Toggle switch rating

[yelliss]

I am almost at the point that I can do some wireing. Ineed some help in determinging the rating for the DPDT OFF CENTER. I have noticed that most responses are recommending 6 amo-10 amp switches. Is this the rating at 120 V ?  Or what!  check out my EE and math.

        Last part of post ,I must have cut off.......

              V= I R    R= V/I       I =V/R

                            R= 120/6  =20 ohms        I= 20 /20=1AMP

              Therefore a 120V @  6 amps   is equal to    1 amp @ 20V   ????

 Still confused

Thanks again Ellis

[SPFan]

The rating is usually specified at 120 volts AC or 32 volts DC but the only way to know for sure is to check the part number against the manufacturers specifications or hopefully the specs that came ith the switch when you bought it.

 

Pete 

[lionelsoni]

Most switches you find will be rated either for 120 and 240 volts AC or for 12 volts DC, depending on whether the manufacturer thinks they will be used with appliances or in automobiles.  If a switch is rated for your current at 120 or more volts AC, it will surely carry at least that current at toy train voltages.  If it is rated for your current at 12 volts DC, it will surely carry at least that current at 12 volts AC.  Since DC operation is much harder on the contacts than AC, it will probably carry the same current at the higher voltages, up to around 24 volts, that we use for toy trains.

[phillyreading]

D.C. may be harder on electronic components but A.C. when looked at under an oscilloscope packs more volts per useable voltage, example  120 volts A.C. measures around 177.8 volts on an oscilloscope where as D.C. at 120 volts will only register 120 volts.  It is the polarity change that makes A.C.(alternating current) more of a danger to work with than D.C.(direct current).

Ask any certified electrician about A.C  verses D.C. and he will tell you the same thing that I just mentioned.

Far as using 12 volt switches on O gauge trains I would not do that!!  I would get at least 50 volt A.C. switches rated at 10 amps or better.    You may not have trouble until the switch reaches it's amp load rating but it will cause trouble, sometimes just the switch will quit, sometimes a small fire when overloaded.

Lee Fritz

[phillyreading]

I am almost at the point that I can do some wireing. Ineed some help in determinging the rating for the DPDT OFF CENTER. I have noticed that most responses are recommending 6 amo-10 amp switches. Is this the rating at 120 V ?  Or what!  check out my EE and math.

        Last part of post ,I must have cut off.......

              V= I R    R= V/I       I =V/R

                            R= 120/6  =20 ohms        I= 20 /20=1AMP

              Therefore a 120V @  6 amps   is equal to    1 amp @ 20V   ????

 Still confused

Thanks again Ellis

Ellis,

Your math is off by a long shot, let me explain, 120 volts at 6 amps is equal to 20 volts at 36 amps providing that you have a transformer capable of providing pure step-down voltages and amperages.  To explain things in electricity without going to an electrical course is very difficult!

Lee F.

[lionelsoni]

Here is a chart from a switch manufacturer for rerating 125-volt AC switches for various AC and DC voltages:

http://www.nikkaiswitches.com/electrical.asp

You can see that there is an enormous difference in the current rating between AC and DC use.  From this, it is completely reasonable to suppose that a 12-volt DC switch can handle more than twice that voltage on AC.

The peak of a 120-volt RMS sine wave is not 177.8 but 169.706, not that it makes any difference, since I don't see what the relevance of the crest factor of a sine wave has to this matter.

[lionelsoni]

Ellis, you are assuming that voltage and current ratings for a switch are proportional to each other, as the voltage and current are proportional in a resistor, according to Ohm's law.  However, those switch ratings actually are related inversely.  That is, as the voltage switched goes down, the current that the switch can handle generally goes up.  Nevertheless, they are not exactly inversely proportional either; and the ratings also depend a lot on whether you are switching AC or DC, as I tried to show in my previous post.

[jefelectric]

Here is a chart from a switch manufacturer for rerating 125-volt AC switches for various AC and DC voltages:

http://www.nikkaiswitches.com/electrical.asp

You can see that there is an enormous difference in the current rating between AC and DC use.  From this, it is completely reasonable to suppose that a 12-volt DC switch can handle more than twice that voltage on AC.

