# How does a battery tester work?

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

1. ### Paul RichardGuest

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
now.

Thanks,
Paul

2. ### Roger JohanssonGuest

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
battery.
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.

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

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 www.arrl.org 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 WebbGuest

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
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
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 RichardGuest

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

Cheers,
Paul