Noisy relay!!

[HopperSJ]

What am I doin wrong here?

I was able to find a 12VAC (10AMP) DPDT throw relay at a local electrical supply store. I am using it to trigger a signal flasher and bell (see my post earlier today). I have it hooked up for the signal only right now as I test things out. I have the transformer power and an isolated rail wired to trigger the relay. Then I have AUX power being sent through the relay to trigger the signal. However, as the train goes over the track the relay chatters and clicks LOUDLY unless I have the transformer power cranked pretty high. Since I am running conventional, this means the trains would be flying downhlll. Not acceptable! Is it that I need the full 12V to trigger the relay? what if I want my train to crawl through the intersection?

[Yog-Sothoth]

Yeah,low voltage is likely the problem. Why not use AUX (presumably constant voltage) power to trigger the relay as well?

Of course you need to have a common ground between your aux transformer and track power for this to work.


Yog

[phillyreading]

How are you wiring the relay and signal?  Are you picking up the common from the outside rail? Sounds like you may have a wire srossed or not enuff power to the signals.  Another more user freindly way but more costly way to wire is with infra-red detectors from DZ Industries, check the Ross Custom switches website for DZ products, DZ Industries only sells whole directly.

Lee F.

[Anonymous]

First,12VAC relays are kind of rare. I use a seperate phased tap dedicated to relay power sharing a common ground to the track. I use  24 volts because I use 24 volt relays but since you have a 12 volt relay you would have to use 12 volts.  To quiet down the relay chatter you could install a 100 uf or 220 uf 35 volt NP (non polar) capacitor across the coil leads.
 
These are not common Radio Shack items so you can make your own out of 2, 220uf 35 volt polarized capacitors. Hook 2 like terminals (either the 2 pluses or 2 minuses) together. Insulate the bare terminals and install the other 2 leads across the relay coil. The resulting assembly becomes a 110uf bi polar capacitor. Similarly wired 2, 470 uf capacitors would become a 235uf bi polar assembly.

Dale Hz  

[jprampolla]

Hi HopperSJ and Folks,

     I have had a similar problem when my wheels were dirty or the insulated rail section is too short in length.  I use several 12 VAC relays that I got from a surplus sales house about 15 years about.  Try cleaning your wheels (I like rubbing alcohol and an old tooth brush) first.  Dirty track can also cause the problem.

    Hope this helps!

Take care, Joe.

[lionelsoni]

Adding capacitance across the coil of an AC relay will only draw more current from your transformer, without affecting the relay.  Two 470-microfarad capacitors in series will draw about 1 ampere from a 12-volt transformer.

The relays should be operated from a fixed auxiliary voltage, which may be any convenient DC or AC voltage, any frequency, any phase.  The auxiliary supply should have its return connected to the non-isolated outside rails.  Twenty-four volts AC is convenient because it is used for HVAC and the relays and transformers are cheap and easy to find.

Did you see what I posted on your earlier topic?

AC relays do tend to be noisy, since the relay sees no voltage and therefore starts to release 120 times each second.  Good ones often have a "shaded pole", a copper ring around part of the magnetic circuit.  The current induced in the ring lags the coil current and provides a little magnetic flux to keep the relay adequately operated during the axis crossings of the coil current.

[HopperSJ]

I Love this Forum!!

Yog-Sothoth - Great idea! I didn't even think I could use the AUX common through the rails, but it worked like a charm!!! Still the slightest clicking, but that is clearly from connection breaks (ie dirty wheels or momentary conductivity loss). It works great. I'll clean up those last wheels and maybe even insulate the relay with cloth/foam to absorb some of the random clicks, but even without that, it is 100 times better!

phillyreading -  I really like those infrred switches. I'll be buying a pair from Z-stuff for one crossing where my road crosses a turnout. No chance of an insolated rail there so the infrared is the way to go. But, it was too costly to do all my crossings that way. They are pretty, however.

jprampolla - I do have a couple of dirty wheel, apparently, but the initial problem was clearly a "low-voltage" issue. just a constant clicking like a drumroll. I will clean off those last few cars though. Interestingly, the last car on the consist makes it click too, I don't know if it is a weight thing or not, but it happens with two different consists.

lionelsoni -  I did see you post on my other thread...right when I got back from the store with my new relays. I was so excited to find AC relays that I had to run home and try them out!

