An old school DC question or two

[ranchero]

While im still i nthe planning stage for the HO layout, i've been pondering controls. Yes. before anyone try to change my mind, i will be using DC. Im sure DCC is great and wonderful, i just dont want to use it on my layout.

Now my question rise fro mthe fact that id like to operate from control panels, In the past id prop up the ole MRC powerpack and operate that way, but my taste have grown  to the point where id rather control everything from a control panel. the bulkiness of the powerpack is to be eliminated... but i still need to control the power going to the track somehow. now reading back old issues of MR, i found a diagram that would enable me to do away wit the bulky power pack. Basicly the positive  from the variable DC screw connects to a circuit breaker, then hooks up to a 0-3 ammeter and then to a rheostat that hook up to the reversing switch. The negative fro mthe variable DC just connect straight to the reversing switch. In essence, you're just moving the control away from the power pack andunto the panel but seeing as the article is from 54 years ago, i wanted to make sure this was all still safe and sound procedure ( a few page before, one author does recommend using asbestos for scenery )

 

now as far as circuit breaker; is this really necessary or is it overkill? isnt the circuit breaker i nthe power pack sufficient?  if not, what type of circuit breaker should i look for? Is the ammeter really necessary? would it be a good idea to hook up both an ammeter and a voltmeter? What can a ammeter and voltmeter tell me modelrailroading wise? finally, what kind of rheostats should i look for?

finally, i also plan on adding load compensating toggle and add a micro ammeter to gauge scale speed, would that still all work using this particualr way of routing power?

 

i'm not sure if this is the proper forum to discuss such a problem so feel free to move to the appropriate one and accept my apologies, thanks for the hlpful answers ( im sure )

[gmcrail]

ranchero

While im still i nthe planning stage for the HO layout, i've been pondering controls. Yes. before anyone try to change my mind, i will be using DC. Im sure DCC is great and wonderful, i just dont want to use it on my layout.

Now my question rise fro mthe fact that id like to operate from control panels, In the past id prop up the ole MRC powerpack and operate that way, but my taste have grown  to the point where id rather control everything from a control panel. the bulkiness of the powerpack is to be eliminated... but i still need to control the power going to the track somehow. now reading back old issues of MR, i found a diagram that would enable me to do away wit the bulky power pack. Basicly the positive  from the variable DC screw connects to a circuit breaker, then hooks up to a 0-3 ammeter and then to a rheostat that hook up to the reversing switch. The negative fro mthe variable DC just connect straight to the reversing switch. In essence, you're just moving the control away from the power pack andunto the panel but seeing as the article is from 54 years ago, i wanted to make sure this was all still safe and sound procedure ( a few page before, one author does recommend using asbestos for scenery )

 

If you are using recently-manufactured (within the last 15-20 years) model locomotives, a rheostat setup won't work.  The model will just streak off down the track at top speed.  The motors in modern models do not draw enough current for a rheostat to function.

 Here's a throttle I found on the net.  It works very well (I have 4 of them), though you can get a wider range of control with a little tweaking - contact me off-forum.  If this is hard to read, copy it into Notepad or something with a fixed-width font to make sense of it.

--------------------------------------------------------------------------------------------------

Here is a simple throttle based on the Troller Auto-Pulse:

                        Radio Shack
Part                      p/n        price
5-pin DIN plug            274-003    1.69
5-pin DIN socket          274-005     .99
DPDT slide switch         275-407     .79
Snap-in light, blue       272-335    1.79
5k linear pot             271-1714   1.19
Knob 1-7/16" dia.         274-430    1.59
TIP-120 transistor        276-2068   1.29
TO-220 mounting hardware  276-1373    .99
Heat sink grease          276-1372   1.59
Rectifier                 276-1146   1.39
Transformer               273-1511   8.99
Box w/aluminum cover      273-231    2.19

1. 12-18 vac in is connected to the rectifier inputs.
2. Rectifier + output is connected to the full on (5k)
   side of the 5k pot and the transistor collector.
3. Rectifier - is connected to the off (0k) side of the
   5k pot, to the light and to the reversing switch.
4. The wiper of the pot is connected to the transistor
   base.
5. The transistor emmitor is connected to the light and
   to the reversing switch.
6. The reversing switch is connected to the tracks.



