How do I measure milliamp?

[Chris333]

I'm trying to measure how many milliamps a locomotive draws at full speed. The meter I have looks just like this:
http://www.doctronics.co.uk/meter.htm#digital
I keep searching for how to measure it and all they do is show how to hook wires up. I need to know what to set the dial on the meter to, like a dummies guide.

How do I do it  ???

[victor miranda]

I did not follow the link.

an ammeter (measures amps) is put into the circuit in series.

the shortest way to do it is to cut  a (only one!) wire to the track,
and connect the cut ends to the meter.

( cut a wire and you get two ends...)

victor
 

[Chris333]

Yeah I understand the part about wiring the meter in series. That is what everything says when I search for it. But I can't figure out what to set the meter dial to. There are 19 positions, two are AC, so 17 choices.

[victor miranda]

oh!

set the meter knob to the A section;  200m setting theis is good for general running.

most locos can use up to 400 ma at full speed.

and I bet you have to move the red lead to a new hole in the meter.

check that...
the other hole is the 10 AMP connection.

be careful with that one, they are rarely fused.

If you meter is the exact same settings you will have to use the 10 amp position.

v

[Chris333]

Thanks. I did try the 200m, but I had the red lead in the mA hole. I thought mA was for Milliamp.

So I got 00.4 at full speed. Does that mean 400 milliamps? That seems high for a Faulhaber motor. I tried another loco and got 00.9. The numbers stay the same for the last 2/3 of the throttle. Is there a way to get a more actuate reading?

[victor miranda]

oh chris...

a couple of answers....

the readings you describe seem correct.

the answer to getting better resolution is to get a better ammeter...

so read the loco is low draw, like starting etc
and then switch over to the less accurate section of the meter.

I would test the resolution my trying that one that uses .9 amps

start it and slowly speed it up  if the meter jumps in .1 increments
you know that is its resolution.

better meters are available.... and cost .... from a little more to astoundiing.

my favorite meter is made by fluke.

it is old and I guard it jelously.

v

[Chris333]

Is there a single meter that only measures milliamps that I can buy?

This is giving me a headache  :-\

The Faulhaber isn't supposed to get over 170mA so 400 would be a tad high  ;D

[Dave Schneider]

I would use the middle and bottom holes, set the meter at 200 m and give it a go. The value should be in mA.

Best wishes, Dave

[mmyers]

Is that reading on an installed motor or free? Friction in the mechanism will increase the current draw. An ammeter is a good way to check modification success or failure.

[victor miranda]

oh you ask the tough questions.

yes you can make a ammeter.

get a volt meter and a resistor of known value....

for example
 a 1 ohm resistor will have 1 volt across it when the resistor is flowing 1 amp
and a half a volt when flowing a half an amp....

the trick is calibrating the resistor.

ask petesky on the A-board.... I am sure he will have a good trick
for this.

victor

[Chris333]

I some-what took care of the problem by drinking a few beers.

A later report as this clears up...

[Chris333]

OK

I would use the middle and bottom holes, set the meter at 200 m and give it a go. The value should be in mA.

When I try this nothing happens at all and I checked my fuse. Under this setting the train will not move.

I'm running the locomotive on the layout while pulling about 25 cars. So I know the max mA it could draw. I spliced in the meter at the leads to the track.

[victor miranda]

mmmm...  take a photo of your meter ?

set the leads in the normal holes for the meter.
The ammeter function should work.  the same as for the 10 amp.

the fuse is for all of the amp reading ranges except the 10 amp hole.
so try another switch setting..

20ma is a good place.  the meter will tell you it is out of range. 
No harm should be caused.

if all the ammeter ranges do not work, a fuse is likely to be the cause.
... maybe you found a fuse for another function?

v

 

[Chris333]

This is it while the train is running:

It fickers between 00.3 and 00.4

[Chris333]

Here it is wired with the red lead in the center hole running at full speed: