# Controlling Switches with Toggles



## SoCalStu (Dec 27, 2007)

Will LGB switches work from DPDT toggles using the AC posts? I want to build them into a control panel but I'm not sure the 2-lead switch motors will work like the 3-lead motors I used to wire in HO switches. Then I had to cross wire the toggle posts and wonder if I need to do the same for a garden layout using LGB or Aristo switch motors.


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## krs (Feb 29, 2008)

The LGB switch motors are essentially DC motors that require a reversal of polarity - very different from the three-wire H0 type switch motors. 

When using AC you need to add two diodes to give you either just the positive or negative half-wave as shown in the diagram below. 
You can also use DC and reverse the polarity but with DC you should limit the time the current is applied to one second or a bit less to make sure the switch motors don't burn out. 
For half-wave rectified 19 to 24 volts that is not an issue. 
As far as the controlling switch is concerned - well I'm sure you can figure out from the diagram what will work.


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## krs (Feb 29, 2008)

Sorry, the diagram didn't show up - try pasting this in your browser: 
http://www.altek.nl/graphtips/EPLsturing.gif


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## stanman (Jan 4, 2008)

Hi Knut,


I've used the "standard" circuit for about 10 years without problem. 

I hadn't seen the "improved" circuit with capacitors before. Do they protect the switch contacts, or the motor?


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## krs (Feb 29, 2008)

Posted By stanman on 16 May 2010 02:39 PM 
I hadn't seen the "improved" circuit with capacitors before. Do they protect the switch contacts, or the motor?




Hi Stan -

The "standard" circuit is exactly what LGB uses in their switch controllers.
The problem with it is that the switch only receives half-wave power as shwn on the right in this diagram:










You can see that the equivalent DC voltage is relatively low - I think it works out to about 7 volts across the switch so for longer wire runs to the switch tere is sometimes not enough power to throw the switch reliably.


The "improved' circuit does not protect either the switch contacts or the motor.

What happens is that each capacitor charges up to the peak voltage of the AC waveform (ie 1.4 times the rms voltage minus the diode drop) and then when the switch is thrown, that full capacitor voltage is connected across the LGB switch motor to operate it. Since the voltage is much higher the switch will throw more reliably especially over a long wiring run to the switch motor.
But because it's the discharge of a capacitor which only lasts a second or less, the motor is also automatically protected against overload and burn out.
If you applied that full voltage, 33 volts or so, for any length of time, the coils in the LGB motor would burn out. 


There are a variety of other circuits that can be used with LGB turnouts to solve specific problems. 
One I find interesting is where a non-polarized capacitor is used in series with the control lead - that allows turn out operation with a control wire that can have a resistance of 100 ohms or even slightly more.


Knut


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## stanman (Jan 4, 2008)

Knut - Thanks for the explanation.


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## toddalin (Jan 4, 2008)

I've run the "improved" version all along. It gives the turnouts a nice initial kick, but the voltage quickly bleeds down if the toggle is held for any reason. Mine fires as many as 20 turnouts simultaneously.


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## SoCalStu (Dec 27, 2007)

Now I could pretend to know what the diagram shows but, being electronically challenged, I'll show my ignorance by asking if there is there a simpler drawing of what goes where for a G gauge newbie? Thanks for your expert knowledge and help!


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## Dan Pierce (Jan 2, 2008)

You need a SPDT (Single Pole Double Pole) center off momentary switch with diodes added to control the LGB EPL units. 

Or 2 push button momentary switches like the above diagram shows.


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## toddalin (Jan 4, 2008)

Posted By Dan Pierce on 17 May 2010 09:04 AM 
You need a SPDT (Single Pole Double Pole) center off momentary switch with diodes added to control the LGB EPL units. 

Or 2 push button momentary switches like the above diagram shows. 



Let's not confuse this any more than we need too. The diagram shows the SPDT. It only looks like two push button momentary switches, but that's just because they are showing the provisions for additional turn outs beyond the one shown.


