Need ideas for a time delay relay circuit

[cruikshank]

Using triggers and stop tracks on multi-train club layout.  Running into problems with shorter trains not triggering the engines in the stop tracks to go, for a long of enough time.  Right now all done with wires, no relays, I realize I need a relay in order to extend the time of the triggers.  Using DC coil relays since they are easier to come by. I know it's a simple R/C circuit.  Could someone refresh my memory on how this is done.  Thanks,  Dave

[lionelsoni]

It's difficult to get much beyond 1 second with no more than a relay and a reasonable amount of capacitance.  I have lately been using field-effect transistors (FETs).  This might work for you:

   (control rail)---(resistor)--
                               |
(ground)---(-supply+)----(pot)---(+cap-)---(ground)
                           ^
                           |
(ground)---(-supply+)---(S G D)---(coil)---(ground)

"Ground" is the common layout return, that is, the outside rails generally.  The resistor is 3300 ohms, 1/4 watt.  The supply is whatever the relay needs, probably around 12 volts.  It should be filtered, not just rectified.  The "pot" is a 100 kilohm potentiometer for adjusting the time, up to about 1 minute.  The "cap" is a 470 microfarad electrolytic with a voltage rating suitable for the relay supply.  "S G D" are the source, gate, and drain of an International Rectifier IRF9530 P-channel FET.

The circuit works by discharging the capacitor through the control rail, to put drop the pot's wiper voltage and turn on the FET, which operates the relay.  When the capacitor recharges so that its gate voltage is within about 4 volts of the supply, the FET turns off and releases the relay.

[eZAK]

Dave,

Check here;

http://www.alliedelec.com/Search/SearchResults.asp?N=0&Ntk=Primary&Ntt=Time+delay+relay&sid=46981200244D617F

They have time delay relays in 12 VAC.

[lionelsoni]

Pat, are you suggesting the "no longer available" MTR-61626?

[eZAK]

Yes Bob,

I didn't know Scott no longer carried them, But Allied Electronics does & they are in stock!

http://www.alliedelec.com/default.asp

I have adjusted the above post to reflect this.

[Anonymous]

I use 24 solid state timer modules in conjuntion with 24 volt relays. I power the circuit with an unused tap of a ZW set at maximum. I trigger the circuit with an outside insulated rail which shares a common with the track power.

Dale Hz

[cruikshank]

I finally got around to doing this Via the R/C method.  The coil resistance is rated at 400 Ohms.  I used a 1000 uF electrolytic cap and was able to get an approximate 2 second delay.  For now that works and total cost was approx $2.50.00

Thanks,  Dave