very new to electronics. looking for starting place.

[BeeJ]

Ask your questions any way you can. Most of us will try to interpret.

Your meter is giving you erroneous reading and may either be inaccurate
of needs calibration. Try some other types of cells with know
potential (voltage). See if you can find an adjustment to make your
meter read a little more accurately. It is not all that important to
be accurate but the meter should give good relative readings so you can
see voltage drop or whatever.

As for the motor voltage, remember you are dealing with both DC and AC
whenever you look at any circuit. Some DC circuits oscillate and give
funny reading when measured on the DC meter. Switch to AC on the meter
and see what that reads. Yes, some motor do produce at lot of "noise"
that will make it look funny to a DC measurement. But that noise is
sometimes very useful.

Keep at it and enjoy the world of electronics. I have been doing it
for 40 years and still enjoy fiddling once in a while.

If you look on line you will find many electronics courses that are
totally free and cover more areas than you probably want to know about.
Pick and choose and enjoy.

Learn about basic components first: resistor, capacitor, inductor,
diode transistor etc. You will later learn that a resistor can look
like a capacitor or an inductor in certain circumstances. All part of
the fun.

I used to host junior year electronics major college students for
summer break. They would come to my lab and learn that they were
taught the fundamental theory but knew nothing about the real world.
Find a local electronics store and, as one example, see how many
different types of capacitors there are and learn what each one is used
for and why. Knowing why is what is important because you can apply
that knowledge to other devices.

 

[George Herold]

The voltage waveform when you drive a motor from a source with any sort
of real-world impedance is crappy.

If you consider that a DC brushed motor is a device that automatically
switches an inductive load with mechanical switches many times a second,
this should help you understand why.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com- Hide quoted text -

- Show quoted text -

Thanks Tim, I can imagine all sorts of 'stuff' from a motor.

I hooked up my sons snap circuits. (I forgot my 'scope though.)
But for the OP (or second OP) I measured 3.1 V DC with no motor and
2.6 to 2.8 Volts with the motor. When switch to AC my B&K 391 (true
rms) read 0.1 to 0.5 V. But fast, big spikes will be missed.

George H.

 

[P E Schoen]

wrote in message

This is my first post to a Google group, so hopefully I'm doing this right
and posting in the right place. My interest is in elementary electronics.
I'm a total beginer who will be trying to learn basicaly on my own. My
first tools are a learning kit called Snap Circuits and a multimeter.

Which brings me to my first question. I built a simple circuit in the kit:
It is 2 aa bateries in a battery holder, a switch, and a small motor. I'm
told that a aa battery puts out about 1.5 volts.And when I measure across
the batteries I get about 3.5v which makes sense. But when I throw the
switch and turn the motor on then I'm reading like 9 volts across the
motor. That does'nt make sense to me. It seems voltage should be decreased
by the resistance of the motor, not increased. Can someone explain?

I have several cheap Harbor Freight meters which are usually pretty good,
but when the battery is low, the internal reference also is low, which makes
the meter read high. That said, it is not unusual for fresh batteries,
especially alkaline, to read higher than 1.5 volts per cell, and may be as
high as 1.65V as you measured:
http://en.wikipedia.org/wiki/Alkaline_battery

Such meters (which usually have AC ranges of 200V and 750V), use a series
diode which responds to the unidirectional peak voltage, calibrated to RMS
based on a sine wave.

The DC motor (brushed PM) will produce spikes which may account for the
higher voltage you read. It could even be inductively coupled to the meter
(which is probably not shielded). A quick and easy fix may be to put a
capacitor across the motor leads.

If you are serious about learning electronics, it would be highly advisable
to get an oscilloscope. You can start with a cheap USB scope which is
probably less than $20, or an older Tek, HP, B&K, Heathkit, or EICO which
might be not much more on eBay, Craig's List, or electronic flea markets
such as Ham festivals. The simpler models are not difficult to fix, and will
present a useful learning experience, although be careful with high voltage
line operated equipment.

And, as others have stated, please start a new thread if you have other
questions.

Good luck!

Paul