Selecting a relay for Tortoise

[Anonymous]

You guys who are electrical geniuses are going to think "here is another one" when yo read this, and you are right. I have an "erector set" in N scale where I enjoy experimenting with different aspects of layout building as a learning process. It is basically a large oval that originally went around the Christmas tree with a double track and some turnout spurs and crossover. My latest has been to learn about turnouts, wiring, etc. so I mounted a tortoise and tried a variety of linkages from model airplane control cable to the thin metal auto wiper blade strips with holes and a bell crank. But wiring is my downfall!! I want to learn how to use a relay with my tortoise (it is powered as shown in their instructions with a pair of 12V 500mA wall transformers) . I read what I could on the web, and then started searching places like Radio Shack as well as the Web suppliers of electronics for a 12V relay and really got lost . One of the on-line electronics suppliers had a help desk, to which I sent the following: "I am a model railroader looking for a relay to switch power on
the "frog" of a turnout. The switch motor is 12 VDC and has auxiliary
contacts to which I would like to connect a relay.. From all the chat I've
read from model railroaders, I need a relay that will use 12 VDC to energize
the coil, and operate with a coil resistance of 100 Ohms or less. The
contact voltage will be no greater than 18-20 VDC, and require 2 amps or
less. The reply I received was very courteous, but obviously shows my ignorance, because I don't even know how to answer: "we need to know how
many sets of contacts you want on the relay (one, two, three, four?).
Is it necessary that the relay have a coil resistance of less than 100 ohms?
(most 12V relays have a coil with a DC resistance between 185 and 300
ohms--so the relay coil doesn't waste so much of your power!)."

Can anyone help. please??

[rrinker]

You don;t really need a relay, you can hook the Tortoise contacts directly to the frog. Especially since you're in N scale, and it's pretty much impossible for more than one powered unit to be on a frog at the same time. If you were in O or larger, I'd consider a relay just because the Tortoise contacts won't handle the 4+ amps larger scale locos can draw. If you aren;t goign to have signalling or position feedback of the Tortoise, you can even parallel the two sets of contacts for greater capacity, but there's really no need especially in N scale.

--Randy

[Anonymous]

Thanks, Randy. That helps my understanding considerably. Just for the sake of my education however, let's say I have position, signalling and frog power needs relative to the Tortoise. I presume that a double pole relay on one of the contact sets would be the appropriate solution. How would I figure the specifications for a relay? Thanks, Jim.

[rrinker]

To switch frog polarity you'd only need a single pole double throw (SPDT) relay. The coil needs to be something within the range of what the tortoise contacts can handle - anything from a 5 to 12V coil will work. Current for the coil isn;t too critical, not too many low voltage relays would draw more than the Tortoise contacts can handle. You just need an appropriate power supply. The more critical spec is for the relay contacts, the ones that are switching track current. 1 amp would be sufficient for N scale frogs.

--Randy

[cwclark]

send me an e-mail and i'll send you a wiring diagram drawn on microsoft word on how to wire a tortoise to power a turnout frog...chuck

[ecdowney]

cwclark: can you post it here please? I would like to see it also.

[cwclark]

I had it on disc and it got formatted by some jerk out here ..(that's what i get for leaving it laying around here at work) I'll have to redraw it when i get a chance...anyway...it's easy to wire... 1. solder a wire to the FROG and connect it (from left to right ) to the #4 terminal post on the tortoise machine.
2. solder a wire to the TOP rail (before the point rails) and connect it to the #2 post of the tortoise.
3. solder a wire to the BOTTOM rail (before the point rails) to the #3 post on the tortoise...

if it shorts out when you try it, swap the #2 and #3 terminal posts around....
one other item ...if you are using select control turnouts then you'll have to cut gaps in the rails before and after the frog to isolate the frog from the other rails...Chuck