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How does a battery tester work?

Discussion in 'Electronic Basics' started by Paul Richard, Jul 12, 2003.

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  1. Paul Richard

    Paul Richard Guest

    Ok, super basic question and I'm almost embarrased to ask, but what exactly
    does a battery tester measure? Is it current that the battery can maintain
    or simply its potential (voltage)? And how could I use a multimeter (does
    A, V, Resistance, etc.) to check batteries? Please go easy on me :)

    Hmmm... while I'm at it, what would people recommend if I wanted to start
    learning electronics and circuit design? My main interest is actually
    programming microcontrollers, but I quickly realised that I would need some
    understanding of circuits before I could do anything useful. Recommended
    books, faqs, online tutorials, online resources, etc would be appreciated.
    I have a pretty technical background (physics and computer science), I've
    just never really studied applied electronics and/or circuits. Well did a
    basic course with a physics point of view once, but that feels like ages ago

  2. It is not very useful to read the voltage of a battery when there is
    no load attached, so you need to measure the voltage when a resistor
    of suitable value is connected to the battery.

    This resistor value is different for different batteries.

    Here is a table of resistors I use to check batteries:
    9 Volt battery, the small common type: 180 Ohm
    big 1.5 Volt (size 20) : 3 Ohm
    medium size 1.5 Volt (size 14) 7 Ohm
    small size 1.5 Volt (size 6) 11 Ohm
    flat 4.5 Volt (rather uncommon type) 21 Ohm
    (table from the Elektor magazine)

    These resistance values are not critical in any way, use what you can
    get hold of in the same range as these values.
    A 10 Ohm resistor is good enough for all the 1.5 Volt batteries.
    But use the same resistor for a certain battery type every time, so
    you can compare the voltage levels.

    Connect the resistor between the probes of the voltmeter, set the
    voltmeter to a DC voltage range which is a little higher than the
    battery voltage, connect to the battery and read the voltage.

    If you try both new and used batteries you will soon learn how much
    voltage you may expect from a new, a half used, and a completely empty
    The nearest library is a good starting point. Read about resistors,
    capacitors, diodes, transistors.

    Buy a small soldering iron, 20-30 Watt with a thin tip.
    Buy a cheap voltmeter, or rather a DMM (digital multimeter).

    Get some old radios and other electronics devices from the time when
    they used transistors, capacitors, etc.. and disassemble them.
    This will teach you how to handle the soldering iron, it will give you
    a collection of components, and you can begin learning to recognise
    different types of components.

    It might give you those resistors you need to test batteries.
    Otherwise you can buy them.

    Find a shop where you can buy components, maybe ask
    radio-tv-servicemen at shops where they sell radios and tv-sets if
    they can sell you a few components when you need them.
    Send for post-order catalogs from component suppliers, or find these
    catalogs on the web. Study them.
    There are also a lot of information on the web, search for "Ohms law"
    for example. Search words like schematic circuit electronics, etc..

    Get a freeware spice simulator program and learn to use it. It allows
    you to try out and study electronics circuits on the computer.
    Serach for "LT cad" from Linear Technology, or look at the signature
    of Kevin Aylward who writes in this newsgroup, he has a spice
    simulator called superspice you can download and try.

    An old spice simulator called EWB (Electronics Workbench) is not sold
    anymore but you may be able to find a used copy, it is the easiest one
    to use.

    If your library does not have it, buy a book called "The handbook"
    from ARRL, Amateur Radio Relay League.
    Check out their web site and read about the books they produce.
    I think it is something like or so, or search for it on
    google. The handbook (for radio amateurs) is a very big and useful
    book, not only for radio amateurs.
    I used to buy the paperback edition and cut it up into 10-12 thinner
    books, easier to handle. It was so heavy as it was.
    No other book gives you the same value in knowledge per dollar and it
    is suitable for beginners. There are chapters about the basics of
    electronics, components, measuring, power supplies, circuits, etc..
  3. Rich Webb

    Rich Webb Guest

    Start with a resistor kit, ceramic cap kit, breadboard, a handful of
    LEDs, a few 2N2222A transistors, a 9 volt battery, and assorted hook-up
    wires. Get a couple 555 timer chips and download the data sheet. Make an
    LED blinker. Maybe add a thermistor so that the blink rate is
    temperature dependent. Or make an LED "brightness controller" by
    adjusting the duty cycle from mostly-off to mostly-on.

    Get an inexpensive bench power supply. You can always make your own
    on-board supplies but it's really handy to just dial-in the voltage you
    want. Also, nowadays most have adjustable current limiting, so there's
    less opportunity to let the smoke out of the little plastic thingies.

    Then get a few LM324 op amp chips and find a copy of "The IC Op Amp
    Cookbook" (Walter G. Jung). Take the time to really learn the first
    three chapters and then play with whatever looks interesting in the
    latter part of the book.
  4. Paul Richard

    Paul Richard Guest

    Thanks for your recommendations guys! I'll try and put them to good use.

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