# Full - Pulse function on MRC transformer



## bluenavigator (Aug 30, 2015)

I have this MRC Throttlepack Model 500. It has power switch set to either Full or Pulse. I took a look inside the box. Clearly, it has the rotary potentiometer and step-down transformer. Without knowing specific diagram on the step-down transformer, on the Pulse mode, does it actually feed AC output or does it cycle at all? 

I am trying to understand the benefits of having Pulse mode on the transformer box.

Turned out that correct term for the big potentiometer is rheostat. Duh!


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## bluenavigator (Aug 30, 2015)

Never mind. I found the answer.

Borrowed this paragraph from NMRA website - NMRA Wiring



> The next step is to take a pack and add a switch for "Pulse." In a pulse throttle, half the AC wave cycle is used to produce a rapidly pulsating DC; a switch controls whether this is on or if the regular rectified current is used in the output. A good example of this throttle type is the MRC Throttlepack 501, which is a strong pack delivering 1.9 amps and has the pulse option. The reason for the pulse feature is better low- speed control, and it does work. In a sense, the pulses "push" the motor armature to help overcome inertia and friction. However, there is a fly in the ointment. The half-wave pulses cause extra heat to build up in the motor. Too much of this heat can cause the motor to burn out; some types of motors are more susceptible to this than others. While this isn't that common a problem, you should be aware of it. Pulse power should not be used for high speeds (it isn't needed there), and any loco that runs too hot may have other problems as well, (lubrication, tight gears).


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## Cycleops (Dec 6, 2014)

Wow, that's more complicated than DCC!


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## gregc (Apr 25, 2015)

Cycleops said:


> Wow, that's more complicated than DCC!


The TAT-III introduced a circuit that leaks one cycle of the AC transformer output to the throttle output thru either a R or RC circuit. Linn Wescott described it as a "smooth start unit". It doesn't require many components.


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