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

Personally, I'd be looking for relays with a higher coil resistance.   Do you really need DPDT contacts?

How about this SPDT relay with a 400 ohm coil?  http://www.allelectronics.com/...mp-spdt-relay/1.html

Jbb posted:

Matt is right, AllElectronics is a little more user friendly...

That website is so straightforward, simple, and easy to drill down to what you are looking for, while being all inclusive - there is no three rail / O Gauge retailer that even comes close.

I'd get the 470uF 35V since it's the same price as the 25V.  While you are operating at 12V DC in THIS application, the 35V rating is useful for general O-gauge applications so why not "stock" something you might be able to use later.  I have to throw in that if you "do" eBay, you can get the same for less than 10 cents each.

Choosing capacitor size 330uF, 470uF, etc. can get into some nerdy math.  I'll throw out some back-of-the-envelope numbers showing the relevant relationships. Use them, study them, ignore them, laugh, cry, up to you!

The capacitor provides anti-chatter protection which keeps the relay closed during brief interruptions of the 12V relay control signal due to dirty track, wheels, rollers, etc..  The capacitor gets instantly charged up to 12V DC when the wheel axle "shorts" the outer rails.  During the interruptions, the charged capacitor provides 12V DC to hold the relay closed until 12V is restored.  The larger the capacitor, the longer the hold time.  Per the datasheet for your chosen relay, it will stay closed as long as the relay voltage stays above 9.6V DC; that's just a worst-case spec and relays will stay closed at much lower voltages but you need something to start with.  Next, for your specific relay with a 135 ohm coil, the current drawn when active is 12V / 135 ohms = 0.09 Amps (90 mA).  How fast does a capacitor drop in voltage when dumping 0.09 Amps?  More math.  A 470uF capacitor dumping 0.09 Amps drops its voltage at a rate of 0.09 Amps/470uF = 200 Volts/sec.  So if starting from 12V, it will drop down to 9.6V in only 0.01 sec.  IMO this is on the hairy-edge but it is a your-mileage-may-vary situation and may be just fine.  Maybe you get an occasional red-green flicker on the signal light but so what?!

You can fiddle with the numbers.  So suppose you got the 160 ohm coil relay version you mention.  Plugging in 160 ohms instead of 135 ohms the hold time increases about 20%...or up to 0.012 sec instead of 0.01 sec.  No cigar...so why bother.  But go to a relay with 3x the coil resistance as GRJ suggests and you triple the hold-time and now we're talking turkey.

I understand the conceptual simplicity of just using a double-pole relay with one pole for the lights.  OTOH there is something curious about using a 10 Amp relay to toggle between Red and Green LEDs that draw about 10 mA (0.01 Amps) or 1000 times less current than the relay can handle!

With an isolated LED supply, it would be very easy to use the unused contact of the relay with the common to toggle between red and green, just need a couple of resistors to accomplish the trick.  I am spoiled by having a ton of salvaged DPDT relays, but they're not really necessary. 

One additional point.  If you're putting a fairly large capacitor behind the bridge, I'd also suggest a small resistor to limit the inrush current to minimize arcing of the wheels as the capacitor initially charges.  Even a few ohms makes a large difference.

Some comments in reply

Hear you on the higher coil resistance.

Right now some of my signals are 151 semaphores and the others are 153 with traditional bulbs (my stuff is all post war conventional).  Once I get things running, will look at upgrading to LED lighting for the O22s, 153's, probably everything.  In the meanwhile, it has proven easier for me to get my simple mind around DPDTs...

Can I clarify on the capacitor -- I put it across the poles of the relay, whether or not I power it with a bridge rectifier or a DC power source?  And the suggested resistor, what does small mean in terms of ohms?

And thanks for the capacitor math - I asked for it!

The capacitor is directly across the relay coil, you don't need it for a true DC power supply, just with the bridge.  I'm thinking along the lines of a 10 ohm resistor, probably a 1 watt one would be sufficient, this is just to eliminate the many amp spike that comes when the capacitor starts to charge.

In my experience the capacitor is also useful for DC operation because of noisy/dirty wheel axles and track making intermittent or high-resistance contact.  Even with a long insulated-section when the consist enters and you're depending on a small number of axles to firmly straddle the outer rails.

It appears All does not have 1 Watt resistors but IMO you don't need that.   Resistor Power = current x current x resistance.  Since your coil is 0.09 Amps, the 10 ohm resistor will dissipate: 0.09A x 0.09A x 10ohms = 0.1 Watts...so a smaller more economical 1/2 Watt resistor would be fine which All seems to carry.  The current of course spikes briefly when turning on but it's the continuous steady current when the relay is closed that drives the dissipated resistor power.

I was just being conservative with the resistor rating, figured a 1W couldn't hurt.  You're right about the capacitor Stan, it'll still prevent that chatter from the poor wheel connections.  With just the bridge, many relays won't work properly even with a good connection, they'll buzz away on the pulsating current.  That being the case, for the bridge configuration from AC, I consider the capacitor a mandatory item.

So, a question.  Re-reading Stan2004's "nerdy" but very helpful math, why not take the capacitor size up to 1000, 2200 or even 3300 uF?   Not terribly expensive, and it increases the hold times by multiples.  Solving a problem with a sledge hammer?   Or will I burn down the house?

I do realize that there may be better pin mounted relay options as suggested by GRJohn but I am intimidated by PCB, perfboard, etc.   Conceptually I get the benefits but it's another learning curve (I want to run my trains!) and I think old fashion sockets with screw terminals eases future reuse of the relays (I have broken down and rebuilt my layout twice in 15 years, and will likely do so again).

