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kcress · 12/29/2008, 01:59 PM

Are you saying your timer puts out voltage rather then just closing a contact that you feed with your own common?

I thought most of that yard stuff was AC not DC are you sure on that?

If it really is DC you can just use a resistor. You need to actually power up each individual device with 12V. Measure the current. Then use these equations to calculate the resistance needed and the power rating of the resistance. Do this for each individual load.

Resistor needed = 12V/measured current @12V
Round up to the next closest available value.

Power rating of resistor = Resistor needed x measured current @12V x measured current @12V x 2
Take the closest power value up or down, though not too far down.

Example: 12VDC load you want to switch draws 0.6A

Resistor value needed = 12V/0.6A
Resistor value needed = 20 ohms

Power rating = 20 ohms x 0.6A x 0.6A x 2
Power rating = 14.4W
Look for a 15W or 20W rated resistor.

12/29/2008, 01:59 PM	#7
kcress Registered Member Join Date: Dec 2007 Location: Central California Coast. Posts: 5,383	Are you saying your timer puts out voltage rather then just closing a contact that you feed with your own common? I thought most of that yard stuff was AC not DC are you sure on that? If it really is DC you can just use a resistor. You need to actually power up each individual device with 12V. Measure the current. Then use these equations to calculate the resistance needed and the power rating of the resistance. Do this for each individual load. Resistor needed = 12V/measured current @12V Round up to the next closest available value. Power rating of resistor = Resistor needed x measured current @12V x measured current @12V x 2 Take the closest power value up or down, though not too far down. Example: 12VDC load you want to switch draws 0.6A Resistor value needed = 12V/0.6A Resistor value needed = 20 ohms Power rating = 20 ohms x 0.6A x 0.6A x 2 Power rating = 14.4W Look for a 15W or 20W rated resistor.