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Old 12/29/2008, 12:16 PM   #1
oldsaltman
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How to convert 24vdc to 12vdc?

I several electronic irrigation timers that have multiple channels and on/off times, but they are designed to operate 24vdc solenoids. I think they could be used to operate dozing pumps, ATOs and/or moonlighting etc. Anyone have an idea how to convert the output on each channel to 12vdc without spending more money than it's worth? Some type resistor or something? I can make something if I know what to make!


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Old 12/29/2008, 12:31 PM   #2
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a 24vdc Relay


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Old 12/29/2008, 12:38 PM   #3
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A 24v relay will just open and close. Then I would need a 12v power supply for each channel. Are you talking about something else?


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Old 12/29/2008, 12:42 PM   #4
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Oh I thought you were just using it as a timer.


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Old 12/29/2008, 12:45 PM   #5
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http://www.radioshack.com/product/in...ductId=2062600


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Old 12/29/2008, 12:45 PM   #6
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I thought it could be used as a controller, if the voltage can be altered.


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Old 12/29/2008, 12:59 PM   #7
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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.


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Old 12/29/2008, 01:06 PM   #8
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I am almost sure that it puts out 24vdc on each of the four channels. Each channel would normally open or close a 24v solenoid. I wanted to see if it could be used as a controller for 12vdc accesseries. Your info looks like what I was talking about. Thanks


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Old 12/29/2008, 01:23 PM   #9
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Kcress

You were right. I went back and looked and those controllers are 24v AC. I guess I need to start wearing my glasses!


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Old 12/29/2008, 01:59 PM   #10
H20ENG
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They are 24VAC and they will only turn on for a limited # of minutes and limited # of times per day. They seem like a great deal, but sadly are not versatile enough for our needs. Maybe for a dosing pump or topoff safety timer...


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Old 12/29/2008, 02:07 PM   #11
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you can run small AC relays and feed the relays 12 volt DC

or you could add a step down transformer to each outlet then add a rectifier and a capacitor


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