I don’t want to hijack the other thread, but I have a question about a different element of it.
I’m dramatically increasing the number of tortoise machines I use, and along with them related LED’s etc. It has moved me well past my understanding of electronics, and power supply in particular.
Specifically, I don’t think a wall wart will do any more, and need to get some detail.
Question 1) Can someone tell me if I’m figuring this right:
The power consumption of one turnout on my layout should be this: 1 tortoise @ stall = 16 mA, 4 LEDs (two on control panel, two for signals) = 20mA each = 80 mA, so 16+80 = 96 mA total per turnout. Call it 100 to make it easy.
1 amp = 1000 mA = one turnout (100 mA) * 10. In other words, I’ll need roughly an amp for each 10 turnouts?
Question 2) If I were to wire up two power supplies in series, do I add the amperage up or not? Specifically, if I wire the + terminal of one 12V 2A power supply to the - of another 12V 2A supply, do I have a 2 amp or 4 amp power supply?
Question 3) Anyone care to recommend a good source for a higher-amperage DC power supply? The ones I’ve seen are tending toward the expensive.
I’d check that figure for the tortoise at stall, 16 mA sounds a bit low.
No. Power supplies in series, you add the voltage. In parallel, you add the amperage. In your example, you have a 2 amp 24 volt power supply. However, I don’t recommend this, too much possibility of ground faults or other power supply burnouts.
If your figures are correct, your best course of action is to have one power supply for the motors and one for the LED’s. Also, if you have many tortoise’s to wire, group them so they don’t exceed the power supply rating and use several smaller power supplies. Of course, document which turnout is connected to which power supply. The first time you need to troubleshoot a short in the system (for example), you’ll thank me for this.
I also think there’s something wrong with your calculations. Circuitron does say 15-16ma at stall, and that a 500ma transformer ought to handle about 30 Tortoises.
Perhaps your LED calculations are wrong. Your figures indicate that all four LEDs are on at all times – or are two on and two off at any one time? That would reduce your power requirement considerably. Or perhaps your LEDS take more power than mine.
I have a pair of 9v 800ma power supplies (wall-warts from Radio Shack), each feeding about half my layout. Each runs over 40 Tortoises and 20 to 30 LEDs in Oregon Rail Supply dwarf signals.
Mr. Diehl is right about not connecting multiple power supplies, and, if you use separate ones, being careful to know which are fed by which supply. My solution was easy; otherwise I’d be inclined to use a different color of wire.
I don’t think, however, you can use one supply for the Tortoises and a separate one for the LEDs, unless you’re using relays for the LEDs. Depending on what kind of LEDs and signals you’re using, you may not need relays or even resistors.
You’re right, Pondini, that I plan to put the LED in series with the tortoise per the diagrams at Tony’s (great site, ain’t it?), so separate power supplies are not doable.
All 4 LEDs for each switch would be lit at all times, I’m using bicolor red/green LEDs so that each track (both signal and on the panel) will always be lit red or green.
But my common sense is itching, and making me think you’re probably right about the 20 mA per LED being off. By that calculation, your 40 tortoises and 30 LEDs would be pulling about 1.2 amps, certainly enough to cause havoc with your 800 mA supply (which I presume it isn’t…)
I think the thing to do will be get out the mutlimeter and do some testing when the darnfool LEDs arrive and see if 20 is really the draw…
Okay, I am now really confused. I knew I had this thought from somewhere and it was from… The Tortoise instructions.
To wire it DC using SPDT switches, they say:
BI-POLAR DC WITH SPDT SWITCHES: This system requires two similar DC supplies of not more than 12 volts each. They are wired in series with the (+) of one supply
connected to the ( - ) of the other supply. This common connection feeds a bus wire that
runs around the entire layout. One of the motor connections from each TORTOISE
connects to this bus. Single pole switches connect either the (+) supply or the ( - ) supply to the single wire that runs from the panel to the remaining TORTOISE motor connection.
They include a diagram that shows two power supplies wired in parallel feeding a bus, just as they say, with one motor connection of the tortoise connected through a switch to either + or -. The remaining motor connection is connected to the wire that creates the serial connection between the two power supplies (i.e. it goes from + on one to - on the other)…
That seems to, by everyone’s account I’ve talked to (here and elsewhere) feed 24V to the tortoises, which the instructions also say is a no-no.
Connecting power supplies in parallel i.e. + terminal to + and - terminal to - is not a good solution to increase amp output. In theory 2 - 1 amp 12 volt power supplies in parallel should supply 2 amp at 12 volts if they are identical. If they have dirrerent internal impeadance (interal resistance) the one with the lower inpeadance or higher voltage output will hog the load. High end power supplies made to be connected in parellel have load shareing circuits.
Things wired in series, add voltage, do NOT add current. Things wired in parallel, add current, do NOT add voltage.
So if your LEDs are wired in series with the Tortoise motors (the “no resistors” method), then the total current draw even with the LED is whatever the stall current of the Tortoise motor is. For the same voltage power supply, the Tortoise will run slightly slower with the LED because of the loss of about 2 volts.
Thank you Randy, that’s exactly the point I was missing. I knew that each LED in series w/ the tortoise would cut a couple volts and make it a little slower… I hadn’t picked up that the amperage wasn’t cumulative. That makes my life a LOT simpler!!!
No, that’s not what that means. It means that if you consider the point of the two power supplies that is tied together as zero, you put +12V or -12V on the Torti.
Your description of the switch motor wiring from Tony’s is correct with respect to the power supply set up. What you are describing here is a set up for developing a common ground. The leads connected in series provide a common ground and the other terminals will provide you with 12 vdc+ and 12 vdc-. This is a very common power supply set up for stall motors and allows the motor control to be set up with one dpdt controlling both the switch motor and the polarity of the frog etc…I believe tortise machines have contacts on them so this might not be as critical in that instance…
I use this technique on my layout with no problems whatsoever.