misterconsisterDo I need resistors to maintain even brightness or can I do this without resistors?
Turn the lights out in the room and do the comparison again. I've found that the bi-color LEDs look much closer in brightness with the room lights out. In the daytime, it can be hard to see the green ones at times.
It takes an iron man to play with a toy iron horse.
I have a 12V 500mA PS running tortoises through DPDT switches on my panel and I have 2 Bi-Polar Red/Green LEDs (Miniatronics) per turnout indicating switch throw direction, also on the panel. When I tried putting the LEDs in line without resistors, the tortoise motor resistance was enough to not burn out the LEDs, but the green LED was considerably dimmer than the red one. When I put in the 470 ohm resistors that come with the LEDs, the brightness of the Red and Green were pretty similar.
Do I need resistors to maintain even brightness or can I do this without resistors?
Eric
I'm kinda likin this stuff
COrrect. LEDs are current devices. They require a minimum amount of current to light and will get brighter up to the current limit, exceed the current limit and they will go poof. LEDs drop a set amount of voltage, varies witht he LED design but most red/green/yellow types are 1.8-2.1 volts and white ones are usually around 3.1 volts. Current flow is determined by the remaining voltage (power supply minus LED drop) and the resistance of the load that is absorbing the remaining voltage. You cna run an LED on 120 volts with a big enough resistor. The Tortoise motor is no more than 15ma, and per electrical laws, all devices in series with each other flow the exact same current - so if the Tortoise motor is 15ma, an LED in series with it gets 15ma, no more, no less. That's a safe current level for any common LED you're likely to have laying around.
Just to be clear on the circuit, you need 2 LEDs wired back to back with opposite polarity. If there is a flat spot on the LED case, connect the lead by the flat of one LED to the lead WITHOTU the flat of the other LED. Connected the other two leads together. Assumign a DPDT switch controllign the tortoise, and that it works (flip toggle, tortoise moves, flip it back, tortoise moves the other way), cut one of the wires heading to the Tortoise pin 1 or 8 (doesn't matter which). Connect one set of LED leads to the wire coming from the toggle, connect the other pair of LEDs to the wire going to the Tortoise. One LED should light up. Flip the toggle, the Tortoise should move, and the other LED light up. The LED will be dim while the motor is moving and as soon as it stall, brighten up.
--Randy
Modeling the Reading Railroad in the 1950's
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I once caught a train in my pajama's. How it got in my pajama's I'll never know... (sorry, Groucho)
You must have had something wired up wrong, a 9.6 volt power supply feeding a Tortoise motor through a pair of LEDs would not fry the LEDs. 4.5 volts is a bit low even for a Tortoise with no LEDs. I'd go with 6-9 volts with no LEDs, 9-12 if using the LEDs
Our club does this with a 12 vdc supply and bi-polar LED's. Works just fine. No resistors needed.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Just getting around to wiring up the control panels for my staging yard and have run into a little problem. I am using a 5.5vdc wal wart to power the torti and have wired DPDT switches in the control panel, with everyting working ok, switches throw fine and all is good. I then wired in 2 ex-Christmas tree light LED's for switch indicator lights as per instructions (relying on the resistance of the motors to limit current - no resistor added) and switches no-go, but LED's work as intended. OK, not enough through voltage to switches, figuring that the LED is dropping voltage to the torti about 1.5-2 volts, leaving only 3.5-4 volts available to drive the switch machine- not quite enough. I had another wal-wart labeled 6vdc, hooked that up and promptly fried the LED. Checked voltage with a meter (I know, should have done that first) and reads 9.6vdc As these are Christmas tree light LED's that now I am assuming they have a capacity of about 3 volts ( I have been able to test these with a 1k resistor with that same 5.5vdc walwart with no issues.) which will not be enough to drive the torti. Obvious solution is to buy LED's with higher voltage, but are there any other options? I have about 200 of these low voltage LED's I would really like to use instead of buying a bunch of new LED's.