Peco Switch Machine Currrent

[Blood Stained Angel]

I was in a club where we used the lowest rated momentary pushbuttons available. The pushbuttons were wired into cheap relays which then fired the switch machines. The system worked faultlessly for years, via a matrix one pushbutton would select the route out of the yard switching as many as six or seven turnouts in the process.

[BigG]

  Hi, you can reduce the back-emf-caused arcing by placing a hefty diode in parallel with the coil of the switch magnet. Place it so it does not conduct when the power is applied; then the big reverse current spike from the magnet will be shorted by the diode and do no damage to the pushbutton. The diode needs a voltage rating (PIV) of several 100s and be capable of a few amps to handle the spike burst. A type "AM" diode should do it; 1 per coil, mounted at the coil.  You need something like this with the large under-table uncoupling magnets too, if you feed them DC. In this case I'd recommend a larger diode. 

      Hope this helps a bit..... George 

[rlandry6]

Actually, that is exactly what I wanted to know. I have a choice between push-button and toggle switches for my turnout control. I'd rather use momentary PB switches, but I'm having a problem finding a source for these that I think would handle the current. Actually, I just didn't know how hefty the switch would have to be. Also, I plan to set up routing controls with a diode matrix, and would be operating possibly 5-6 turnouts at once, maximum, so if anyone has a source and a part number for a suitable push-button switch for this application, it would be appreciated.

[fwright]

The current is momentary (drops off quickly) from the CD power supply, so you can get away with lower ratings than if the switched current were steady state.  However, it's really the initial and break contact arcs that destroy switches much more so than the steady state current.  Because you are powering an electromagnetic coil, the building magnetic field opposes an instaneous rise in voltage.  Therefore, the initial arc is much less severe.  Without a CD unit, the collapsing magnetic field does create a serious reverse voltage arc when the circuit is broken (button released) that tends to break down switches.  Because the CD unit reduces the current over a second or so, the break contact arc is reduced to almost nothing.

Bottom line: 3 amps minimum is optimum, but I know plenty of folks that have used 1 amp switches successfully for long periods of time.

Actually measuring the current draw is quite difficult because keeping the current on for any length of time (for meter to stabilize) may burn out the switch machine.  Also, the current will decrease as the coils heat up and increase resistance.  And none of this considers the impact on the current of changing magnetic field as the machine powers up and throws. 

You can get a ball park idea of the current by measuring the resistance of the coils with an ohm meter - power off and disconnected.  I would think you will see on the order of 10 ohms becasue Peco switch machines are known for higher current draws than Atlas (which I have measured at around 16-17 ohms).  Which means current will be around 1.5 to 2 amps depending on voltage supplied.

probably more than you wanted to know

Fred W 

[rlandry6]

Has anyone actually measured the current draw of Peco Switch Motors? I'd like to know what rating pushbutton switches to buy for turnout control with a CD power supply..