It finally occurred to me to get out my multimeter and actually measure the voltage of my power supply. I was just using an old wall wart that stated the output as 12v DC, 400mA. Turns out it was putting out 17 volts. So using your formula: 17 x 17 / 560 is over .5 watts. Once I tried using a PS that actually measure 12v output, I got very little heat on the resistor. Thanks again for your responses.
pfenbach Thanks for the response. I'm no electronics expert, but I am using the 560 ohms 1 watt resistor that Tansey recommends. Should a 1 watt resistor get that hot dissipating .25 watts?
Thanks for the response. I'm no electronics expert, but I am using the 560 ohms 1 watt resistor that Tansey recommends. Should a 1 watt resistor get that hot dissipating .25 watts?
Probably.
pfenbach I'm late to this discussion, but am interested as I am trying to use Tansey's Option A myself and wanted to find someone who had actually implemented it. The issue I am having is that if I choose position 1 on the rotary switch, for example, then the first resistor that receives power gets very hot - too hot to touch even. And the same thing happens as I move to other positions on the rotary, so it's not just one resistor. Since I can't believe that this is how this setup is supposed to function, I'm wondering if any of you that actually use Tansey's config could provide me with any guidance as to what I might be doing wrong. Thank you.
I'm late to this discussion, but am interested as I am trying to use Tansey's Option A myself and wanted to find someone who had actually implemented it. The issue I am having is that if I choose position 1 on the rotary switch, for example, then the first resistor that receives power gets very hot - too hot to touch even. And the same thing happens as I move to other positions on the rotary, so it's not just one resistor. Since I can't believe that this is how this setup is supposed to function, I'm wondering if any of you that actually use Tansey's config could provide me with any guidance as to what I might be doing wrong. Thank you.
Yes, that first resistor has to dissipate ~0.257 watts (12 x 12 / 560), so I would expect it to get pretty hot. 0.257 watts may not sound like much, but consider that the typical through hole resistor that we often use in model railroading application is often only rated at 1/4 or 1/2 watt.
A few points. First, Greg has delt with the resistor codes and polarity. The correct code for 560 ohms is green, blue,brown.
One half watt resistors are plenty adequate. I never did understand Tansey's 1 watt recommendation. The actual dissipation at 12V is about 1/4 watt (12x12/560).
A tortoise takes 2-3 seconds to fully move. Therefore the worst case for your four motors in line would be 12 seconds, but only if all four had to change from their previous positions. That is highly unlikely. In your case The usual operation will be two motors moving; the base main turnout and one other.
I assume you plan to wire the opposite ends of each individual spur in parallel. BTW, if you do you could use two 270 ohm 1 watt resistors per Tortoise pair instead of four 560 ohm 1/2 watt resistors. 270 ohms is the closest standard value to two 560 Rs in parallel.
Each dendrite in Tanseys configuration will draw about 31 mA. at 12V so your 500 mA wall wort should be good for 16 Tortoises. I think you're OK.
Charlie
ROBERT BRABANDHas the resistor identification system undergone a change since 2009 or are there different kinds of resistors?
it's a generic picture of a resistor in the link. the same for all resistors
ROBERT BRABANDAnd just to make sure, resistors do not have an "orientation" in the circuit. There is no "in" and "out" side; it just has to be in the circuit between other components to reduce the current. Right?
right, resistors are not polarized
greg - Philadelphia & Reading / Reading
CharlieM Both approaches are clever solutions and either will work. Your choice. Over to you, Robert.
Both approaches are clever solutions and either will work. Your choice. Over to you, Robert.
"Clever" it is. Though current exchanges between the two of you about bemf is complex. I'm still thinking the Tansey Variation A (with resistors only instead of Variation B with resistors and diodes) is still going to be my selection. The advantage of using one power source readily attainable in my electronic discard box (a 12 volt 500 mA wall wart should do the trick and cost nothing to me now) outweighs the "downside" of watching Tortoise machines run sequentially instead of simultaneously. For the four track yard the track furthest from the main that means waiting 20 seconds instead of five. I can live with that in a staging yard.
Speaking of resistors, Tansey identifies 560 ohms, 1 watt, with three identification bands of green, blue, and brown. My search found these identified by the vendor as 560 ohms 1 watt, but the identification bands don't match the article's description:
https://vetco.net/products/560-ohm-1-watt-resistor/nte-1w156
Has the resistor identification system undergone a change since 2009 or are there different kinds of resistors? If I need to use a different resistor, your suggestion please. And just to make sure, resistors do not have an "orientation" in the circuit. There is no "in" and "out" side; it just has to be in the circuit between other components to reduce the current. Right?
Thanks for the education gentlemen. Keep it up and someday I might have enough intelligence to be insulted from time to time.
Robert
the Tortoise instructions only specify a max voltage of ~12V, but they draw about the same amount of current as an LED (max 20ma). so a relatively lightweight supply, what you might use for driving LEDs on a panel is usually sufficient
max ~8ma flows thru a 2.2k resistor driven by 18V, or ~13 ma when that terminal is driven directly by -9V.
i'm using a pair of LM324 op-amps to drive pairs of Tortise machines in an interlock controller
Greg,
Only to point out that the motor sees a respectable 9-10V while running. This could be a concern when the Tortoise is returning to its "normal" position, being supplied via the 2.2K resistor. Usually the Tortoise would be supplied from a relatively stiff power source. The 9-10V readings are a bit of a guess due to the sampling and display delays of my DVM.
