Push Button Switches /

[amdaley]

Hello Everyone.

I am searching for decent push button switches for point operation. All the switches I have looked at are low amps type which I reckon won't last long with the 3 or 4 amps that Peco or Seep point motors draw. Does anyone know where decent push button switches can be got.

These will be used on a control panel so will need to be tidy in size but will also need to be about 3amp 125volts ac capable.

Thanks everyone.

[Dagworth]

If you are using a CDU with your point motors then once the CDU has fired it won't recharge until the circuit is interupted. Therefore the switches will not be breaking heavy current so you can get away with using much lighter duty switches than you would think. It is the arc on breaking a heavy current that will destroy the life expectancy of smaller switches more than the current flow on making the contact.

 

Andi

[amdaley]

If you are using a CDU with your point motors then once the CDU has fired it won't recharge until the circuit is interupted. Therefore the switches will not be breaking heavy current so you can get away with using much lighter duty switches than you would think. It is the arc on breaking a heavy current that will destroy the life expectancy of smaller switches more than the current flow on making the contact.

 

Andi

 

Hi Andi.

When I press the switch will the heavy amps going through the switch not cause the same problem ? I was going to wire in an old CDU I have here (unused from years ago) I wired up the CDU this evening to try it. I was using the AC output from an old DC controller.This output measured 17volts Ac. When I had it connected up I measured the CDU output & I got 22.9volts DC. I thought that using DC in an Ac rated switch was what did the damage to the contacts ?

There is a diagram here of what I was going to do.

 

http://www.flickr.co...and/4727193632/

 

So I suppose what you are saying is that if I use a CDU I won't have a problem with lighter switches. I would only have a problem if using the AC from a power supply where the heavy amps would flow all the time.I hadn't thought of it that way.

[Dagworth]

Tony,

 

Are you aware of this circuit which allows the use of an ordinary SPDT switch to control a twin solenoid point motor? No push button required, and the switch gives an indication of which way the point lays.

Each time the switch is thrown one cap charges through the point motor coil, and the other cap discharges. Once the cap is charged then no further current can flow. It can be worth adding a diode in series with the input resistor to prevent back feeding of other point motor cap networks. It's also possible to put a pair of LEDs with 10k series resistors across the coils of the point motor to give a remote indication of point correspondance

 

Andi

[amdaley]

Tony,

 

Are you aware of this circuit which allows the use of an ordinary SPDT switch to control a twin solenoid point motor? No push button required, and the switch gives an indication of which way the point lays.

 

Andi

 

Hi Andi.

No I had not seen that diagram. I take it that it is run on 16volts DC. Is there a limit on the amps that the DC power supply can put out ?

I ask because I have a laptop power supply/adapter which put out 15.2 volts Dc @10amps or is it easier to just use a CDU using the 17volt Ac output from the old DC controller & cheap push buttons ?

[Dagworth]

Hi Andi.

No I had not seen that diagram. I take it that it is run on 16volts DC. Is there a limit on the amps that the DC power supply can put out ?

I ask because I have a laptop power supply/adapter which put out 15.2 volts Dc @10amps or is it easier to just use a CDU using the 17volt Ac output from the old DC controller & cheap push buttons ?

The circuit will run quite happily on a low current power supply as the input resistor limits the charge current to the caps to only a few milliamps per circuit, and it's unlikely that more than one circuit would be charging at a time.

I've used the circuit for years on Dagworth and have continued its use on the non tortoise controlled points on Ravensclyffe. I've NEVER had a point motor fail in use on either layout, though I did get a huge bang once when I had one of the caps wired up back to front The cap exploded!

 

Andi

[amdaley]

The circuit will run quite happily on a low current power supply as the input resistor limits the charge current to the caps to only a few milliamps per circuit, and it's unlikely that more than one circuit would be charging at a time.

I've used the circuit for years on Dagworth and have continued its use on the non tortoise controlled points on Ravensclyffe. I've NEVER had a point motor fail in use on either layout, though I did get a huge bang once when I had one of the caps wired up back to front The cap exploded!

 

Andi

 

I wonder what effect that would have on the cat ?

Do you have a part no for those caps ? And do you also need a separate circuit for each point

Thanks.

[Dagworth]

I wonder what effect that would have on the cat ?

Do you have a part no for those caps ? And do you also need a separate circuit for each point

Thanks.

The cat wasn't bothered, it made Sheena and I jump out of our skins at the time. It had been installed for about 6 months when it decided enough was enough.... and the smell was awful, that was what led me to the cause of the bang.

