Amp Readings

[Steve Lancaster]

Good Afternoon All,
I was wondering the best way to measure the milliamp draw of a locomotive.
I do not even want to atempt chasing the locomotive around the track with
a meter.
Thanks Steve

 

[ezdays]

That's a lot simpler than that. Just clear the tracks of everything, open the positive wire going from your power pack to the rail. Then take an ammeter and connect one lead to your power pack and the other to the wire going to the track. Set your meter to around one amp, dependent on what scales you have. 500 mA will probably be OK. Turn you power pack on to the setting you would run your train at, and see if you get a reading. You shouldn't unless you were using the DC to light a light or some other accessory. Turn the power pack off and put your loco on the tracks and repeat. The difference between what you read the first time and what you read the second time is the current draw of that loco.

Let us know how you did.

 

[N Gauger]

By The Way.... This is why people permanantly mount amp meters in series with some power leads to sections of track.

if the meter reads full power (Pinned) there's a short somewhere - Derailed wheelset somewhere?? Wheels shorting across a switch???

If the meter reads 0 (open) it means your locomotive either derailed - or it completly fell off the track.. This is perfect for any hidden track you have.....

 

[N Gauger]

............ and like Don said - this meter must be connected to a dedicated line - nothing can be connected to it - only the track your permanantly monitoring or testing the engine on...

 

[ezdays]

BTW, I'm assuming you would be using a digital meter. That being the case you would not have to worry about the polarity of the meter leads. If you're using an analog meter that goes from zero to positive (as opposed to a center zero -0+), you will. If you don't know the polarity of an analog meter, the best thing is to hook it up, put an engine on the track and just barely turn the power pack on and see which way the meter needle goes. If it goes up, you're good to go, if it goes backwards, reverse the two meter leads before you go any further.

You can get a really cheap digital meter that will do the job at Harbor Freight. They are selling a small pocket-sized meter for $2.99 at our local store and it measures AC and DC volts, AC and DC amps and resistance.

 

[tillsbury]

Note that these techniques will give you the current draw while the train is running, not the stall current. You might want to know the stall current (particularly when installing DCC or whatever), which is the maximum draw the engine will take. Most decoders come with instructions on how to measure stall current, or check the www.digitrax.com website...