       |-----|
 ------|  R +|----------|---------|
       |  E  |          x       |C|
       |  C  |   5k ohm x------B| TIP-120
 12-18 |  T  |          x       |E|         |------|
       |  I  |          |         |---------|      |-----
  vac  |  F  |          |              |    |DPDT  | to
       |  I  |          |            light  |rev   | track
       |  E  |          |              |    |switch|
 ------|  R -|------------------------------|      |-----

---------------------------------------------------------------------------------------------------------------

now as far as circuit breaker; is this really necessary or is it overkill? isnt the circuit breaker i nthe power pack sufficient?  if not, what type of circuit breaker should i look for? Is the ammeter really necessary? would it be a good idea to hook up both an ammeter and a voltmeter? What can a ammeter and voltmeter tell me modelrailroading wise? finally, what kind of rheostats should i look for?

CIrcuit breaker:  Yes - it's necessary.   An easy solution is an old-school one:  Hook up a #1127 automobile brake/turn signal bulb with both filaments in parallel in the circuit.  One wire from the throttle to both contacts on the bottom of the bulb, and another wire from the brass side of the bulb to the track.  It will limit the current to approx 1.25a, and serve the dual purpose of eliminating throttle circuit burnout and providing a visual indicator of a short circuit.  

Ammeter:  handy in tracking down some problems, but not really necessary.  If you're going to have an ammeter, might as well have a voltmeter, too.

You can use them to tell the difference between a short and an open circuit:  If you have amps but no volts, it's a short;  If you have volts but no amps, you have an open.  Beware:  modern locomotives draw current in the milliamp range, so a 10-amp meter won't even register one. 

Rheostats:  Avoid them like the plague.  There are dozens (probably) of easy-to-build circuits out there that work much better than rheostats for controlling speed.

 

finally, i also plan on adding load compensating toggle and add a micro ammeter to gauge scale speed, would that still all work using this particualr way of routing power?

 Well, the easiest way to judge scale speed is with a stopwatch and a speed chart.  Again, contact me off-forum, and I can supply you with the chart. 

Load compensators are usually just resistors which are switched into the circuit.  Again, they don't work at all with a modern model locomotive, because of the low current draw of the motors.

i'm not sure if this is the proper forum to discuss such a problem so feel free to move to the appropriate one and accept my apologies, thanks for the hlpful answers ( im sure )

 

 Well, it's worked so far....

Edit:  Rob Paisley's site has a plethora of circuits to do almost anything but put out the cat:

http://home.cogeco.ca/~rpaisley4/CircuitIndex.html#3 

[tomikawaTT]

gmcrail's circuit is valid, but there's a quicker solution.  Instead of a pure-resistance rheostst, use an 80-100 ohm, 100 watt, rotary resistor as a potentiometer.  That way, the knob setting will control voltage to the rails (and, ultimately, the locomotive.)  It will be equally happy controlling a modern, "Whisper of power," can motor or a Pittman DC-91, at a cost of about 0.15 amps of parasitic power draw.

The #1127 12-volt bulb in series with the basic pack's output is the cheapest and, IMHO, best answer to limiting current to a short circuit.  The best part is, it's self-re-setting.  Clear the short and the bulb goes out.  Be sure to put it between the pack and the potentiometer.  That way it can also detect potentiometer failure.

If you have reversing sections, the output of the DPDT should be routed to another DPDT which sets "timetable direction" for through operation.  Output to reversing sections must be taken off between the two DPDTs and handled separately.  If you always enter a reversing section at one end, it can be hard-wired for that direction of travel.  (When running, once your train is completely on the reversing section, just flip the "direction" switch from West to East.  Mounting that switch so that it throws parallel to the main line trace on your control panel makes its purpose and proper setting a no-brainer.)

DCC advocates will come in here and say that all of this is too complicated.  Analog DC wiring IS more complicated than DCC - as long as one is happy with having mysterious black boxes in the circuit.  I prefer to have discrete components that I can understand, wired together in ways that I can comprehend.

