I think that Peter Riddle's article on signals on page 48 of the October, 2011, CTT needs some comment.
On page 50, "Relay Basics", Riddle seems to imply that one can use only a DPDT 12-volt AC relay, when an SPDT would suffice for the problem at hand and an AC or DC relay of any (safe) voltage rating would work if coordinated with the power supply for the relay coil. A DC supply, whether for the coil or signal or both, can easily be made from a dedicated transformer and a bridge rectifier.
But, as I have frequently pointed out here on the forum, there is need for neither a relay nor a contactor to operate a two-lamp signal. Albert Kalmbach, for one, figured out how to do it with no more than a single resistor many years ago. I independently came up with essentially the same idea, using a lamp instead of the resistor to reduce the power consumption, and have described it here many times.
Actually, it is not clear what advantage there is in operating the crossing gate with a relay at all, since there is no trick to connecting it directly to the control rail.
The description of the construction of the control rail mentions using insulating pins, but overlooks the need to insulate the rail from the metal ties of the tubular track depicted.
I also noticed that figures 1 and 2 on page 49 suggest Lionel's arrangement of the 153's lamps, green on the bottom, red on top. But the picture on the previous page caught my eye: That signal has had its lamps swapped, to put the red on the bottom. This is not the way Lionel intended; but it is prototypical and the way I would do it.
Bob Nelson
I just finished reading that article about half an hour ago, and I agree that there's no straight reason given why a relay is neccessary at all. However I missed that Peter also forgot to mention that the insulated rail needs to be insulated from the metal ties too. Good eye Bob!
Personally I prefer the direct method no matter what type of track I use. To elaborate, on my 4x6 RealTrax bedroom layout I created an insulated section by simply removing one of the outside rail contacts from each end and added a piece of styrene shaped to fit the rail. Since Realtrax has a plastic base all 3 rails are already insulated from each other. I put "terminal posts" on the roadbed too since I need to switch out accessories depending on seasons. I have 3 wires installed. One to the center rail, one to the unaltered outside rail and the third to the insulated outer rail. With a gateman or crossing gate the wire to the unaltered outside rail is unneccessary, but for semaphores with arms I need all 3.
On tinplate O or Standard Gauge track I insulate one rail from the ties with pieces of cardstock and use either plastic or wood pins to insulate the rail from the next section. Then I just use a lock-on to power gates and gatemen and 2 lock-ons connected to opposite outer rails for semaphores.
Of course, this only works for solenoid accessories and the level of track voltage applied to operate the train regulates how well the accessories work. Also, you can't use this method of activating solenoids if you're running a train on DC. I have 2 O gauge MPC locos that run on DC so I have a slide switch installed next to the track so I can turn the accessories off when I run those trains. (One is a James Gang General and the other is a Chessie 4-4-2 in case anyone's interrested.)
So I agree that more could have been said as to why a relay is neccessary in the first place. However I'd also like to say that from my experience this is a rare oversight on Peter Riddle's part! He's usually extremely accurate and I always enjoy reading his books and submissions!
Becky
Trains, trains, wonderful trains. The more you get, the more you toot!
Why a relay? Simply put you can have say 14v through the contacts to your accessory, and use the voltage from the track to activate the relay. That way you have consistent operation no matter what the voltage is running the trains. If you use a rectifier and a DC relay your accessories can still be used no matter if your track is AC or DC powered.
Becky, there is no reason for the accessory to be limited to the track voltage when using a control rail. The accessory can use whatever voltage, frequency, or waveform that you or it want, as long as the source supplying it is returned to your outside rails.
I'm a little puzzled that you think that a solenoid cannot be run on DC. It can, although the appropriate voltage may be different because the solenoid's inductance affects only the AC impedance. In any case, whatever source you want to use can remain in place and active, whether the track is powered by AC or DC or not powered at all.
I'm afraid I don't share your opinion of Peter Riddle's electrical expertise.
Moozuki, you can simply connect your 14 volts to the accessory and complete the circuit through the control rail. Why would you need the relay to operate (or not) on the track voltage? If you have an accessory that you want to run on DC, then connect it to a DC supply and, again, complete the circuit through the control rail. The track voltage, of whatever level and whether AC or DC, has no necessary relationship to the voltage, of whatever level and whether AC or DC, used to power the accessory.
lionelsoni I'm a little puzzled that you think that a solenoid cannot be run on DC. It can, although the appropriate voltage may be different because the solenoid's inductance affects only the AC impedance. In any case, whatever source you want to use can remain in place and active, whether the track is powered by AC or DC or not powered at all.
They do work all too well. They don't turn off and just keep buzzing away. That's why I have an inline switch to turn them off. I should have mentioned that.
If you have the solenoid connected between the center rail and the control rail, I don't see how it could be buzzing when there is no train on the control rail. That's an open circuit.
I believe the author also stated that the 151 semaphore was wired the same as a 153 block signal in that article, to pick another nit
I can think of one reason a relay would be beneficial for hooking up a crossing gate. I have one crossing on my layout that has two tracks crossing a road. The road is protected by 2 252 crossing gates and an automatic gateman. If I remember correctly, it's close to 3 amps to power all this. The slightest dirt on the track or the wheels causes some pretty big arcs, compared to my less power hungry devices. One of these days, I'll throw a relay in the circuit to prevent pitting on the wheels.
Also, isn't it possible to add a capacitor in the relay circuit to keep a gate lowered during intermittent power loss?
J White
Yes, but watch out. Simply putting a capacitor across the coil (of a DC relay--it doesn't help at all in an AC circuit) could make things worse. The capacitor will draw a very high charging current when the wheels first close the circuit, possibly briefly arc-welding the wheels to the rails and doing more harm than good. There are ways to get around this and still slow the relay's release.
Using a relay to control a heavier current is certainly a legitimate application.
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