12-VOLT ANTI CHATTER RELAYS

[CB&Q]

[:p] WHERE ELSE BESIDES SCOTT'S ODDS N ENDS CAN I GET THESE TYPE OF RELAYS PREFER AC POWER. THX PAUL

[Anonymous]

Try Mouser Electonic

www.mouser.com

[Roger Bielen]

I'm not an electrical engineer, but I'm guessing that if using a 12VDC relay and AC power you could put a diode into the feed to convert to half wave, false DC, and possibly a capacitor. Any one more versed have more detail?

[jkerklo]

Try the 2RC from www.Three-Rail.com .

Be glad to help with application, if needed.

John Kerklo
TCA 94-38455
www.Three-Rail.com

[lionelsoni]

Roger, better full-wave with a bridge rectifier, which you can get cheaply in a single package. That way, the output voltage will be close to the input voltage, there will be much less liklihood that the relay will buzz, and the current drawn from the source will not have a DC component, which can cause some trouble with transformers and especially with newer electronic "transformers". You are right that a little capacitance will take care of any buzzing that may remain. However, enough capacitance to make pure DC will also significantly raise the output voltage (about 40 percent). Which is okay if one is aware of it and takes it into account in selecting the relay.

[Roger Bielen]

Thanks for the input Bob, now that you mentioned it I did use a full wave rectifier with my conversion, I hadn't had my second cup of coffee yet when I wrote the reply.

[Anonymous]

Actually AC relays are no more prone to chattering than DC relays.The coils are wound a certain fashion to accomidate the AC sine wave.Also there is a lag between pull in and drop out voltage. 24VAC relays will pull in at 18 volts supplied by a ZW transformer. I run about 80 24VAC relays on my layout by simply dedicating one ZW circuit to relays and using insulated ground rails to activate them.
12VAC relays are very uncommon. You can use 12VDC relays by putting a bridge rectifier in series with each coil. A diode can be put across the coil leads for spike suppression and a polarized capacitor across it to reduce chatter. So in short you can build your own "anti-chatter relay" On an AC relay an RC circuit can be put across the coil leads for spike suppression.
Good deals can be had for relays on Ebay.

Dale Hz

[lionelsoni]

Ac relays operated on ac can and do buzz or hum, but may not. Dc relays operated on dc never buzz. The winding trick that Dale alludes to is called a "shaded pole" and is a separate section of the magnetic pole with a copper "shading ring" around it. This shifts the phase of the magnetic flux in that area of the pole so that there is never a complete absence of flux over the entire pole. This phase-shifted flux is only a fraction of the strength of the main flux; so its success in keeping the armature from moving depends on the same discrepancy seen between pull-in and holding current in most relays. Whether the relay actually buzzes depends on the design of the relay, how well it is built, and the coil current used.

The bridge rectifier goes not in series with the coil but in cascade. The ac voltage goes to two of the bridge's terminals (often marked with a ~ symbol) and the dc appears at the other two (often marked with + and - symbols).

As I said above, you have to be careful about putting capacitance across the coil since that can significantly increase the coil voltage. Neglecting the voltage drop in the diodes, without a capacitor the rms dc voltage, which is what determines coil heating, is the same as the rms voltage of the ac source. The average dc voltage is about 90 percent of the rms voltage. With a large capacitor, the dc voltage, average and rms, becomes about 140 percent of the rms ac voltage. The coil heating doubles.

Putting a diode across a coil supplied from a bridge rectifier to reduce voltage spikes is useless, since the bridge itself provides two pairs of series diodes in parallel doing the same thing. When a dc relay's coil is switched off downstream of a rectifier or other supply, such a diode, called a "snubbing diode", will suppress spikes.

A snubbing diode can cause trouble however, since it causes the relay to release slowly, "teasing" the contacts open and prolonging any arc between them, leading to premature failure of the contacts. A good practice is to put a resistance comparable to the coil resistance in series with the snubbing diode. Unfortunately, this cannot easily be done when using a bridge rectifier.

[Anonymous]

Dont know if we are talking about the same things regarding "chatter." I wasnt refering to buzz or hum but rather unstable voltage to the relay coil when energizing it via insulated rails from rollingstock wheels. The capacitor smooths this out to a degree. While true that the capacitor charges to peak voltage this quickly drops in nano seconds to RMS voltage when current is pulled through the circuit. Unless you use a very large capacitor no damage to the coil should result.
My point is that there is not really an anti chatter relay but rather a circuit added to reduce this tendancy when used with an insulated rail.You can easily add this yourself. Mine work fine and I have never needed to. It would also help to simply keep the track and wheels clean.
I have used both AC and DC relays on my layout and really dont have problems with either one. I dont bother with capacitors at all but I believe the ones Scotts odds and ends sells has one incorporated in its circuit.
As far as price I picked up 50 new 24VAC 3Pdt relays with sockets and 10 amp contacts on Ebay for $68. These work fine off the 20 volts provided by an old ZW transformer.

Dale Hz

[lionelsoni]

Dale, it sounds like what you mean by chatter is erratic operation at a rate much less than the power frequency. To smooth out something like that, you would need much more than the amount of capacitance that would boost the voltage to 140 percent. With a 500-ohm coil, it takes only about 250 microfarads to get 7 percent peak-to-peak ripple. Allowing for 1.5 volt drop in the diodes, the coil would be getting over 31 volts with 24 volts rms into the rectifier, which would generate 70 percent more heat than 24 volts dc would.

There is nothing wrong with using a lot of capacitance across the relay, as long as the design allows for the voltage increase.

[Anonymous]

Thanks much for the imformation. I work on pinball machines as a hobby and have a lot of interest in the subject. The old pins use mostly 28VAC relays. Spikes are not important in the old design electromechanical ones. The newer ones use 28VDC and all coils usually use diodes across the leads to protect the solid state electronics.

Dale Hz

[jwse30]

The relays I use are made by a company called Functional Devices. They are called "Relay in a Box", and I believe the part number is RIBU1C. These relays come in a plastic box that has an indicator LED. Inside the box is some kind of magic that lets the coil energize chatter free from 5 to 30 Volts, AC or DC. (The 5 volts I measured with a meter; the 30v is what the spec sheet said it was rated for.) Coming out of the box is 6 or so wires for the coil, a NO, a NC, and a common for the points.

I buy them at a local heating and air supplyhouse and they cost roughly $15, including tax.

J White