Using DCC for Turntable Control.
When I heard modellers were fitting DCC decoders to their turntable to operate them, I thought I would never use this method to control any of my turntables, just why would you, when there is a small control panel supplied with a motorised turntable, to “drive it”. Sometimes, I feel we use “excess” technology just for the sake of it. I let this type of drive “rest”.
2 of the 5 turntables on my layout are motorised indexed models, while the other 3 are manual.
I had a Lloyds 90 foot that I have had for 15 years and was all but thrown out due to the plastic moulding holding the centre bush having broken away. I needed an extra turntable when I built Sydney Staging area on my layout. I resurrected the turntable by fitting a new bush complete with spindle and a motor gearbox. This rejuvenated turntable now needed some form of “electrics” to drive it.
To make a power supply and “control panel” for the turntable “electrics”, it would cost about $20- 30, the same as a cheap DCC decoder. Why not relent and give DCC a try, I had a couple of spare “noisy” decoders in the spares box. This method would not provide any “indexing”. Did I need “indexing?
As this turntable is located at 1200 mm and close to the front facia, it has a “helicopter” view, so just turning the deck and lining it up by eye should be good enough. I’ll give it a try.
My initial tests using the old “noisy” NCE decoder were a little disappointing because I could not get the slow running I envisioned I should get. I programmed CV 5 and 6, no apparent improvement. I added a 15 ohm resistor, in series with one lead to the motor and the speed reduced significantly, but still not completely happy. I did not want to play around with this decoder any more as I had what I thought an “ideal” decoder for the job at hand – an ESU Lokpilot Back EMF decoder.
Connecting the Lokpilot gave the results I contemplated. The results were sensational. Wind up the throttle up, the deck starts to move and when you get near the desired “road”, slow down and at Speed Step 1 (out of 28) the speed is so slow, just crawling. Actual speed, 1 revolution in 4 minutes or a 1/4 RPM, that’s pretty slow. Stopping the bridge “lined up” with the “road” becomes easy, with this slow speed crawl.
I programmed CV 5 with 10 and CV 6 to 5 to provide a maximum of 3 volts to prevent any operator from burning out the 3 volt motor in the turntable. Note: I could get this voltage reduction by programming CV5 and 6 with two NCE and one TCS decoder for some reason.
At Speed Step 1 equalled a 1/4 RPM or 4 minutes per revolution and .3 Volts
At Speed Step 28 “Full Speed” equalled 3 RPM or 20 seconds per revolution and 2.7 volts DC.
For NCE users, a throttle like the Cab04 and set up in Yard Mode, it could be left at the turntable permanently. Yard Mode sets the throttle knob to be a “Centre Off” and turning one way, one direction, the other way the other direction. A Cab04 throttle costs $110.
The Lloyds turntable comes with a “split in two” printed circuit board plate under the bridge that reverses the polarity of the table’s DCC power to give proper DCC control. Without this “split in two” circuit board, or something similar, you would need a DCC Auto Reverser. I need an Auto Reverser on my Fleishmann turntable.
Take the type of “track feed” to the turntable bridge into consideration, when either buying a turntable or modifying it for DCC. Using a turntable that requires an Auto Reverser will increase the cost of the turntable. Auto Reversers cost about $65.
I have rigged up one of my Walthers “60 footers” with a couple of micro switches that are operated when the bridge is in one position to change the DCC track polarity. This is only possible for a turntable that is used in TWO positions, just to turn a loco. This is the case at Murrurundi and Willow Tree.