Per manufacturer instructions I've added a 3300µF capacitor to my NCE Snap-It so I can power a pair of crossover turnouts with a single device. This is in addition to the 1000µF capacitor on the device. I've been thinking of installing a momentary switch that I can wire up so that it discharges the capacitors before I handle the stationary decoder for maintenance. How do you discharge capacitors when necessary - or do you just man-up and take a 4300µF zap every time you want to work with it?
I would rig it up so that the momentary switch just switches the points, using the Snap-It's manual pushbutton connections. If you toggle it after the power to the Snap-It has been turned off, then this should discharge the capacitors.
I'm actually going to be doing something similar on my own layout, for a CDU.
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tbdanny I would rig it up so that the momentary switch just switches the points, using the Snap-It's manual pushbutton connections. If you toggle it after the power to the Snap-It has been turned off, then this should discharge the capacitors. I'm actually going to be doing something similar on my own layout, for a CDU.
RR_Mel Use a low value resistor (5 to 10 Ω) in series with the switch, both the cap and switch will last longer.
Mel,
Would I be correct in assuming this would also apply to relay switches?
Cheers,Tbdanny
tbdanny RR_Mel Use a low value resistor (5 to 10 Ω) in series with the switch, both the cap and switch will last longer. Mel, Would I be correct in assuming this would also apply to relay switches? Cheers,Tbdanny
Shut the power off and throw the switches one more time. This will discharge the capacitor, and with the power off, they won't get re-charged.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Hmm, wonder if the electronics stay powered on after track power is removed, so that the local pushbutton would still work - I kind of think not, so there's no way to just throw the switch after removing power to use up the juice.
I must say, with the CD supply I build eons ago when I still used solenoid switch motors in N scale, I don't recall ever being zapped by it. Mine was the quick recharge type from Thorne's Electronic Projects for Model Railroaders, with a 2N3055 transistor for fast recharge of the cap once the button was released, and I built it as one big chunk of electronics, no neat perf board - everything was soldered around the transistor and heat sink, with the cap hanging off the whole thing by its wires. Hard to touch it without spanning the cap leads, but like I said, I don't remember it ever zapping me.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Get out your volt meter and find out. if you are concerned the system stays live when track power is removed, measuer voltage across teh cap and see.
Likewise, when concerned with discharging caps, depower the system, and measure voltage stored in the cap. A few measurements over time will tell you how fast the caps naturally discharge in the circuit.
Our club has a DIY CDU and it holds a charge after the power is shut off. Don't remember how long. One time I hit a switch for a turnout after the power was shut down and it did hit the twin coil but only once and did not sound normal. No doubt the cap was very slowly bleeding off.
Not a big deal.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
A high value resistor across the cap will discharge the cap when power is removed; however, not wihtout drawing a small amount of current when the power is on. Using this method it's a tradeoff between the size of the cap, how fast you want it to discharge, and how much current it draws when powered.
Use a shorting probe.