The other alternative is to go DC with your transformer and a #15 Rectifier or the #14 rectiformer
Ok, my tester is a $20 radio shack #22-810. The more I use it here the less I trust it for this task.
I tried testing two ways: touching the probes to various places on the posts, and securing wires to the posts that are connected to alligator clips and attaching the clips to the tips of the probes.
Why test two ways? Because using the probe approach, I got different readings in different places on the post. And sometimes the reading would change around while I held the probes perfectly still. Sometimes it would start iwth a reading of 2.0 v or so, then jump around a bit while heading down to zero. The strongest readings I got was on the end of the post screw cap. Actually unscrewing the cap a bit and touching the threads led to lower or zero readings. I got readings at times and places of 0 or 1.5 or 2.0 that stayed steady, and also lots of readings in between as it jumped around.
Wheee!
So I tried the bare wire on the post to alligator clip approach. There I got consistent readings of 1.5 at stop and 0 at half way. Except I noticed that it still read around 1.0 to 2.0 v when I had disconnected the red lead, and only the black lead was still attached. I waved the red lead around, stuck into in my pocket, hid it under the table: still reading 1.0 or so AC volts with only one lead connected to the transformer.
Double whee!
Ok. So should I buck up and get a better meter? I can't drop $400 on one. So what's the minimum price level and best maker to buy in a lower price range? (I ask this knowing it might launch a forum debate about the best meter, but hey, I am not in a hurry).
Thanks. I am actually enjoying my muddle through here, I hope you are too.
Your problem seems to be your meter. Not that it's too cheap, but that it's too good. A more expensive one will probably have an even higher input impedance; but yours is already too high for what you're trying to measure. For example, when you put the probes on the transformer output and turn the control all the way down, you are measuring the voltage on a wire that isn't connected to anything inside the transformer. Because your meter isn't putting any significant load on that wire, it is picking up whatever stray voltage is being capacitively coupled to the wire. When you turn the handle up half way, the transformer secondary connects that wire to the common through the much lower impedance of the secondary winding and suddenly you measure zero voltage.
The various voltages you are measuring as you wave the probes around are due to the same kind of effect. If you had a traditional passive analog meter, you wouldn't be seeing that stuff. You can simulate that situation by connecting a resistor, perhaps 1000 ohms, between your probes while you take your measurements. You should get something much closer to what would make sense.
Radio Shack makes a simple analog meter for $17, similar to the one I use: http://www.radioshack.com/product/index.jsp?productId=2999093&filterName=Type&filterValue=Analog It would be better for your purposes.
Bob Nelson
To make 'em DC=
or
Jim
Tim
Here is the inside
I use it mostly for testing and have not had heat up issues. If I am going to run much DC I use my #14 or #15
Sturg,
That bridge looks like it might be this Radio Shack part,
http://www.radioshack.com/product/index.jsp?productId=2062583&filterName=Type&filterValue=Rectifiers
which is rated at 8 amperes, without a heat sink. That should be plenty for one train.
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