# SCRs & Latching relays

#### maassmi

Joined Oct 30, 2011
81
Hi Again, I tried to send out a question about a project and messed up. Sorry. Here is my second attempt:

I have been told that I can use a SCR to replace DPDT "latched" relays in the following project: From a transformer, I have both AC and DC power. The AC goes to a "momentary" on-off-on slider switch. Slide to left, push it in and release, hense the momentary. This engages my track turn out in that direction. Slide the button to the other side, push and release and it switches the turnout to the other direction. The momentary switch has three wires connecting it to the turnout motor, one for one direction, one for common and one for the other direction. The switch motor is an engerized coil that mechanically moves the switch.

Here is where I need your assistance: From the same outputs on the momentary slider switch, I connect wires to a DPDT latching relay. This latching relay has an input for DC + power and two DC + outputs. Engage the the switch in one position, the DC power goes out one output, for example a Red LED. Engage the switch in the other direction and the DC power goes out the other output terminal to my Green LED. I have been told that I can use a SCR to replace this latching relay. I can't figure it out.

I am a novice at this electrial stuff and can't read electrial diagrams worth a beans. I don't know that I want to quit using the latching relays, but the one provided by the "hobby" and Atlas #200 Snap Relay takes up allot of space and are expensive if you need allot of them, which I do. I am looking for a space and money saving method of replacing the the snap relay (DPDT Latching relay). I will attempt to attach a diagram that I created using "Paint" (bitmap drawing) illustrating what I am currently doing. Maybe some out there can help me save money and space. Because I had to shrink it in size in order to post it, you may need to open it, save it and enlarge it in order to view the diagram. Thanks.

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#### praondevou

Joined Jul 9, 2011
2,942
Because I had to shrink it in size in order to post it, you may need to open it, save it and enlarge it in order to view the diagram. Thanks.
It's too low in resolution now. Can't read any of the comments.

Take your original diagram and save it as .png .

#### bertus

Joined Apr 5, 2008
21,360
Hello,

The drawing is to small to recognize anything.

The drawing is im BMP format wich needs an external program to view.
Please post drawings in .PNG format if possible.
If that is not available you can use .JPG.

Bertus

#### maassmi

Joined Oct 30, 2011
81
Here goes. Hopefully you can view this:

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#### SgtWookie

Joined Jul 17, 2007
22,221
Schematic for the Atlas #200 relay & misc info: http://www.customsignals.com/documents/Atlas200SnapRelay0001.pdf

I'm afraid that SCRs won't work for you, as once they are turned ON, they need the current flow through them to drop to near zero before they will turn OFF. Also, since you want to power LEDs with them, the current flow through the LEDs will be so low that it will be difficult to find SCRs that would stay ON with that little current.

The Atlas #200 relay has a property that will be tough to match electronically; a "memory" that stays whether power is on or off. You can set switch points to straightline or turnout, then kill the power for 10 seconds or 10 years, and the #200 will still be "in sync" with the switch points when powered back up. That won't be the case with an "easy to build" electronic circuit; you would have to manually set each switch point to sync the lights.

Rather than try something electronically, it may be possible to do something electro-mechanically by using a lever-action SPDT switch that's tripped by contacting something that's moved by the turnout motor - but we have no idea what your turnout motors look like.

Something like this:
http://search.digikey.com/us/en/products/MS0850504F020S1A/EG4547-ND/1628284

