Differences in loco speeds with different controllers

[NIK]

Hi,

 

As part of selecting chassis for various multiple unit kits I've been doing tests of the top speeds of various modern designs of OO locos using a Bench Power Supply set at 12 volts.

 

In most cases the top speeds were lower than the prototype.

 

I've just tried a Gaugemaster series 100 controller instead and got a much higher top speed - just over the prototype.

I then cranked up the bench supply until I got the same speed which occurred at 16.1 volts.

 

Loco: Dapol Class 73 12V DC pre warm up : ~60mph.

Left running for 5 minutes to minimise warm up effects differences:

Gaugemaster 100 post warm up: 92mph.

Bench power supply @16.1V DC post warm up: 93mph.

 

Has anyone else noticed differences in loco top speeds between DC controllers or between DC and DCC?.

 

Regards

 

Nick

[34theletterbetweenB&D]

8 hours ago, NIK said:

...Has anyone else noticed differences in loco top speeds between DC controllers or between DC and DCC?.

 

Short answer: Yes, Yes, and supplementary answer, also between DCC systems.

 

In order to have all my traction able to achieve a scale maximum speed, my DCC system has the track voltage set significantly higher than the ex-factory setting, so that there is typically about 15.5V available at the motor terminals. (Between decoder designs there are slight variations in output voltage.)

 

And there is a further factor, even if only considering a single model manufacturer's range there is no consistency in the maximum speed on offer.

[AdamsRadial]

You need to examine the voltage waveform with an oscilloscope to get a proper understanding of why a motor reacts to different controllers in different ways. A pure DC output from one controller will have a different effect to a chopped output from another controller, (the chopped output types often put out higher voltages at the top of the waveforms). It would be nice to state that the total areas beneath each type of waveform would be similar and therefore the motor speeds would also be similar, but the motors themselves would react differently. An old heavy three-pole armature type would probably not react to the higher voltage spikes in the same way as a much lighter armature.

[DCB]

It is worse than just different locos running at different speeds.   With feedback controllers and cheap and nasty resistance controllers and those with a chopped output some combinations of locos will have one skidding furiously and another not moving.  Generally I find 90% of 00 locos will move at pretty much a consistent speed on variable transformers such as Hammant and Morgan Safety Minors, and the OnTrack and Morleys which also vary the voltage.   You can test this with a voltmeter, Morleys give less than 1 volt on minimum speed off load, plenty of others give 21 volts. off load.

There are some odd balls in 00, the Hornby 42XX is ridiculously slow, and the Bachmann std 5 isn't anything like fast enough for express work but by and large most double head with a Morley.    Even a Triang DMU and a Lima DMU run happily coupled together.