Microswitches

[Stevebr]

I intend using microswitches for frog polarity in my fiddle yard.  The switches are the changeover type. Can I use a single switch or is it more reliable to use 2 switches?

[Nigelcliffe]

Most people I know would use one, as a change-over.   

[DCB]

One is more reliable than two as the pair may get out of phase and short.   Its bad enough when the single switch gets out of phase with the older tag fitted points.   I use the little chinese micro switches surface mounted on the outside branch, but that's DC, 12VA max, usually less than half that.    I think they would have a short life on 48VA or what ever DCC pokes out.

[Nigelcliffe]

14 minutes ago, DCB said:

One is more reliable than two as the pair may get out of phase and short.   Its bad enough when the single switch gets out of phase with the older tag fitted points.   I use the little chinese micro switches surface mounted on the outside branch, but that's DC, 12VA max, usually less than half that.    I think they would have a short life on 48VA or what ever DCC pokes out.

 

 

There is no switching current on typical normal use, for either DC or DCC.    Unless there's a loco sitting on the turnout, no current is flowing.     

 

The problem with burnout is more likely if the loco shorts the turnout, and the operator corrects the short by moving the turnout to the correct position.  In that situation there is current flowing, and it will be the maximum current the system allows (DC or DCC).  

 

However, even with that, switches are usually rated for much higher power on an AC (or approximately AC) signal than for a DC signal. 

 

 

- Nigel

[DCB]

There is a  full on 4 amps ish 12 volts ish flowing all the time the layout is on with DCC so a dead short will destroy the little Chinese microswitches.   I would use 4 amp microswitches for track power DCC.  

[RFS]

55 minutes ago, DCB said:

There is a  full on 4 amps ish 12 volts ish flowing all the time the layout is on with DCC so a dead short will destroy the little Chinese microswitches.   I would use 4 amp microswitches for track power DCC.  

 

How? Surely the DCC system will cut out immediately when a dead short occurs so this current will only be flowing momentarily. If it doesn't, then there's something wrong with your DCC wiring. 4 amps at 12v is only 48 watts of power. 

Edited August 5, 2022 by RFS

[AndyID]

5 minutes ago, RFS said:

 

How? Surely the DCC system will cut out immediately when a dead short occurs so this current will only be flowing momentarily. If it doesn't, then there's something wrong with your DCC wiring. 4 amps at 12v is only 48 watts of power. 

You beat me to it 😀

[Stevebr]

The feedback is really appreciated. It makes sense to me to use a single switch. The unit I intend using is rated at 6A and is supplied by the excellent RS Components. 

 

[AndyID]

19 hours ago, Stevebr said:

The feedback is really appreciated. It makes sense to me to use a single switch. The unit I intend using is rated at 6A and is supplied by the excellent RS Components. 

 

 

Well that should work but at GBP 3.12 a pop they are nor exactly inexpensive 😀

 

Are the sidings in your fiddle-yard all dead ends? If they are, depending on the type of points you are using, you might not need any switches for the frogs.

 

 

[BR60103]

A photo of my installation in a slot beside Peco points.

It also shows my tester to make sure the wires are the right way round. (3 small bulbs).

 

[Crosland]

On 05/08/2022 at 16:13, DCB said:

There is a  full on 4 amps ish 12 volts ish flowing all the time the layout is on with DCC so a dead short will destroy the little Chinese microswitches.   I would use 4 amp microswitches for track power DCC.  

 

Please! Stop digging yourself even deeper!

 

The ONLY current flowing in a DCC system is that which is drawn by the locos being operated.

 

If there is no loco on the frog then there is NO current flowing through the switch.

 

[kevinlms]

19 hours ago, Crosland said:

 

Please! Stop digging yourself even deeper!

 

The ONLY current flowing in a DCC system is that which is drawn by the locos being operated.

 

If there is no loco on the frog then there is NO current flowing through the switch.

 

You do if you connect your DDC power supply at one end only and switch all your tracks etc, from one feed.

How else are you going to get the rail joiners glowing red hot?

[Pete the Elaner]

On 05/08/2022 at 16:13, DCB said:

There is a  full on 4 amps ish 12 volts ish flowing all the time the layout is on with DCC so a dead short will destroy the little Chinese microswitches.   I would use 4 amp microswitches for track power DCC.  

