Contact relay loud HUMMM

[mogogear]

I have a couple of Astra Gourmets that I am tweaking a couple of details on. Pretty easy machines to work on, but I have run into a moderately loud contact relay humm on one of them- to me louder than a hummm, when it first kicks in, pretty loud, then it settles down to just mildly annoying. Goes to almost quiet when the element cycles off, but of course kicks in again. ( almost)
I am lucky enough to have a parts machine ( another astra) around and I switched relays with it. Same but different sound. Both were in machines not used for a year or so. Are the points just dirty? And I did all that swapping for nothing? Cause it sure didn't go away!! So now instead of lifting one more screw driver, I am calling for advice.

Do I just need to clean the contact points? With some emory cloth or something? Or does the relay have to be replaced? BTW I have also gotten the sound with a complete boiler / element change out also..... What gives?

[another_jim]

Welcome to the wonderful 60 cycle humming world of AC coils. It's not the contacts (they just go CLACK); solder in a bridge rectifier across the coil to shush it (full wave, 4 diodes, otherwise it'll really hum).

[mogogear]

Welcome to the wonderful 60 cycle humming world of AC coils. It's not the contacts (they just go CLACK); solder in a bridge rectifier across the coil to shush it (full wave, 4 diodes, otherwise it'll really hum).

Ok, I can do that but Do I get one at Radio Shack or something and do you have any place on line to give me an idea about what points to use?
Odd, I have another Astra G - quiet as can be?????. This one will change pitch from crazy "buzzing" to less so If I switch the main power off and on ( maybe not advisable - but i did so just to see if it helped or changed).

So thanks for getting me started- I just need a little more info.
Thanks Jim

[another_jim]

AC relays vary; only about half of them buzz. radio Shack is fine for a rectifier. they are pretty self explanatory: a plastic square with two quick connect tabs for the AC in, two for the DC out at the corners; cost about $2 to $5 depending on load.

[mogogear]

AC relays vary; only about half of them buzz. radio Shack is fine for a rectifier. they are pretty self explanatory: a plastic square with two quick connect tabs for the AC in, two for the DC out at the corners; cost about $2 to $5 depending on load.

Ok, I think I can find the right item at RS- Now this relay has a bunch of connections on top and bottom( that are what the contactors are connecting) the main power wires to the pressurestat etc and stuff for the electronics etc. and there is the coil, kind of behind the contactors plate. There is a single small wire hooked to each side of the coil.
I guess I should take a picture cause I just dont know how to determine the place to attach said rectifier bridge.

Thanks for your help Jim

[another_jim]

You'll see a pair of connectors for the coil -- one wire will be neutral, the other will be coming from the Pstat. The rest of the contacts will be in threes -- a common, and the normally closed and normally open -- you'll see the hot and a wire to the boiler element going to the C and NO. These will usually be labelled. Manufacturers tend to get creative on the coil labels, but the contacts are always {C, NO, NC}

Connect the two wires going to the coil now to the AC tabs on the rectifier; connect the coil to the two DC tabs of the rectifier. Take about 15 minutes to sort out what's what, and 5 minutes to make the connections.

[bobcraige]

Relays are specifically designed with coils for AC or DC operation. Their impedance is very different for AC or DC inputs. While Jim may have gotten away with this, this is a really bad idea and likely to burn up some relay coils and might even cause a fire. If you look at a relay catalogue, you will find that the DC resistance of the relay's coil totally different for a relay whose coil is designed for AC vs one designed for DC. DO NOT DO this unless your relay's coil is specifically rated for DC use. Do not confuse the contact rating with the coil rating.

[another_jim]

Relays are specifically designed with coils for AC or DC operation. Their impedance is very different for AC or DC inputs. While Jim may have gotten away with this, this is a really bad idea and likely to burn up some relay coils and might even cause a fire. If you look at a relay catalogue, you will find that the DC resistance of the relay's coil totally different for a relay whose coil is designed for AC vs one designed for DC. DO NOT DO this unless your relay's coil is specifically rated for DC use. Do not confuse the contact rating with the coil rating.

Must have changed since the 80s, when I handled thousands of relays, and all the standard ones were rated for AC and DC operation.

[bobcraige]

This is basic physics and has not changed-ever! This is seriously dangerous advice. Please be careful about what you advise others to do. Contacts are rated for both AC and DC operation, but the coils are not.

[another_jim]

http://www.ecmweb.com/mag/electric_using_ac_coils_4/index.html

[mogogear]

I love the help both of you are providing- I am too stupid right now to be hurt or helped by it though. So my confused brain is going to not do anything yet - I'm will need to get a diagram to the Astra people and ask them where to install a rectifier bridge. That may seem the most prudent way to solve my problem and aching head