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View Full Version : Lipo voltage - 3 meters, 3 results


John D
09-06-2005, 08:20 AM
Hello

How do I find out which voltmeter is showing the correct voltage. My old multimeter reads 11.38v, my new emeter:D reads 11.48v, my electricians new multimeter reads 11.41v.

The reason I ask is that every time I charge my 2 lipos on either my Apache 2500 or Swallow Advance, the maximum charge I can get according to my old multimeter is 12.48v.

This happens when I use my car battery or my converted pc power supply to power the chargers.

When I got my new emeter:D, I found that it read 0.1v higher than the old multimeter and thought everything was ok and the lipos were getting a full charge. Now that I've checked the battery with my electricians multi I'm not so sure.

regards

John

Matt Kirsch
09-06-2005, 08:42 PM
Would it ease your mind to tell you that you're getting 97-98% of a full charge?

Frankly, I would put the most faith in the most expensive meter, the one you use professionally, especially if it has been calibrated at any point in its lifetime. The only way to truly know is to compare their readings with a calibrated meter.

rahtware
09-07-2005, 12:34 AM
Let's see if I remember the formula...

I think it goes, old meter over new meter times the power of the electricians meter...:rolleyes:

Or would you add all three and devide by three???;)

I wonder what the "fade" factor of each is... I have one metr that reads close at 12 VDC, but tells me my house is running on 99VAC. My other meter (cost about 4X the cheaper one) reads about the same at 12VDC, but says I have a 119VAC house... I agree with MK, cost is a factor with the reliability of meters.

crash_alot
11-14-2005, 04:50 PM
Like many items, multimeters come with a lot of different capabilities and accuracies. Just because it is "digital" doesn't mean it has the accuracy you are expecting. Just because it is expensive does not mean it has the accuracy you expect. To answer your question regarding the difference in voltage readings several questions need answered. What is the resolution of each of the 3 meters (2 1/2 digits, 3 1/2 digits, etc.)? When was each meter calibrated last? What are the manufacturer and model numbers of each meter?

coro
11-14-2005, 05:28 PM
Old type of dry zinc-carbon batery has 1.55V exactly (with no load) even when not new. Cheapest way is to measure couple of them in series. I found no way to get accuracy for my meter, other than ask for calibration at Institute of metrology :(. Another usable way is to ask vendor of dvms, to compare values measured by Your meter, with more than one >1000$ Fluke or such DVMs (they are mostly well accurate with differences less than 1-2 mV @20V.

ForestCam
11-14-2005, 05:52 PM
I just use my buddy's $2000 Fluke graphic meter.:D

spark
11-14-2005, 08:06 PM
If you go to www.digikey.com you can look at these (and many more) precision voltage references that you can use to calibrate your Dvm.

LM4040AIZ-2.5-ND LM4040AIZ-2.5 IC VOLT REF PREC MICROPWR TO-92 National Semiconductor Micropower Precision Shunt 2.5V ±0.1% 100ppm/°C TO-92
Datasheets
LM4040AIZ-5.0-ND LM4040AIZ-5.0 IC VOLT REF PREC MICROPWR TO-92 National Semiconductor Micropower Precision Shunt 5V ±0.1% 100ppm/°C TO-92
Datasheets
LM4040AIZ-10.0-ND LM4040AIZ-10.0 IC VOLT REF PREC MICROPWR TO-92 National Semiconductor Micropower Precision Shunt 10V ±0.1% 100ppm/°C TO-92

Price each $2.37

hoppy
11-14-2005, 08:22 PM
Anything cheaper than that? LOL

ForestCam
11-14-2005, 10:02 PM
Anything cheaper than that? LOL

These go on sale at Harbor Freight for $3.99 all the time.:D

Rugar
11-15-2005, 11:32 AM
These go on sale at Harbor Freight for $3.99 all the time.:D

Yep and cheap they are. But guess what? I have one and it reads identical to my Astro Watt meter.

ForestCam
11-15-2005, 05:28 PM
Yep and cheap they are. But guess what? I have one and it reads identical to my Astro Watt meter.
Me too and it rides around in my field box.:D