CharlieMInterestingly the Tortoise actually sees 9-10 volts while the motor is spinning due to back emf. When it hits the stop it sees a bit over 4 volts which is enough to hold it in position.
not sure why you bring this up.
don't know what the bemf voltage of the tortoise while turning. bemf is proportional to RPM. bemf is zero when a motor isi not turning. so more mechanical resistance causes the motor to turn slower which reduces the bemf, increasing the current thru the motor and increasing the force.
there's more force holding it in place while stalled than while turning.
Now I've had a chance to look at both articles thanks to Greg forwarding Robert's email. They both seem to be viable and they both have advantages/disadvantages. The Smith approach may be a bit simpler, especially if wall worts are used as Greg suggests, but it does require two. Also, 18V wall worts may be harder to find. A higher voltage unit could be substituted but the 2.2K resistors would have to be changed. Interestingly the Tortoise actually sees 9-10 volts while the motor is spinning due to back emf. When it hits the stop it sees a bit over 4 volts which is enough to hold it in position. The speed is slower than with 12V but not too noticeable. The circuit does overcome the sequential turnout problem that I see as the primary disadvantage of the Tansey approach. However, the Smith approach does require two power supplies of rather non standard values (-9V and +18V). The Tansey approach uses a single 12V supply which is very useful for many other applications on the layout. The extra resistors and/or diodes with either approach are about a toss up and nothing like the full diode matrix would require. Both approaches are clever solutions and either will work. Your choice. Over to you, Robert.
having now seen both articles, it seems the Smith article from Nov 2000 is the simpler approach. it's application to a yard ladder, where just one turnout needs to be diverging while all others would be set normal is very straight forward.
it wires all the motors for normal position using one supply (+) thru a ~2k resistor and the other motor terminal to ground (common). a single pole rotary switch can then be used to connect the motor terminal with the resistor to the opposite supply (-) causing the motor to the diverging position.
in the above case only one motor needs to be set to diverging. but is describes how using diodes connected between the motor and rotary switch, more than one motor can be diverging.
it is somewhat confusing how it describes using a center tap transformer and half-wave rectification to generate +18V, -9V and ground. i see no reason why wall warts, ~18V and ~9V can't be used and avoid the need to build the half wave rectifiers. (note that only one direction would be "slow-motion")
the Tansey articles uses a single power supply voltage. it wires the negative supply to both motor terminals thru a 560 ohm resistor. connecting the postive supply to either terminal overrides the negative voltage causing the motor to switch.
the articles describes using diodes as well as an SPDT contact on the motor to route the positive voltage.
the obvious advantage of the Tansey approach is a single supply but requires twice as many resistors.
I believe on this forum you have to save your images to some third party host and link to it. No thanks. I'll scan the Tansey article and email it to you.
CharlieMIf your listed gmail address is good
it is. thanks
CharlieMWould be easier if this forum accepted pictures
isn't that what i did earlier?
it's the icon that looks like a mountatin and moon
If your listed gmail address is good I can send you a scanned copy of one of the articles. Would be easier if this forum accepted pictures but.......
Charlei
since i don't have copies of the articles, would if be possible for someone to post schematics (possibly hand draw) of the two approaches being discussed?
... or a descent text description of the circuits?
[quote user="ROBERT BRABAND"]
CharlieM robert, My first question would be why not use Tansey's version A?
robert,
My first question would be why not use Tansey's version A?
Certainly not for the final time in my life someone asked the question I needed to hear. When I was aiming toward Tansey's Version B it was because I wanted to keep one set of terminals on the Tortoise machines open to use eventually with some kind of trackside signalling systems. Then the question sunk in, and why would I ever need trackside signalling in a staging yard? Go figure.
So Version A looks sweet, though I will use 2-pole rotary switches so that if I ever want to add panel lights for the staging ladder tracks. You are good, sir, if you can get me to understand what's going on without the use of bat or a brick. Thank you.
My first question would be why not use Tansey's version A? The Tortoise has two sets of internal contacts that work well and avoid the diode issues. I typically use one set of contacts for the "dendritic" control and the other to power the frogs. Panel lights can be controlled by a second pole on the rotary switch. Unless you're heavily into trackside signalling systems you can afford to use one set of Tortoise contact sets for route control. However I would give the fourth Tortoise a try if you have to go with the diodes. The neat thing is the motor draws much less current while moving than when stalled. With three sets of diodes in series (four Tortoises) and starting with 12V the last motor would see 9.9V (12-3x0.7=9.9). The 560 ohn resistors will further drop this but the motor will see almost the full 9.9V while it is running. When it stalls there still is plenty of current available to hold it in position. I've read where some guys run tortoises on 6-7V but things slow down. That said, I still would try to use the Tortoise contacts and avoid diodes and micro switches.
