# Relays?



## ftauss (Sep 18, 2012)

Thinking of trying relays on the layout to trigger some of the old school accessories I have. My thinking is that a more constant voltage will give better results, contactors are not useable with RMT Super Snap and FastTrack, the 153 IR types are a bit expensive. So I did a little research and a little looking.

I'm guessing AC vs Dc is really more about the specific accessory and what it likes. How about voltage rating, max? min? Is the rating for both ends, trigger and output voltage? One book I have says 50 volts is good max. Anyone have a good source for units that would be appropriate for hobbyist use? Appropriate being fairly small and not real expensive.

Thanks!


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## Lynn D Bennett (Jul 27, 2013)

ftauss:

I don't really understand what you are trying to do with relays but relays are nothing more than remote switches. There is a coil that moves internal contacts. There are many contact arrangements but to just turn on an accessory, single pole normally open is the most useful.

The coil can be any voltage, AC or DC. The coil voltage does not have to match the voltage of the signal going through the contacts. The contact voltage rating needs to be at least more than the voltage going through them and the contact should be rated for more than the current they are expected to control going to the accessory. The contacts can handle AC or DC but often the ratings are different for AC loads than for DC loads.

The main use of relays is to remotely control a large current locally in contrast to running long wires that cause a voltage loss at the accessory being controlled. The coil requires minimal current and is much more tolerant of voltage loss from the long wire runs to the accessory.

How about you give us more details like wire run distances, available power forms, accessory requirements. To run accessories like we use, switches are normally more than adequate. A control panel with a series of switches is usually adequate if wired with 18 gauge wire to the accessory unless the layout is huge and the wire runs very long. I wonder why you think the voltage to your accessories will be more constant with relays (??). More details are required.

Sorry if I don't understand what you are trying to do. More info will help.

LDBennett


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## gunrunnerjohn (Nov 10, 2010)

What I so is use a 12VDC coil relay with a diode, capacitor, (and an optional choke if you run DCS). This is wired to an insulated track segment to trigger signals. We use this scheme on our modular layout, I build little relay boards with the components and we just screw them down under the modules where we need them. The relay contacts just have to be rated to handle the load. The load switched by the relay can be AC, DC, or a combination of both, that's a totally independent determination.

I have no idea what you're talking about for voltage, but I wouldn't bring 50 volts anywhere close to my trains!

Tell us a bit more about exactly what you need these for. We're been using salvaged relays from industrial plants, so I've been paying $0.00 for the relays.


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## BigAl56 (Dec 14, 2011)

DC relays are much easier to obtain than AC. I use DC relays with a bridge rectifier feeding the coil. That usually works although a cap may be needed with some relays if the relay chatters.


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## ftauss (Sep 18, 2012)

gunrunnerjohn said:


> What I so is use a 12VDC coil relay with a diode, capacitor, (and an optional choke if you run DCS). This is wired to an insulated track segment to trigger signals. We use this scheme on our modular layout, I build little relay boards with the components and we just screw them down under the modules where we need them. The relay contacts just have to be rated to handle the load. The load switched by the relay can be AC, DC, or a combination of both, that's a totally independent determination.
> 
> I have no idea what you're talking about for voltage, but I wouldn't bring 50 volts anywhere close to my trains!
> 
> Tell us a bit more about exactly what you need these for. We're been using salvaged relays from industrial plants, so I've been paying $0.00 for the relays.


Yeah I thought the 50 volt thing was odd, that was why I am asking. I'm thinking maybe the writer was allowing for spikes, frankly I was thinking being able to handle a max of 20 volts would be sufficient. 

To clarify, I want to connect the relay to an insulated outside rail and center rail. When that trips it allows the constant voltage to get to the accessory. 

I noticed last year that the switches got real dicey if the voltage wasn't high enough. Had a few instances where I had trouble throwing the switch with the train going slow. I can obviously be more careful, but I have my daughter running trains, too. I let her run them whenever she wants, even if I'm not there. She does a good job, but there is a limit as to how much you can explain to or expect from a 10 year old. And I want her to feel free to bring in her friends and play, too. So I figured if powered all the accessories and the switches with constant voltage it would solve that problem. I know the switches don't need relays, BTW, just trying to plan out the accessory/switch wiring plan.

I ended up with 2 CW-80, a 1033, a little train set brick from the 50s that still works (a 1015?) and the one I got with the trolley. Plus I have up to 4 DC power packs I can borrow for DC power.

Sorry if I wasn't clearer.


