# What Source Do You Use to Calibrate a Voltmeter?



## stp57 (Dec 12, 2007)

I thought that a new 9v battery would work but it shows to be around 9.5v when out of the package. Do you know of anything consistent within .05v?
Steve


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## Teetorbilt (Feb 12, 2004)

Don't worry about it, you're not in the electronics end of things. .5 volts is nothing in most cases.

Re-read. 

You have a new, fully charged battery. The half-life will be 9.0V. I'd keep a careful eye on it, most of mine (Alkeline?) only last 5+ yrs.

I'm bad!


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## Speedy Petey (Sep 30, 2003)

Cali-what a what?????? :laughing:


Seriously, read this:


Teetorbilt said:


> Don't worry about it, you're not in the electronics end of things. .5 volts is nothing in most cases.



Unless you work for IBM or some other high-tech industry this is a total non-issue.

To answer your question though; You sent out to a testing lab and they put a sticker on it with an expiration date.


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## mickeyco (May 13, 2006)

Would "calibrating" a meter at around 9 volts DC ensure it's accurate at 120, 240 or 440 VAC? I doubt it, you could use a diode to see how acccurate you are at a particular voltage but those have a tolereance value as well.


.


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## stp57 (Dec 12, 2007)

Thanks Mickeyco,
I have a couple of identical digital voltmeters (the $16 variety from HD) & I use them exclusively to monitor my work van's battery (Odyssey) to make sure it doesn't drop below a certain voltage. The meters are .2 volts off from one another, but I don't know which one is right. 2 tenths of a volt is a big difference with a dry cell deep cycle battery.
So all I need is the 20v range, but I can't think of what I can calibrate it with?
Steve


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## Speedy Petey (Sep 30, 2003)

stp57 said:


> 2 tenths of a volt is a big difference with a dry cell deep cycle battery.


You really think so?


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## newenergy (Mar 5, 2008)

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

or 

http://www.maxim-ic.com/products/references/

next one looks expensive

http://www.troemner.com/cal_elec_time_freq.php

For the problem at hand though I would probably try to borrow an expensive multimeter and see which one of your cheaper meters it agrees with.


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## jrclen (Jul 10, 2007)

I think you buy a very expensive Fluke and check your meters against that one and call it good. Or rent my Fluke for a few days at a nominal cost. :laughing:


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## stp57 (Dec 12, 2007)

I have a Fluke that I use for work. It doesn't display decimals. I just picked up another of the same HD cheapies today & it reads different than my other two voltmeters (by about a tenth). 
Steve


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## Speedy Petey (Sep 30, 2003)

You didn't answer my question.
Even considering this is 12v, do you honestly think 2 tenths of a volt is a "big" difference???


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## Teetorbilt (Feb 12, 2004)

Why are you worrying about an Odyssey battery? The things are almost bulletproof, we've used them in boats for years. The only problem is if they go totally flat you need at least a 40A charger to get them starting to charge back up.


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## Dustball (Jul 7, 2006)

Battery testing-



Speedy Petey said:


> You didn't answer my question.
> Even considering this is 12v, do you honestly think 2 tenths of a volt is a "big" difference???





> State of Charge / Specific Gravity / Voltage
> 100% / 1.265 /12.7
> 75% / 1.225 / 12.4
> 50% / 1.190 / 12.2
> ...


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## hbiss (May 23, 2007)

Ok, if you want that kind of accuracy you are going to need to spend some money on a good meter, not some $20 piece of junk from Home Despot. Even if you did compare it to a meter of known accuracy, the only thing you can be sure of is that it will never stay that way. Quality meters like Fluke are designed to maintain their accuracy over temperature changes, aging and use. They are capable of being calibrated to a standard, not so with the cheapies. 

-Hal


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## stp57 (Dec 12, 2007)

Thanks Dustball,
I couldn't have said it better myself.

You are right Hal. But, the cheapies are so convenient. Not a lot of settings & I have it installed on my dash & directly wired to the battery. It is real simple to calibrate it if I could find something with certifiable voltage. How does it work calibrating it with a diode? 
Steve


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## Ponsse (Dec 12, 2007)

I've tried the measuring voltage method of finding a bad battery on either a 12 volt paralleled vehicle (diesel trucks) or 12 volt batteries in series (24 volt construction equipment). You can have 2 brand new batteries and the voltage can be a few 10th's of a volt off. 

The only accurate way I've found to test them is to "load test" them. I pull the stop magnet wire off of the injector pump so it won't start then crank them over, the good battery will pull down maybe only a volt or so, the bad battery will pull down to whatever, 5 or 10 volts.

It will work with only one battery too, I was talking about 2 batteries to illustrate the voltage difference in new batteries.

Anyways, it works for me. If you bring a battery into the parts store and have them check it they don't put a voltmeter across it, they "load test" it.


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## Leo G (May 12, 2005)

Use a new watch battery. Get one with a voltage of 1.55v [381R]


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