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Thread: Playing with the RadioShack 22-812 Meter

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  1. #1
    *Flashaholic* Mr Happy's Avatar
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    Default Playing with the RadioShack 22-812 Meter

    For anyone unfamiliar with it, this is a moderately good digital multimeter you can find in RadioShack for about $70, maybe less on sale. What is really neat about it is that it has a RS232 serial interface for connecting to a computer. This means you can use it for unattended data logging!

    (I have noticed the 22-812 seems to have disappeared from RadioShack’s web site, suggesting it might have been discontinued. If you want one, I would suggest grabbing one quick before the remaining stock runs out.)

    The meter comes with some PC software that is functional but limited, but using standard software is no fun. It also doesn’t install nicely on Vista or Windows 7. What was more fun was to write my own program to capture data from the meter and record it the way I wanted. (The protocol can be found in the link at the bottom of this page).

    Two meters is twice as much fun as one meter! I wrote my program to capture data from one, two or any number of meters at the same time and record all the results in a single file. If you have not got that many (or any) serial ports on your computer you will need a USB to serial port adapter for each meter (this is a good one).

    Today I got all the pieces assembled and ran a real life test. Here is the result of charging a UltraLast Hybrio (not a Hybriloop) on the GP PowerBank Smart 2 charger I picked up recently. The plot shows voltage and temperature. The temperature was captured using a Fluke thermocouple adapter that was actually more expensive than the meter , though I have to say I was seriously impressed with the quality of it. I can see why Fluke products are worth the money.

    The GPPB14 charges at 2000 mA, hence the rapid charging time. It is interesting how high the voltage went. I’m going to have to charge the same cell at 2000 mA on the C9000 for comparison sometime. (Edit: The chart below shows the closed circuit voltage with the charge current present, while the C9000 displays the open circuit voltage with the charge current disconnected. The difference between the two values can be quite significant.)

    Here’s the pretty plot produced in Excel:



    Notice how the −∆V signal can be seen just prior to termination, and how flat most of the voltage curve is.

    Note: The code for this example is included in post #12 by request.
    Last edited by Mr Happy; 03-24-2010 at 10:15 AM.

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