PWM controller with noise interference capacitors

[moawkwrd]

Hi all,

 

I’ve recently embarked down an N gauge rabbit hole whilst taking a break from TT:120.

 

I built a twin track PWM controller supplied by Handem for a small desktop oval layout I’m building, which works great with an older example of the Graham Farish Class 25. However, the similarly aged Class 4F that I got doesn’t run so well.

 

I have to turn the power quite high before it starts to move and it shoots off - then I can reduce the power and it steadily maintains motion. Could this be due to the capacitor that was wired in to prevent noise interference? I don’t think the Class 25 has one due to the split chassis design. I’ve also got a Jinty of the same era which needs fixing so I could experiment by removing the capacitor on that first once I’ve fixed the pickups.

 

Sorry if this is an obvious question, quite new to the hobby and still learning.

 

Thanks,

[SHMD]

I really suspect that the 4F's running properties are nothing to do with the absolutely tiny value of the suppression capacitor. (It sounds more like "stiction" or too much grease.)

 

If the PWM controller has feedback, then there is a small possibility that this could interfere but normally not.

 

You can, of course, just remove the suppression capacitor, (they are hardly relevant today), and re-check the 4F's performance again.

 

 

Kev.

 

[moawkwrd]

Thanks

 

I ended up fitting both my 3F and 4F with coreless motors to see if this would improve the running properties and it has somewhat. However, using my PWM controller they're a bit... lurchy. Seems to require at least 3-4V (track measured) before they move off at some chat and can then be wound back in to around 2-3V but even that is too fast for shunting and results in frequent stalling. Not like my Class 108 (DCC Ready version, not the older one) or 25 with original GF motor which require more voltage but are much more controllable albeit with a lower top speed at the full 12V. Considering my layout is a sleepy-ish branchline that's far preferable.

 

I'm thinking of putting back in the original GF motors to the 3F/4F with new brushes and no suppression capacitor. Shouldn't be too difficult to chip out the araldite I put in to secure the coreless motors.

 

From reading around, it would appear these controllers doesn't have any kind of feedback just straight PWM at around 16KHz. I'll be quite happy with it if I can get the motor combination right for these locos, and intend to mount the components in the frame of the layout for a neater solution for twin track operation.

Edited March 17 by moawkwrd

[SHMD]

When the motors were removed did you try pushing the locos around to gauge (sorry) the rolling resistive forces opposing your hands pressure - especially at starting/stopping?

 

On the steam locos, did you rotate the gearing to see if there were any 'tight' spots anywhere when the main drivers had completed a full 360 degrees of rotation?

 

Do these (older) locos have a flywheel? Replacing the old (heavy) motor, with a coreless one, will reduce the rotational inertia - which is not a good thing.

 

I still think there could be too much grease, and as you are 'ok' at replacing motors - have you tried removing all the wheels from the chassis - thus allowing inspection/cleaning of the bearings/journals? (I realise that the coupling rods are an added obstacle/complication to doing this.)

 

 

Kev.

[moawkwrd]

Just as an update, in case anyone is interested, I ended up refitting the GF motors back into both models and with some spare parts from BR Lines, they're running pretty well now on both a gaugemaster series u and my kit built PWM controller. I think the combination of bearings, armature housing and how tightly things were screwed in all play a factor on these older models.

 

I think I'm going to go with gaugemaster to control my layout though, as even with a bit of noise the slow performance is much better than with PWM.