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On board battery meter $1.48 — Parallax Forums

On board battery meter $1.48

bulkheadbulkhead Posts: 405
edited 2006-02-19 18:51 in Robotics
RadioShack has an "Analog RC Car Battery Tester" on clearance for $1.48, it's usually $15 (what a profit they make!). See link here: www.radioshack.com/product/index.jsp?productId=2103163&cp=&pg=2&kw=rc+battery&parentPage=search

It can test 1.5V, 6V, 7.2V, 9V, and 9.6V. If you have any battery voltage other than the ones listed, you can create your own battery meter by simply substituting a different value resistor (if you open up the meter, you can see the resistors they use). Most likely, these different voltages should be suitable for most applications.

To modify it, all I did was remove the casing, and attach the meter's readout panel onto the circuit board (so it's more compact). I disconnected all the wires except the 6V one (that's for my battery). I also utilized the slide switch that's used to switch from 7.2V and 9.6V to make an "on/off" switch. I hooked up the power and ground wires permanently to my robot(on the plug where the battery plugs in), and use the modified switch to connect/disconnect the meter (so it doesn't slowly drain the battery, I suppose).

Here are some pictures:


The best part is not only do I know when my batteries are getting low, but I can also see the voltage drop on the battery during high current usage (when my robot lifts something).

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-02-19 07:53
    You might want to check the circuit with an ammeter.· I believe this tester is also putting a significant load on your batteries with the wire-wound resistor in the picture.· I would use it on a battery and test the current draw while testing.· That will tell you how much this thing is taking from your batteries during use.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • bulkheadbulkhead Posts: 405
    edited 2006-02-19 08:05
    Chris, I did as you suggested and checked with a 9V battery, it draws about 10.3mA. With a 2000mah AA battery, this would last about 200 hours then? I suppose this excess current draw is not noticeable when the battery powering a bunch of servos. Anyways, I have the switch connect and disconnect the meter, so when I'm not using it, it's not draining my battery.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-02-19 18:51
    Only 10.3 mA?· Oh well, I somehow expected it to be higher based on the guts of the tester.· That's really only about what an LED draws so you're good I guess.· I was expecting around 250 mA of draw.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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