CW-80 question

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CW-80 question
Posted by silentman on Monday, July 09, 2018 5:42 PM

Any thoughts why this transformer is stuck at 18 volts when I hook it up to a multimeter on the side which should be variable voltage? Could not get a modern MTH to run, it was stuck with bells and horn blowing and wouldn't get out of neutral. Works fine with my LW minus all the bells and horns. SadI believe these to not be very good transformers from what I've read, that they are just a beginner transformer but wondering if this was common and maybe an easy fix? Can they be reset somehow? Thanks in advance 

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Posted by lionelsoni on Tuesday, July 10, 2018 3:46 PM

There may be something wrong with your CW-80; but it may also be your voltmeter.  Inside the CW-80 is a transformer with an 18-volt (RMS) secondary winding.  The CW-80 controls the voltage that it puts out by switching on the connection between the transformer and the output terminal for only the last part of each voltage half-cycle, using a triac.  The earlier the triac turns on in each half-cycle, the higher the voltage.

But it also has a network, comprising a 1-microfarad capacitor in series with a 10-ohm resistor, that shunts the triac.  If the output is lightly loaded, this network can provide enough of a connection that the full voltage appears at the meter.  This is especially true with the digital meters that are popular today; an old-fashioned analog meter works better.  But a load like an incandescent lamp will give you the best result.

Bob Nelson

KRM
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Posted by KRM on Tuesday, July 10, 2018 6:11 PM

Reset the side for the variable voltage! It must be set at full power?

 

 

 

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Posted by silentman on Tuesday, July 10, 2018 6:28 PM

The MTH engine acted as though full juice was being put on it and no opening and closing the throttle changed its mind. When I hooked up the LW the engine ran fine. Does Lionel still exchange them if it was one of the CW80's they had problems with years ago? 

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Posted by dougdagrump on Tuesday, July 10, 2018 8:34 PM

Which terminal lugs are you using on the CW-80 ? There are two pair of lugs, one identified for track power(variable) and the other for accessory power(fixed). To "zero" the accessory power with the throttle at zero press and hold all three buttons(direction,bell,horn) then move the throttle up then back to zero while holding the three buttons down. This will zero out the accessory power.

However the CW-80 is not compatible with MTH engines, it uses a chopped sine wave versus a pure sine wave as the LW produces. Check the back pages of you engines "Owner's Manual" for a transformer compatibility list.

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Posted by lionelsoni on Wednesday, July 11, 2018 5:49 PM

While it is literally true that the CW-80 and other voltage controllers, like dimmers for incandescent lamps, "chop" the waveform, that term usually would imply a rapid switching on and off, so that the average output voltage over a time short compared to the power-line cycle is proportional to the chopping duty cycle.  The use of a fairly simple low-pass filter can do that averaging, resulting in very little distortion of the original sinusoidal waveform.

But what the CW-80 does is different, and it is usually called "phase control".  The switching occurs just once in each half cycle, which results in a very mutilated waveform that would be impractical to clean up.  It works satisfactorily for incandescent lamps, which respond very sluggishly to their input voltage and thus provide a sort of thermal averaging, but can be problematical for more complicated electronic loads like compact-fluorescent or LED lights--or modern toy trains.

Bob Nelson

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