Basics: Current measurement of locos

Before digitalization of a loco you have to select the right decoder.
Manufacturer’s data of current draw are not available in most cases or it is not reasonably usable.
So it make’s sense to build a small measuring equipment for each loco, to measure the current.

You need: (see picture)

  • A LGB-transformer with apr. 22V(alt. a power supply)
  • A meter for current measurement (Multimeter or analog instrument) .
  • A bumper with a short rail
  • Connection cable with track connectors.

The transformer must have enough power for the locos to be tested. 5Amps are enough in normal ways.
Also the measurement range must be selectable.
The bumper must be fixed with the track (like LGB 10320 and track fixed with Massoth rail-clamps)

Select on the meter DC-current measuring and connect it in one of the feed lines to the transformer (connect in series).
Place the loco on the track and drive it to the bumper.
Now turn on full power on transformer and read the current drain on the meter.

Notice following on measurement of the current:

  • Make that test only short-time, while the wheels are damage fast your track.
  • Make several measurements when your loco have a mode-switch.

(Measure only light, only motor or only sound if it possible.)

  • Otherwise measure in several steps and build differences.

(Measure light, Motor +Light, Motor = Motor+Light-Light)

  • Important are the “Motor-current” and the “Common-current” who is flow through the decoder.

(You can find both values in the technical data-sheet of the decoder).

The measured current is the maximum value, who is flow on wheel-spin by max. voltage.
On wheels who are not wheel-spin the current can be much higher.
Add a security value of 50% to the measured value (On a measured value of 1 Amps the decoder should be supply 1,5 Amps motor current.
If you connect accessories like light, vaporizer or sound, you have to consider it.)

After fitting and check of the decoder you can measure comfortable the current with your navigator, if it is the only current drain on track.
The value should be measured on max. speed with longest train and at biggest uphill grade.
The value should not be bigger as the characteristics of the decoder.