MRC Tech-II 2800 Dual Power Pack

Discussion in 'N Scale' started by mtntrainman, Dec 12, 2008.

  1. mtntrainman

    mtntrainman TrainBoard Supporter

    Anyone else own one of these or know anything about them?

    I have a few questions:

    1) I see that each control has its own 2 wire connection on the back for each track...BUT...can one terminal be used as the common for both so one only has to run 3 wires under the layout? I will be rewiring soon and would like to know.

    2) Speaking of rewiring....what is common wire size to use for the track wiring buss?

    I am currently using telephone wire but it is so small it breaks anytime anything is slid under the layout an barely touches it !

    Will #20 AWG Bell Wire work ok?

    Will #14 solid wire be ok?

    Which is better...solid or stranded wire?

    I appreciate any and all recommendations...thnxs :tb-cool:

    * BTW... I am running DC not DCC if that makes any difference...thnxs

  2. Tudor

    Tudor TrainBoard Member

    I believe these units are simply two completley sepatate, and isolated units within one plastic casing. I think you might be able to wire them with a common ground and run a single wire for that common, along with the two individual control wires. I would have to tinker with that, before I actually did it tho, and would want to know the actual internal wiring for those units. So, take this with a grain of salt. It is DC voltage, so you can use both those units with a single common ground I do believe. Personaly, I would rather run the 4 wires, and keep them completley isolated.

    As far as wiring, it really doesnt take much, because you are running a single amp give or take, so the bell wire is plenty, or a small 18 or 20 gauge speaker wire would be more than enough. I can't remember the formula for current flow vs wire gauge, but an amp isn't a whole lot. I know a 14 gauge wire can hold around 12 amps, so I would assume you could take a 24 gauge and pull 6 amps through it.

    I like stranded wire better than single, simply due to it being more flexible, and less prone to cracks.
  3. mtntrainman

    mtntrainman TrainBoard Supporter

    Thnxs Tudor...

    I will be running approx 30 feet of each run. 90 feet total versus 120 feet makes a difference $$ wise when I go to my local HomeDepot/Loews/Ace to have em cut me some wire...

    * I noticed at Ace that their #14 solid comes in green. Will be nice to have 3 or 4 wires each in a diff color when laying on my back trying to figure which track feed goes to which wire...;-)

  4. Tudor

    Tudor TrainBoard Member

    IMHO #14 is WAY overkill. For a small to medium layout, I would go with maybe 16-18 to common bus bar, then tap off multible feeds of #20 or so from that main power buss and feed the rails every 6 feet or so... You want to be sure to pull plenty feeds to power your rails on both sides of turnouts, for ample power. If you don't you will overheat the motors of your locomotived trying to pull power from long distances, or burn up turnouts by pulling power through the points...

    food for thought..
  5. Hytec

    Hytec TrainBoard Supporter

    George, The MRC Tech II 2800 is designed to operate with the negative(-) terminals wired in common. I've used my 2800 wired that way with DC block control for 20 years without any problems.

    I wired both negatives together at the 2800, then ran that common wire to the common rail throughout the system. I then ran the A and B cab positives(+) separately to the control panel where I used single-pole double-throw (SPDT) switches to select which cab would power each selected block. That way I could run a yard engine on A cab while the main was running on the B cab....never had the first problem.

    As for wiring, I run the common bus over 14 AWG stranded throughout the system. I then solder a short (1-2") 22 AWG pigtail up to the common rail for each block. I also ran both the A and B cabs on 14 AWG stranded to a terminal block on the control panel. I then daisy-chained 16 AWG uninsulated from the terminal block to each of the SPDT switches, A to one outside pole, and B to the other. I then ran separate 14 AWG wires from the SPDT switch center poles out to each block, and used 22 AWG pigtails up to the "hot" rails in each block.

    I use 14 AWG copper instead of 20 AWG to reduce voltage drop for the common and A/B wire runs. I agree that current draw of N Scale locos is less than 1/4 Amp, but 20 AWG copper has 4 times the resistance of 14 AWG copper. I run a Kato F7 ABBA lashup which draws 1 Amp total, and the increase in speed was very noticeable when I switched from 20 AWG to 14 AWG. BTW, my 2800 was at one end of a "U" shaped layout, so the common and A/B wire runs were 11 feet down one side, 7 feet across the bottom, and 15 feet up the other side, for a total wire run of 33 feet, which causes a significant current loss with 20 AWG.
  6. Grey One

    Grey One TrainBoard Supporter

    If on a limited budget with lots of time you might find a source of wire in old power cords. I'm not sure if 120 feet worth but on a small layout such as mine, (3x10 + a little more), it took less than 10 computer / printer / monitor power cords to wire it for 2 train operation.

    I had to do a lot of splicing using electrician's tape. It was not pretty and it took much more time than if I just bought rolls of wire.

    Just an idea.
  7. mtntrainman

    mtntrainman TrainBoard Supporter

    Thnxs guys...

    I went out to a friends house this afternoon. He is a worse packrat then me. We rummaged through his stuff and I found at least 60 feet of twisted pair of 20 guage solid copper Bell Wire !! I will use that with the phone wire as drops from the tracks.


    I understand what you posted and will use my tester tomorrow to see if those connections on the back can be connected together at the commons. I appreciate the tutorial...will come in handy.

    Thanks again all :)

  8. LOU D

    LOU D TrainBoard Member

    Hytec,if it's 2 seperate powerpacks to run 2 seperate tracks,how is there a common from each pack? When you reverse it,the polarity changes..
  9. Hytec

    Hytec TrainBoard Supporter

    I agree that it seems illogical, but it works fine. When the two left-hand (or right-hand) output lugs of each cab are connected in common, they become the common zero volt reference for the two cab's other output lugs which are not connected together. That way each cab's unconnected output lug will be either a positive or a negative voltage when measured against the common lug, depending on the setting of each individual Reverse switch. (This morning I realized that the cab output lugs are not labeled, so I'm using "right-hand" and left-hand" to identify them. I apologize for using the terms "+" and "-" in my previous post. I was running from memory, which is not what it used to be...:tb-hissyfit:)

    BTW mtntrainman, if you measure the outputs with an ohmmeter, you will see an open (infinite resistance) between all posts. I can't explain the internal circuitry because I don't have a schematic for the 2800, but the connection described above works fine and has not harmed my 2800.

    Please understand that I'm not encouraging you to do this if you feel uncomfortable with it. It's only what I did with my 2800 and had no problems, so thought I would pass it on.
  10. LOU D

    LOU D TrainBoard Member

    I don't mind the extra wire,LOL!!!

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