I am confused about the amperage rating of switches for a control panel. I am using DCC but have broken my layout into power districts. I want to use SPST switches rather than Atlas connector switches but I don't understand what amperage switch I should use. I have found many miniature switches on ebay that are rated at 6 amps or 10 amps. how do I determine which switch to use?
My second question is along the same lines. I've got some ultra bright 5mm and 3 mm LED lights that I wanted to use on the control panel to indicate power to a district and switch postion. I know that I have to use a resistor to step down but how do I determine which resistor to use? Likewise should I use a dpst switch instead of the spst to acomplish this??
Switch amperage ratings are for a 110 Volt AC (house current) circuit, so the 6 amp ones are more than adequate for the control panel's low voltage wiring.
A general rule I use for LEDs is a 1K (1,000) Ohm (Brown-Black-Red) resistor instead of computing individual resistances. Most LEDs require only 1.2 Volts at 30 mA, and a 1K resistor even on track voltage will still let them be bright enough. LEDs are polarity sensitive, so you need to be aware that they won't light if connected backwards.
Unless you're using Tortoise or similar slow motion switch machines that receive a constant voltage, the LEDs won't be able to be used to indicate switch position.
I always use DPDT toggle switches for track wiring and cut the power to both rails instead of using common ground wiring.
Instead of e-Bay where you never know the quality of what you're receiving, I get my toggle switches from All Electronics in Van Nuys, California. Check them out at http://www.allelectronics.com
6 amps is plenty for what you are doing. unless your are building a welder or using it for 110VAC you should be fine with a 6 amp rating. With DCC at about 15 volts or so the chances of melting a switch are low. what are you using the switches for? May I suggest allelectronics.com. they have a good selection of switches and reasonable prices. Determing what switch to used depends on the application. are you using to turn on and off track power or are you throwing switches?
To answer your second question. Yes you need to add a step down resistor.Ohms law (V=IR) can be used to figure out the correct resistor. V is the voltage of power supply (DCC= 15 volts, DC for switches =12 volts), is the size of resistor you are looking for, and I is the current rating of the LED. so for a 15 volt power supply and a 25 Milliamp LED you need at minimum a 600 Ohm resistor (R=15volts/.025amp) for a 12 volt power supply you need at least a 480 ohm resistor. I generally go higher than those values because the LEDs are generally way too bright at these levels and also if any kind of power spike occurs you lose your LED's. Generally a 1000 Ohm (brown black red color code) resistor is about right for this application. LED's are current driven which means you will break them if you exceed there maximum operating current.
Again about the switches we need to know what you are trying to do with them to know what kind of switch you need. Here is the website I mentioned earlier.
http://www.allelectronics.com/make-a-store/category/700275/Switches/Miniature-Toggle/1.html
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
These particular switches are just for turning on and off blocks of track. I followed one of the atlas plans which I regret but I already wire the track with buses and drops as the plan showed. I am using DCC and understand that the 27 blocks I have are overkill but whats done is done. So I am aware that the switches will always be on. I guess the advantage might be easier troubleshooting. Is there an advantage to using dpst switches with the LEDs or is that a waste of money...should I just have to wires coming off each contact???
I do plan on using tortoise switches and I want switches on the control panel for these.
If you are just using the LEDs to indicate power to a district, you can just wire them in series with a conventional diode and a resistor across the feed to the district. Even the diode is optional, but a good idea. I would start with a 2k resistor insted of the usual 1k, since the peak voltage of DCC may be above 12 volts.
The mind is like a parachute. It works better when it's open. www.stremy.net
larak If you are just using the LEDs to indicate power to a district, you can just wire them in series with a conventional diode and a resistor across the feed to the district. Even the diode is optional, but a good idea. I would start with a 2k resistor insted of the usual 1k, since the peak voltage of DCC may be above 12 volts.
Even simpler - a bi-color LED with a 1K resistor. It'll be a reddish-orange when the track power is on. If you're using a DCC system that supports running a DC loco on address 00, the color will be more red or more green depending on the speed and direction of address 00. Since the bi-color LED is actually two LEDs wired back to back internally, this takes care of the reverse voltage problem that the extra diode in larak's idea resolves. Although to be correct the LED shoudl be in reverse-parallel with the protection diode, not in series. Anode of LED to cathode of diode, cathode of LED to anode of diode. One joint to one rail, the other joint to the resistor and then the resistor to the other rail.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
quote: Switch amperage ratings are for a 110 Volt AC (house current) circuit, so the 6 amp ones are more than adequate for the control panel's low voltage wiring. end quoute
T'ain't necessarily so. Most miniature toggle switches are not rated at 110VAC (actually most ratings are at 125VAC if rated for household voltages) because they are not intended for use with household wiring. Those that are rated for 125VAC tend to be physically larger, with larger terminals to accommodate 14-18 gauge wire.
However, voltage ratings are really not a concern 99.9% of the time in model railroading. Almost all switches and toggles are rated for at least 12 volt work, which is sufficient for our use. Just like in circuit breakers, it is the current rating that matters. Amps is amps, regardless of voltage. How big a current rating does the OP need? It depends on the rating of his DCC booster. A 6 amp toggle will work fine for everything but an 8 amp booster. If boosters or power districts are set up with circuit breaker protection at less than 3 amps, then 3 amp toggles are fine. Just like wire size, the toggle current rating should be greater than or equal to the maximum current allowed by the circuit breaker/power supply.
The Atlas Connectors/Selectors do not have a published current rating that I know of. They are conservatively designed banks of slide switches that work well with DC block wiring currents (2 amps or less). I'm not sure how well they would hold up if continually asked to switch 5 amp DCC loads. Of course, how often do you actually load your DCC system to 5 amps?
my thoughts, your choices
Fred W
Check this place for your switches.http://www.mpja.com/searchprods.asp
rrinkerEven simpler - a bi-color LED with a 1K resistor. ... Although to be correct the LED shoudl be in reverse-parallel with the protection diode,
A good idea if you don't mind the color. Saves the need for the diode. Yes, reverse parallel will work too. It has more advantages than disadvantages as well. Must have been asleep when I typed my post. At least you were awake Randy.
Karl