How long can a 12v circuit be?

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Old 05-08-17, 06:33 AM
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How long can a 12v circuit be?

I have a gate opener that works off of a 12v automotive battery charged by a solar panel. In addition to the normal remotes, there is a momentary switch (a button) on the side of the control box that activates the gate just like the remotes do.

I am wanting to add another switch at my house which is about 600 feet away. Would the switch work from that distance? And if so, what gauge wire would I need to run?

This is my first post to the forum. I found the forum while searching for an answer to the above questions. Thanks in advance for any help.
 
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Old 05-08-17, 07:33 AM
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Welcome to the forums!

What I would recommend is installing a 24 VAC relay at the location of the opener and then running low voltage direct bury cable, such as the type used for landscape lighting, back to your house where you would have a 24 VAC transformer and pushbutton. The relay contacts would be wired across the contacts of the existing pushbutton at the opener.

It's possible that just extending the pushbutton circuit to the house would work, but it's hard to know for sure without knowing the internal design of the opener. The above suggestion would avoid some potential problems with electrical noise by providing isolation between the long cable run and the opener.

If you are interested in pursuing that option, we can provide more details if needed.

You might also contact the manufacturer of the opener to see if they have a suggested solution.
 
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Old 05-08-17, 08:19 AM
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Thanks for your reply. Using a relay had not occurred to me. I think I will go with that idea.

Thanks again.
 
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Old 05-08-17, 08:24 AM
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If you don't use a relay assuming trigger amperage is 0.5 amps or less #10 landscape lighting cable copper would have a voltage drop of 6%. giving you ~11volts. You would need to as the manufacturer actual amps needed and if that would be enough voltage.

The same cable if used with a 24 volt transformer at the house and a relay at the gate would give you a 2.9% drop which should work for a relay.

The price of the wire may send you in to shock though. Example: https://www.amazon.com/voltage-lands.../dp/B001GP4VKS
 
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Old 05-08-17, 08:28 AM
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FYI - Following is an automotive wire size chart (DC electricity). Note how large the wire sizes are for just a short distance!

https://images.crutchfieldonline.com...auge-Chart.jpg

AC travels MUCH further without voltage drop. So the suggestion above is excellent.

You can also search for a voltage drop calculator - these will be AC and DC. You input your information and it will tell you the wire size to use. Home AC electrical is "single phase".
 
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Old 05-08-17, 01:40 PM
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I have wired gate systems well over 1000'.
There are relays available with minimal coil loads.
There are also powered relay modules that work off a minute switching signal voltage.

ELK-924 Sensitive Relay
 
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Old 05-08-17, 07:27 PM
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That should work just fine with a door bell or thermostat wire (18AWG). That momentary switch is for sending control signals only. It doesn't really carry any current. Some voltage drop over long distance will not matter.

Only thing is thermostat wire is not made for direct burial and will need conduit for burying. Direct bury landscaping light wires will work, but personally I'd use conduit to protect wires from any future landscaping work and also allows pulling new wire later, perhaps a video intercom .
 
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Old 05-08-17, 08:56 PM
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Yeah all the button is doing is triggering a relay in the gate controller. It's only going to be a handful of milliamps for very short durations (a button press is what, half a second? 1 second tops?), and 12V relay coils will activate with as little as 7.5V.
 
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Old 05-09-17, 07:04 AM
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Thanks for all the replies. I appreciate the input.

After doing some guessing with the voltage drop calculators, I've decided to run some landscape lighting cable and try the switch. If it doesn't work, I can add the relay using the same cable. The cable will be the hard (and expensive) part. It's good to know I have a backup plan if the switch doesn't work.
 
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Old 05-09-17, 10:45 AM
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Landscape cable comes in various sizes. Consider that when buying. #10 is most likely to work without a relay but with a relay smaller sizes will work.
 
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Old 05-09-17, 05:27 PM
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Landscape cable comes in various sizes. Consider that when buying. #10 is most likely to work without a relay but with a relay smaller sizes will work.
He doesn't need anything anywhere near #10. Do you realize how much 600' of that would cost? It's like $500. 18/2 sprinkler cable will work just fine and costs about $400 less. Hell, he could use #24 Cat5 and it would work. Like I said, it is already just a relay trigger, there is almost no current, therefore almost no voltage drop.

Edit: I just did the calculation, and even factoring for 100mA (which is WAY more than any relay coil will draw, most are in the 10-50mA range - and if it's solid state it's going to be more like 1-2mA) the voltage drop in 18ga wire over 600' is a little over 4%, which equates to about half a volt. WELL within the tolerance.
 
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Old 05-10-17, 02:03 PM
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Just wanted to give a follow-up.

First of all, I want to thank everyone who answered.

I got a 500' spool of 16/2 landscape cable from HD ($86). Hooked it up and it works. Didn't need the relay. Now I just have to bury the cable.

I know I said it was 600' but that was an eyeball measurement. 500' just reached with about 2' to spare.

Thanks again for the help.
 
 

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