12v Relay on 24V output

Hey guys I have a bunch of 12v relays I want to use for a project. To hook one up to my 24v outputs on my micrologix plc what is the best method. Im pretty new to all this stuff Im a student, I know about the programming . Can I just hook up two resistors of the same value and tap the relay to the center. Or is there a better way to do this cause I would need higher wattage resistors to do that wouldn't I?

Kevin

In series would work with lightbulbs for sure. We used to test 480-volt DC drives with four 120-volt 100watt lightbulbs in series. Don't know why you couldn't put two 12vdc relays in series and put 24volts across them. Since you have a bunch of them...

Just determine the resistance on the 12volt coils and put them in series with a similarly-sized resistor. Doesn't have to be exact. Most 12 volt relays will work fine anywhere from about 10.5 to 16 volts.

kevilay said:

Hey guys I have a bunch of 12v relays I want to use for a project. To hook one up to my 24v outputs on my micrologix plc what is the best method. Im pretty new to all this stuff Im a student, I know about the programming . Can I just hook up two resistors of the same value and tap the relay to the center. Or is there a better way to do this cause I would need higher wattage resistors to do that wouldn't I?

Kevin

Click to expand...

Well, I am sure there will be other suggestions, but I would measure the current the Relay Coil draws at 12 VDC. You might be able to get it off the Relay itself, or the Manufacturers Data Sheet.
The put a resistor in series between the 24VDC Output, and the Relay Coil. R=E/I so say the current is 0.1A and we want to drop 12V across the Resistor, then R=12/0.1=120 Ohms. The Power Rating for the Resistor is P=ExI P=12x0.1=1.2W. So, I would use a 2W Resistor.

The other option if you have lots of Relays, and this is just for experimentation and testing. Put two of the Relays in series.

I look forward to the clever methods others come up with.

Stu.....

well i have like 8 of them and i need 5 of them I dont have enough to double up on them all. I dont have anywhere around here where I can get a 2w resistor

Kevin

kevilay said:

Hey guys I have a bunch of 12v relays I want to use for a project. To hook one up to my 24v outputs on my micrologix plc what is the best method.

Kevin

Click to expand...

The outputs of a micrologix are done in groups so take one group of say 4 outputs and use the 12 volts to power that group of outputs and use 24 v to power all the other groups, the rest of the outputs

A LM7812 comes to mind...

Personally, I think you should get the right plc to match the relays or vice versa. However, just for school experiments only I suppose it will be ok.
Maybe you can use an automotive lamp bulb in series with the relay coil. If you do try this, be sure to measure and verify that the correct voltage is applied across the relay coil when it is energized. Experiment with different lamps if necessary, (brake light, taillight, interior light, trunk light) for example.

Edit:
This is similiar to what Paul B said in post #2.

Depending on your PLC module you might be able to feed it 12 Volts instead of 24, that's providing you don't have other 24V loads on the same power supply.