I don't have a specific part no for the caps, and often will use larger values if Maplins don't have the normal choice. The critical bit is the voltage rating, it must be enough to withstand the power supply voltage. Higher value caps will give a bigger throw pulse but a longer recharge time. One pair of caps is required for each point motor. My circuits actually run off of a 24 volt 1/2 amp supply. That supply runs all the points on Ravens, there are more than 60 points on the layout, of which 25 are tortoise, the rest peco motors.

If you use a DPDT switch then the other contacts of the switch can be used for frog polarity switching, and the circuit works equally well using relays instead of switches, whereupon you can throw lots of points at the same time as each has its own caps and is not waiting for a CDU to recharge before the next point can be thrown. This is very useful if you have any kind of automatic route setting as I have. This is why I started using the circuit in the first place.

 

Andi

[amdaley]

The cat wasn't bothered, it made Sheena and I jump out of our skins at the time. It had been installed for about 6 months when it decided enough was enough.... and the smell was awful, that was what led me to the cause of the bang.

I don't have a specific part no for the caps, and often will use larger values if Maplins don't have the normal choice. The critical bit is the voltage rating, it must be enough to withstand the power supply voltage. Higher value caps will give a bigger throw pulse but a longer recharge time. One pair of caps is required for each point motor. My circuits actually run off of a 24 volt 1/2 amp supply. That supply runs all the points on Ravens, there are more than 60 points on the layout, of which 25 are tortoise, the rest peco motors.

If you use a DPDT switch then the other contacts of the switch can be used for frog polarity switching, and the circuit works equally well using relays instead of switches, whereupon you can throw lots of points at the same time as each has its own caps and is not waiting for a CDU to recharge before the next point can be thrown. This is very useful if you have any kind of automatic route setting as I have. This is why I started using the circuit in the first place.

 

Andi

 

Thanks Andi.

I will take a note of the parts & take a look the next time I get to a Maplins.

Would these be OK ?

 

http://cpcireland.farnell.com/multicomp/mcgpr35v108m13x21/capacitor-85c-35v-1000uf/dp/CA04760

[Crosland]

I thought that using DC in an Ac rated switch was what did the damage to the contacts ?

There is a diagram here of what I was going to do.

 

I would only have a problem if using the AC from a power supply where the heavy amps would flow all the time.I hadn't thought of it that way.

Any Switch can be used for AC or DC, but the DC current rating will be lower.

 

The problem comes in breaking the circuit when any arcing between the contacts will rapidly degrade the contacts.

 

Switching AC is much more benign since the current falls to zero twice every cycle, extinguishing the arc. Thus the AC current rating can be very much higher than the DC rating.

 

If you really are switching AC then just choose a suitable switch for the current you expect.

 

If you are switching the (DC) output from a CDU then you can use the fact that the current and voltage fall rapidly as the CDU discharges and a lower rated switch will be happy to break what current is flowing by the time you release it.

 

Andrew Crosland

[66C]

Hello Everyone.

I am searching for decent push button switches for point operation. All the switches I have looked at are low amps type which I reckon won't last long with the 3 or 4 amps that Peco or Seep point motors draw. Does anyone know where decent push button switches can be got.

These will be used on a control panel so will need to be tidy in size but will also need to be about 3amp 125volts ac capable.

Thanks everyone.

 

Hi Tony

 

Have a look at Maplins:

 

http://www.maplin.co.uk/Module.aspx?ModuleNo=2504

 

This type is also available from Squires - page 419 in their current catalogue - ref PTM262 and PTM265 at 75 pence each.

 

Regards

 

Bill Campbell

[amdaley]

Any Switch can be used for AC or DC, but the DC current rating will be lower.

 

The problem comes in breaking the circuit when any arcing between the contacts will rapidly degrade the contacts.

 

Switching AC is much more benign since the current falls to zero twice every cycle, extinguishing the arc. Thus the AC current rating can be very much higher than the DC rating.

 

If you really are switching AC then just choose a suitable switch for the current you expect.

 

If you are switching the (DC) output from a CDU then you can use the fact that the current and voltage fall rapidly as the CDU discharges and a lower rated switch will be happy to break what current is flowing by the time you release it.

 

Andrew Crosland

 

Hi Andrew.

Thank you very much for the excellent explanation. I will be switching the DC output from a CDU which I have measured as 22.9volts. That way I reckon I can use cheaper switches because as you said above when I break the circuit the voltage will be very small.

[amdaley]

Hi Tony

 

Have a look at Maplins:

 

http://www.maplin.co...x?ModuleNo=2504

 

This type is also available from Squires - page 419 in their current catalogue - ref PTM262 and PTM265 at 75 pence each.

