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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.

  2. #2
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    SilverFox's Avatar
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    Default Re: Playing with the RadioShack 22-812 Meter

    Hello Mr Happy,

    Nice...

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  3. #3
    Flashaholic* TakeTheActive's Avatar
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    Question Re: Playing with the RadioShack 22-812 Meter

    Quote Originally Posted by Mr Happy View Post
    ...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 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...
    I don't understand the voltage curve - more precisely, I don't understand how it got over 1.47VDC so fast.

    It's my understanding that when we ask a charger to charge a cell at xx mA, it varies the voltage to maintain the current. Thus, to supply 2000mA, the GP PowerBank Smart 2 had to ramp up the voltage to over 1.50VDC. Going by this graph, if you were to attempt to charge these same cells on the C9000 @ 2000mA, it appears that one would expect the C9000 to terminate on Max Voltage of 1.47VDC in about 3 minutes.

    My first thought was high Internal Resistance, but since the temperature didn't begin to climb in earnest until ~45min, the cells appear healthy.

    What am I missing?

    Thanks!

  4. #4
    *Flashaholic* Mr Happy's Avatar
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    Default Re: Playing with the RadioShack 22-812 Meter

    Quote Originally Posted by TakeTheActive View Post
    I don't understand the voltage curve - more precisely, I don't understand how it got over 1.47VDC so fast.

    It's my understanding that when we ask a charger to charge a cell at xx mA, it varies the voltage to maintain the current. Thus, to supply 2000mA, the GP PowerBank Smart 2 had to ramp up the voltage to over 1.50VDC. Going by this graph, if you were to attempt to charge these same cells on the C9000 @ 2000mA, it appears that one would expect the C9000 to terminate on Max Voltage of 1.47VDC in about 3 minutes.

    My first thought was high Internal Resistance, but since the temperature didn't begin to climb in earnest until ~45min, the cells appear healthy.

    What am I missing?

    Thanks!
    I thought exactly the same thing, and I did a test on the C9000 to find out.

    It seems the voltage indicated by the C9000 when it is operating is not exactly the voltage you can see with an external voltmeter.

    The voltage shown on my plot is the maximum voltage across the cell terminals when the charging current is present. However, the C9000 applies the charging current in pulses and it measures and displays the cell voltage in the intervals when the current is turned off. It is difficult for slow acting voltmeters to catch this, apparently. (The C9000 has an internal microprocessor that can coordinate the voltage measurements at exactly the right time.)

    To get an idea of the difference, see how the voltage dropped from about 1.61 V to 1.53 V when the charger stopped at the end. If you subtract about 0.08 V from the whole voltage curve you will get an estimate of what voltage the C9000 is looking at.
    Last edited by Mr Happy; 02-15-2010 at 08:32 PM.

  5. #5
    *Flashaholic* Mr Happy's Avatar
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    Default Re: Playing with the RadioShack 22-812 Meter

    For comparison with the previous chart, here is a similar cell charged on the C9000 at 2000 mA indicated (1800 mA actual).



    Notable features:

    1. The voltage goes through a slight minimum between 10 and 20 minutes;
    2. Charging terminates before the −∆V point is reached due to the max voltage cut-off of the C9000, but this results in a lower peak cell temperature.

    It is unfortunate I could not obtain a true 2000 mA charge rate for a direct comparison with the GPPB14. Due to the 90% duty cycle of the C9000, 90% of 2000 mA is the highest charging current that can be obtained.
    Last edited by Mr Happy; 02-16-2010 at 09:26 AM.

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    Flashaholic* Russel's Avatar
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    Default Re: Playing with the RadioShack 22-812 Meter

    A while back I used my CBAII to monitor the charge voltage of an Eneloop charged at 1000ma on my BC-900 charger. Below are the results. I may have to try the same thing with my MH-C9000. (The voltage seems a little high here also.)


  7. #7
    *Flashaholic* Mr Happy's Avatar
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    Default Re: Playing with the RadioShack 22-812 Meter

    I smoothed out the spikes in my plot by picking the maximum voltage seen in each sample period, which should correspond to the closed circuit voltage when the charging current is turned on.

    A peak voltage of 1.6+ V for a modern cell under high rate charge is typical, actually. The C9000 can be misleading since the voltage it displays is the open circuit voltage sampled between charging pulses.

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