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should be OK. That much inrush current could drive a modern transformer a bit nuts if it has a sensitive breaker (K-Line power chief for example) but a standard breaker no problem. There is a slight possibility that you could tickle the contacts but train relays are not used under severe conditions usually. If there is a problem put in a small value resistor as John advised. The relays I use I put up to 10,000 uf on them. The relays I use have a 480 ohm 12VDC coils and  DPDT 15 amp contacts. The time delay is about 1 second per 1000uf of capacitance in practice so I actually use them as crude timers. For example using 4 relays and the insulated rail method I make such a circuit where the whistle is automatically triggered as the train approaches a crossing. The whistle sounds long,long,short ,and then long as the train passes through the crossing.  The amount of time lag depends on the relay used. This crude timing method is actually more realistic as it does not always ring exactly the same.

 

Normally just to keep a relay from chattering 470 uf usually works well.  If you want long durations you could use a timer module or 2 relays in a latch-unlatch circuit.

 

Dale H

Is the relay with capacitor being energized by wheels on a section of insulated track?  If so, there might be an arc when the wheel first makes contact to charge the capacitor.  I would recommend a few ohms of resistance.  This might induce a very short delay on the charge-up time, but probably not a significant amount compared to the charge decay time.

Well gentlemen, I have failed in my efforts.  I have been able to hook up the #415 Lionel signal bridge using 14vac and a MTR-12T relay from Scott's Odds & Ends.  It works perfectly.  But of course as soon as the train leaves the isolated track section the lights change back.  Starting over - can either of you describe a circuit that will allow me to delay the light switch back for even a few more seconds after the train exits the block? I can only assume that I have hooked up the capacitor and the small initial resistor the wrong way. But now I'm stumped.

Bob

If the capacitor is backwards it would explode.  It should be hooked directly across the relay coil in proper polarity. 6800 uf if charged should hold the relay for at least 5 seconds  if it charges .  Not sure of the circuit used by the relay in question. If there is a bridge rectifier in front of the coil it should not bleed back.  You can use an additional relay and timer module and delay it as long as you wish. 

 

Dale H

Dale/John,

Another few questions:

  • If I use a rectifier to supply dc to both relays (each side of the bridge is controlled by a separate isolated track) can I use a single lead from that rectifier to power both relays?
  •  If that's possible can I use one capacitor and split the lead after the cap to supply both relays?
  • Should both sides of the relay coil be powered by the same dc lead from the rectifier?

Bob

No problem using a common power supply that I can imagine.

 

I would NOT try to use a single capacitor, you want the cap directly across the relay coil, and the switching of the DC to be after the current limiting resistor.

 

I don't understand the third question.  One side of either relay is to the positive output of the power supply (bridge rectifier), and the negative is supplied by the isolated track section.  The negative output of the bridge rectifier goes to the track power common.  So, when a train rolls onto the isolated section, the common is connected to the isolated rail and charges the cap and closes the relay.  When the train leaves the isolated section, the cap discharges through the relay and then the relay opens after the discharge delay.

Post

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