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## Wesley Furman (Jan 2, 2008)

Or on the lighter side, why not just throw the switch using Legos.

http://gizmodo.com/5535743/the-most...go-machine

Wesley


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## Dan Pierce (Jan 2, 2008)

Sorry, but the diagram does not have text with the fact the switches need to be momentary and center off. 
Electronic gurus would know this, but others may not.


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## krs (Feb 29, 2008)

Posted By Dan Pierce on 19 May 2010 06:06 AM 
Sorry, but the diagram does not have text with the fact the switches need to be momentary and center off. 
Electronic gurus would know this, but others may not.




Yes - there is no text but the symbols shown for the switches do show a centre-off switch the way the one arm of the switch is drawn pointing to the centre part of the switch and not being connected to either of the two contacts.

As to momentary, the need for that depends on the rest of the circuit.

If the current through the switch is low enough, ie using the half-wave rectified arrangement, then the switches do not have to be momentary but in that case there would be continous current drawn from the supply. The EPL switch motor is designed to operate in this manner since this is electrically the same as the switch being trown by the LGB track contact (reed switch) and the engine stopping at that point keeping the track contact operated continuously.

Some people like that way of operation since it gives them a visual indication of the position of the turnout at the control switch. It's not position feedback from the switch which is rather difficult to implement on those switches controlled by just two wires and a polarity reversal.

If one uses +/-24 volt DC to operate the switch one needs to limit the amount of time the DC voltage is applied. One second maximum is recommended as I noted earlier. In those cases a momentary switch would be the way to go.


With the capacitors and an 18 to 24 VAC supply (and the two diodes) one could use a regular two position SPDT switch without a centre-off position if one doesn't mind the continuous current draw - as long as it is half-wave rectified AC it will not burn out the switch motor.

All seems very simple but many years ago LGB put a lot of thought into the electrical control of this system.
The very first LGB switches actually used the conventional three-wire switch motors - I just saw those ancient ones on sale at a dealer in Germany.


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## toddalin (Jan 4, 2008)

Posted By krs on 19 May 2010 07:38 AM 

As to momentary, the need for that depends on the rest of the circuit.

The EPL switch motor is designed to operate in this manner since this is electrically the same as the switch being trown by the LGB track contact (reed switch) and the engine stopping at that point keeping the track contact operated continuously.


With the capacitors and an 18 to 24 VAC supply (and the two diodes) one could use a regular two position SPDT switch without a centre-off position if one doesn't mind the continuous current draw - as long as it is half-wave rectified AC it will not burn out the switch motor.




Couple problems here.

While the EPL can take continuous half wave, I don't believe they were really intended to, nor does LGB power them continuously with any of their accessories that I am aware of. While stopping an engine with a magnet over a reed switch, keeping the reed active, does happen on occasion, this is definitely _*NOT*_ intended, and the train is supposed to pull past the reed before coming to final rest. If you are running a "leap frog" and have a magnet parked over a reed sending continuous power to the turnout(s), when the other engine comes home to roost and trips its reed, the combination is sending simultaneous + and - voltage to the turnout and _can_ pop a fuse (or worse). (I smoked diodes simultaneously receiving + and - 22 volts when trains have "parked" over reed switches. But I've revised my circuits so this just can't happen anymore even if both reeds are activated simultaneously.)

If the capacitors are big enough, this essentially becomes a quasi-pure dc supply and the continuous application of power can overtax the EPLs in short order. If the caps are too small, then the continuous application of power to the EPLs will bleed off some/most of the voltage increase associated with the caps so their addition becomes near pointless.


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## krs (Feb 29, 2008)

You're right - I shouldn't have posted the option to apply permanent power to the LGB switch motors. 
To use that option successfully one needs to understand electronics in general and the characteristics of the LGB switch motor itself. 

Using a momentary switch is pretty much foolproof.


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