24 vdc relay on 24 vac

[bensonelectric]

Re: 24 vdc relay on 24 vac

This cool old guy owns the place, and lets me dig through all his surplus and lets me get a normal grocery size bag full of whatever for 20 bucks.

It is really outrageous nowdays the cost of a really cheap part and how much some retailers sell it for.

 

[physis]

Re: 24 vdc relay on 24 vac

AAhh, surplus. Surplus is way fun. The stuff you might come across is truely amazing.

 

[hbiss]

Re: 24 vdc relay on 24 vac

Go to ADI or any other security supply house. They have full wave bridges all wrapped up nice in shrink tubing made up with four leads coming out just for this use.

These are used with magnetic door strikes to convert the AC usually from a 16V doorbell transformer to DC. Sometimes people don't want the strikes to buzz. Then you use a DC strike and a rectifier.

Nothing says you can't use them for a relay coil.

-Hal

 

[bensonelectric]

Re: 24 vdc relay on 24 vac

Most of the stuff I find I dont need, but you never know when you might need one of them there dingies or doodads.

Most of my electronics projets on the other hand I get the parts from the school supply room, well stocked since 1952 with some parts from back then too

 

[steve66]

Re: 24 vdc relay on 24 vac

templdl:

Can you explain exactly how a AC contactor or relay works? I haven't worked through all the math or thought about it in depth, but is seems like the magnetic field would pull in the contact on one half cycle, and push it away on the next half contact when the current is going the other direction.

Steve

 

[physis]

Re: 24 vdc relay on 24 vac

I'm probably not seeing what you're getting at Steve but, the armature's not a magnet.

 

[rattus]

Re: 24 vdc relay on 24 vac

Steve, the magnetic field induces an "mmf" in the armature. This mmf is such that the armature pulls in on both lobes of the alternating current.

A "shader ring" is employed to reduce the buzz.

See:

http://relays.tycoelectronics.com/app_pdfs/13c3250.pdf#search='ac%20relays'

 

[templdl]

Re: 24 vdc relay on 24 vac

Steve, This explaination may mat be complete but should give you some idea of the workings of a relay.
A relay in all simplicity is a iron core with a coil of insulated wire wound around it. When current, either AC or DC in run through the coil it magnetizes the iron core. If AC the core is magnetized in alternating direction, DC extinguishes a N and S pole.
A simple piece of steel is pulled against the iron core when it is magneticed by either the AC or DC current. This steel plate type clapper is often hinged and held away from the core by a spring when the coil is demagnetized. The steel place actives a set of contacts by moving a moving contact against a stationary contact.
Bottom line? there is no magnet, only that which is created in the iron core when current is passed through the coil.
With AC current the cores N-S poles do alternate which can cause a hum or a buzz but it does not cause the metal plate to repel a the magnetism reverses directions.
Because AC causes current to also flow in the iron core the core is laminated and other design features are used to reduce core heating and reduce noise.

 

[steve66]

Re: 24 vdc relay on 24 vac

Thanks, I got it now.

Physis: you knew exactly what I was thinking and where my error was - two magnetic fields. I don't know where that came from. Probably something to do with motors.

Steve

 

[physis]

Re: 24 vdc relay on 24 vac

I'm just glad I never get anything all sideways and upside down or lopsided and backwards or twisted all around and all mangled up and stuff.