These switches require a ground to light the led. Some act as a SPDT, in that when off, they have a direct path to ground. Normally OK, but if you mistakenly run a car or engine with two roller pickups onto an unpowered siding, you will get a direct short from the powered track to the unpowered siding. If you never forget to power the siding, no problem.

John

Located in the real Upstate NY

I use these auto type switches. They are rated at 12 vdc and that matters for the LED. When you apply 18 vac, the LED rectifies the AC and the half wave rectified voltage equivalent is about 12 vdc. Also it is advisable to put a diode in series with the ground terminal with the arrow pointed to ground or common. You can connect all the ground pins of all the switches together and just use one diode. 
These switches also have the issue of the switched terminal getting connected to the ground pin when the switch is off.CaltermSwitchCaltermSwitchWiring

Chuck TCA LCCA ARRL BMWMOA

Attachments

Photos (2)
stan2004 posted:

See this OGR thread to dig deeper in the use of 12V DC LED-lighted automotive switches.

Note that if driving the LED with AC (even with the external diode), the LED is flashing on/off 60 times per second.  Most folks over the age of 40 (?) can't see it though. 

Thanks for this thread. I'll just have to be careful when running trains that I have the siding on before I pull in. 

Add Reply

Likes (0)
Post
OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
330-757-3020

www.ogaugerr.com
×
×
×
×
×