I have a Bagnall 0-4-0 shunter and an HST125 power car. I've set up a length of flexitrack and soldered my homebrew PWM controller to the ends. I've also attached a multimeter via croc clips to the end (saves on buffers, right? )
The Bagnall will pull away at around 1.6V and I can drop it to 1.3V before it stalls. The HST needs about 6V to pull away and stalls at around 5V. Needless to say, it's a bit slow too.
Does anyone know what the standard value should be, and perhaps a clue to the problem?
There is no standard value. The smaller motor of the 4 wheel shunter is less powerful so does not need so much voltage to turn the wheels. The HST is more powerful so needs more voltage before it will run.
Even two locos the exact same make and model will be slightly different.
MG is correct. Gearing, type of motor, drag caused by slightly stiffer wheel bearings, length/size of loco, number of wheels etc all play a part in altering the current (power) needed to turn the motor and produce tractive effort.
Two identical locos will be different too.
Just to say that the motors themselves on 00 gauge model locos are designed to run on 12V DC when the controllers are turned up.
The amps they draw will vary according to their load, friction, size and power of the motor (As in a nice beefy motor will draw more current but will (If it can get the traction) pull heavier trains).
So if one has a controller which is only pushing out half an amp, and the loco motor could do with an amp, then the loco will be struggling and running slow (If the overload cut out has not tripped).
If a loco that only needs a quarter of an amp will go on a half amp controller, then it will have full use of its power and will speed along happily and pull some nice trains.
With controllers, as long as they are of a higher amp then the trains one has needs (Double heading with two fairly equally matched locos will need more current capability then if running a single loco, so I personally prefer a controller to have around an amp to an amp and a half available if possible... No need to go beyond this on DC unless one has a large garden railway where the current has a long way to reach the locos so there will be a current drop where the locos are at their furthest point from the controller... Rarely an issue indoors but can in some circumstances be an issue on large outdoor railways.... (If one ever builds an outdoor railway ALWAYS ensure the controllers and powersupplies are kept in a dry shed or building. The track can get wet and so can the trains but not the controllers), and ensure any mains power is properly done and checked for safety by an electrician etc.).
DCC is different in a way in that one has lots of locomotives on the same layout (As DCC ideally needs all track on the layout to have power) so even parked locos will draw a little current, so that their systems need to push out more amps, so 3 to 5 amps are usually required, especially if DCC sound is used.
There are circumstances where one may be looking at changing to a lower voltage motor and this is where one wants to run ones trains with radio control with on board batteries. The reason for this is that the space that batteries need as more cells to up the voltage takes more space, and one is already trying to find room for the radio gear and the switch and charging socket... So finding space for a battery or batteries as well can be a challenge even for some of the larger scale locos! And yet radio control has been done in some larger N scale locos which is quite something! (I thought it was pushing it to try to fit DCC decoders in N gauge but some now even have DCC sound).
You say it is a "PWM" controller. This suggests a square wave where the voltage is either full or zero. How are you measuring voltage? Presumably some sort of average or RMS using a volt meter?
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