Blueandwhiteton Posted June 3, 2020 Share Posted June 3, 2020 I was watching a video the other night about making a controller with a pwm circuit, as I only have a R912 controller I was wondering if this would have any adverse effect on my lima class 55 and intercity hst's with the pulsing is it more for newer type locos , thank you for any info supplied Link to comment Share on other sites More sharing options...
Chrissaf Posted June 4, 2020 Share Posted June 4, 2020 A commericially purchased PWM controller shouldn't have any issues. Can't comment on DIY made one, it depends upon the quality of the circuit design and build..If you use the 'Search Forums' tool and use the search term PWM then you will find that others have asked a similar question to yours and recieved answers to it. Link to comment Share on other sites More sharing options...
ColinB Posted June 4, 2020 Share Posted June 4, 2020 I made my own PWM controller years ago and no it should not harm your locos as long as the maximum voltage is within the range of the loco's voltage which is about 12 volts. Before I went DCC, all the Lima Diesels worked OK. I know my one is limited to 12 volts. In actual fact your locos should run better as the motor gets the full 12 volts even at a low setting, they actually say you get better starting torque. Any motor that is controlled by a computer is generally driven by PWM as it is much easier to generate with a digital device, than a 0 to 12 volt variable signal. Most of the actuators on your car will be driven by PWM it is easier to generate. The actual loco filters out the pwm to get its power. The latest controller I got from Hornby is PWM and I have noticed no issues, although you get a lot of "whining" from the motor as is acts as a sort of tuned circuit. The only other thing to consider if you are making your own is that you need some some of short circuit protection for those occasions when the loco short circuits when it crashes or you drop something metallic across the tracks. Link to comment Share on other sites More sharing options...
Rana Temporia Posted June 6, 2020 Share Posted June 6, 2020 In reply to your post and my own from about 2 weeks ago I ordered one of the ready made circuits off the internet. I also ordered a power supply which apparently was from a UK supplier only to find it's coming from China so have around 6 weeks to wait! Undeterred I got one of my old Tri-ang controllers, checked the polarity of the leads (multi-meter is handy here) and connected it to the PWM controller. After a 5 minute test I am impressed to say the least. One of my 'pocket rockets' will now crawl along at a much more realistic speed and it's not too noisy. Starting is also improved for all the locos I tested with it. The unit I bought has a reverse/off switch included and was around £7 including postage although after buying it I received a notification that someone else was selling them for around £2.50, as I only need one I didn't bother to check it out. I don't know if this unit has short circuit protection built in. I might add one anyway. Link to comment Share on other sites More sharing options...
Chrissaf Posted June 6, 2020 Share Posted June 6, 2020 At the low £2.50 price, why not just purposely short circuit the one you have to see. If it blows, just buy another. Link to comment Share on other sites More sharing options...
Rana Temporia Posted June 6, 2020 Share Posted June 6, 2020 I have just checked and the cheap one is from China so it'd be a wait plus doesn't include the DPDT centre off switch (I have some left from when I used to build guitar pedals so that wouldn't be a problem). Apparently the one I have has a 3A fuse but I can't find it. Link to comment Share on other sites More sharing options...
Chrissaf Posted June 6, 2020 Share Posted June 6, 2020 The 3A fuse will be a PTC fuse. They automatically reset and are extremely difficult to tell apart from ceramic disc capacitors, they both look very similar..PTC = Positive Temperature Coefficient. The term fuse is a little misleading. They are more akin to a Thermistor. In normal conditions, the PTC is virtually zero resistance. When the current drawn through them approaches the factory set value (in this case 3A), causing a temperature increase, the resistance of the PTC rapidly rises, to block the current flow..Note however that Thermistors are 'Negative Temperature Coefficient' and the resistance change is opposite. The resistance starts high and goes down as the temperature increases. Link to comment Share on other sites More sharing options...
Rana Temporia Posted June 7, 2020 Share Posted June 7, 2020 I hope I'll never need to test it as the power supply I will be using is 12v 1A And the controller can be used up to 24v at 3A 😀. The unit is all surface mount apart from a large cap across the input terminals, I would have expected a diode there as well to protect the the board in case the power is connected the wrong way round. I can't see anything on the board that would be the fuse. It may be in the main IC which has a large heatsink on the back and four terminals, unless that is the fuse? There is a transistor and another 8 pin op-amp type IC on the board. Link to comment Share on other sites More sharing options...
Rana Temporia Posted June 8, 2020 Share Posted June 8, 2020 To follow on I actually found the same one I had bought from the UK complete with DPDT centre off switch available from China for £2.38 including postage. When I originally looked at building my own from the Penfold Babani book the IC I needed (a TDA2006) was £2.50. I have ordered another complete circuit just to have a spare, at that price I couldn't not do. Link to comment Share on other sites More sharing options...
ColinB Posted June 8, 2020 Share Posted June 8, 2020 Glad to hear you got it working. I found that with relay boards and points switching boards, they were cheaper than I could get the bits for. The way Hornby have done it on my controller, is to use I suspect a quad op amp, of which one is configured as a ramp and the rest are comparitors and buffers. Even with that you couldn't make it for less than £2.50. National semiconductors (I don't even know if they are still going) used to do applications in their data sheets, that is how I used to make most of my analogue circuits. Link to comment Share on other sites More sharing options...
Rana Temporia Posted June 22, 2020 Share Posted June 22, 2020 Just to update this post (and my earlier one) my power supply arrived today from China and I loaded everything into the 3D printed case I'd bought. This little controller works perfectly and took just 10 mins to assemble with the only tools being a Philips screwdriver and a set of wire cutters/strippers. It seems to work especially well with X04 type motors and some of my old Tri-ang locos run very slowly and smoothly with it. Not too noisy and the motors don't seem to get hot. Ordering the circuit board and the 1A power supply from China with postage included is less than £5, there is just a wait. For the cost I can't think of any reason not to build one if you are on analogue 12v. The only change I made was that the 2PDT centre off switch now comes with a rubber boot which you have to remove to get it to clip in if you use one of the cases I did. Link to comment Share on other sites More sharing options...
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