PWM and Hornby Locos

[Theakerr]

A conundrum for the electrical genii on the forum.  I have several (cheap) PWM (Pulse Width Modulated) controllers on my layout.  They are fed from a standard 4 track Guagemaster controller.  On my Bachmann locos (B1 old and new chassises and J11), on locos powered by Mashima motors and on my Hornby Claude they work fine.  My Hornby B17 and Black 5 after one circuit (50') start to slow down and if I don't increase the controller speed they eventually come to a complete stop.  Measurement of the load voltage shows a drop.  Increasing the controller voltage gets them running again but eventually they also come to a stop.  On occasion, they will be running fine, then suddenly slow down and just as suddenly speed up.  However, they will eventually come to a stop.  When I take the PWM controller out of the circuit and apply power directly from the Guagemaster, initially they run slowly but over time they speed up and the voltage can be reduced, almost as though they are undergoing a time related self healing process.   If it was just one loco I would be replacing the motor but two is starting to push co-incidence although statistically it is possible that I do have two 'funny' motors.  My next plan is to connect an ammeter into the circuit to see if that gives me some insight.   I do have a constant 12V power source that could be used as the feed, but it is capable of putting out 15Amps, so if for some reason the load draw has increased I could very quickly ignite the built in smoke capsule.  I do have a 2amp (smallest I could get over here) but the motors are can motors and I suspect that even 2 amps might ignite the smoke capsule.  Any thoughts, especially to eliminate the problem, would be greatly appreciated.  Also from a purely academic perspective any thought are appreciated.

[DCB]

I found PWM controllers make motors run hot especially at low speed so I simply won't use them.   The motors get hot and slow down, eventually failing completely.   You definitely need overload protection with your 12 volt 2 amp power supply, I would stick a 1/2amp poyswitch in the circuit.   If it is 12 volt, as in has a 12 volt output offload not a 12VA 21 volts off load typical model railway "12 volt " unit then it probably won't let trains run at scale speed, I find the Bachmann 5MT simply can't run  at more than a scale 60 on 12 volts.

As for the 154 Amp unit, er keep well away from a model railway unless you  have a very good overload cut out. I reckon a 1/2 amp Polyswitch would shrivel up into a smoking blob of melted gunge if you shorted that 154 Amp unit but a good old car bulb or 1960s solenoid based cut out in series might do the trick. Thing is 154 amps will turn 5 amp wire into a glowing heating element in seconds if you get a short or partial short. 

Edited January 17, 2020 by DavidCBroad

[kevinlms]

If the locomotives work properly on the Gaugemaster, why bother with the Hornby controllers? You seem to have the solution. 

[Crosland]

13 hours ago, DavidCBroad said:

As for the 154 Amp unit, er keep well away from a model railway unless you  have a very good overload cut out. I reckon a 1/2 amp Polyswitch would shrivel up into a smoking blob of melted gunge if you shorted that 154 Amp unit 

 

It's 15A, not 154A. A polyfuse will typically have a fault current rating of around 40A, according to the Littelfuse web site.

 

It does sound like the PWM frequency is too low. This is the classic issue with coreless motors which must not be used with low frequency PWM (but are fine when used with the high frequency PWM from a DCC decoder). It may be that some of your motors have less "iron" and cannot get rid of the heat caused by the PWM. The heat may be causing mechanical effects such as binding in the bearings. As it slows down the motor will draw more current which causes more heating and so on...

 

Do you really mean increasing the controller voltage, i.e., the voltage into the PWM controller, or simply turning up the throttle which increases the pulse width?

 

 

[Theakerr]

The consensus seems to be what I was suspecting, that the motors in the two locos are getting hot, probably starting to bind and thus slowing down.  Would appear that there isn't a direct solution although I might try a replacement motor just to see.  To answer the question I was increasing the Guagemaster voltage into the PWM controller and I am using the PWM controller remotely as a second controller from the main control panel containing the Guagemaster.

[bigherb]

I've had this before on a Bachmann, Hornby and Electrotren locomotives. It was the interference supressor failing. Removed the sepressor out of circuit cured the problem.

[Pete the Elaner]

On 17/01/2020 at 07:52, kevinlms said:

If the locomotives work properly on the Gaugemaster, why bother with the Hornby controllers? You seem to have the solution. 

You mean more expensive controllers are more expensive for a reason & it is worth paying the extra for them?

[34theletterbetweenB&D]

Crosland has identified the root cause in my opinion, low frequency PWM. But there is still a question, relating to why some of the motors are affected, others are not.

On ‎17‎/‎01‎/‎2020 at 04:02, Theakerr said:

.On my Bachmann locos (B1 old and new chassises and J11), on locos powered by Mashima motors and on my Hornby Claude they (PWM controllers) work fine.  My Hornby B17 and Black 5 after one circuit (50') start to slow down and if I don't increase the controller speed they eventually come to a complete stop. 

Of all the motors, it would be the 3 pole unit in the J11 that I would expect to be most sensitive, it's a tiddler, not much heat sinking, compared to the larger motor in the Black 5 which is Hornby's old 'Black Can' (a good quality knock off of the Mashima 1624) which is one of those heating: if it is only the motor we are considering.

 

I would suggest another known problem with Hornby products having an influence. The tender pick ups can become very draggy after some significant running has accumulated, and the loco motor has to draw more current for the power to overcome this. Presumably the Claud hasn't run that much, being the newer product? I would have the tenders of the Black 5, B17 and D16 off their locos and compare for free rolling or lack thereof. If there is a perceptible difference, try one of the heating motor locos with the tender off the Claud, to see if that fixes it.

[Theakerr]

In response to the comments,   I did cut one side of the capacitor, no difference.  The J11(Little Engines) does have a Mashima motor as does a recently added A5 and both work well.   Also, I have just added Bachmann 3 Car DMU and it works.  I did check the tender pickups and they both seem OK and the Claud has actually run more distance than any of them.