Current sense mains relay

[Heinz]

I'm trying to make a current sense relay.
Took a standard RS 11 pin relay, unwound the 12 volt coil and replaced it with ten turns of live wire stripped out of some scrap twin and earth. Hooked it up to see what happened, coil in series with the live wire. Mega buzzing from the contacts. Tried removing the return spring to see if it was too powerful, just the same. Decided the new coil must have too few turns, so found a chunk of enamelled wire about the same gauge as the twin and earth I had used and rewound the coil with it. Now have about forty turns in the coil and the contacts still buzz like a demented wasp in a biscuit tin. Any ideas???

Heinz

[johnrae]

The buzzing is caused by the magnetic field switching directions.
Chances are your original relay was a DC model. 
The cores of DC relays are different to those in AC ones. 
If you really (no pun intended) want to continue with the experiment then find an AC relay and work from there.
Without wishing to spoil the fun, what current levels are you trying to push through the 11-pin relay base - or to put it another way, are you working within the limits of its rating.
jack

[Heinz]

What's the difference in the core? I did wonder about some AC v DC difference, but had a look at the current sense switch off a fridge and it doesn't seem to be any different in operation/construction to what I'm trying to do.
Current levels are less than 10 amps, so within the 11 pin rating.

Heinz

[johnrae]

DC is generally solid and AC is generally laminated (to minimise eddy currents)  AC may also have a bare copper shortened turn around the end of the core
What was your original relay, DC or AC ?

[Heinz]

It was DC, just because I happened to have a pile of them. So the shorted turn, is it just a ring round the end of the core? I can make that.
I could just order up an AC relay, but that's a least another three days and I'm now interested in how it works + making it work....

Heinz

[johnrae]

Sucked the following off a google search
As you'll see the shortened turn, or shaded pole is on half the core - which must be laminated if you don't want it to cook.

With an AC source, the 'pull' pulses 120 times a second (100 times a second
on 50hz).  This uneven magnetic pull causes the relay to chatter/buzz.  AC
coils deal with this by putting a short-circuited shading coil around 1/2 of
the pole face.  The eddy currents induced in this coil build up a magnetic
field.  Because of the inductance, the current in this coil is out of phase
(time shifted) from the main current.  So although the magnetic field in
this section of the pole face alternates at 120 hz (or 100hz), it crosses
zero at a different time than the rest of the pole face's magnetic field.
Result is a steadier 'pull' and no chatter.

[Heinz]

Wandered up to the workshop and cut the pole piece not quite in half for most of it's length, made a D shaped copper sleeve to fit in the slot and round one side. Hooked it up and it is a lot better, but still too noisy. Dug through some of the electrical junk box and found a low power AC relay which has a copper ring in the end of the pole piece, that's probably what I should have made, but enough learning and playing around for the evening.... Off to acquire an Ebay AC relay.
Thanks,

Heinz

[rogeriko]

Why not just buy one of these http://download.hager.com/Hager.no/files_download/Bedienungsanleitungen/EU103.pdf This is what I use to monitor the current DC from the turbine and I use the built in adjustable relay to disconnect the turbine for a few seconds when the turbine stalls. Couldnt be easier AC or DC 0.1 amp up to 10 amps relay contacts fully adjustable and hysterisis adjustable. Why mess around??

[Heinz]

Why not just buy one of these http://download.hager.com/Hager.no/files_download/Bedienungsanleitungen/EU103.pdf This is what I use to monitor the current DC from the turbine and I use the built in adjustable relay to disconnect the turbine for a few seconds when the turbine stalls. Couldnt be easier AC or DC 0.1 amp up to 10 amps relay contacts fully adjustable and hysterisis adjustable. Why mess around??

You're probably right, but there are several reasons.
1/ Money. Can't find your relay, but similar ones are around £100 I'm trying to do this on a very low budget, think it's around £600 total so far, with much of it made from junk.
2/ Interest. I'm interested in how things work, always have been, so I'm curious as to exactly how a current relay works in real life, not a book. Learnt a bit last night while messing around with it while most of the country was glued to the TV.
3/ Simplicity. If a low cost relay with a dozen turns of wire round it will do the job, why use a fancy relay with loads of functions, settings and programming modes?
4/ Fragile. We live at the end of the mains power line, wires on poles stretched over the hill to here, so anything electronic tends to die suddenly during storms. Lost count of the modems, phones, computers, routers, etc. which have been killed by voltage spikes.
5/ I'm stubborn...

All that said, your relay does look interesting and if I fail to make something which works well in less than a few hours of fun time, I'll bit the bullet and buy one.... 

Heinz