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## gunrunnerjohn (Nov 10, 2010)

The reason I use a diode and cap on the relay is because the relays I normally have available are 12 VDC, so a bridge rectifier would be overkill and probably damage the coil at some point. I size the capacitor to get the proper DC voltage reading across the coil and prevent chatter. If you can find some 24 VDC relays, they work perfectly with the bridge rectifier and a capacitor around 100uf as a rule.

I'd look at surplus places for your relay stash, that's where you get the cheap ones.


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## Lynn D Bennett (Jul 27, 2013)

John:

This may be a little complicated for the poster but here is a solution that might work without relays:

Use an auxiliary AC power supply and tie its common to the track common outer rail and the hot to the accessory. In the section where he wants the accessory to run, only isolate one outer rail and connected the isolated outer rail to the other terminal of the accessory. When the train hits the isolated section the wheels conduct from the un-isolated outer rail to the isolated outer rail completing the circuit for the accessory and the auxiliary power supply. It may be necessary to phase the track power to the auxiliary power supply just as we do when using the TIU and AIU with separate power supplies. It also depends on how the power supplies are made internally but if they are as most are made it should all work.

What do you think?

LDBennett


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## sjm9911 (Dec 20, 2012)

Or you could just directly power the switches? That way you have a constant power to them and no problem with slow switches.


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## ftauss (Sep 18, 2012)

sjm9911 said:


> Or you could just directly power the switches? That way you have a constant power to them and no problem with slow switches.


I believe that is what I said. I am seeking to directly power all switches and accessories at a constant voltage so as to avoid slow reaction times (or failures to activate) at lower train speeds. I am trying to determine the most cost effective and efficient way to trigger the accessories since I really can't afford to buy a half dozen or more 153IR or the MTH equivalent. Relays would seem to be a cost effective means since wiring for manual activation kinda defeats the purpose of a kid friendly layout.


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## callmeIshmael2 (May 28, 2012)

There are some great suggestions in this thread for using relays, but why go to the expense of anything other than wire when you're using FasTrack? If you google, "Insulate your own FasTrack", you'll get several hits on how to insulate FasTrack sections for accessory activation. It only takes a few moments with some care and a screwdriver and a trip to your local electronics store for under-the-rail connectors. Easy, fast, and the only expense is about 3-7 bucks on a little bag of connectors for the FasTrack. If you use your 1033 to power your accessories, you could have two separate feeds for, say, 12-14 volts and then less, or more for other action accessories on the variable 1033 (track power) signal.


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## Lynn D Bennett (Jul 27, 2013)

My suggestion of using the track as a switch without any relays is exactly the way the FasTrack switches do the anti-derailing feature when used with an auxiliary power source. It could be used for accessories too.

LDBennett


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## jwse30 (Jun 30, 2012)

I use insulated rail sections to activate relays for a few of my accessories. I think the 50 volt max you are referring to is the maximum voltage you can apply to the contacts before they burn up, so that's likely a good number (you can't get more voltage out of a relay than what you put into it).

I only use the relays for accessories that do something until the insulated rail has voltage on it, such as a green light on a block signal. When there is no train on the insulated rail, the light is on. As soon as the track is occupied, the relay turns on and turns off the light (and also turns the red light on).

For accessories that do something only when the insulated rail is occupied, such as a crossing gate, I use a second transformer set to a constant voltage as mentioned earlier in this post. To do that, I wire the constant voltage terminal to the accessory itself and the common to the insulated rail. I then run a wire between the insulated rail to the other terminal of the accessory. No relay needed, and constant voltage is applied to the accessory when the insulated rail is occupied.

Hope this helps,

J White


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## sjm9911 (Dec 20, 2012)

Ok, I don't have fast track and don't fully understand relays. But I do use insulated track, easy to make, for accessories activation. The wheels on the train running on the track complete the circuit. I also have my turnouts directly wired from a set terminal on my transformer, I assume you can do the same with fast track? My lights are also on a separate feed. The only problem I run into is finding the right operating powers for each accessorie. Once this is done you can hook it up to set power feeds from your transformers. Sorry if this is a bit scattered my daughter keeps saying trains over and over again. Time to fire up the layout!


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## ftauss (Sep 18, 2012)

jwse30 said:


> I use insulated rail sections to activate relays for a few of my accessories. I think the 50 volt max you are referring to is the maximum voltage you can apply to the contacts before they burn up, so that's likely a good number (you can't get more voltage out of a relay than what you put into it).
> 
> I only use the relays for accessories that do something until the insulated rail has voltage on it, such as a green light on a block signal. When there is no train on the insulated rail, the light is on. As soon as the track is occupied, the relay turns on and turns off the light (and also turns the red light on).
> 
> ...