The peak of a 120-volt RMS sine wave is not 177.8 but 169.706, not that it makes any difference, since I don't see what the relevance of the crest factor of a sine wave has to this matter.

Bob,

That is a very interesting link.  One thing I would like to point out though, is that the switches we use with our trains are operated most often without any load on them.  They will withstand a lot more load if not operated.  As an example, I have toggle switches that control sidings.  I can't recall ever turning one of these on or off with the load (engine) turned on.  In conventional you normally engergize the siding, then run the engine into the siding, remove power from the engine, then turn the switch off.  In this type of operation the ratings are not as meaningful as when used to to start a load.  When I had my RR set up with blocks, before TMCC, I often ran trains that were close to the 10 Amp limits of my fuses ( Double headed pulmor powered engines with lighted passenger cars) through 6 A toggle switches and never had one fail, but I can't ever recall using the switch to start or stop a train.

Just my

[yelliss]

Thanks for the info it is most helpful. the assumption that switch is a resistor is wrong!

 But the answer that I am looking for is that toggle switch rated 6 amps @ 120 V AC is OK to use for section blocks , sidings and accesories. CORRECT?

YOU CAN TELL THAT A CIVIL ENGINEER DOES NOT PERFORM WELL AS AN EE.

THANKS AGAIN,  Ellis

[lionelsoni]

Yes.

[phillyreading]

Bob,

I can see that you don't understand electrical theory at all!

A.C. is more powerful per volt than D.C. That being said using 12 volt D.C switches on a 20 volt A.C system is a major safety hazard waiting to happen. From my electrical knowledge I am going with 120 volt 6 amp switches as they can more than withstand any model train load! Just wait until a derailment happens with a KW or ZW transformer from the post war era and see what happens.

Lee F.

[martinden]

While I don't always agree with the arguments Bob makes, I'd never suggest he lacks understanding of electricity. And I think that anyone who could write the sentence "A.C. is more powerful per volt than D.C." should be very careful about suggesting that someone else does "not understand electrical theory at all!"

[SPFan]

Bob,

I can see that you don't understand electrical theory at all!

A.C. is more powerful per volt than D.C. That being said using 12 volt D.C switches on a 20 volt A.C system is a major safety hazard waiting to happen. From my electrical knowledge I am going with 120 volt 6 amp switches as they can more than withstand any model train load! Just wait until a derailment happens with a KW or ZW transformer from the post war era and see what happens.

Lee F.

 

Lee, You meant to put a smiley at the end of this right? Bob, is one of the most knowledgable electronics experts on this forum. In fact, a switch rated at 12 Volts DC is more than capable of switching 20 volts AC. Its true that AC has a higher peak voltage value but AC is self extinguishing of arc over current since 120 times a second its voltage is zero.

 

Pete 

[ADCX Rob]

Bob,

I can see that you don't understand electrical theory at all!

A.C. is more powerful per volt than D.C. ...

Lee F.

Which is why you can pick up a 100 amp-hour / 850 CCA car battery by the terminals - one in each hand - & not get shocked...

Rob 

[trigtrax]

I am almost at the point that I can do some wireing. Ineed some help in determinging the rating for the DPDT OFF CENTER. I have noticed that most responses are recommending 6 amo-10 amp switches. Is this the rating at 120 V ?  Or what!  check out my EE and math.

        Last part of post ,I must have cut off.......

              V= I R    R= V/I       I =V/R

                            R= 120/6  =20 ohms        I= 20 /20=1AMP

              Therefore a 120V @  6 amps   is equal to    1 amp @ 20V   ????

 Still confused

Thanks again Ellis

Your making this more difficult that it is. In a switch the contacts are either closed or open. The current rating 3 Amp, 6 Amp, 15 Amp is what the closed contacts can safely carry. When the contacts are closed the voltage drop across them is zero. There should be no resistance. Your V=IR doesn't apply. The voltage rating on a switch has do with the arc and spark during the contacts opening and closing. So your selection of common switches say 120 VAC is more than adaquate for the 20 Volt Max of your O-Gauge layout. What you need to know is what current the train you want to stop in the block draws and select switches based on that.

3 amp switches will be okay in most situations.. But if you want to lash 3 dual motor engines and 20 lighted passenger cars you'ld need more current.

[Buckeye Riveter]

YOU CAN TELL THAT A CIVIL ENGINEER DOES NOT PERFORM WELL AS AN EE.

