component electrical specifications?


Dave Emery
 

I want to use microswitches on a drop-gate to power track (when the gate is up). There’s lots of different kinds and power (voltage/current) specifications. What’s the recommended min rating for a switch handling DCC?

Thanks!

dave


Blair
 

I'd go for something with a 5A rating, Dave; "overkill" is better than "marginal".  Voltage is only about 15V, so pretty much anything will do that way.  I presume what you're doing is removing the DCC signal from the bus feeding the tracks on both sides of the bridge.  In that case, remember, you only need to interrupt one of the signals, not both.  Don't ask how I know...

Blair

On 8/18/2021 6:25 PM, Dave Emery via groups.io wrote:
I want to use microswitches on a drop-gate to power track (when the gate is up). There’s lots of different kinds and power (voltage/current) specifications. What’s the recommended min rating for a switch handling DCC?

Thanks!

dave




Robin Becker
 

Voltage depends on your scale, i
I believe it can be up to 27 Volts or so for larger scales per the DCC specs.   Current depends on the command station or circuit breaker that is feeding your switch and I think you would want to be able to handle short circuit current without your switch failing.

Robin

Robin Becker

San Diego CA

https://DRGW.n3ix.com



Swanny
 

Robin, I have a "lift" gate that I protect with magnetic reed switches, such as used in alarm systems.  You can easily find them by searching for the item below on Amazon.  I use one on each end, running the rail feeder (drop) through the switch, which is closed when the gate, or bridge, is down.  
John

7939WG-WH - Ademco Surface Mount Contacts


Robin Becker
 

John,

That reed switch is rated for only 300 mA @ 30 V.  If you have multiple locos, sound loco, etc or a short circuit you might have problems especially if it ever switches while under load?

Robin


Blair
 

I suspect over-currenting the alarm switch will only result in it's premature failure, not a fire or other calamity.  In a protective situation like this, switch failure is fail-safe.  Still, it might be better if the alarm switch simply dropped power to a SPST cutout relay.  Or, as the OP asked, use a switch capable of dropping the DCC bus by itself.
Part of this discussion should revolve around topology - you want to drop the DCC power for 'some distance' either side of the bridge, to prevent running into the abyss, but also to prevent backing into the abyss.  So it's not about dropping power to a 12" section of rail, but rather a significant length of power bus.  As such, it may be more convenient to locate relays on opposite sides of the bridge to drop their respective sections of bus.  IF that's the case, then use the alarm switch to drop the control voltage to those relays, thereby reducing it's current requirements as well as increasing your protection.
No one can tell you the right approach without more information than has been given.
  
By the way, I do this on my 'guillotine' wall gate, which has tracks on both sides, and rises 24" to make life easier when working, not running trains - if the gate is down in position, it powers a relay that allows DCC power to that whole section of the layout; if the gate is lifted, that whole section of the layout dies.  Since the gate never opens in regular operation, that works for me.  My lower level drops and liftouts (4 of them) will need to be more "subtle", as one or more may need to move during operation (as I get older and less limber), but for now, all-or-nothing is acceptable, as only the upper level is constructed and operable.
Blair


Blair
 

Swanny, it sounds like all you've done is depowered the track on the bridge - but I hope that's just a misreading.  What should be done is removing power from the approaches to the bridge, which can get very complicated in the case of multiple routes approaching the bridge.
Blair


Dave Emery
 

What I want is for both the track on the drop-gate itself and the leads in either direction to be controlled by the position of the drop-gate. (i.e. when the gate is down, the leads have no power.) To do that, it seems I will need two switches, one on either end, or use a contact switch (e.g. a ‘pogo peg’) that passes power across the closed gate’s gap.

dave


Blair
 

Dave

That's up to you.  I'd rather use contacts in the bridge area to simply energize relay(s) that are placed where it is best to interrupt the DCC bus.  But, as usual, Rule number 1 applies - it's your railroad!

