12v relay for a 24v coil

[David Anderson]

I have some 24volt solenoids I need to open by putting relays on them.  I only have 24v power to activate the coils.  I tried one circuit with a 12v relay and it seems to work fine.  Can put 12v relays on all the circuits with 24v coil power?  I can find them cheap at Autozone, $5.00.

David

[boogiethecat]

You can do this for a while.... until the 12v coil burns out or catches fire, which will most likely happen sooner than later!!!

Actually if you just can't find a 24 volt relay anywhere, you can put the coils  of two *identical* 12 volt relay in series; use one relay for it's contacts and let the other sit unused except for it's coil, which will eat 12 of the 24 volts up, leaving the other 12 volts for the relay you're using.  Kind-of "mouse" but it will be reliable and not pose a fire threat.

Here's two "stores" on ebay that have nice 24 volt relays. I'd recommend just buying some and do it right....

    Item number: 130070105120   
    Item number: 180087025107   

There many more here, like tons of choices:
http://search.stores.ebay.com/24-relay_W0QQcatrefZC5QQdfspZ32QQfclZ3QQflocZ1QQfromZR6QQfrppZ50QQfssZ0QQftrtZ1QQftrvZ1QQnojsprZyQQsaaffZafdefaultQQsabfmtsZ0QQsacatZQ2d1QQsacqyopZgeQQsacurZ0QQsaobfmtsZexsifQQsaslcZ0QQsaslopZ1QQsbrexpZWD1SQQsbrhrlinkZstrQQsifZ1QQsofpZ4


Just don't get "solid state" relays, for this application they aren't the right choice.

Cheers
G

[Don4107]

First choice would be to find a 24V relay with the proper current rating. 

To use the 12V relay, measure the resistance of the coil and put a resistor of the same resistance in series with the coil.  If the resistor is the right value you will measure half the voltage across the resistor and half voltage across the coil when activated.

If you use Boogie's idea of two relays, put the coils in series as he suggests, but put the contacts in parallel to double the current carrying capacity.

Good luck
Don 4107

[Sean]

... but put the contacts in parallel to double the current carrying capacity. ...

Parallel contacts on separate relays are not rated for twice the single-contact rating, for a variety of reasons.

If you need the additional capacity (I can't tell from the OP), then you need to de-rate the contacts by whatever amount the manufacturer of the relay recommends.  That's usually at least 25%.  The break rating is usually more critical than the continuous rating, which may be much higher.

-Sean
http://ourodyssey.blogspot.com