[Yog-Sothoth]

Glad that worked!

If you want to eliminate the intermittent contact loss you would really have to go DC: a bridge rectifier, a DC relay, and a capacitor across the relay coil. While a little more complicated, this actually works out cheaper than an AC relay. DC relays can be had for about a dollar, and rectifiers and capacitors for pennies.

Yog

[HopperSJ]

DC relays for a dollar? Both at Radio Shack and the electrical store I went to were selling them for about $8-$9. That's what I bought my AC relay for. You can reallly get one for a buck or two?

[Yog-Sothoth]

Yes, from an on-line electrical supply place like Mouser or Digi-Key. Though if you just need one or two it's not worth it paying the shipping etc.

Yog

[Anonymous]

A DC relay will not chatter if a polarized capacitor is put cross the coil leads. That was not the question,the question was how to reduce the tendency for an AC relay to chatter. The bi polar capacitor will work. As Bob mentioned it does use energy so it is a solution only if you just have a few relays. The capacitor has no effect on the coil but when continuity is intermittant it will hold the coil in as it discharges slightly. I use these on a few 24VAC relays I have. I know the whole thing pulls less than 1 amp because I bench test them with a 1 amp fuse in series with the circuit. The caps will get pretty hot so I know it uses energy but it takes away chatter to a degree.

I buy relays with sockets surplus,they cost me about $8 each for name brand DPDT ones.

Dale Hz 

[lionelsoni]

An incidental advantage of using DC (as the supply, not just rectified at the coil) is that it makes diode logic possible.

[Anonymous]

Bob

I did a bit of experimenting on a 24VAC relay I have. I half waved it with a diode then put a 470uf cap across the leads. The relay pretty much works like a DC relay and does not chatter. Do you think operating it this way on DC will damage the AC coil long term? I left it on about an hour and the coil did not seem unduly hot.

Dale Hz

[lionelsoni]

I'm sure some of the coil impedance is reactive; and that would go away when you operate it on DC; but just how much is impossible to say without trying it (as you did).  If it didn't overheat, then, for that relay, its impedance is mostly resistive; and so the impedance must not change much between AC and DC operation.

I have measured the reactance of an e-unit coil and found it comparable to the resistance; but I don't have any trouble when I run a locomotive on DC.  The e-unit is surely getting hotter, just not enough to harm it.  However, I found that when I rewired my two NW2 switchers' motors in series, effectively doubling the e-unit voltage, in addition to the DC operation, that pushed the e-unit over the edge.  I had to wire a lamp in series with the coil.

[Anonymous]

Thanks Bob

I have about 30 AC relays on my layout for a block system. I was going to replace them with DC ones but it would be a lot of work because the terminals are all soldered. I think I will run them on DC as described. All I have to do is install a cap and a diode. If I start burning coils I guess I will replace them.

Dale Hz 

[lionelsoni]

Dale, try a little bridge rectifier first, without the capacitor.  It should make the coil inductance work for you by allowing the coil current to continue to flow during the dips in the voltage waveform.  This may be enough to quiet them.

 

[HopperSJ]

Did you ever feel like a thread you started ended up moving way over your head!

Great feedback, though, and I look forward to the day I have 30+ relays. Now that would be a layout!!!!

[Anonymous]

Dont wish to alarm you but I use over 200 on my layout. I have 7 automated loops plus 2 reverse trolley loops and also run accessories on timers and relays. The 30 I am talking about I used AC ones where I should have used DC.Trying to get away with not replacing them. They work but they do chatter.I like relays,I used to repair pinball machines.

Dale Hz