Rotary switches - contact rating

[ejstubbs]

I am planning to use a rotary switch to control routes and power feeds from my double track main line into my three track fiddle yard.  I've looked around online (including Maplins closing down sale!) and although four pole three way rotary switches are easily found, the contact ratings on most of them seem to be quite low - 0.25-0.5A@125VAC, compared to 3A or more for the toggle switches I am using for the rest of the layout.

 

Is this likely to be a problem?  The contacts will be switching track power, and powering slow action point motors which draw 150mA according to the spec sheet.

 

I also want the switch to be break before make aka non-shorting (vs shorting).  I am surprised how many vendors don't seem to bother stating which type the switches they are selling are!

 

Can anyone recommend a rotary switch that would meet my requirements, at a reasonable price?

[rdr]

try a more responsible company like rs, farnell, and possibly rapid. maplin are well known for not giving info on the products they sell.

[DCB]

Is this DC or DCC?  for track power 0.5 amp will be marginal on DC and DCC with potentially 3 amps or more would be even more likely to melt the switch.

 

For points I find the plastic sealed unit rotaries cope with shock loads of switching several point motors at once from a Capacitor discharge but go soft if overloaded for more than a few seconds.    They should cope with several of the 150ma point motors at once but they might be marginal with stall motors.

 

I use open frame rotary switches from my local electronics retailer Hardings in Cheltenham, I never had one fail in over 30 years but they are getting rare.  I found some on eBay US site 4 pole 3 way and 3 amp break before make for about  £1.25 a throw but about Fifteen quid postage, so they are still about.   The 3 amp good ones have fibre baseplates and holes on the solder tags, the ones with straight tags are usually 1 amp.

Edited March 20, 2018 by DavidCBroad

[Dagworth]

 

I use open frame rotary switches from my local electronics retailer Hardings in Cheltenham, I never had one fail in over 30 years but they are getting rare.

Nice to see Norman (Or rather his son now) get a mention on here!

 

Andi

[ejstubbs]

try a more responsible company like rs, farnell, and possibly rapid. maplin are well known for not giving info on the products they sell.

 

I did say "including" Maplin.  I have been looking elsewhere, including RS and Rapid.  I'll take a look at Farnell.

 

Is this DC or DCC?

 

I use open frame rotary switches from my local electronics retailer Hardings in Cheltenham, I never had one fail in over 30 years but they are getting rare.  I found some on eBay US site 4 pole 3 way and 3 amp break before make for about  £1.25 a throw but about Fifteen quid postage, so they are still about.   The 3 amp good ones have fibre baseplates and holes on the solder tags, the ones with straight tags are usually 1 amp.

 

DC (hence why I posted in the non-DCC forum).  The ones I have found so far that seem to meet my requirements seem to cost in the region of £10 a pop.  I'll pay that if that's what it takes - but not the ~£40 that one I found was priced at!!! (To be fair, I think it was rather over-specced for what I want.)

 

Oh for the heady days when I could pop in to RF Potts on Babington Lane!  I would if they're still there?

 

I guess I'll have to do a bit more searching...

Edited March 20, 2018 by ejstubbs

[kevinlms]

I am planning to use a rotary switch to control routes and power feeds from my double track main line into my three track fiddle yard. I've looked around online (including Maplins closing down sale!) and although four pole three way rotary switches are easily found, the contact ratings on most of them seem to be quite low - 0.25-0.5A@125VAC, compared to 3A or more for the toggle switches I am using for the rest of the layout.

 

Is this likely to be a problem? The contacts will be switching track power, and powering slow action point motors which draw 150mA according to the spec sheet.

 

I also want the switch to be break before make aka non-shorting (vs shorting). I am surprised how many vendors don't seem to bother stating which type the switches they are selling are!

 

Can anyone recommend a rotary switch that would meet my requirements, at a reasonable price?

But your switches should not be switching large currents, they will be carrying the current. That is not the same thing.

[John ks]

If you are using 1 0r 2 poles of the rotary sw for the point motors & 1 or 2 poles for the track power, have you considered those poles on the rotary switch to switch a relay for the track power

 

​John

[John ks]

I'm not sure of the layout of the fiddle yard

3 tracks fed from a 2 track main like this could be controlled like this

 

 

A relay is used for isolating each siding (you will need plastic fishplates in the appropriate places)

You may notice that point A is not powered when track 3 is selected(doesn't matter which way it is set for when point B is straight so it may as well be unpowered)

 

The only current going through the Rotary Sw is slow motion point current & relay current

 

If you don't want relays then track power will have to go through the rotary sw & you're back to your original question regarding current rating of the rotary

 

Snubber diodes across the relay coils are probably not necessary but could prolong the life of the rotary sw.

 

The above is not exactly what you asked for but I couldn't help myself

 

In the days before I went to DCC I used cheaper rotary switches for block control  & can't remember any failing over a period of 30ish years

 

John 

 

 

 

 

[DCB]

But your switches should not be switching large currents, they will be carrying the current. That is not the same thing.

 

In practice when faults occur you switch the section off and back on again at the rotary and that is controller power into a dead short, which is why I like 3 amp switches on 1 amp rated controllers.

 

I don't know the "Layout" of your Layout but I attach a very simplified schematic of my hidden siding layout and wiring with. 3 pole 4 way rotary,  3 live positions 1 off, 3 poles, positive negative and indicator lights (never actually used)

 

MO drive train in on Green, shunt on Black, drive out on Red.   Added wiring means any one of four controllers can be Red or Green but only the local one can be Black

[Suzie]

The Maplin rotary switches will be OK for switching DC track power or slow motion point motors.

 

If you want to switch solenoids it will be cheaper to use the Maplin switches, and replace the solenoids with slow motion motors rather than buy the bigger switches required for solenoids.

[ejstubbs]

The Maplin rotary switches will be OK for switching DC track power or slow motion point motors.

 

Thanks for that: you prompted me to pop in to my local Maplin on the way home this evening and eyeball the product in question, as a result of which I am much more confident about its ability to do the job.  The information on the small card attached to the placcy bag it comes in was vastly more relevant and useful than the data sheet that they posted on their web site.  So I came away with one, as well as a knob for it, and - since I was there, and stuff was going cheap - I also picked up a set of spare bits for my soldering iron.

 

I might even pop back later in the week to pick up another one of the switches (as a just-in-case) and some heat shrink tubing.

Edited March 20, 2018 by ejstubbs