THANKS AGAIN,  Ellis

Another one out playing golf instead of going to his EE Class.  A common problem with CEs.

[phillyreading]

Pete, and others,

Bob may know about electronics but he seems to forget about A.C. having more power behind it than D.C.  The arguement about it having negative voltage 60 times a second and having positive voltage 60 times a second is what makes A.C. more powerful than D.C.  Just because you think that it has a zero voltage 120 times a second is very deceiving because a lot of people think due to that zero voltage it is less powerful but that is the farthist from the truth that you can get.

Have you tried using 120 volt switches rated for D.C. in your house?  I would never do that because of what I know about electricity both A.C and D.C.  I have knowledge of both commercial A.C, 480 volts, 207 volt industrial and three phase A.C. transformer wiring and even have automotive certification in electrical work.

One other subject while I am on electrical work, do you know why the auto industry went to alternaters? They use A.C. that is rectified back to D.C. or in the electrical field this is called pulsating D.C. because it is not battery voltage but gotten from an A.C. source.

Lee F.

[ADCX Rob]

...

...One other subject while I am on electrical work, do you know why the auto industry went to alternaters?

... 

Lee F.

-Slip rings - less wear than commutator, no brushes bouncing at high speeds

-Higher ouput at lower shaft speeds

-Better regulation at all speeds w/ field current variation - non-linear output possible

-Smaller size-to-power

-Better wave form for battery charging

There may be more...

Rob

[lionelsoni]

I do forget things occasionally, but I'm sure one of them is not "about A.C. having more power behind it than D.C."  AC voltage is conventionally measured in RMS volts.  "RMS" means "root mean square".  That is exactly the equivalent DC voltage which would deliver the same power, averaged over a complete AC cycle, to a resistive load.  So, by definition, 120 volts RMS delivers the same power to its load as 120 volts DC.  The instantaneous power is sometimes higher, as at the 170-volt peaks, and sometimes lower, as at the axis crossings; but the average power is the same.  If you connect a 60-watt 120-volt incandescent lamp to 120 volts AC you will get precisely the same light as if you connect it to 120 volts DC, and it will consume the same average power--60 watts.  This is the closest I can get to the truth.

A 120-volt DC light switch would be a very rugged device.  If I had one, I would have no hesitation using it with 120 volts AC.  I would do that because of what I know about electricity, both AC and DC.

Why did the auto industry go to alternators?  Because they can get away with using slip rings instead of the more complicated commutators, using silicon diodes for commutation.  (The same thing happened to Diesel-electric locomotives, as soon as the rectifier diodes became available.)  The three-phase bridge rectifiers commonly used actually produce only a modest ripple, which is filtered almost to nothing by being connected to the battery.  (Looks like Rob beat me to this one.)

[phillyreading]

One other thing about A.C. current is that it is more economical to use than D.C. on large motors.  So basically D.C. is left behind as far as economics are concerned, it fine for H.O. trains.

Where I live the A.C. line voltage that, provided by Florida Power & Light Company, can be read by a multimeter goes as high as 132 volts or as low as 114.5 volts, depends on peak demand.

I don't mean to step on peoples toes but just state some facts about using 12 volt automotive toggle switches.  They may be less expensive and more plentiful but in my opion not as good as A.C. toggle switches rated around 20 volts, 15 to 20 amp range. To go up on the voltage rating for a toggle switch won't hurt but to go lower than the supplied voltage is never any good!

Lee Fritz

[Birds]

You could always go with the DPDT model "S7A" found on this data sheet:

http://www.nkkswitches.com/pdf/stogglesmedcap.pdf

• 20 amps @ 125 v AC
• 10 amps @ 250 v AC
• 20 amps @ 30 v DC

Seems to be somewhere in the ball park for running trains at 18-20 v. AC.

They might be more expensive, but they will last. 

I went with the SPDT version (15 amps @ 125 volts AC, and 20 amps @ 30 volts DC).  Originally I was using smaller switches from Radio Shack.  They worked fine, but they were small.  These NKK switches are a nice size, have a good thread height for mounting on a board, and have a lever large enough that you won't miss it when trying to find it in a hurry (none of us have ever let their trains go airborne - right?).

Chris