# what is a self latching relay?



## Big Mike (Dec 2, 2011)

I am told I need a self latching relay,I have heard of them but never needed one before,now I have a need for one ,where is the best place to buy them?........mike


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## gunrunnerjohn (Nov 10, 2010)

I asked in the other thread, what do you need it for?


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## BWA (Jun 16, 2012)

A normal non self latching relay is "on" when you apply power to it, too keep it "on", you need to keep power to it. They run warm.

A latching relay only needs a short application of power to keep it "on", and, it will stay on without needing to keep the power applied. They run cool.

Any online electronics supply house will have either.


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## gunrunnerjohn (Nov 10, 2010)

I posted an example in his other thread, the Atlas Snap Relay M200.


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## Big Mike (Dec 2, 2011)

gunrunnerjohn said:


> I asked in the other thread, what do you need it for?


 
well, sense I have been having trouble with Atlas turntables,but still have a need for one,I googled "how to build an "o" scale turntable " and found several ways to go,including ones custom built to your specs.but,they don't have the" auto stop" it's a line of sight,you stop it your self,and hope its lined up with your track, set up ,this might be fine if your turntable is close enough to you to see that,mine wouldn't be,it would be hard to make sure every thing is in line.
so taking the idea from Atlas,..kinda,, and using self latching relays,to stop the rotation every 15 deg.,it would line up perfect every time. 

your thoghts,comments,ideas, pros and cons are welcome, so please feel free to tell them to me...Mike


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## Big Mike (Dec 2, 2011)

BWA said:


> A normal non self latching relay is "on" when you apply power to it, too keep it "on", you need to keep power to it. They run warm.
> 
> A latching relay only needs a short application of power to keep it "on", and, it will stay on without needing to keep the power applied. They run cool.
> 
> Any online electronics supply house will have either.


this is what I tought, ok but what makes it un latch? braking a ground with a micro switch or somthing ?? ..............Mike


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## gunrunnerjohn (Nov 10, 2010)

Well, a latching relay won't stop the rotation exactly in line. What is really needed is feedback from the table to indicate when it's aligned. A latching relay is a simple two-state device that makes or breaks electrical contacts.

There are a couple ways to do the table. You can have a servo with optical sensor to index the table. You can also use a stepper motor and count steps to index the table.

I've often thought that a good system for the table would be a stepper with a mechanical lock. When you drove the stepper motor, you'd retract the locking pin and rotate the table with the stepper motor. When you reached the end point, you'd de-energize the stepper motor and drop the pin to position the table exactly.


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## Big Mike (Dec 2, 2011)

gunrunnerjohn said:


> Well, a latching relay won't stop the rotation exactly in line. What is really needed is feedback from the table to indicate when it's aligned. A latching relay is a simple two-state device that makes or breaks electrical contacts.
> 
> There are a couple ways to do the table. You can have a servo with optical sensor to index the table. You can also use a stepper motor and count steps to index the table.
> 
> I've often thought that a good system for the table would be a stepper with a mechanical lock. When you drove the stepper motor, you'd retract the locking pin and rotate the table with the stepper motor. When you reached the end point, you'd de-energize the stepper motor and drop the pin to position the table exactly.


UMMMM,key-mo-sobie,me dum,me don't understand dis,UMMM :laugh:...Mike


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## Big Mike (Dec 2, 2011)

*turntable*

Ok,how about I forget the hole thing with the turntable idea,cause now I am seriously confused .............Mike


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## gunrunnerjohn (Nov 10, 2010)

What can I say, you asked the question. 

It takes a bit of technology to automatically index a turntable and stop it exactly, I can't change that fact.


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## BWA (Jun 16, 2012)

The next shot of electricity unlatches the relay.

Kind of like, a push/on, push/off, push/on thing with just the one on off button.

I'm with grj, I would use a stepper motor, with a tooth belt, and, a programable driver board. If the stepper motor is geared about 20:1, you could get dead nutz alignment with no relays, no detents or, latches of any kind.

The table would stop within a couple of thou. every time wherever you programed it.


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## BigAl56 (Dec 14, 2011)

Self Latching relays were used all the time in my pinball days. Its using one relay to hold closed another. I use this principle to operate signals. Back in the day you would reset the extra ball relay on an old E&M pinball machine with a eb relay controlled by the ball reset relay. It's just putting the coil of one relay in series with the contacts of another.


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## gunrunnerjohn (Nov 10, 2010)

I used to fix pinball machines and jukeboxes in high school for the local distributor. I built my last HS Science Project from old bowling machine parts. Those latching relays are a tad large for our use however. 

In Mike's other thread, I posted a picture of the Atlas Snap-Relay M200, which is a train oriented latching relay. Here it is.


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## sjm9911 (Dec 20, 2012)

I know nothing of turtables or low voltage switches . But taking grj idea of having a hard pin to set the table. Having it automated would be better but I would never be able to do that. Here is my low tec idea. How about somthing like a slide spring bolt that has pressure behind it when it reaches its set point the spring pushes the bolt into a hole locking the turntable in place. You would need to figure out how to disconect power at this point. Maybe when the bolt latches it automaticly cuts off power to the motor? The slide spring then could be disingaued mechanically or manualy by use of springs and pullys. Just an idea it could be a bad one. I dont even know if this is even possible.


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## gunrunnerjohn (Nov 10, 2010)

You can just use a spring loaded detent on the table and when the motor runs it's pulled in with a solenoid to allow the table to rotate freely, when you stop the motor, the pin drops. Of course, if you're doing all of this manually, you need to be able to see the table so you know where to stop. The pin will solve the problem of the tracks not exactly indexed. Using this method, I'd use a belt drive so there's a little "slop" in the system to allow the pin to center the table without fighting some gears.