Blair

On 2021-08-19 9:58, Dave Emery via groups.io wrote:
What I want is for both the track on the drop-gate itself and the leads in either direction to be controlled by the position of the drop-gate. (i.e. when the gate is down, the leads have no power.) To do that, it seems I will need two switches, one on either end, or use a contact switch (e.g. a ‘pogo peg’) that passes power across the closed gate’s gap.

dave





Blair
 

To me, it's of little use to de-energize the bridge track itself, as if you actually drop the bridge when a train is on it, "you ain't paying much attention!".  YMMV, though, as perhaps your bridge is remotely operated, where the person causing the opening isn't standing at the bridge waiting to go through the opening?

Blair

On 2021-08-19 9:58, Dave Emery via groups.io wrote:
What I want is for both the track on the drop-gate itself and the leads in either direction to be controlled by the position of the drop-gate. (i.e. when the gate is down, the leads have no power.) To do that, it seems I will need two switches, one on either end, or use a contact switch (e.g. a ‘pogo peg’) that passes power across the closed gate’s gap.

dave





 

I would use a 1 Ampere "Microswitch" or sometimes called a lever or roller switch.  Note that a magnetic reed switch is not a "Microswitch".   This rating will only be exceeded under a rare condition where there is a short circuit and the lift gate switch activates at precisely the same moment as the short.  All DCC systems will remove power milliseconds after the short occurs.

If you use a higher rated switch the contact material will be silver or similar metal and constitutes what is called a wet contact.  The reliability of this contact depends on enough current being present to wet or partially melt the contact material on making the contact.   Most of the time you will have little or no current flowing when the contact is made.  A high current contact will fail over time by oxidizing the surfaces.  There are exceptions but in general you want a gold or dry contact and gold contacts are rarely rated for more than 1 Ampere.  Exceptions are switches that are designed to rub off oxidization each time they are made, or combination contacts that are silver with a gold over plating.  Combination contacts will remain dry contacts  if the current is always low.  In a high current situation the gold layer of the combination contact is burnt by the current leaving a silver contact.

There are a lot of engineers out there that do not know this information.  It is rarely taught in school and in my case was learned in the field.

Best Regards,
Ken Harstine


Robert Hughes
 

Blair. I am considering a drop down bridge across a door way to access more room for future expansion of my lay out. It would be of great interest to me to see what, how you have built yours. I have seen several posted in different groups and YouTube, but most are not conclusive on how to do the gate and to power it in it's dropped position. This blog is interesting to me, but I am afraid I need more detail (pictures). 
Thanks in advance for your response.

Robert 

On Thursday, August 19, 2021, 09:24:40 AM CDT, Blair <smithbr@...> wrote:


To me, it's of little use to de-energize the bridge track itself, as if
you actually drop the bridge when a train is on it, "you ain't paying
much attention!".  YMMV, though, as perhaps your bridge is remotely
operated, where the person causing the opening isn't standing at the
bridge waiting to go through the opening?

Blair

On 2021-08-19 9:58, Dave Emery via groups.io wrote:
> What I want is for both the track on the drop-gate itself and the leads in either direction to be controlled by the position of the drop-gate. (i.e. when the gate is down, the leads have no power.) To do that, it seems I will need two switches, one on either end, or use a contact switch (e.g. a ‘pogo peg’) that passes power across the closed gate’s gap.
>
>     dave
>
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whmvd
 

Cutting power works well, right up until the day keep-alives are put into your locos. Maybe something to think about...?

Wouter


On Thu, 19 Aug 2021 at 14:58, Dave Emery via groups.io <deemery=icloud.com@groups.io> wrote:
What I want is for both the track on the drop-gate itself and the leads in either direction to be controlled by the position of the drop-gate. (i.e. when the gate is down, the leads have no power.) To do that, it seems I will need two switches, one on either end, or use a contact switch (e.g. a ‘pogo peg’) that passes power across the closed gate’s gap. 

        dave