building a walkaround throttle out of a stationary power pack

Discussion in 'HO Scale Model Trains' started by Bill Nelson, Oct 19, 2014.

  1. Bill Nelson

    Bill Nelson Well-Known Member

    a_walk_around_throttle_build_a1a.jpg a_walk_around_throttle_build_a1b.jpg a_walk_around_throttle_build_a1c.jpg

    I have been a big fan of walk around throttles for a very long time, back to when I was a teenager, and we are talking way back in the dawn of time here. at that time there were no commercial walk around throttles. Ok now a days many folks are going the DCC route. I play with DCC at the club but with my tiny logging locomotives, any of them forty or more years old with ancient open frame motors, and no room for electronics.

    I have several very nice memory walk around throttles, where the throttles can be un plugged. and the locomotive will keep going, you can walk ahead of it, and plug the throttles back in to control the locomotive. this is nice, as with multiple throttles the cables can be shorter, and you don't get your cables tangled. Back in the dark ages I used to buy rheostats from MRC, or disassemble MRC power packs. I would get a DPDT switch, a spst switch and a project box from Radio Shack, and a long 4 conductor cable. I'd put the DPDT switch wired as a reverse in the project box, with the other switch as an on off switch, and have the rheostat in the box. I'd take a power pack somewhere, with the throttle set at full, or at a lower setting, If I wanted to try to get better slow speed. two of the conductors in the cable would be hooked up to the track outlets from the power pack. they would run through the reverser circuit, and the rheostat, back down to the other two conductors, one conductor would go to the common rail, and the other would go to the various block controls.

    Ok I used to do this 40 something years ago, and now I have three high quality memory walk around throttles, and two radio walk around throttles; why would I want to step back into the past, and do something the old fashioned way. It comes down to a power pack. My dad got this power pack with a Bachman On30 train set. I inherited it with some of his train stuff; and it found it's way to my workbench. I found out that locomotives had a much better starting speed, and remarkable slow speed control than with the more expensive throttles on my RR, so I have better control on my workbench than I do on the layout, and I can't tolerate that, so I'm going to cannibalize that power pack to build an old school tethered walk around throttle. I'll share that process with Y'all in case it will come in handy. Walk around throttles are much cooler than stationary throttles as you are there to see the trains from any angler, and can throw switches, uncouple and couple cars as needed.

    an example of the slow speed control provided by this power pack is shown in this you tube video link.


    if this throttle works as well as a walk around, it will be my favorite throttle even if the tethered cable gets in the way. I'll document the build, in case it may be usefull for others.

  2. Bill Nelson

    Bill Nelson Well-Known Member


    It took we a while to get to this next post. I flipped the unit upside down, and it had these tamper proof screws in it. Clearly the Bachman lawyers did not want me to open this puppy up. No matter. I could not tamper with the screws, so I tampered with a screw driver; using a grinding wheel on a dremil tool to cut a notch in the tip of a cheap screw driver. It did not work well, but with persistence it worked well enough. an alternative would have been to drill the heads off the tamper proof screws.

    SAFETY NOTICE!! never open up a piece of electronics when it is plugged in. and be careful even if it is not. some items like televisions and computer monitors have capacitors, which can store an electric charge even when unplugged, one should have a pretty good idea of what is in there before opening. when in doubt, consult someone more knowledgeable on electronics than yourself .


    Once I had it opened, I could identify all the goodies that were in there. One lead from the power chord went directly to the transformer, and the other lead went to the on / off switch, and then had a leg to the transformer. I left those leads intact. I would want power to the transformer, and being able to turn it off might come in handy.

    On the other side of the transformer are the AC outputs. one of them goes directly to one of the AC accessories terminal. the other goes to that little glass vacuum tube alongside the transformer. That houses the overload protection. there is a bi metallic switch in there. it's normal position is closed. One of the reeds of the switch is made with two dissimilar metals, with the metal that expands the most due to heat on the inside. In an overload situation the excessive power running through the metal causes the bi metallic reed to curve away from the other contact; breaking the circuit, and hopefully preventing any damage to the rest of the circuit. we leave that thing alone, we like it. I'm old enough to remember when power packs did not come with overload protection; and you don't want to be without it.