You're in good shape with 6 or less positions on each side. The Grayhill switches are available in 2 pole, 2-6 position models; one pole for route control and one pole for panel lights.
ROBERT BRABANDPS I did not see in the Forum editor a way to insert that Omega symbol in reference to resistors
BTW the unit the omega represents is "ohms" if you are trying to write out something like this again with no symbols.
Chris van der Heide
My Algoma Central Railway Modeling Blog
ROBERT BRABANDΩ Hey, it worked. Any other magic out there?
[quote user="CharlieM"]
I can refer you to the May 2009 issue of MR in which Oliver Tansey describes a route control system for Tortoises that works very well. It only requires a single polarity 12V supply and a single pole rotary switch with the number of positions equal to the number of routes you plan. I am using this approach several places on my layout and it works very well. The only drawback to it is a bit more complicated wiring under the table and the addition of 2 resistors per Tortoise. There is also a slight delay when waiting for several switch motors to move is sequence but it's by no means objectionable. A lot faster than the prototype with one or two switchmen .
So the "Second Lesson Learned" here is to read the post of an expert carefully enough to get it all in your head. I just picked up the reference to the plan from the Tansey May 2009 MR article and I much like his "Dendritic Control System" version B (and in addtion here I get to use some of the Latin I had to learn in years gone by). I'm thinking that's the approach that makes the most sense.
And I've figured out that what I really have are two staging yards side by side. The double track mainline runs through the center of the yard with a four-track yard ladder attached to the East mainline and a two-track yard ladder attached to the West mainline. Putting one Dendritic system on the East yard and another on the West yard means I really only need six (6) routes controlled by rotary switch power, four for East, two for West.
So my next question for CharlieM is do I need to use Tansey's Version B with his micro-switch system controlling subsequent motors, or can I get away without the microswitch and wait for motors to throw on that four ladder yard? Or to put it another way can I stretch "with two to three turnouts in a row" to "with three to four turnouts in a row"?
Finally, for CharlieM, I assume the route selector switch Tansey includes in his design is basically tht same as the 1 pole 12 position rotary switch in the Smith Nov 2000 MR article only with fewer positions, in my case a 5 position and a 3 position switch, each controlling eith the East or West systems. Right?
Again, thank you to all. Robert
PS. I'm still waiting for the Old Testament Hebrew I had to learn in my pre-Seminary work to appear in this feed. Hope to keep waiting for that.
ROBERT BRABANDAny other magic out there?
You can have ∞ fun. I keep an alt-code chart handy for those infrequently used characters.
https://www.alt-codes.net/
Regards, Ed
gmpullman My Greek may be rusty, but this I can handle! ROBERT BRABAND PS I did not see in the Forum editor a way to insert that Omega symbol in reference to resistors. Regards, Ed Hold down the "Alt" key then type 234. Ω Hey, it worked. Any other magic out there? Robert
ROBERT BRABAND PS I did not see in the Forum editor a way to insert that Omega symbol in reference to resistors.
Hold down the "Alt" key then type 234.
Hey, it worked. Any other magic out there?
ROBERT BRABANDPS I did not see in the Forum editor a way to insert that Omega symbol in reference to resistors.
Thank you all for everything to this point. I have a .pdf copy of the Nov 2000 MR article which might be of help. Is there a way to attach that file to this discussion? And would doing so violate MR copyright needs?
More clear specifics of what the article's author is asking for are:
12.6V, 1.2A center tap transformer
Silicon diodes, type IN4001 (quantity 2)
4700 mf electrolytic caacitors (quantity 2)]
2.2k - Omega symbol - 1/2 watt resistors, (quantity 14)
1 pole, 12 position rotary switch
Tortoise machines, knob, 5 lug terminal strip which is optional
I understand that there is way to control staging yard track with a matrix system, but this system seems rather simpler and more elegant.
PS I did not see in the Forum editor a way to insert that Omega symbol in reference to resistors. Nonetheless it took me back to my college days of learning Greek. Turns out I am quite happy with having that part of history behind me. Though I am tempted to think about going back and reading an ancient Greek work on the fear of foreigners which we were required to translate, the word "xenos" has something to do with the title. We get our word "xenophobia" from the same place. Just need to get some stuff in my head these days.
2-pole 12-position rotary switch
GregC,
First, I don't see any edit button on the existing posts, even on mine after I log in. The only edit button I see is on the reply composition page. and is of no use after I post and discover a goof.
Second, the posted schematic is the basic diode matrix approach. I hate diode matrices.. The OP has 8 routes so the matrix will require a large yacht load of diodes. The beauty of the approach I suggested is all logic is handled by a single pole switch and the switches built into the Tortoises. The only price paid is a third wire to each tortoise, the sacrifice of one pole in each Tortoise, two added resistors per Tortoise pair, and the need for a second pole if a route indicator light system is desired. There is also some delay is cases where several motors must actuate in sequence but this should not be a problem for staging situations. The delay becomes noticeable in a yard where lots of fast switching is happening, but a staging yard should be OK. I suggest the OP take a look at the article if it is available and report back here. There's plenty of expertise available on this forum