure the current.

Push the meter off the bench...

If it falls then it's in calibration.
A battery is no reliable standard for anything except maybe size.

I remember having to explain to a consultant that if you wanted decent life from a 9 volt battery you had to run it down to 6volts. He thought it gave 9volt... he was a twonk.

The next day, he explained to me how a 9v battery was only good for 6v (I refrained from punching him, but it took all my fortitude)

Del

He might have invertalexia, which inverts the "V"

Use this:

It's all you need.

Lyn #9. I've got one. It was the recharged batteries only reaching the yellow band that prompted me to try a voltmeter as well.Then trying different chargers and different batteries - some OK. But it got me thinking about voltmeter accuracy.

Del #7. Does the height of the bench matter? There's no reference to acceleration in the formula. My digital meter is OK after the drop test, but my analogue meter seems to have jammed at half scale.

Well, there's the rub.

Check the specs on most rechargeable batteries. You will see that they are 1.2 V nominal.

Exactly...GA !

But it doesn't often make any difference as they have a flatter discharge curve and a regular (1.5v) battery needs to go down to below 1 volt to get any decent life out of 'em anyway!

There is a lot more to batteries than most people realise.

Or as Harold said at the battle of Hastings... There's more to arrows than meets the eye!

Del

Cool! Now all your measurements will be repeatable!

If you really want to have an accurate Volt reference at your house (and don't be affraid of a bit of chemical mess ) so look into making a "Weston Normal Element"

Westonelement

(nach einem amerikanischen Physiker) wichtigstes Normalelement,
Es besteht aus 2 Elektroden 2. Art; als Minuspol dient 12,5%iges Kadmiumamalgam, als Pluspol reinstes Quecksilber, das mit Quecksilber(I)-sulfat, HG₂SO₄, bedeckt ist. Der Elektrolyt ist eine gesättigte Kadmiumsulfatlösung, in der sich kristallisiertes Kadmiumsulfat, CdSO₄* ⁸/₃ H₂O, befindet. Das Westonelement hat bei 20°C eine Spannung von 1,01865 V; Der Temperaturkoeffizient ist kleiner als 10^-4 Volt je Grad

sorry I only found a german information on that unit. When I was a student around 1970 I was presented with this unit as the lab where I was working on assignment did no longer need that unit. It was standing many years in my office, but in 2010 when I retired, I decided to give it to a small exhibition of old test equipment at the place of our EMC testing consultant. First thing they did was to test the output voltage - it was with 1,01862 Volts not totally exact - but we have to consider the unit was produced around 1950! So we for sure can understand that the "Volt got some wrinkles" - or was the reason the precision voltmeter of recent production?!

Uli #14. Thanks. I will not be able to make such a cell. But for anybody else who might, here is a Google translation of the German text.

"...important (for an American physicist) Normal element, It consists of 2 electrodes 2nd type; the negative pole is 12.5% pure cadmium amalgam, pure as positive mercury sulfate with mercury (I), Hg2SO4 is covered. The electrolyte is a saturated cadmium sulfate solution in which crystallized cadmium sulfate, CdSO4 * 8/3 H2O, is located. The Westonelement has a voltage of 1.01865 V at 20 ° C; The temperature coefficient is less than 10-4 volts per degree..."

I think your reference source of 1.01862 volts when it should have been 1.01865 volts has got the edge on "...about 14 v ...of a car battery.." by Codemaster #1

But perhaps a little bit closer at 14.7 v, because I seem to remember from my old RAF ground equipment training days that the voltage of alead-acid battery, (suitable and serviceable for flying duties) fully charged on charge, at the 10 hour rate, gassing freely and correct level of acid, was 14.7 volts - assuming that the ammeters and voltmeters used for charging them were correct. Or put another way, a flat battery put on charge after 10 hours was expected to be 14.7 volts.

In practice the charging voltage/current was checked regularly at early intervals to prevent over-charging (and to save time) because batteries were often only partly discharged where operational rules did not allow them to be flattened in service.

You didn't give the nominal voltage of the battery you want to check but if it's much more than the 1.2 volt rechargeable that was mentioned, if the multimeter agrees with a Weston standard cell (to 6 places of decimals!) you have to assume it's linear for higher volts, or put a few Westons in series.

Ref your RAF days, the on-charge voltage depends on the charger voltage regulator setting as well as the battery nominal volts. Was this on a mains charger or on an engine? On a dynamo, the vibrating-contact voltage regulator usually adjustable, setting ~ 14.5 - 15.5. With modern (vehicle) alternators the regulator is electronic and non-adjustable, and for a test if it's suspect, volts ~ 13.6 - 14.4 OK (both sets of volts vary a bit with different suppliers).

That's why I suggested 14V as a rough check on the multimeter, should be near enough unless you're doing something fairly precise.

More simply put:

Volts = Work Done per Unit Charge

units kg.m.sec^-2.q^-1

where q = i*t

VI = Power = N M / s = Kg m /s2 x m / s = Kg m2 /s3

V = Kg m2/s3/A

That is as far as your Unit is concerned...

But all these SI units are based on certain Fundamental Units (Ampere, Kelvin etc are one of these) and hence everything is broken down to the fundamental and then measured.

If you see here too, if you have an ammeter (that too reversed i.e. you should measuere 1/A, and timer 1/s) you could measure the volt.

Or in other way, if you measure the current, and the time and then let it do the work on a known mass, then obviously you can calculate the volt (which has to remain constant over that time, and battery shouldn't discharge, else you would get the avrerage)

SB. Thanks. That's what I thought. But to save time I will settle for a voltmeter.

Have you tried the new batteries with the "meter" on the side? Push a spot on the battery and it is supposed to give an indication of life left in the battery in terms of percentage charge. I've tried them in my camera twice, and both times, with 75% still showing, the camera was flagging the low battery indicator. Pull them out and they still run other devices just fine. I suspect a lowered voltage output on these to extend life. This isn't the batteries you are trying to measure is it?

Cameras are picky about battery power.

I've noticed that too.

Phys. Yes, but probably only by chance purchase. My use is fairly ordinary for clocks, torches, alarms, remote controls, etc. It is a question of changing batteries when the equipment fails.

And then repeatedly recharging the batteries until such time they gradually fail after a couple of hours use. Then I bin them.

Now and again I get curious about things, and out of interest do a bit of research - as here.

I appreciate the help I have been given by everybody.