    From the overload protection switch the wire goes to the remaining AC outlet terminal. On the back side of each AC outlet terminal there was a wire that Jumpered off to the speed control and diode bridge assembly. I cut both of those wires flush with the terminal. the diode bridge/speed control unit will be mounted in the project box. I will fasten two of the wires in the four wire tether cable to the AC outlet terminal, and the other end of those two wires will fasten to the wires on the Diode bridge / speed control module that used to lead to the SC terminals (I'll provide a wiring diagram later).

    The diode bridge / throttle control module also had wires running to the reversing switch. I cut those wires, and the wires from the reversing switch to the track terminals on the power pack. I left the reversing switch in the box. I won't use it ; I will use a better DPDT switch on the project box as a reversing switch. I will show how to wire it to make it into a reversing circuit later.

    Having cracked open this puppy, I can see why it's got such good slow speed control. most power packs have a simple diode bridge to rectify the current (convert it from AC to DC) this has got a fancy circuit board in there, and a potentiometer instead of a rheostat. I could be wrong, but a rheostat takes full power DC and applies a varying amount of resistance to reduce the voltage. I'm thinking a potentiometer actually changes the voltage it self. Not sure about that, but what I do know is a rheostat has two terminals and A Potentiometer has three. I know how to wire a rheostat. got no idea how to wire a potentiometer, but hey; it's wired into a assembly with two wires in and two wires out; and I know how to deal with that.

    More later with home made wiring diagrams covering the parts I understand. I'm excited about this. I love my memory throttles the smaller cables are handy. This throttle runs locomotives with such a fine control at low speeds, and incredibly slow speed starts, I won't mind trailing around a 23 foot cable if I can make this thing work as well as it did on the work bench.


  3. ----zathros---

    ----zathros--- -----SENIOR---- Administrator

    You wire a potentiometer by wiring the negative and max positive voltage to the fixed terminals, the ones not connected to the swiper arm. By moving the swiper arm you tap off of the carbon trace inside the potentiometer, a shorter trace less resistance, less of a voltage drop, more output voltage. When you move the swiper arm to the high end of carbon trace, you are creating more resistance, and dropping the voltage across the potentiometer. You then end up with less voltage. You can wire a Potentiometer to work as a Rheostat by running a wire to the swiper, and the other lead to either, but not both fixed leads,

    Since Potentiometers are used for varying Potential (Voltage), they do not pass much amperage, very little in fact. So a Potentiometer rated at 20 Watts is a rating for the "WHOLE" carbon trace, and they burn out when used as Rheostats, as they are touching only one point, and it gets hot and burns a spot in the carbon trace, then stops conducting.

    Rheostats are made far more robust and are designed to run amps through them. They sometimes have extra lugs, but that is just to give you more connection points. Rheostats are inherently noisy, and unsuitable for audio applications. Rheostats are great for making dimmer switches for car interior lights, etc.

    That's basically the difference. Potentiometers also come in what's called an audio taper used for making volume, bass, and treble voltage controls, amongst other things. :)

    Potentiometer inside look: Simple small DC motor speed controller


    Best use for a Rheostat, high current devices (Turns your typical soldering iron into a precise soldering tool):


    The robust insides of a Rheostat:

  4. Bill Nelson

    Bill Nelson Well-Known Member

    Thanks for the technical explanation. fortunately I don't have to wire the Potentiometer, as it is wired to the diode bridge. I have two wires that come from the AC input, and two wires that will be DC speed controlled out put. I will run those wires to a DPDT switch, wired as a reverser, and the output from that switch will go back through the tether wire to my electronics case, where one wire will go to the common rail, and the other will go to the contol panel, where it can be routed to the common rail of any desired block.
  5. ----zathros---

    ----zathros--- -----SENIOR---- Administrator

    I'm an electronic tecnician, so, maybe, a big maybe, I will be able to offer up something helpful. :)
  6. Bill Nelson

    Bill Nelson Well-Known Member

    I only know what I have learned working on model trains for 47 years and working an old house for 35 years, and working on cars for 24 years. thankfully tose sentances were served concurantly.

    as a result I know just enough to be dangerous.
  7. ----zathros---

    ----zathros--- -----SENIOR---- Administrator

    Sometimes, experience trumps book knowledge. :)
  8. Bill Nelson

    Bill Nelson Well-Known Member

    "Sometimes, experience trumps book knowledge" That is true, and sometimes some one with no experience tries something he doesn't know is impossible, and finds a way to make it work. But usually I just muddle along . the old saw goes that the Titanic was built by professionals, and the ark was built by an amatuer. That is fun to say, but we don't know how many amateur built boats have sunk.