Those are about $1/ea when you buy 10 of them. There are 3 terminals; one common, one N.O. and one N.C. You could use one current limiting resistor on the common terminal going to your DC+V, and connect the anodes of the LEDs to the N.O. and N.C. terminals; the cathodes of the LEDs going to your DC return (V-). No seemingly complicated electronics involved. There are MANY such switches available. They're basically known as snap-action limit switches with levers. Radio Shack even sells a couple of them, but they are rather large, and you want them to be quite small. There are ways to determine the position of the switch electronically using optoelectronic sensors (optointerruptors), but I suggest you have a look at using the lever limit switches to see if that works first. Last edited: #### djsfantasi Joined Apr 11, 2010 7,688 From your post, I am guessing that you are also using Atlas switch machines to move your turnout points. There are other solutions,such as the Tortoise Switch Machine that includes the contacts necessary for displaying the position of the switch points. I have also used the microswitches suggested by SgtWookie by extending their level with a piece of stiff wire through a hole in the roadbed and the switch tie Thread Starter #### maassmi Joined Oct 30, 2011 81 Sgtwookie, thank you for providing this solution. Only problem is that I don't want to have the switch on the top of the table and I don't really want to crawl around under the table and find a way to attach the switch to the turnout. Basically the turnouts have one loose tie that slides back and forth moving the sliding rails from one position to another, so, physically this is a great idea, but visually, not so much. I am attaching another drawing I have made. Hopefully it will fit. It shows two Latching relays that I have been shown. For the first one, I don't know how to connect the wires. This is also a very inexpensive relay. For the second one, I have been shown how to connect the wires, but I am not positive I got it right. This the relay I was shown costs about as much as the Atlas snap relay. I am looking for something a little less costly. Are you familiar with either of the relays I am attempting to illustrate? Or is anyone out there familair and can help? Thanks. #### Attachments • 32.2 KB Views: 48 Thread Starter #### maassmi Joined Oct 30, 2011 81 I am trying to stay away from trying to mount the under the table switch machines because crawling around under the table and mounting these to track that is as much as 9 inches above the table top is not practical for me. My skill level is just not that good. Thanks for the suggestion though. #### SgtWookie Joined Jul 17, 2007 22,221 We need the part number for the relay. We also need to know what is the AC voltage that you have available. Is it 16VAC? I suggest that using a relay with 110VAC/120VAC coils would NOT be a good thing for your RR. It would involve high voltage wiring that would be a safety hazard. It IS possible to use low voltage AC for LEDs, but you would need to use a DPDT relay or switch. #### djsfantasi Joined Apr 11, 2010 7,688 Why are you trying to replace the Atlas Snap Relays? Where are they mounted? I have hidden microswitches on the table top with scenery tricks in my layouts (I am a model railroader)... was wondering if that could be viable for you. What track gauge are you working with? How many turnouts are there? And what is your budget? I have several ideas, but it depends on where the relays are mounted and if you can modify your control panel as well. I am guessing that you are using the Atlas controllers, as the description of the control mechanism matches the Atlas product. Since you don't have good access under the table, I was wondering where you were planning on mounting any control circuit that we can devise for you. Last edited: #### SgtWookie Joined Jul 17, 2007 22,221 I found a couple of low-voltage latching relays that might work for you. DPDT single 12vdc coil, latching, 2A @ 250V contacts,$2.40/ea when buying 25:
http://search.digikey.com/us/en/products/D3046/PB1117-ND/1634003
DPDT dual 12vdc coils, latching, 2A @ 250V contacts, $2.50/ea when buying 25: http://search.digikey.com/us/en/products/D3066/PB1115-ND/1634001 Datasheet for both: http://documents.tycoelectronics.co...08-98005GpdfEnglishENG_SS_108-98005_G.pdf These could be used with AC and diodes to set or reset the relays. Once a relay is set or reset, it will stay in that position. I think you use 16VAC to set/reset your switch points. If 16VAC is half-wave rectified, the output will average ~11.3v. Thread Starter #### maassmi Joined Oct 30, 2011 81 Hi Fellow model railroader, I am using HO scale. I will try to attach a couple of photos so you can see what I am currently doing. Cheap, cheap, cheap... I have a little panel (sheet of plywood) mounted on the table side just to the right side of the panel that is visible in one of the attached photos. Also, for additional pictures and videos, you can go to my Facebook Page (Michael Maass) Photographs are shown in the folder titled "Rocky Lines" and short videos are somewhere in the collection of videos. These photos have been set up for public viewing so you don't have to "friend" me if you choose not to. I really don't have a budget. I used whatever my wife lets me which until Christmas shopping is nothing. Yes, I am using all Atlas controllers, etc. I have some Peco turnouts with table top switch motors, but they function just like the Atlas ones do, three wire AC. I am using an old MRC Command 2000 DCC controller which also allows me to operate an anolog engine as well as two DCC engines easily enough. My layout has only about 1/3 of the track laid. Eventually the main layout will be horseshoe shaped layout with a single tip out across a walkway to a yard. I am using an old standard transformer with DC and AC outputs to engergize the switches and LEDs. This section alone has 12 turnouts. When the mail layout is completed I will have at least 8 more turnouts and the yard will probably have an additional 12 to 20 if I have enough space. The yard has not been planned out yet. I was just going to "wing it" here. The Atlas snap relays cost around$10 each, even on eBay used. Every now and again I have a dealer who has a supply of old stock which are considerably less expensive, but even at $8 a piece plus shipping, I would rather buy the little relays at$3 to $5 each, especially since they take up much less space. In addition to using LEDs at the sight of the Atlas switch controllers I am setting up switch lights at each of the turnouts. I really appriciate the willingness of everyone out there to help "brainstorm" with/for me. My brain has been going numb with frustration over the additional costs for this project of mine. Michael #### Attachments • 294.1 KB Views: 41 • 292.8 KB Views: 34 Thread Starter #### maassmi Joined Oct 30, 2011 81 Hi again. I more of the information that has been requested for you: I am attaching a couple of photographs which will answer those questions. #### Attachments • 294.6 KB Views: 34 • 293.9 KB Views: 27 #### SgtWookie Joined Jul 17, 2007 22,221 Hmmm - you're going to run out of current mighty quick if you want to power lots of LEDs. Your supply is rated 5.5VA (basically, 5.5 Watts) - that's about 290mA @ 19VAC. One of the old-fashioned Christmas tree light bulbs is 7 Watts! You might consider converting an old ATX or ATXplus12 form factor personal computer power supply for use as a "bench" supply. You would have LOTS of power available then; and those computer supplies can be pretty efficient. One of my favorite surplus suppliers has 150W ATX power supplies on sale for$5.95:
http://www.mpja.com/150WATT-ATX-COMPUTER-POWER-SUPPLY/productinfo/18034+PS/