 

Maybe you should try connecting up one of DCC Concepts Alpha Meters? I have one out of curiosity & have just checked what my layout is actually using.

I have on mine & have just powered it on to see what it is drawing: 1.04-1.10A. But I have 30 locos (none moving) & 21 coaches with lighting drawing this current around the entire layout.

As stated above, a switch providing current to 1 section (a frog) will only be powering 1 item.

You are also judging switches by their maximum rated current, which is continuous. The components will momentarily cope with a little over this temporarily before they melt, although it is definitely not recommended to try it.

DCC overload protection is typically very fast & your decoder will fail before a 2A-3A microswitch, except that many also have their own overload protection.

Edited August 8, 2022 by Pete the Elaner

[Crosland]

24 minutes ago, Pete the Elaner said:

You are also judging switches by their maximum rated current, which is continuous. The components will momentarily cope with a little over this temporarily before they melt, although it is definitely not recommended to try it.

 

Switch ratings are more to do with the current they can interrupt (i.e., when the switch opens), hence the same switch will have a much higher rating for AC.

 

Opening a switch when a high current is flowing causes an arc. In extremis it will destroy the contacts, within spec it's fine, in-between will lead to greater and greater degradation of the contacts over time.

 

The AC rating for a switch will always be higher than the DC rating as AC current decays to zero twice every cycle, extinguishing any arc. The much higher switching frequency of DCC (compared to the usual 50Hz switch rating) means any arcing will be extinguished even quicker.

 

For as long as the contacts remain closed, it will probably handle a much higher current that that which it is rated for.

 

[Nigelcliffe]

"Crosland" above is correct (and echo my post much higher up the thread).   

 

But, it does remain the case that the frog switch probably gets full DCC system current when a loco is driven into an incorrectly set frog, though the contacts will be closed ahead of the current flow (so low chance of failure, even if over the rated switching current).   If a system constantly tries to reset (some do), and the operator throws the turnout under the shorting loco thus changing the contacts, then the full system current may be experienced by the breaking contact as the switch moves.  

 

The way to reduce the maximum current is to arrange the layout into power districts, and have district cut out devices set to sensibly low currents.  That protects switches, loco pickups, and lots of other things, plus the layout wiring can be less exacting.    As Pete indicated above, he can run lots of stuff on a little over 1 amp, so district cut outs set to under 2A would appear "more than adequate" for many 4mm and smaller scales, and thus limit the current that anything will experience.    

 

Overpowered systems are of little benefit.  

 

 

 

2 hours ago, Pete the Elaner said:

DCC overload protection is typically very fast & your decoder will fail before a 2A-3A microswitch, except that many also have their own overload protection.

 

I'm not sure of the relevance of decoder power handling.   Typically a short circuit will by-pass the decoder.   

 

 

- Nigel

 

[AndyID]

On 08/08/2022 at 09:55, Nigelcliffe said:

"Crosland" above is correct (and echo my post much higher up the thread).   

 

But, it does remain the case that the frog switch probably gets full DCC system current when a loco is driven into an incorrectly set frog, though the contacts will be closed ahead of the current flow (so low chance of failure, even if over the rated switching current).   If a system constantly tries to reset (some do), and the operator throws the turnout under the shorting loco thus changing the contacts, then the full system current may be experienced by the breaking contact as the switch moves.  

 

The way to reduce the maximum current is to arrange the layout into power districts, and have district cut out devices set to sensibly low currents.  That protects switches, loco pickups, and lots of other things, plus the layout wiring can be less exacting.    As Pete indicated above, he can run lots of stuff on a little over 1 amp, so district cut outs set to under 2A would appear "more than adequate" for many 4mm and smaller scales, and thus limit the current that anything will experience.    

 

Overpowered systems are of little benefit.

 

 

I'm not familiar with DCC power systems but I would hope they do what any well-designed electronic power supply will do. In the event of an overload it does not supply full power again until the resistance of the load is greater than a minimum value. It determines the load's resistance by feeding a small test current into the load. If the voltage at the terminals is not greater than some value the supply stays shut-down.