    I have the power pack closed up, with masking tape, because I'm lazy, and did not want to re use those ***** tamper proof screws. the defective reverser switch has been removed along with the diode bridge/potentiometer Assembly; and the back has been taken off of the I have a big roll of indoor out door speaker wire . the wires are stranded, so they will be a little bit flexible, and it has the four conductors I need for the tethered throttle. two wires to take the AC power to the hand held controller, and two wires to carry the speed and direction controlled DC back to my electronics cabinet, an Army surplus moartar round ammo box, where one of the DC wires will attach to the common rail bus, and the other will be routed to the control panel on the dispatchers desk. these are documented in my main thread over in the logging Mining and industrial railroad section; but I will show photos of them here later so folks don't have to wander through some sixty pages of extraneous drivel to find the pertinent information.

    right now routing the cable under my RR will be the hardest part of this job remaining. In my rebuild, my lowest deck is considerably lower than my previous plan. This has resulted in a decrease of storage room under the layout, at the same time the rebuild has added huge amounts of material. I have to try to feed this wire back behind all the ********, so I can fix it in one location, and test the reach of the cable before I cut it to size to ensure that the throttle will reach everywhere in the room where one might want to control a train. I love my memory walkaround throttles, but if this build is successful, this will probably be my favorite throttle, as I love good slow speed control that should be worth the hassle of dragging around 20 feet of cable.
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  9. Bill Nelson

    Bill Nelson Well-Known Member


    In the top photo, I have the diode bridge/potentiometer/heat sink mounted in the case with the support for the cable entry fastened into the case. The DPDT switch is wired as a reversing switch. the short leads on one end are the inputs from the potentiometer/ diode bridge assembaly. they are hooked to one end of the DPDT switch, and then cross over to opposite corner of the switch the output wires come off the middle terminals


    here the components are all in the case; the black and green wires will go to the wires out of the throttle, and the AC in wires on the teathering cable will go to the nearly invisible brown and red wires comming off the diode bridge circuit board. I have the cable routed through the messy train room; so tommorow, if I have time , I can hook the throttle up to the teather cable, and hook the teather cable to the base unit, the common rail buss, and one of the throttle inputs to the control pannel. Throttle #2 is an Aristocraft radio throttle that has been flakey; and I will likey make this either throttle #1 or throttle #2 , as if this works it will likely be one of my favorates, cause I love slow speed control.

    I have to cut some firewood tommorow, and that might cut in to train time. Today I washed and groomed our Lassa-Appso. the poor little fellow is diabetic now, and that has caused him complications to the dry eye problems he has always had. I washed him out and trimmed all the hair away from his eyes, as the eyeball gunk was getting into his hair and pasting his eyes shut. he is usually not real coperative with grooming, but he was today; and left me time to work on my throttle.
  10. Bill Nelson

    Bill Nelson Well-Known Member

    I got in a good nap after church on Sunday, and still had some time to get that firewood on the porch, and route the cable from my electronics cabinet to the end of my central peninsula. I left a lot of slack in the cable between the layout edge, and the electronics box, so If I have to re route it up down or sideways under the layout for any reason in the future, I have some slack to work with. Then I tied a loose not in the cable just inside the layout, and used a wire clip inside the lose knot to secure the cable end at the layout edge, so tugging on the cable there will not remove the slack under the layout. with one end of the cable secured to the layout near the center of the central peninsula , I unrolled the cable off the spool till I could reach the farthest edge of the layout; and then added about six feet for good luck, and cut the cable.

    I striped the outer insulation off of the cable leaving about eight inches of wire hanging out the outer cable insulation. Then I fed the cable through the metal fitting at the top end of the project box. I wrapped electrical tape around the end of the outer insulation until the cable could not be pulled back through the metal fitting on top of the project case. then with the cable pulled tight against the project case I wrapped electrical tape around the end of the fitting, continuing for a short distance down the cable securely attaching the project box, now a throttle, to the cable. I stripped a little bit of insulation off the wires in the cable, after cutting them close to size. You always want to have a little extra wire in case you mess up; but you don't want a lot of extra wire, because you want to fit everything in the box.