That indeed was clear. I had not thought of this. Makes sense since the hot is on the accessory and returns via the common rail the loco itself does not get any additional voltage. Well then I think that works for me.


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## gunrunnerjohn (Nov 10, 2010)

One issue with using isolated tracks directly to activate stuff is the "chatter" you get as the conductivity changes with the rolling wheels. That's why my preferred method is to use a DC relay, a diode or bridge rectifier, and a capacitor. This allows me to have constant power without any variation until the insulated track is cleared. YMMV


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## Lynn D Bennett (Jul 27, 2013)

*John:*

Now I understand what you were doing with the capacitor and why you were using DC (diodes and rectifier)…. To hold a voltage on the relay coil so the relay stays energized regardless that the isolated track as a switch is opening and closing. But a longer isolated section of track would also solve that problem, I would think.

*For those in the dark about relays:
*
The capacitor charges up when the coil voltage is applied and discharges slowly when the voltage is removed, holding the relay energized. So as the charge on the capacitor is dissipated by the relay coil, the voltage on the coil has to drop well below the voltage at which the relay picked up. That is called hysteresis. 

LDBennett


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## gunrunnerjohn (Nov 10, 2010)

Actually, the longer section doesn't solve the chatter issue. Yes, once a bunch of wheels get on the track, it's no longer an issue. However, when the train first enters the section, the contact is not that good, that's when the relay chatters. That looks pretty silly with crossing gates, for instance. They bob up and down like they were possessed! Same effect as the train leaves the section, that last couple of sets of wheels can cause the same effect.


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## sjm9911 (Dec 20, 2012)

Lynn, thanks for the info. Grj, good thing I don't have any crossing gates! I do see the chatter on other stuff.


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## gunrunnerjohn (Nov 10, 2010)

sjm9911 said:


> I do see the chatter on other stuff.


That's what the capacitors are for.


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## Lynn D Bennett (Jul 27, 2013)

But the capacitor can only be used with DC power. Use it with AC and it will short out the power source. You have to use the diode with it to isolate it from AC.

You can get to DC from AC by putting a diode in series with the coil. John then puts a capacitor across the coil to act like a min-battery. Once the circuit is energized the capacitor charges and maintains a voltage on the coil if the circuit is momentarily interrupted. The time it maintains the coil is dependent on the value of the capacitor and the resistance of the coil and the drop-out voltage of the DC relay. John (gunrunnerjohn) has recommended about 100ufd as the value for the capacitor with the relays he uses.The voltage rating of the capacitor must be greater than the voltage being applied to it. 

LDBennett


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## Hutch (Dec 19, 2012)

I wouldn't have that that the coil resistance of a relay would be large enough to be significant. After measuring one on my bench at 719 ohms I can see that at is. Learned something today!
Thanks


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## Lynn D Bennett (Jul 27, 2013)

Hutch:

The time for the voltage to dissipate to 63% of the applied volute is the RC time constant. In the case of a 700 ohm coil and a 100 ufd capacitor that is about 70 milliseconds. The drop-out voltage is probably close to that 63% voltage factor so the capacitor will only hold the really energized for around 70milliseconds or 0.070 seconds. But that might be (??) enough to eliminate chatter as we would see it in a train layout running accessories. 

I have no such isolation track sections used as switches so I have no experience with this chattering of accessories. The exception is the anti-derail feature of RealTrax switches and they have internal switches on them that are actuated by the moving points to remove the coil voltage once the switch changes direction and there is no chattering there. But John has the experience and I would send you to him for experienced help if you or anyone else needed more info or help.

LDBennett


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## gunrunnerjohn (Nov 10, 2010)

The chattering is most evident on things with lights that will flicker, or in the case of our modular club, the scale crossing gates that wobbled for most trains coming through at the start and end of the signal period.

Non-derailing switches are a different animal, they have their own protection from these issues.


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## Pontiac787 (Aug 14, 2011)

jwse30 said:


> I only use the relays for accessories that do something until the insulated rail has voltage on it, such as a green light on a block signal. When there is no train on the insulated rail, the light is on. As soon as the track is occupied, the relay turns on and turns off the light (and also turns the red light on).



Hi J,

What relay type of relay are you using for this application? I want to do the same thing but I don't know what specs I should be looking for.

Thanks!