 

Regards

 

Bill Campbell

 

Thanks for the link Bill. Its like being between a rock & a hard place. Looking for small push button switches that can handle the bigger DC volts but as Andrew has explained above the damage is done when breaking with Dc but if I use a CDU the Dc volts will be almost nil when I break the circuit so cheaper push button may work.

[Pete the Elaner]

the damage is done when breaking with Dc but if I use a CDU the Dc volts will be almost nil when I break the circuit so cheaper push button may work.

 

I have been trying to figure out how this works....

 

When you break the circuit, the magnetic field around the coil collapses rapidly. This creates a large back emf (or voltage) which is enough to generate a spark across the open switch contacts & will eventually burn them out.

 

A capacitor is the opposite to a coil (or inductor): An inductor reacts against a rapidly changing current but will allow a constant current to flow. A capacitor reacts against a constant current but will allow a fast changing current to flow. By placing a capacitor across the inductor, it provides an easy escape route for the current generated by the coil's back emf. Because this is an easier path than across the contacts of the open switch, they do not burn out.

 

I'm sure many of us are doing things in inferior ways because they are simply 'the way we've always done it' so I've decided to build a new, small layout to try 'alternative' ways of doing things including point switching & route indication.

[Crosland]

I have been trying to figure out how this works....

 

When you break the circuit, the magnetic field around the coil collapses rapidly. This creates a large back emf (or voltage) which is enough to generate a spark across the open switch contacts & will eventually burn them out.

 

A capacitor is the opposite to a coil (or inductor): An inductor reacts against a rapidly changing current but will allow a constant current to flow. A capacitor reacts against a constant current but will allow a fast changing current to flow. By placing a capacitor across the inductor, it provides an easy escape route for the current generated by the coil's back emf. Because this is an easier path than across the contacts of the open switch, they do not burn out.

 

You are making things far more complicated than they really are.

 

The point about a CDU is that the capacitor is discharged when you fire the point motor. The voltage collapses and there is very little current flowing (depending how the recharge circuitry works in the CDU). With such a small current flowing you can use a modest switch to break the circuit.

 

Andrew Crosland

[JonathanB]

Late to this thread, but would the kind of circuit posted further up be suitable to use for SEEP motors instead of a CDU? Thinking it might be cheaper for my small (3ft x 1ft) N-gauge layout.

[Brian]

Late to this thread, but would the kind of circuit posted further up be suitable to use for SEEP motors instead of a CDU? Thinking it might be cheaper for my small (3ft x 1ft) N-gauge layout.

Hi

There are two circuits shown or linked to.

This is one...Link to fist item

Yes it will work with any solenoid point motor.

I have to say I have never seen the point (excuse the pun) in that linked circuit? It uses two switches per point when really one would do! It just adds 100% more contacts which equals more potential failure places! Plus it doesn't prove a thing, other than the switch has been moved.

 

The swapping of capacitors drawing shown by Dagworth also works ok. But you must have one pair of capacitors per motor. Again it doesn't give any real indication of point movement. Only that the switch has been operated!

 

 

Why not use non locking toggle switches and have LED indications fed back from the point motor operated change-over switch, giving a true and probably more prototypical point indication that the point has moved rather than the position of a toggle switches lever?

[JonathanB]

Thanks Brian, since posting my reply I have found your website and am avidly reading and digesting! You have some great information that is really helpful.

[Dagworth]

My circuit unfortunately doesn't work for all point motors. It needs seperate connections to each side of each coil, if one of the connections is common to both coils(for instance the Peco above board low profile motor - is it the PL11?) then the circuit cannot be used. I don't know the connections on the SEEP motors and whether both sides are independant or not.

 

Andi

[Edwin_m]

The Seep does indeed have a common connection for the two coils (the one marked C) so Dagworth's circuit would not work.

[smokebox]

A simple modification of Dagworth's circuit should work

 

 

The switch is changed for a double pole double throw (S1A and S1B) and wired as shown. I've not built this circuit to try it but it should work

[Dagworth]

A simple modification of Dagworth's circuit should work

<snip>

The switch is changed for a double pole double throw (S1A and S1B) and wired as shown. I've not built this circuit to try it but it should work

 

Now why didn't I think of that? I had a location where one of the new Peco motors would have been ideal due to space limitations, but ended up going for a linkage to a normal peco motor... Doh!

 

Thanks for that, that's a really useful suggestion. (Just wish I'd seen it myself )

 

Andi