Sourcing Block Control Components

All Electronincs (http://www.allelectronics.com) has 30-amp Automotive SPDT relays and sockets for about $3 each. They're designed for fog lights, but are inexpensive enough to use for model railroading. You need a 12-volt source (10VAC through a bridge rectifier will work). I believe they also sell the bridge rectifiers.

Don't I need DPDT - one pole for the signal light, the other for the train power?

And what capacitor should i get

Thanks !

Why don't you start with a schematic of what you want to do, then someone can recommend the parts to get it done.  You need to design the application before you start picking the parts.

Their a lot of good ideal out there.

Maybe post some pictures so we can see what your trying to accomplish here.

I'm sure one of us can help you out here.

Good Luck, John

Is this what you want?

Here is what I want to do.  I have a series of blocks each at least as long as my longest train.  If a train is in say Block C, I want to slow a train in Block B by changing the power to the rail from Terminal A at 14V to Terminal B at 5V.  I also want to turn the signal light from green to red.  Below is my diagram - apologies for the art work.  I have not shown a capacitor because I am unclear on how to use.  I also did only partial diagrams of Relay A and C.

So here are my questions

1. I wonder whether instead of switching from Terminal A to Terminal B whether it is better to re-route the power through some resistors.
2. Instead of using the bridge rectifier, should I get a cheap DC transformer, especially if I plan to use some LED lights down the road?
3. I think for each block I need one DPDT relay, a bridge rectifier or a DC transformer, a capacitor, and some resistors if that method is preferred - can I get some part numbers from someone's preferred supply house?

Many thanks

And yes Rob I think what you posted is the same idea as my diagram - but much prettier.  What's it from? Thanks

Forum member Dale H has lots of good information on this type of conventional block control on his J&C Studios site. Look here for his site: Dale H - J&C Studio 

Jameco Electronics is another source that may be a little easier to find parts.

Jbb posted:

... same idea as my diagram - but much prettier.  What's it from? Thanks

Lionel. It was from one of the pamphlets "How To Operate Lionel Trains and Accessories".

I use 12V DC relays with a fairly large capacitor across them to prevent any chatter.  I salvage the relays from old discarded servo system boards.

I am still using 24v DC relays salvaged from a wrecked Cessna over 35 years ago. They work fine with little or no chatter at 12-14 volts from a transformer tap rectified with a  FWB rectifier.

I was able to get hands on 72 ITT Phone Relays 12 volt  DC, 4 Pole Double throw and plastic enclosed casing . Only had one fail in Twelve years. I used them for my Subway Signals System on my Train Board. I purchase them from Blair Electrics. in NYC.

 There longer around.

They had some very good  available items for surplus back then. 

Good luck, John

What specs do you recommend for the capacitor?

Thanks

The capacitor specifications are really dictated by the coil currents of the relays.  I like them to be large enough to impose at least a small delay in dropping out to prevent any chatter.  With low current relays that have 10-20ma coils, something like a 330uf cap works great.  For higher current relays, you need more capacitance.

Jbb posted:

Don't I need DPDT - one pole for the signal light, the other for the train power?!

Not necessarily.  It sounds like you're considering a 12VDC supply and isolated outer-rail block occupancy detection.  And you're considering red/green LED signals?  In the same way the relay gets 12V DC when occupied, that same switched 12V can turn on a Red LED while turning OFF the Green LED (which is normally ON).   This can be accomplished with a 25 cent solid-state circuit (and SPDT relay) rather than requiring another pole (DPDT relay). 

I'm not suggesting you go this route but simply answering your question.

Jbb posted:

Hi all

...What I want is classic block control -- slow down a faster train behind a slower train while turning the  signal lights from red to green.  

Just to be clear, are you trying to slow down a faster train or stop it?  I notice you mention applying 5V to the trailing block.  It seems the speed of a 5V engine might vary wildly or even stall depending on load.  Or do you fully expect it to stop and you're just applying some kind of electronics sustaining keep-alive voltage to run lamps, a sound-board, or whatever?

Integrated Signals systems. I would supply along with a order a wiring schedmatic for a Red, yellow and Green Signal head.  Just like you was talking about above.  Good luck, John

Jbb posted:

...

1. Instead of using the bridge rectifier, should I get a cheap DC transformer, especially if I plan to use some LED lights down the road?
2. I think for each block I need one DPDT relay, a bridge rectifier or a DC transformer, a capacitor, and some resistors if that method is preferred - can I get some part numbers from someone's preferred supply house?

As I mentioned in above post, if you go with an isolated 12V DC supply as what gets switched across the outer-rails, then you don't need a bridge rectifier for each relay.  You would still need/want a capacitor for each relay for anti-chatter chosen as GRJ describes.

Like you say, you can find "cheap" DC transformers.  For example for about $3-4 on eBay (free shipping) you can get a regulated 12V DC, 2 Amp wall-wart style transformer.  Here's a recycled photo from another thread showing a 1 Amp wall-wart and use of an adapter jack (about 50 cents on eBay) so you don't have to mess with cutting the plug and splicing wires.  There are zillions of 12V DPDT or SPDT relays as you have discovered but for the application at hand let's say each requires 50 milliAmps of coil current.  Let's say you go with LED signals that draw, say, 10 milliAmps of current and are powered by the 12V DC relay supply.  Then a 2 Amp (2000 milliAmp) supply can power over 30 relay + signal LEDs.  And of course you can get 3 Amp, 4 Amp, etc. regulated 12V DC supplies for just a few dollars more.

All

So here is what I think I am doing.  Matt is right, AllElectronics is a little more user friendly.  I have selected the following

Ice Cube Relay LY2N. 12VDC, 135Ω coil. D.P.D.T. contacts rated 10A (alternatively I could go with a 162 Ohm coil)

Regulated 12Vdc 1.5A power supply and adapter to power the relays

In terms of capacitor, and this is where I would really love some help because Ohm's law and I are not good friends, the type that seems to provide the capacitance I want is Radial Electrolyic, and my choices seem to be 470 uF at 10, 16 or 25 volts, 330 uF at 50 volts.  Help!

Thanks all