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## T-Man (May 16, 2008)

For using relays I found this helpful ,, The Toy Train Revue It's in the information section.


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## Pontiac787 (Aug 14, 2011)

gunrunnerjohn said:


> What I so is use a 12VDC coil relay with a diode, capacitor, (and an optional choke if you run DCS).


So to get this up an running for a two color signal it looks like the parts list is a 12VDC SPDT relay, a diode, and a 100 uf capcitor if using a short piece of insulated track. I am running DCS so do I need a choke? If so, is it anything specific?


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## gunrunnerjohn (Nov 10, 2010)

The choke (if included) is used for DCS (Protosound) compatibility. If you run strictly conventional or only TMCC, you don't need the choke.

The contacts of the relay are used to control the signal just like you'd wire it to a 153C contactor.


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## Pontiac787 (Aug 14, 2011)

I am running DCS. What type of choke should be used? What is the implication of not using one?


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## rkenney (Aug 10, 2013)

T-Man said:


> For using relays I found this helpful ,, The Toy Train Revue It's in the information section.


This is a terrible article. It refers to a section of center rail as insulated when they mean isolated and provide meaningless numbers on their relay with no explanation.

So to add to the confusion, if you're going to use readily available automotive 12v relays (buy them on e-bay bulk) there is a numbering convention that may be useful (most/not all, auto relays in use today).

The schematic is usually printed on the top or side of the relay:









The terminal 30 is connected normally to 87a and switched to 87 when terminals 85 and 86 (coil) are energized:









All the terminals accept readily available spade type crimp connectors:









For those of you still trying to figure out the schematics in the first article, the key is knowing that terminals 12 and 9 are the center (allways used) switch contacts (terminal 30 above).


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## gunrunnerjohn (Nov 10, 2010)

Pontiac787 said:


> I am running DCS. What type of choke should be used? What is the implication of not using one?


The capacitor across the tracks without the choke will degrade the DCS signal, so it's a real good idea to include one. 22uh is the value, I get them at Digikey.


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## T-Man (May 16, 2008)

Nothing like an honest revue. 

I don't have a problem with relays. Obviously the bridge connects to the coil. The in put is in the center two of the six pins. I see this setup on pc board type relays. This article is written off a video so maybe that is what they want you to do. 

It appears the GRJ method prevails here.:thumbsup:


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## gunrunnerjohn (Nov 10, 2010)

I use low current relays, that way the capacitor offers a time delay before they drop out, it avoids any chatter. Also, to avoid a spark when you start to charge the cap, a small resistor, say 22 ohms, is a good idea in series with the diode. The cap goes directly across the relay.


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## Pontiac787 (Aug 14, 2011)

GRJ, T-Man, and rkenney,

Thanks for all your input/advice. I have been able to learn something from all of your posts. I am a fairly mechanically minded person but I know very little about AC current and the Digikey website is a little overwhelming when you don't know what you don't know! I'm learning, slowly. GRJ - what do you mean when you say the cap goes across the relay? Does it not get wired in series to the input side of the relay?


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## gunrunnerjohn (Nov 10, 2010)

Here's a diagram of how to use this with an incandescent two-lamp signal. An LED signal gets switched the same way.


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## Pontiac787 (Aug 14, 2011)

Thanks for the diagram. Does the choke get wired in or does the wire get wrapped around it/run through it? The only chokes I have had experience with are RF chokes for noise reduction.


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## gunrunnerjohn (Nov 10, 2010)

The choke looks just like a resistor, it just gets wired in like any other component. It should have a current handling capability for the relay plus the surge charging current. I use 1/2A chokes, plenty for the job.


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## T-Man (May 16, 2008)

Nice diagram!:thumbsup:

I looked at my reverse thread and found the relay I used, a DPDT 12 v relay 275-249. That is the Radio Shack number. The little bag has the diagram and data information on the back.
I thought the car relay idea is a very good replacement suggestion. Buying in bulk has an appeal to me too.


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## gunrunnerjohn (Nov 10, 2010)

I like these relays to be low coil current devices, as that allows the capacitor to hold them up longer and kill any chatter due to the wheel contact.


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## Pontiac787 (Aug 14, 2011)

Alright, so I hooked up a SPDT relay to my Marx signal tonight. Green to NO Red to NC. When power is applied to NO the green light is lit. When I power the coil the red light goes on and the green light dims, but doesn't go out completely. What could be causing that? If I disconnect the power from the NO terminal the green light doesn't light so it doesn't seem to be that the current is leaking through the relay. Also, it there a way to quiet down the chatter? I did add a diode inline to the coil but it didn't make a difference.