#### maassmi

Joined Oct 30, 2011
81
How would I "half wave rectify" my current? Just these words are above my head...

I have to say though, the replies I have received thus far have been quick and full of great information and ideas.

#### maassmi

Joined Oct 30, 2011
81
Thanks for the power supply idea. If I do run out of power, I have two more of the old model train transformers available. I am thinking that with only 50 or so LEDs on at one time, I should have plenty of power as the LEDs I have set up now are quite bright and could use a little dimming. But one thing at a time.

Oh, on the other side of the "U" of my layout, I will have an additional control panel for those turnouts, so I will be using one of my other old model train transformers for that panel. and it will probably look much like the mess I have already, but without the Command 2000 controller. And then later, the yard will have its own control panel as well. Hopefully I will be able to acquire and old walk around 2000 unit on eBay or something to make running the engines in the yard easier. Either that or I will have to save up some money to upgrade my DCC equipment. Keep the ideas coming. They are all helping me think about what I am doing...

#### djsfantasi

Joined Apr 11, 2010
7,688
SgWookie had a great find! Those latching relays can be used to do what you need. But we need to figure out how to connect them with diodes so that the Atlas controllers can be used. Basically, the Atlas controller switches AC (DC will work) to either one or the other coil of a dual coil solenoid. We need to reverse polarity to the set/reset inputs of the latching relay, while routing the AC to the normal or reverse coils of the Atlas switch machine.

#### maassmi

Joined Oct 30, 2011
81
Ok, that is cool. But I am confused by such things as reversing the polarity, etc..... Here is a photo of one of my LEDs that I have attached a resister to. This one happens to be green, hense the green wire that is used for the positive feed.

Ok, in regards to the great find by Sgtwookie, which has me excited, can you draw me a picture making it easy for me to understand what to do, similar to those I have drawn using "paint" a basic program in the "accessories" section of the menu which comes preloaded on all "Windows" computers? If I need stuff I don't have, what are these things other than the relays which Sgtwookie found and where in the picture do they go?

I am getting real excited here!

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#### maassmi

Joined Oct 30, 2011
81
On another forum it has been suggested that I use an SCR. This person sent me a diagram as well. These are also pretty inexpensive. What do you folks think, or is this going in a different direction?

Either way, I need someone to draw a diagram that is more simple than schematics like this one to illustrate which wire goes where because my knowledge is a little below this level.

Thanks.

Mike

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#### SgtWookie

Joined Jul 17, 2007
22,221
On another forum it has been suggested that I use an SCR. This person sent me a diagram as well. These are also pretty inexpensive. What do you folks think, or is this going in a different direction?
The trouble with using SCRs and "active" latching relays, is that for one thing they constantly use power when energized, and the other thing is that they "go stupid" when the power goes off. They have no memory once the power goes away.

The latching relays I linked to at the top of the 2nd page are both latching-type relays; once you send a burst of electricity through a coil in one direction, they will stay latched in that position until you send electricity through the coil the other way. It won't matter if the power goes off; it will "remember" it's last state.

Either way, I need someone to draw a diagram that is more simple than schematics like this one to illustrate which wire goes where because my knowledge is a little below this level.
It's quite a bit too late tonight to do that. Perhaps later in the day.