My power setup: a lab quality DC switching mode power supply rated at 0-30 volts and 0-3 amps. This powers a PIKO 5 amp analog throttle, which in turn is securely connected via a 14 gauge power cable to a small oval of LGB R2 radius track. The DC supply has an LCD screen which reads out volts and amps. The voltage output is finely set at a constant 22 volts feeding into the analog throttle. With the PIKO analog throttle at zero, the amp display on the power supply reads 0.13 amps. When my train headed by a new BR 24 analog loco pulling three PIKO two-axle beer reefers plus an LGB 3019 postal/baggage van is energized, the train accelerates smoothly to running speed. The DC amperage display then fluctuates between 0.71 and 0.85 amps as the train negotiates the oval, the difference being as much as 0.14 amps, yet the train runs smoothly. The brass LGB track is clean and this is an indoor layout. My question is why the fluctuation in amperage of 0.14 amps? What am I missing here? Explanations welcome!
Something to do with curves and straights? The drag is larger in curves and might cause extra amperage.
An interesting hypothesis. Did not consider that!
Agreed, that it has to be the increased load when negotiating curves. When the load is increased on a DC Permag motor the motor slows, which reduces the counter-EMF in the armature windings, which in turn allows a higher current flow, which increases motor torque to offset the increased load.
When I took a DC motor lab course dinosaurs still roamed the Earth and we didn't have permanent-magnet motors. A shunt-field motor does simulate a Permag motor in this regard and I remember demonstrating the above speed regulation principle.
Sounds reasonable, especially since there is only a single 12" straight between each quarter section of the track circle. The fluctuation sometimes is as great as 0.19 amps. Also, the six drive wheels on my BR 24 are about 1 3/4" in diameter, which might add to the increased friction on the curves.
THANK YOU, gentlemen! ☺
I’m surprised at the amperage draw when the throttle is set at zero. That’s a pretty high percent of the current draw when the train is running. Is the throttle circuitry drawing that much current by itself, or are there incandescent pilot lights that are on even if the throttle is not?
Bill in FtL
There is a power monitor green LED on the analog throttle that remains lit while the 22 volts is fed in from the power supply. Whenever the throttle handle is moved, there is also a yellow LED that indicates the relative voltage being applied to the track. I guess the green pilot LED could account for the static 0.13 amp reading?
I suppose the throttle circuitry itself is drawing some current from the power supply even when set to zero?
Bottom line: the train runs smooth as the DC supply has a regulated and filtered output with very low ripple, so I guess I will have to live with the amperage fluctuations. The analog throttle has no pulse width modulation.
One of my power supplies also has an ammeter. I look at it when I see something irregular when running a train. When there is nothing irregular I look at the train and not at the ammeter; the train is much more interesting
Fred: Point well taken!