Relay_operaing current

[hinal111]

Hi, everyone...

I need to use lesser operating currrent relays in my project.
I want to interface 8 relays with atmega16 using 12v/24v smps.
My confusion is which relay (12v or 24v DC) would be better one for low operating current?

 

[Ogu Reginald]

The type of relay to use depends on:

1. the current requirement of your load (that is: the load the relays will switch).

2. the current output of your power supply unit and the current the individual relays require for its coil to switch ON.

 

[Audioguru]

Ohm's Law says that current is voltage/resistance.
If two relays are identical except #1 has a 600 ohm coil and is 12V and #2 is 1200 ohms and 24V then the current used by #1 is 12V/600 ohms= 20mA and for #2 is 24V/2400 ohms= 10mA.

 

[hinal111]

I got it guru...!!! but normally which relay (5v or 12v or 24v) has lesser operating current ??...Is there any standard practice or rule ?? OR it differs from vendor to vendor.

 

[Surendhar M]

The operating current of a relay depends on your load so decide on basis of that.

 

[kam1787]

If two relays are identical except #1 has a 600 ohm coil and is 12V
and #2 is 1200 ohms and 24V
then the current used by #1 is 12V/600 ohms= 20mA and
for #2 is 24V/1200 ohms= 20mA.

corrected the boo-boo. so the current draw is Voltage/coil resistance

relays are provided with the coil resistance or current draw. pick one with the lowest current draw that will handle the load

 

[chuckey]

For a given package, the power of the relay coil tends to be constant, i.e. a DIL relay can switch say, 20 W with its contacts and requires .1W for its coil. So the .1W, might be .02 A @5V, .01A @ 12V, .005A @24 V. If you want to switch 1 KW at mains you will need a much bigger relay, so this might need 2.5W for its coil,i.e. .5A @5 V, .2A @12V. . .
Frank

 

[Audioguru]

The operating current of a relay depends on your load so decide on basis of that.

Absolutely not!
The operating current of a relay is the current in its coil that has nothing to do with the load that it is switching.

- - - Updated - - -

corrected the boo-boo.

You saw my error before I corrected it one minute later.

 

[BradtheRad]

I wanted to operate a relay at 5V. I found it would not work on a relay which has a 6V coil. 5V is insufficient to push through the required amount of m-Amperes.

I visited Radio Shack. They had a 'super sensitive' 5V relay. It operated on 'low' current. The coil appeared large, as though it had a lot of turns. That's what made it possible. Nevertheless it needed more current than a 12V relay.

The pull-in mechanism requires a certain amount of power. Lesser operating voltage, greater current.

Specs of relay coil resistance should tell the story.

If you wish to minimize power usage, look into latching relays. A pulse activates them. They stay pulled in, and do not need continual current applied.