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## trains galore (Jul 22, 2013)

Hi there
Relays can be a little confusing, the first thing is to understand what the contacts mean. NO (normally open) means that power will not flow from that contact to COM unless power is applied to the coil. NC (Normally closed) just means that power can flow from it to com unless power is applied. In short, normally just means the state of the connection WITHOUT any power
First thing is make sure the relay is hooked up right

If your relay has 2 contacts at the front and two behind them, you need to connect a signal to each set, then apply power through the set of contacts just above the coil, so that when the power is applied it will either flow to one or the other, but not at the same time

If on the other hand you have three contacts and the coil, you wire it a little different.
You need to connect both negative leads of the signals together. then connect the positive of your power supply to com and the remaining positive leads from your signal to no and nc. this will switch power through com to either nc or no contacts.

Without seeing it I can't tell if the wiring is wrong, but connect power to COM, NOT no or nc. Also you don't want to put a diode inline with the coil, always solder the diode ACROSS the coil (put it the right way though) You really don't need to worry about it too much while testing though, all it does is stop flyback
Also make sure your relay is operating correctly, you should hear a definite click when you apply power. If you have a multimeter, put it on continuity/buzzer and NO should conduct with com when the power is applied, and stop as soon as you diconnect the coil power.
If it fails this test, ditch it and get another one
If you have wired like I said and it still won't work, I would replace the relay, it may not be switching properly anymore
If you could post a picture of the wiring I can probably tell you what is wrong
Good luck!


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## Lynn D Bennett (Jul 27, 2013)

*Relays*

Maybe this will help understand relays.

The coil is energized by power applied to its coil's two input connections. That power energizes the relay.
The coil is an electromagnet that moves some contacts inside the relay. The contacts are labels NO, NC, and COM. The COM or common is where the lamp power for the lights is applied. One contact is labels NC or Normally Closed. When the relay is NOT energized the power on the COM will flow through the Normally Closed contact and light whatever lamp is connected to the NC contact if the other side of the lamp is connected to the opposite lamp power source terminal. When the relay is energized the power on the COM will flow through the Normally Open contact and light whatever lamp is connected to the NO contact if the other side of the lamp is connected to the opposite power source terminal. So one lamp is on with the relay coil not energized and the other lamp is out. They reverse illumination when the relay coil is energized.

The idea is to use separate power sources for the relay coil from the power source used to illuminate the lamps. For a signal the track power is used to energize the relay coil and the accessory power source is used to illuminate the lamps. That is usually the way it is done.

In your case you want the one lamp connected to the NO contact. The other lamp connected to the NC contact. One side of the power source connected to the COM contact and the other side of the power source connected to the opposite side of both lamps.

With more info we could give you a wiring diagram.

LDBennett


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## Pontiac787 (Aug 14, 2011)

Thanks for the replies. I do believe that I have the relay hooked up correctly. I was tired when I was typing last night. I have power to common, green gong to NC and red going to NO. When I apply power to the coil the red light comes on but the green light does not go out fully, it just dims. The relay also makes a buzzing sound as opposed to a single click. The relay in new but maybe it is bad.


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## Lynn D Bennett (Jul 27, 2013)

Most relay coils are DC. If you try and operate them on AC you might get the buzzing you described. The relay is literally turning on and off at 60 cycles per second. A diode in series will change the sine wave AC to half wave AC (the negative part of the wave is blocked). A capacitor across the coil will smooth the coil control voltage even more. I have not used relays on AC powered trains so I don't know how other do it but a series diode is what I'd try first then add a capacitor if that was not successful. I'd need more details about the relay coil to determine what size capacitor.

What do other do? Anyone?

LDBennett


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## Dave Sams (Nov 24, 2010)

Pontiac787 said:


> Thanks for the replies. I do believe that I have the relay hooked up correctly. I was tired when I was typing last night. I have power to common, green gong to NC and red going to NO. When I apply power to the coil the red light comes on but the green light does not go out fully, it just dims. The relay also makes a buzzing sound as opposed to a single click. The relay in new but maybe it is bad.


When I had an issue with one light not going out, I determined I had the common and power wires reversed. The result was the lights were wired in series.

Look at your wiring agian with a clear head.

