Measuring a stall current

In my first installment on what a stall current is I briefly touched on measurements but didn’t really provide a step by step description of the process, so let’s remedy that. First the setup. You will need a volt ohm meter, a DC power pack, a piece of track, and some wire. As an option jumpers with alligator clips on them are great for making temporary connections instead of using hookup wires.

  1. Connect one terminal from the power pack to one rail on the track.

  2. Connect the second power pack terminal to one of the leads on the volt ohm meter.

  3. Connect the second lead on the volt ohm meter to the other track rail.

  4. Set your meter for amperage and if it is not auto-ranging set it for either the 0-1 or 0-10 amp range, depending on what you think the motor may draw and what your meter offers.

  5. Finally place your loco on the track.

  6. For a slipping stall current hold onto the coupler and crank up the throttle to full speed. Allow the wheels to spin freely and note the amperage.

  7. For a locked rotor stall current either press down on the loco so the wheels can’t tun or remove the shell and grasp a flywheel, then crank up the throttle to full power and read the amperage.

The slipping stall current is the most common and what most decoders will take–a locked stall current is uncommon and usually larger. They are the result of something getting jammed in the drive train or the motor itself. If you look at enough HO decoder specifications you will see that most can handle a stall current up to 1 amp and many now are rated at 2 amps. A couple may only take 0.7 amps, and N or Z scale decoders may have lower ratings. Use your stall current readings when selecting a decoder for your locomotives. I usually only worry with the slipping stall current because most decoders now can take a lot of current or have overload protection built in to them. However always follow your manufacturer’s advice since that will affect their warranty support if you burn up a power transistor or completely smoke the decoder–and that is why Justin asked me what the stall current of my loco was.

3 comments

  • I just finished installing 2 Tsunami2’s in old Proto 2K Alco PA’s. Both had a locked stall current of 3.5 amps. Suffice to say, I replaced both motors just to be safe. A lot cheaper than replacing 2 $100 decoders. I always use a Sharpie to note stall current on one of the flywheels.

    • Yes, some of the early PA’s were made with motors that had their armature’s wound with either the wrong wire or the incorrect number of windings. This resulted in an operating current that often exceeded 1 amp and stall currents like you found. I too have a pair of these that I had to remotor. Oddly enough LifeLike never did offer to replace the defective motors. Good thing you checked.

  • Could the stall current be measured on a DCC system using a Ramp Meter?