Converting old locos to dcc

[Midland Pullman]

I have successfully converted old Triang and Lima locomotives to dcc with limited success and to date most run well. When I started I tried to check the stall amps of the motors. I’d like to do more now and saw a volt ammeter display for sale on eBay and Bangood after some difficulty set it up and works fine. I powered it from my old H&M Clipper and find the voltage varies quite dramatically as I think I read earlier elsewhere. Whilst an old fashioned meter shows 8-14 volts the electronic one shows up to 22 volts. Is this then best described as an unregulated supply? What damage could I cause to new models with modern motors? I have two railways one dcc and one dc which I use to run new locomotives in before adding the chip. I’ll continue to run my old favourites on the dc.

[Brian]

Hi
Many older and some new ones too, Train controllers will output far above the 12 volts DC. Typically around 18 to 22 volts DC under little or no load. These are unregulated supplies. Regulated means the rated output DC voltage is 'Clamped' at the stated voltage +/- around 0.5V AFAIK no train controller produced has a main Track or Auxiliary output that are Regulated. This is usually only found on specialist power supplies.

To check Stall Amps you need a meter (Multimeter) that can read 10Amps DC.
Disconnect one track feed wire from the rails coming from the DC controller.
Set the Multimeters range switch to its 10Amp DC range and move the red test lead to the 10A socket.
Connect the red lead of the multimeter to the end of the removed wire. Connect the meters Black lead to the place where the feed wire was removed With your Multimeter set to its DC Amps range is now in series with the DC supply. Place the loco to be checked onto the track with all other locos removed. Place a finger or other fix item in front of the loco to stop it moving forwards and then turn up the controller to full power. The meter will show a reading as the loco spins its wheels on the rails. This is roughly the normal loaded running current.
Now, and only for a second or two, either press down hard or use a finger stop the wheels turning. What the meter shows now is the Stall Current. Do not allow the loco to remain stalled for more than a second or so.
Don't forget to restore the track feed wire to where it was removed form and then remove the red test lead from the Meters 10 Amp Socket and return it to the Volts/Ohm etc socket after the above test, then turn Off the multimeter.

[Midland Pullman]

Thanks for that Brian typical readings are around 1/2 amp at full pelt and between.8 and oddly a few at 1.03 on stall
My previous experience is to ignore the high ones and use the lower stall ones. My most recent job was to put a hornby MTU TTS in my youngest Blue Pullman The revised moulding version. It works well with a 4 car unit any more and It struggles and I imagine smoke. I didn’t check the amps on that so could be better not to try!
Back to my new engines with flywheel etc am I causing damage with my unregulated supply?
Many thanks Roger

[Brian]

Hi
I dont think so! Your DC train controller regardless of make will be unregulated. I have never come across any DC train controller thats regulated.

[Chris]

As Brian says it can be a feature of the controller design that means under no load modern meters dont give accurate results. One way that you can normally stabilise it is to fit a constant drain to the supply so you have controller a light bulb then in parallel your electronic meter which is connected to the track.

with regards to the TTS decoder from memory they dont have a particularly high current available for the motor. if you want to as a work around you could fit the TTS into a second socket so that it provides sound and then a same address decoder with higher power can be used for the motor. it probably gets closer to the point of being as expensive as a fancier sound chip but as you have the TTS already

[Midland Pullman]

Hi Chris
Thanks for the reply. If I understand correctly I put the bulb straight across the in out of the controller?

As to the TTS for the double Ended blue Pullman I bought the twin pack MTU sound for the class 43 and have one end power and sound and the other end just sound. It’s actually not bad with just one lot of sound. So using your suggestion I could use a Lais dcc decoder to drive it and the TTS for the sound. I chose the MTU as I’m sure very few people can remember what the Pullman really sounded like I can’t anyway. Cost wise it would be around £50. Similarly if I did the same for a straight diesel or steam locomotive though space might be an issue with steamers.
Your ideas set me thinking outside of the box
Many thanks Roger

[Chris]

With the bulb, yes, across the output so it forms a parrallel circuit with the track, it should give a steady draw on the controller and stabilize the readings.

for the different decoder, what i was meaning was fit it into the driving end along with the TTS chip, so the TTS chip works just like the dummy end providing sound but no motor control, will require a little extra wiring. Its a bit of a bodge though and if the decoder you want is expensive it may be better to just get a single better sound chip. and sell the TTS or fit it into something else that could do with some sounds

[Midland Pullman]

Thanks for that confirmation Chris.
There’s quite a bit of space in the driving ends so I will probably go for the lais dc to power the motor and the tts at each end for sound.
I’ve just received the newly released lais decoder tester so I’ll probably set it up on there first.
For anyone else reading one of my early triang dmu power bogies was serviced and cleaned about 2 years ago using the method described it was using about.8 of an amp. After another service it now reads .42!
Thanks again Roger