PWM controllers

[Rana Temporia]

Has anyone any experience of assembling a PWM controller from components available on line? I have looked at the BMR version and I am particularly interested to know how they will cope with older current heavy motors such as Tri-ang X04 and diesel Bogie type. I have a couple of H&M Clippers with half wave switches but they are noisy and I'm not convinced they are good for the motors, I wouldn't dream of using them on modern motors. 

[Yelrow]

Rana, hi, know nothing about PWM,s but daily run DC, with 4 duettes and 6 clippers.. I have many modern locos, and none have had any motor problems. I agree, they are a tad noisy. I have even run DCC,  locos, of which i have 14, without any probs. Just thought i would let you know.

[Seacommander]

Back in the early 1970s using a circuit diagram in Wireless World (July 1972) I built a PWM controller from individual components. This particular circuit also allowed automatic acceleration and deceleration. It provided incredibly smooth control of XO4 and Ringfield motored locos and gave me many years of utterly reliable service. Although I have moved on to Hornby based DCC I still use my PWM controller to test new locos before converting them to DCC. 

[ColinB]

I made my own, you need one op amp to generate a ramp, one op amp to act as a comparitor then you feed the output to a high power transistor something like a TIP41a. You need to add current limiting but that is the basics. You can do with Max 555 chip again feeding the output to a TIP41A. Alternatively on EBay you can buy a PCB from China for less than £10.00 that does it all. I will add, I used to be an Electronics Design Engineer, so it was a lot easier in my case.

[Rana Temporia]

Thanks for all the replies. The reason I was looking at one was my old controllers can supply easily enough power to run my old locos. If I want slower running that is where the half wave switch comes in on my Clippers which is when the locos get noisy and hot in some cases. I read an article that said you could achieve smooth and quiet running with a PWM controller. 

 

I probably have most of the parts to build one (I used to build guitar effects) but to be honest I would probably buy one with the board ready assembled off eBay that could deliver 1A at 12v. With power supply it'd still be less than £10 and I have quite a few aluminium hobby boxes left. 

 

The reason I would like something is that I am planning a layout with a small narrow gauge feeder and haven't decided whether to have it as an industrial feeder or a preserved railway.  Most of my 009 locos are powered by Kato tram chassis which go from nothing to a most unrealistic speed within a tiny movement of the control on my existing controllers whether H&M or Tri-ang. I would also like to have some slower speed available for some of my other locos within what will be the station area. 

 

I am never going to go DCC with several hundred mostly old locos, although I am on a downsizing attempt so I am looking at options for control that will power the likes of Tri-ang, Trix and the odd Wrenn loco as well as a small amount of 009. 

 

Most of my Jouef locos will crawl along at a very slow speed and draw hardly any current and work fine on my current controllers So they aren't a problem. One 'fun' loco to run is the Playcraft French pacific which has a large can motor that drives through a gear train and acts as a flywheel so will coast along for quite a distance once the power is switched off. It was designed to be useable on battery power so despite being from the 1960s is extremely efficient elctically speaking. 

[ColinB]

The PWM controller I designed used a chopping frequency of about 10 kHz, Hornby in their PWMs use a much lower frequency, which means you get a growl or buzzing on some motors, with the much higher frequency you just get a slight high pitch whine. You definitely get better starting torque with PWM.