I just purchased two MRC Model 55 Cab Control throttles. The very brief instructions say that these throttles are designed for “expansion” of the layout track There are four terminals on each of these throttles; two for power from the power pack (DC) and two for power to the track. It talks about hooking positive to positive and negative to negative terminals from the throttle to the power pack. It also says to hood the Track Output terminals either directly to the track or to a block selector switch (which I intend, of course, to do the latter). I so far understand this part of the instructions.
The “fuzzy” part of these instructions includes a note at the bottom of the page which says that both rails of the block that the throttle is going to control have to be insulated so they will be insulated from all other blocks. The exception would be if I had a power pack (fixed 12 volt power supply) which powers no other blocks is used to power the throttle.
My questions then are these: Can I not power more than one block at a time with this type of throttle?
If that is the case, can I somehow “fool” the system so that I can just have one rail insulated, thus powering more than one block at a time?
Maybe there is something I am missing in these instructions. I know that if I just power the rails from my power packs (without throttles) that I can power as many blocks as I want; I don’t get what the difference is here. The power, it seems is channelled through the throttles in this case, rather than going directly from the power pack to the track (via a block selector).
The instructions for my Tech4 280 implied the same thing, yet I use it with one block active or all blocks active. I think what they are referring to there is that the blocks must be set up so that both rails of a block are gapped and not set up for common rail (one rail gapped). My 280 gets really touchy about that.
Oneof the mandatory requirements for using common rail wiring is that each power pack or controller MUST have its own independent transformer. Without the isolation of the independent transformers, the power supply will be short circuited when the two controllers, connected by common rail, are set to opposite directions. This is
As Fred W has stated, using a separate power supply eliminates the problem of double gapping the rails. In order to use common rail wiring, all throttles must have their own transformer. If not it is a dead short.
Here is another reason to use a separate transformer. I found out the MRC 55 drops the input voltage by quite a bit. When I connected mine to a couple of MRC Tech II power packs I realized that power to the rails felt a little low.
I checked the voltage at the fixed DC output screws and measured 15v for one pack and 14 for the other. The most power I could get to the rails was a couple of volts less. I was dropping over 2 volts in the MRC 55.
What I did was use a power supply for a paper shredder. The input to the MRC 55 was now around 16v and the output power to the rails was around 14v, more in line with normal track voltage. Performance was much improved. So far the extra input voltage has not hurt the 55 throttle.
I never had the instructions, so I do not know what MRC recommends for a Max input voltage for this unit. It seems like a decent throttle, especially if you want flat line (non-pulse) DC.
The Tech 4 280 must share the same transformer, which makes me wonder what MRC was thinking. Someone purchases this pack thinking it will replace 2 other packs and then they find out they have to double gap their entire layout.
Thanks, guys, I was planning on having a one-cab-one-throttle system anyhow and this answers my questions. What I will do is have both throttles connected to a cab selector so that either throttle may operate anywhere on the layout. The other “wire” from the power source will be connected to a block selector. I am guessing then that I will not be able to use modular telephone cord with phone jacks but a cable (such as that which is used for underground lawn sprinkler systems for control). This cable, then would contain at least 4 wires within for the four terminal hookup.
Jim, I am disappointed about the news of the power drop with these throttles. I am, however, operating a switching layout, where the entire trackage is “yard limit” so drops in speed on any continuous “main” will not be a factor.