Chuck (Modeling Central Japan in September, 1964 - analog DC, MZL system)

[ranchero]

thanks for the input, ill have to look into hte circuit you mention. I have to point out though that my load compensation circuit worked very nicely in On30 with bachmann engine. I have a switch with 6 position, one off, 1 full on and 4 with various resistance. the lowest resiatnce would cut about 20% of the power and the highest would all but enable a crawl. a small switcher with 2 cars would be set at notch 2 or 3 and would struglle to bring the train while a steamer would be set at notch 1 and huff along.

thnakd for the help so far

[fiatfan]

 Another good site for RR circuits is www.awrr.com .  The owner of the site is also very helpful when you have problems.  I have built a couple of his throttles with momentum and they work quite well.  It would be easy enough to mount the circuits on the control panel rather than as a walk-around throttle.  Good luck!

 

Tom

[shayfan84325]

I use a solid state DC throttle and love it.  These use a transistor circuit to create an output of 12 volt pulsating DC.  The time between pulses is what determines the train speed.  Because the output is always 12 volts, gradual start-ups and very low speeds are possible without stalling on minor dirt.  In my opinion, the performance of your trains will be on-par with DCC (I think it's a little better, but I don't want to start an arguement).

The actual control is hand held, about the size of a cigarette pack, with a throttle knob and a directional switch.  I bought mine on eBay for about $40 from Ken Stapleton; he makes them.  Here's his e-mail: [e-mail].

The connection is easy:  2 wires connect to a 16 volt AC power supply and the other two wires go to your track.

[rrinker]

tomikawaTT

gmcrail's circuit is valid, but there's a quicker solution.  Instead of a pure-resistance rheostst, use an 80-100 ohm, 100 watt, rotary resistor as a potentiometer.  That way, the knob setting will control voltage to the rails (and, ultimately, the locomotive.)  It will be equally happy controlling a modern, "Whisper of power," can motor or a Pittman DC-91, at a cost of about 0.15 amps of parasitic power draw.

The #1127 12-volt bulb in series with the basic pack's output is the cheapest and, IMHO, best answer to limiting current to a short circuit.  The best part is, it's self-re-setting.  Clear the short and the bulb goes out.  Be sure to put it between the pack and the potentiometer.  That way it can also detect potentiometer failure.

If you have reversing sections, the output of the DPDT should be routed to another DPDT which sets "timetable direction" for through operation.  Output to reversing sections must be taken off between the two DPDTs and handled separately.  If you always enter a reversing section at one end, it can be hard-wired for that direction of travel.  (When running, once your train is completely on the reversing section, just flip the "direction" switch from West to East.  Mounting that switch so that it throws parallel to the main line trace on your control panel makes its purpose and proper setting a no-brainer.)

DCC advocates will come in here and say that all of this is too complicated.  Analog DC wiring IS more complicated than DCC - as long as one is happy with having mysterious black boxes in the circuit.  I prefer to have discrete components that I can understand, wired together in ways that I can comprehend.

Chuck (Modeling Central Japan in September, 1964 - analog DC, MZL system)

 No I won't. That circuit's dead simple. In fact I built the same thing but with a low power 2N3904 and minus the light bulb to use as a jump port throttle on my Zephyr. Oh and a 9V battery instead of the transformer.

 Actually, I never said dual cab wiring is complicated - in fact it's rather simple, since everythign is at the panel and only a pair of wires run to each block of track (don;t use common rail if you can avoid it - plus if you ever convert to DCC it makes it that much easier). It's when you have 5-6 cabs, and want to be able to assign your current block plus the next one to your cab, and don't want to have all this ganged on one giant control panel, and don't want the panel crowded with multideck rotary switches (which aren't cheap) - that's when it gets complicated, when you move to progressive cab control, or zone control. Not to mention what happens if someone forgets to free their block after their train exits..

                       --Randy

[da_kraut]

 Hi,

I bought one of his throttles as well and must say it works quite well.  Ken is a great person to talk to as well and makes the throttles himself.  Here is his web site http://www3.sympatico.ca/kstapleton3/851.HTM .

Hope it helps.

 Frank