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16mm Simplex - finally got the fan working!

Fen End Pit

Entry posted by Fen End Pit

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I recently purchased a copy of Roy Link's new Crowsnest Chronicles book. An very good read full of inspirational modeling. This finally inspired me to get my, not quite completed, Slater's 16mm Simplex kit out of the cupboard where it has been languishing for a year or more. I'd been frustrated by not managing to get the cooling fan to work with the DCC decoder. The loco also had rather a lot of emotional baggage attached as I'd bought it as a present to me shortly after receiving a nasty shock a couple of years back.

 

I had purchased a Nigel Lawton 12v motor to drive the fan and wanted to drive it from one of the function outputs from the DCC chip. Obviously if I just connected the motor between the common negative and the function output the motor would work but be much too fast. If I used the 'dimming' function of the chip it uses Pulse Wave Modulation which meant the motor went slower, heated up and made a heck of a noise. I tried just adding a resistor into the circuit, but if I used a value that made any difference to the speed there wasn't enough current to give the motor enough torque to turn the fan.  This weekend I finally cracked it, using a lower value (100 Ohm) resistor in series with the motor and a 100nF capacitor in parallel with the motor. The capacitor smooths the pulses from the chip and I can now dim the output without the motor making a nasty humming noise and getting hot.

 

I also upgraded the bearing in the fan to use a pair of tiny 2mm ID ball races, this greatly reduces the friction. I painted up a figure as a driver (still a work in progress) but I'm very much happier with the project than I was before. The loco is now flaunting itself on my desk rather than hiding in the cupboard.

 

I'm mulling over a 16mm narrow gauge 'side project' to give some variety while working on the Stour Valley - more details soon.....

 

IMG_8174a.jpg.cd5566c3973ec4687c84341e09c3cbff.jpg

 

There is a clip on Youtube in all its noisy glory.

 

Enjoy with the sound turned up.

 

David

 

 

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Dave John
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Heh, very nice, I like all the extra sounds. 

 

Years ago I had the same problem of running a coreless motor from a pwm drive, in a non model railway context.  I ended up using a series diode and resistor together with parallel capacitance as you haver done. This effectively forms a charge pump. I seem to remember that the result was pretty much straight DC across the coreless motor so it was happy and gave a good speed range. 

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26power

Is it wrong to wonder if the driver’s head could be made to rotate to face towards the direction of travel?!  Or even do that but randomly look around?!

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