A SIMPLE AMMETER
Here is a simple way to make a reliable, safe ammeter
for ... ? I use mine to monitor power coming into/out of my batteries.
Undoubtably one could make many modifications; it would not be too dificult
to convert this to a full function multi-meter. Mine shows DC amps,
plus or minus 15. This meter is simple, and reliable enough to serve
many applications. With just a little work, it could be a fine addition
to any shop, or living room.
The meter consists of a wooden back, a long wooden
needle(14" long), which pivots on a nail. To the bottom of
the long wooden needle is a surplus computer hard drive magnet glued on
with super-glue. You can get the magnet out of most computer hard
drives, or...we sell them, between $1 and $12, depending upon the scale
of meter you have in mind. (it would be great to make a BIG one)
Pictured above is the surplus computer hard drive magnet.
This is a NdFeB (Neodymium Iron Boron) rare earth magnet, the strongest
permanant magnets currently developed. These are many times stronger
than AlNiCo or ceramic magnets that we are all acustumed to, they make
possible many new things! Without this magnet, this meter would
not work nearly as well. The shape, strength, and polarization of
these magnets make them perfect for a 0 centered ammeter. The steel
back serves as a nice counterweight. Again, magnets similiar to these
can be found inside almost any computer hard drive, or...if you like, go
to our products page and you'll find several sizes available.
Behind the hard drive magnet (attached to the wooden
back) is a wooden peg, around which is a coil (3 windings) of 12 gauge
romex (normal copper wire for wiring houses). In the picture below, I swung
the meter such that you can see detail of the magnet, the pivot, the bottom
of the needle, and the coil of wire that drives it.
There isn't much resistance, the meter works
well because of the extremely strong rare earth magnet. More windings
on the coil could make the meter more sensitive, less windings would make
it less so. It can also be calibrated/centered with a small weight
on the back of the magnet or the needle. I have mine set up to read
+/-15 amps, this is appropriate for my power consumption/generation.
The meter shown in the picture is somewhat inaccurate, as the scale should
compress, especially near the ends of the scale. Mine is accurate
between 0 and 10 amps, after that it becomes conservative. Simple
thing, I think it can make for a more attractive meter for monitoring power
systems than most available...at very little cost, if one has a couple
hours to spend on it! As somebody who enjoys making/using my electricity,
I also enjoy watching it come and go. This meter is sensitive, and
moves freely enough that it responds very noticably to a small 12 volt
car stereo, you can easily see it respond to music played at a reasonable
©2000 by OTHERPOWER