Like I said, there are many ways to skin this cat, it depends on how high-tech you want to go, as well as the requirements you have placed on the operation.


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## NIMT (Jan 6, 2011)

Mike,
What you want is a relay latch, to act as a stop when the tracks are alined.


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## T-Man (May 16, 2008)

The easiest way to line up a turntable is a piece of metal and magnets at the stop. When turned of close to the point the magnets take over and line it up. Hopefully will be weak enough to let go when you restart. This is just a theory and may never have accomplished before. Maybe the metal track may be enough or get fancy and use an electromagnet. That will give on and off locking.


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## sjm9911 (Dec 20, 2012)

Grj, I was hopefully using the pin as the stop and line up. It would have pressure on it all the time sliding along untill it hits the hole where it would engage. The seloinod would be used momentarly to pull the pin out. After the table moves a bit the pin would be engaged sliding along the table untill it stops at the next spot. You would need to see the starting position only and count off stops from there. In theory anyway. Six of one a half dozen of the other. You are right though, lots of way to achieve the same thing!


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## gunrunnerjohn (Nov 10, 2010)

Actually, you don't want the pin sliding all the time I would imagine, makes it harder to turn the table smoothly.


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## sjm9911 (Dec 20, 2012)

Good point.


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## servoguy (Jul 10, 2010)

For me, the easiest thing to do would be to build a servo. I make servos for a living, and have built about 2000 servos over the last 45 years. Easy way to build a servo is to use a DC motor with a gear head attached. Good old Skycraft in Winter Park Florida has bins full of DC servo motors with gearheads. Now I need some feedback which could come from a Sine/Cosine pot so it will be continuous. Then a Sine/Cosine pot to drive it and some detents to cause it to align properly with the track. 

An alternative way to do it is to use a stepper motor. Steppers are very cheap but the easiest way to do it is to use a stepper big enough for a direct drive. Then concerns about backlash in a gearbox don't exist. Realize that the positioning of a stepper can be quite accurate, but if there is backlash between the stepper and the turntable, the turntable will not necessarily be where you expect it to be based on the position of the stepper motor. It should be possible to use a toothed belt drive to get some reduction between the stepper motor and the turntable. It should be possible to get a kit or controller from someone to drive the stepper.


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## Big Mike (Dec 2, 2011)

NIMT said:


> Mike,
> What you want is a relay latch, to act as a stop when the tracks are alined.
> View attachment 25329


well, with this relay latch,I could use a clutch drive witch would run,and turn the turntable,this latch would drop into a hole ,stoping rotation,then the clutch would "slip" until power is cut,or the relay alowed it to go to the next stoping point..............no?........Mike


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## Big Mike (Dec 2, 2011)

BWA said:


> The next shot of electricity unlatches the relay.
> 
> Kind of like, a push/on, push/off, push/on thing with just the one on off button.
> 
> ...


 
Thanks.............Mike


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## gunrunnerjohn (Nov 10, 2010)

servoguy said:


> For me, the easiest thing to do would be to build a servo. I make servos for a living, and have built about 2000 servos over the last 45 years.


While I've designed a few servo driven items in the past, I doubt for most folks that would be the easiest method.  For one, for precise positioning, you have to have an accurate feedback mechanism to determine the table position. For aerospace applications we frequently used synchro feedback, and sometimes for a precision pot. However, most of the instrumentation servo loops gave way to stepper motors, as they were easier and cheaper to build.

Steppers are much easier as you can adopt the low-tech solution and just count the pulses to position the table. For steppers, I have an index point with an optical sensor to determine the "zero" point. That way you can determine where you are from a cold initialization.


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## NIMT (Jan 6, 2011)

Big Mike said:


> well, with this relay latch,I could use a clutch drive witch would run,and turn the turntable,this latch would drop into a hole ,stoping rotation,then the clutch would "slip" until power is cut,or the relay alowed it to go to the next stoping point..............no?........Mike


That will work, or when the latch drops into place it hit's a micro switch which cuts power to table motor. 
The start would be a simple push button switch that would disengage the latch long and start rotation you would release the button when close to your stop then the latch would kick in.
Oh and if you want the relay latch that I have just say so I'll send it to you!


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## Big Mike (Dec 2, 2011)

NIMT said:


> That will work, or when the latch drops into place it hit's a micro switch which cuts power to table motor.
> The start would be a simple push button switch that would disengage the latch long and start rotation you would release the button when close to your stop then the latch would kick in.
> Oh and if you want the relay latch that I have just say so I'll send it to you!


That would be cool YES please at least I will have a starting point.
I will PM you my address... THANKS.............Mike


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## timlange3 (Jan 16, 2013)

I have buddy that built a HO turntable. He used a DC motor with a rubberband to a large wheel under the table to act as a reduction unit. A lot of motor rpm rotates the table slowly. Using an old controller with rheostat he 'runs' the motor like a train, at slow settings he can eyeball the rails and stop the table where needed without a problem, it can move that slow. When I tried it, took about 20 seconds the first time to line the rails, I got quicker the more I used it. This would be prototypical operation!


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## servoguy (Jul 10, 2010)

I like the simplicity of this approach


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## sjm9911 (Dec 20, 2012)

Big mike , I hope you find a solution soon. Good luck!


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## Big Mike (Dec 2, 2011)

sjm9911 said:


> Big mike , I hope you find a solution soon. Good luck!


 
I'm gaining ground and new ideas by the min.with all the help here,plus all the info on line,I don't see how I could miss,I would like to take pictures in stages,and post them with breef discriptions of each step so if some one else would like to try one,they could skip all the mistakes I am going to make :laugh:.............Mike


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