Sometimes, I just have to walk away for a while


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## BigAl56 (Dec 14, 2011)

If this is a DC relay I find it best to use a small bridge rectifier to power the coil. The bridge has 4 connections. 2 output for DC and 2 input for AC. Connect the DC output leads to the coil (polarity should not matter), and the remaining 2 AC leads to the track power. That usually does it but if there is still chatter with a bridge place a 100uf 25v or greater cap across the coil and that should kill any chatter.

As for how to wire to a block signal it's a really simple circuit. The NO connection goes to the red and the NC to the Green. The common pole goes to power.


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## Pontiac787 (Aug 14, 2011)

Thanks all. Time to get back to the cellar for some more experimentation.


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## trains galore (Jul 22, 2013)

NEVER use 16vac power (without a bridge rectifier) as the relay may not operate properly. Check the output of the power source to the coil, and ensure it is DC. Also check the relay and make sure it matches with the voltage, eg if you have a 12v output to the coil make sure you have a 12v relay, I have picked up the wrong relay out of the box sometimes so double check
It is easier to just get the right relay/power source than to go through the hassle of making a bridge rectifier when you don't have to.
Relays should NOT buzz. Does it buzz on it's own, or only when you connect the lamps? I really don't think the relay sounds like it is working right, try testing it as you can waste alot of time only to find out it doesn't workhwell:
Also you want a seperate power source for the coil and the lamp.
I would start by checking what output voltage you have to the relay coil, I know how annoying electronics can be, you just have to go through systematically with the problem. Nothing in electronics is ever really random
Good luck with it!


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## Pontiac787 (Aug 14, 2011)

I was not able to get the relay to stop buzzing using a single diode. I hooked up a bridge rectifier and it worked like a charm. I also built my own using some extra diodes and the schematic on the back of the rectifier bag. Thanks all.


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## Lynn D Bennett (Jul 27, 2013)

Pontiac787:

If you take 60 HZ AC power which is a sine wave and only chop off the bottom by using a single diode then half the time the voltage to the relay coil is zero. That is what causes the buzzing…on then off then on and so on. When you add a capacitor of the right size it stores energy in the on cycle and gives it back in the off cycle which will eliminate the buzzing. Using the full wave bridge flips the negative going half (which was eliminated by the single diode) and inverts it to fill in the hole of the half wave rectified (single diode ) wave.

It is best to choose the full wave solution (bridge) because it might be difficult to find the right capacitor without some math and a box full of capacitor. It varies with the different relay coil resistances. Because the capacitor has to initially charge it can slow the response of the relay. The bridge is the real way to go and it is not that expensive. They make them in a single small package that you can get at a electronics supply house like Newark or Jameco.

LDBennett


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## Pontiac787 (Aug 14, 2011)

Thanks for the explanation Lynn. I think the bridge set me back $1.50. Definitley worth the price!


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## Dave Sams (Nov 24, 2010)

Lynn D Bennett said:


> Pontiac787:
> 
> They make them in a single small package that you can get at a electronics supply house like Newark or Jameco.
> 
> LDBennett


I just received 10 2A 1000v rectifiers from China for $2.15 shipped.

Of course, it took 6 weeks to arrive.......


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## Pontiac787 (Aug 14, 2011)

Can't beat that price!


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## gunrunnerjohn (Nov 10, 2010)

I use a single diode and a capacitor. It's really not that difficult to choose the capacitor, and one that's too large isn't a problem. For our signal relays on the modular club RR, I use a much larger than necessary capacitor so that there are several seconds of hold time to eliminate relay chatter because of poor track connections to the insulated rail.


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## Lynn D Bennett (Jul 27, 2013)

John:

Don't you find that as the capacitor voltage decays when the signal voltage is removed and the voltage passes through the relay dropout voltage that the relay chatters a bit? That would be my concern but whatever works. I don't have any relays on my layout so I have not run into this problem at all. Filtering the bridge output with the correct capacitor to match the load may be overkill (??). Its easy when you know electronics to get carried away when you spent your whole working life trying to make electronic circuits work perfectly and per the book.

Lynn….


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## gunrunnerjohn (Nov 10, 2010)

The relay doesn't chatter at all, and I would be amazed if that ever happened. The pickup voltage is significantly greater than the dropout voltage, so that is not going to happen. Even with low value capacitors that barely do the job, I've never seen one chatter if they have enough capacity to ride out the half-wave rectification.

I've had 40 years of electrical engineering, but for tasks like this, I don't typically waste my time trying to find the "perfect" match. I know by experience what will and won't work, and I can usually grab a few components from my parts bins and make it happen.

We like the relays for the signals on the modular layout as they totally isolate the signal power from all the spikes and the like on the tracks.


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