Just because you’ve switched to DCC doesn’t mean you should toss or sell your old DC power pack. Well, if you are like me you have 5 or more in the tickle trunk so I guess you could sell some of them. I need to know the free running and stall current of an old Athearn GP9 to ensure the decoder I have is suitable. Out comes my meter, power pack and a few clip leads to hook things up.

This is an inexpensive meter that I bought at Canadian Tire for less than $10. You probably don’t have a Canadian Tire in the States but any meter will do. Litchfield Station has one for sale for $7.95 ( http://www.litchfieldstation.com/xcart/product.php?productid=999003515&cat=&page=1) but you could probably pick one up at any hardware store. One that autoranges is nice but I have to set mine. In this picture I have it set to read Volts, Ohms (resistance) or mA and for a max of 20V DC.

Here is the meter hooked up to my old Hammond & Morgan power pack. I have a red and white clip lead on the DC power out at the back of the power pack connected to the test probes of the meter. The meter is reading 18.92V but that is without a load, once connected to a locomotive, the voltage will drop.

Here is what the meter reads at full power when running a locomotive freewheeling. The meter is reading 13.47Volts. This is also the output of a 12Volt car battery. It’s spot on for our testing.

Here is the meter set to read a maximum of 10Amps. Note I had to change the input leads and set the dial for 10A.

Here is the meter’s reading of the current draw while the locomotive is free wheeling at full voltage. The meter reads 0.63Amps

What we really need to know is the stall current of the motor. While running at full speed, I squeezed the flywheel of the locomotive briefly and captured the current reading of the meter. The value will fluctuate but you are interested in the highest current reading. You don’t want to fry your decoder by putting too much of a load on it. The highest reading I could get was 1.26Amps. That’s a lot of current. However, the Digitrax DH163D decoder I plan to install in this locomotive is rated at 1.5Amps continuous and 2.0Amps peak. Since I couldn’t get a reading over 1.26Amps or so, I know I am safe to use this decoder.

The other consideration is the current draw of any lighting. As it stands I have no lighting in this unit but plan to install LEDs when I install the DCC Decoder. I chose LEDs because they draw much less current that incandescent bulbs and knew I would be pushing the limits of this decoder with the old Athearn motor.

Athearn motors are known for their high current draw. However, it is more than acceptable to install a 1.5Amp (2.0Amp peak) decoder. What you want to keep in mind is how many locomotives you are running and what their current draw is. With my NCE PowerCab I would be limited to about 2 Athearn locomotives max, with more modern can type motors I could stretch this to 3 or 4.

While the Athearn GP9 shows its age and also knowing it is not a scale width hood, I am willing to install DCC in it because I am attached to this particular model. It was my first custom paint and decal job. I do plan to remotor this unit at a later date. I am sure there are many who have fleets of Athearn locomotives on their roster and are contemplating a switch to DCC. It is possible, you just need a little information on what your locomotives are drawing for current.

GregW66