Hello, I was at my hobby shop and the guy there is trying to have me go DCC. He mentioned that digitrax allows two DC throttles to be added and operate as if they are DCC throttles. Is this true and would this work with the MRC tech 4 250/ 350 with walkaround control? Would I have to program them to max power output to override their pulse technology? Or would I have to get another DC throttle to jump into digitrax technology? thanks Steve
Only the Zephyr/Zephyr Xtra have this feature. Whether those particualr DC packs will work properly is questionable. The instructions say pure DC, but even an old MRC rheostat pack isn;t pure DC and they work fine. The Tech 4 ones may use PWM though and that probably will not work. It's possible to add a filter to smooth the pulses, or for about $10 in parts at Radio Shack you can make a jump port throttle, however instead of inventing any money into such things, it would be better to buy an actual DCC throttle.
The idea, if what you have works, is that you hook the DC power pack to one of the 'jump' port connections on the Zephyr. On the Zephyr console, you select whichever jump port is to be used, and assign a DCC loco address. That DC power pack then controls throttle and direction for that loco address. To activate functions like whistle and bell, you have to use the Zephyr console, there's no way to do it via the jump ports. IF you existing power packs work, it's like getting two free limited function throttles. If they don't, it is NOT really worth it spending money on a different DC power pack to use the jump ports, the money would better be spent on a real DCC throttle like the UT4.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thanks Randy, I like the 250 and 350 since they have a walkaround throttle so if they could work with the zeph it would be great. I do not plan to have sound units so all I need is to control the direction and speed. I do not think I use the jump ports for another digitrax dcc throttle so I could still add the UT4 and have the two MRC throttles with walkaround as well. What kind of filter are you suggesting to make them compatible?
ps what is PWM?
A filter for the pulse would have to be a capacitor, possibly some resistors to restrict the peak voltage - when you filter a pulse with capacitors to smooth it out, the capacitor charge to the peak voltage, not the average voltage. For example, take 12V AC, rectify it to DC, then filter with a capacitor to produce smooth DC. Output voltage will be more like 15V DC.
Compounding the problem, large electrolytic capacitor are generally polarized - so you have to work around that because you need to flip the polarity of the power pack output to reverse the train.
PWM is pulse width modulation, another way to control the speed of a DC motor. Decoders use it, because PWM works by adjusting the ration of 'on' time to 'off time' in a pulse that is always at the peak output voltage. Compared to actually adjusting the output voltage. Less on time, the average voltage seen by the motor is low and it turns slow. More on, the average voltage is higher and the motor turns faster. For conventional DC, say you have the throttle at half way, the output transistor is going to allow half the power and block the other half. The blocked half has to dissipate somehow - usually as heat. Thus to drive a 1 amp motor you need a pretty hefty transistor with heat sink. That would never fit inside a loco. With PWM, the driving transistors are either full off, or full on. Full on, there is little heat build up, full off there is none. So a small decoder that fits in the loco can handle 1 amp or more, despite being quite small. Some DC power systems use PWN as well. Crest Train Engineer is one, supposedly the newest MRC DC packs are PWN. Unknown about the Tech 4,, MRC uses their own terms for things and doesn;t tell you what it's really doing.
many thanks randy I have been in touch with digitrax and mrc and the best I can make out is I will have to try it. Hopefully the local hobby shop guy will do this for me and then if it works I will the Zephyr Xtra from him. Steve