As always, thanks all

Larger capacitors will increase the hold time, it's as simple as that.  As long as you use a resistor to limit the inrush current, you won't suffer any adverse effects from a larger capacitor.  Of course, reducing the coil current is actually a more effective way of increasing the hold time, but maybe that's another topic.

JBB,

I like AllElectronics.com as well.  I totally agree regarding Digi-Key.  You should see their paper catalog.   If you drop it on your foot, you'll break it.  And picking a (the right) component out of it?  Forgettaboutit!

Best of luck with your application.  You're in the right place to get good advice.

George

George, you miss out on a valuable resource if you ignore places like Digikey and Mouser, they have an incredible inventory and are my "go to" places when I need a part.  Once you learn to navigate around them, it's really not that hard to use if you go there knowing what you want.  AllElectronics is fine, but they have a fraction of the parts, they are first and foremost a surplus shop, so their inventory changes with the seasons.

Jbb posted:

...   Or will I burn down the house?

Hmm.  There was a guy on OGR who was messing with a DIY circuit, hooked the capacitor (IIRC of similar value to what you're proposing) backwards, it exploded and started a fire.  He happened to have a fire extinguisher and took care of it.

Increasing the capacitor increases the amount of stored energy and the amount of power flowing into the lower resistance coil.  I suppose electricity is still "cheap" in the US and we aren't talking megawatts.  But as a rule-of-thumb I try to reduce power consumption in circuits which generally improves reliability, allows use of smaller and less expensive components, reduces heat-management issues such as needing ventilation, etc.. 

It's a tradeoff with how much "math" you want to deal with, waiting weeks for stuff from eBay Asia, using Radio Shack as your supplier-of-choice because it's down the street, soldering seemingly microscopic components, dealing with geeky schematic diagrams, and so on.  Whatever works for you...

gunrunnerjohn posted:

George, you miss out on a valuable resource if you ignore places like Digikey and Mouser, they have an incredible inventory and are my "go to" places when I need a part.  Once you learn to navigate around them, it's really not that hard to use if you go there knowing what you want.  AllElectronics is fine, but they have a fraction of the parts, they are first and foremost a surplus shop, so their inventory changes with the seasons.

I hear you, John.  The problem is determining what I need.  I'm not an EE or electronics hardware expert, so designing or building a circuit to do something other than produce smoke is an issue.  I'm a software guy with some exposure to hardware.  That's why I ask people about circuits.

Best analogy I can think of is the old Unix "man" pages.  If you knew what you were looking for, great.  But if you didn't know the cryptic and byzantine name assigned to something, welcome to the snipe hunt.

George

The cure for the Unix "man" pages and using Digikey and Mouser is practice.

Thanks to the good electronics folks here on the forum I have learned to somewhat use the Digi-Key (and Mouser) website to order things. Digi-Key is my preferred site (great service and shipping prices on small orders). From a Digi-Key parts list, I find that there are usually only a couple of things I need to select to narrow my search and find what I am looking for. Many times selecting the desired voltage and amperage and maybe through hole (as opposed to surface mount or SMT) are all I select and that usually narrows it down pretty well.

Of course, this won't apply to the knowledgeable folks here as they know what all the different columns mean and just what to look for. It does take some practice, but once you poke around on their website for a while I think you will get the hang of it. I really think it's worth it too. The electronics folks here could also tell you the important things to look for about specific items when searching.  

All Electronics is ok, but the main thing I don't like about them is they have little or no data on the electronic parts they sell. I tried ordering a couple of things there and was unable to find data on proper connections for the items. The parts were not marked, no brand name or model number and I am not knowledgeable enough to figure it out. This is ok for a 12vdc DPDT relay or switch or something like that, but more information is needed for the electronic parts. This is where Digi-Key (and Mouser) excels. They have good data sheets (from the device manufacturers) on all of their items. If you want to learn more about electronics, these data sheets are a must for learning about the individual parts and their functions and uses. In addition to very reasonable shipping, Digi-Key has very good prices as well.

Just thought this might help someone to try taking another look at Digi-Key or Mouser which would provide them with, as GRJ said above, another valuable resource for electronic parts and maybe learn something along the way. 

Here is a DCS control system that uses 12vdc relays to control indivdual track blocks. This system allows the use of miniature toggle switches and/or output from a DCS AIU "SW" output. The relays are high current automotive types.

I must be missing something obvious, but I cannot get my relays In my block control system to work.

To review, i have created a loop with 8 isolated blocks.  The relays are 12 VDC and get power from a standalone DC power source at 12v.  AC is from two ZWs that are in phase and thanks to good advice here I have added circuit breakers and TVS.  Otherwise, all my equipment is post war

I have checked whether the relays work by connecting them directly to the + and - of the DC power source - all good.  I checked that each relay is getting power from the source - yes

I then put a car in a block, and checked whether  indeed the axles are  creating a link between the ground and control rails. I connect the control rail wire to negative post of the relay and nothing happens.  It should complete the circuit and activate the relay, righty?

As a further test, I took my volt meter and ran it from an AC post at 15 vac to the control wire and got a good circuit.

What am I missing?  I thought AC and DC could use the same common? 

Thanks all

AC and DC can use the same common as long as they are otherwise isolated.

How about a diagram of what you have?

gunrunnerjohn posted:

The cure for the Unix "man" pages and using Digikey and Mouser is practice.

Uh, no.  In the case of Unix "man" pages, you can't fix stupid.