    The output wires from the reversing switch to the cable I twisted together and attached them with wire nuts. the input wires to the diode bridge and Potentiometer circuit board are smaller, and the wire nuts I have wouldn't grab. that is probably irrelevant, as at that end of the box I don't think there is room for the wire nuts anyway. I have twisted those wires together, and will solder them together, and cover the joint with heat shrink.

    After that is done, and the back of the project box is screwed in place I will just need to but what is left of the power pack in my electronics case, a re-purposed wooden Mortar ammunition crate. I will wire the two input wires to the AC/accessories terminal on the power pack. one of the output wires will go to the common rail bus; and the other will go to the throttle #2 input wire for my control panel on my dispatcher's desk. On that panel I have a bunch of six position rotary switches , one for each block on my railroad, allowing the control rail of each block to be powered by one of whichever throttles I have hooked up to the system.

    Currently I have one innovator 2000 memory walk around throttle, which is my throttle #1. This tethered throttle will be throttle #2, replacing an ancient Aristocraft radio throttle, which has become flaky. Throttle #3 is a more modern Arristocraft radio throttle, which is still reliable. I have two GML memory walk around throttles, which I have yet to wire in. each will require a three wire control loop around the entire layout; and I will need to make an annex to the electrical cabinet, as they are facia mounted, but my current design has no room for them anywhere near the electronics cabinet. I want all the power packs centralized there so the power striop on the side of the electronics cabinet will turn off all the trottles,

    Nelson a_walk_around_t_with_wires_a1b.jpg a_walk_around_t_with_wires_a1a.jpg
  11. Bill Nelson

    Bill Nelson Well-Known Member

    This is the inside of my main electronics cabinet. It is a Military surplus crate made to hold ammunition. I think this one is marked for mortar rounds, but I have one almost identical to it that looks to be marked for small arms rounds. I'm going to cut down the other one to hold my two GML walk around throttles,, and I will fasten it to the top of this cabinet.

    The vertical gray cable is the cable to the new hand held controller. the white, and red wires are connected to the AC/ accessories terminal on the Bachman power pack's case. the blue post it note on the case has notes about what color wires go where. later I will transfer that info to the masking tape on the power pack with a laundry pen. I wasn't going to do that until I had the unit working, and was sure I had not messed something up


    This photo shows the throttle hook up terminal in the main electronics cabinet. My control panel has 6 position rotary switches. I'm unlikely to ever have six throttles; six operators would be elbows to ***holes in my aisles, I have five throttles, only three are hooked up right now, but the cabinet, and the control panel are wired for six, in case I loose my tiny little mind.

    at the throttle hook up terminal, I have spaces to hook up two wires from each throttle. across the top of the terminal strip I have red wires daisy chained from every other terminal, to create the feed to the common rail. the solitary black wire is the wire that goes out, and makes a complete circuit of the RR, feeding the common wire for each and every block. the terminal for the control wire from each throlle is hooked to a wire that goes to the back side of the control panel

    Here is the back of the control panel. this looks worse than it is. there is a terminal strip for the control wires for each possible throttle, for a total of six wires in. I have 14 blocks shown here, and will probably add one more. each block has a six position rotary switch. each of the 6 control wires for the throttles is hooked to the appropriate terminals of each block's rotary switch. the output wire from each rotary switch is routed through an on / off switch (so each block can be turned off), and then to the output terminal strip, where there is one terminal for each of the eventual 15 blocks. I'm going to re work the labels on the control panel with printed stick on letters and numbers to neaten it up. The control panel is in a very nice modern roll top desk, that was made to hold a computer

  12. Bill Nelson

    Bill Nelson Well-Known Member

    Here is a video of the new hand held throttle running #14, a PFM Climax, and #22 a Oriental Powerhouse series Little River camera glitches some, causing the occasional jerk to the video, the trains run silk smooth in real life. the loud clicks are the direction switch being thrown. the music is recorded from a player piano roll Scott Joplin produced before the advent of other music recording technology, hopefully skirting any copyright issues

  13. Bill Nelson

    Bill Nelson Well-Known Member

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