capatitors and relays ?

Larger value electrolytic capcitors are pretty cheap these days.

I would try a 220, 330, 470 mfd or larger, up to 1000 mfd.

Voltage rating should be 25 VDC or higher.

The cap would be connected across the + and - outputs of your bridge rectifier.

The automotive relay will trigger on 12 VDC; presumably the other one is also 12 VDC, you did not indicate. The 24 volt 10 amp rating is likely the contact rating.

Rod

Note that some relays don't like excess voltage and if it's there for some period of time, it may cook the coil.  Depending on the specifications, you might consider feeding the DC from the bridge & cap into a three terminal regulator to drive the relay coil.

Don't ask me how I know this.

The 24V relay has a operating coil rated 24VDC. the output of the relay is rated for 1/3HP, 10 Amp, 120VAC also at higher voltages, 240 and 600VAC.

I do not forsee any long period of time that the coil would be active.

From an earlier post, I am just picking up a ground inside the "OS" of a switch to activate the signal system when a train passes the signal instead of waiting for the signal to drop Red when it enters the next isolated block on the other side of the switch.  

Thanks for the info.

Dan 

What happens if the train parks on the signal track?  That's a possibility, I know that for sure.

Most general purpose relays are made for continuous use. The capacitor value needed depends on the relay coil characteristics,and how dirty the track is. 1000 uf works in most all cases but even 220 uf is usually sufficient. The 12VDC automotive relay  usually has an 88 ohm coil so it is a it power hungry and would need a bit more capacitance,but it is a good cheap relay.Newer ones have a diode built in for spike suppression so they are polarity sensitive.  Some of the relays I use have 500 ohm coils and timing circuits can be made up to 10 seconds..  It is definitely designed for continuous use.  If sparking is experienced on the train wheels ,a small resistor,say 18 ohms,1/2 watt can be put in series with the capacitor.

Dale H

If 18 VAC is rectified and a capacitor is used,the input voltage is about 24 VDC,a perfect input. For a 12VDC relay,10VAC in is good. Most coils can take even 50% over their rating and pull in a little over half their rating. A 24VAC relay works fine on 18VAC. 

I won't press the point, but I've cooked several relays running them at about 130% of the rating.  These were small signal type relays, but I'd be somewhat careful running any relay way outside of the coil rating.

I did electronic repairs for a while. Very rarely have I changed a relay because of a burned out coil,not that it never happens. Most but not all relays are designed for continuous use.  Usually the contacts fail when replacement is needed. All this assumes they are placed in a proper application.  Many solenoids however are not rated for continuous use and they often fry when the cancel circuit is inoperative.   I do not advocate running relays a lot over their rated value, I just state that many of them spec for 50% over their rated voltage. It is not usually a problem for example to run a 12 volt relay on 14 volts or a 24 volt relay on 28 volts.

Just remember for AC input on a DC relay that voltage is increased 41% when a bridge rectifier is used with a capacitor. I would use a capacitor with DC relays since pulsed current is less kind to the contacts and may shorten contact life. AC relays are designed for pulsed current.

Dale H

Dale, you have to remember that for most electronics that are properly designed, they're not running the components over their ratings.   I designed electronic equipment for a long time, and a major consideration in component selection was the specifications of the component and the characteristics of the circuit.  I spent 20 years in aerospace, primarily in fuel systems and cockpit instrumentation.  When you build stuff that has to function properly at and ambient of 85C and down to -40C, you select the components very carefully.   Running stuff outside it's rated specifications just isn't a real good idea. 

Take your DC relay as an example.

Let's say you have a coil resistance of 100 ohms and 12V supply, that is 1.44 watts into the coil.

Now, let's increase the voltage to 18 volts, and now you're dissipating 3.24 watts, over twice the power.  That heat has to go somewhere, and if the ventilation isn't good for the relay, you may end up with toast.

John

You are correct. Like I said I do not advocate running them way over their ratings. An automotive relay is called a 12 volt relay but the system I think is closer to 14 volts.  My point was that it was not a big deal to do that. Most any electronics,(Not speaking of PC chips) can take 10% over their ratings with no harm. They are also designed for continuous use with no harm to the coil,when you turn your headlights on for example. I think I also said they had to be put in proper applications.

Aerospace relays I think were sealed in a vacuum made to very high specifications. Those are a bit different but work the same way. Some of them are for pulsed applications.  I have a few of them laying around,twin coiled latch relays. I put power to the coil for a few hours and they did not burn up or get hot. Still when I circuit them I only pulse the coils. 

Some of the relays I use are DPDT with 15 amp contacts,12VDC 500 ohm coils. (NAIS SP-2_P).  They use just a little more amperage than an LED (.025 amps) or 1/3 watt. With a 470 ohm resistor in series to the coil they can be used in 24 volt applications. These are great for time delay since about each of 1000 uf capacitance will hold them in for 1 second.  I picked a bunch of them up for $6 each,they normally sell for about $30 from electronic suppliers. Maximum input is 18 volts on these. 

Dale H

That does look like a great product for trains, perfect ratings!   I'm going to save the datasheet for that one.

The relay has been available for several years through Scotts Odds-n-Ends, now Train Electrics, LLC.

Neil