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Discussion Starter #1
Some of you may know that I'm installing driveway gate openers at my house (see this thread: http://tw200forum.com/forum/off-topic/15395-tunneling-under-driveway.html ). I have a question about voltage drop.

I am going to install my control box in the basement and the driveway gate 11' from the side of the house and the conduit to cross the driveway is in the front yard, I have about a 115' long run from the control box to the slave opener where I am worried about voltage drop over a run that long. The opener arms have 7 wires in the cable (two 14 gauge wires which are power and five 16 gauge wires which are for control). The wire connections in the control box will only accept this small size wire so I plan to connect 2 short leads of 14 gauge wire for the power and immediately upsize to larger wire (10 gauge) to make the run to the slave arm and then I will downsize the wire back to the original size wire at the opener arm. The other 5 control wires I will run 14 gauge wire from the box and then downsize to the original size wire at the opener arm. Think this is going to work?
Thanks
Ryan

gate opener manual pages 9-10 & 21-22
http://www.homedepot.com/catalog/pdfImages/16/16107fcd-3e7d-4889-bbf8-7ba567587b9a.pdf

 

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Ryan,
I would suggest you contact the manufacturer of your controller and ask them what the maximum distance would be with the small wire. Yes, upgrading the wire with larger wire should eliminate any problems you would experience.
Mel
 

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Rather than extra connections, I do understand your predicament, I think if the 10 gauge wire is stranded I would just trim out some strands at the connection so it will go in.

GaryL
 

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Discussion Starter #4 (Edited)
thanks Mel...i have contacted them but i didn't talk to an electrician...waited on hold fora half hour to talk to some guy that has never heard of a situation like mine and and just said it wouldn't work cause that's not how it was designed to be installed...basically they want the control box outside so it fails at some point from being exposed to the weather and you have to call them to get a replacement...i asked an actual electrician and he said it should work...my questions is will it?...will the small wire lead from the control box to large wire and then back to small wire at the arm create a voltage choke point leaving the control box?

thanks Gary...yea it will be stranded wire so maybe I will try doing that
 

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thanks Mel...i have contacted them but i didn't talk to an electrician...waited on hold fora half hour to talk to some guy that has never heard of a situation like mine and and just said it wouldn't work cause that's not how it was designed to be installed...basically they want the control box outside so it fails at some point from being exposed to the weather and you have to call them to get a replacement...i asked an actual electrician and he said it should work...my questions is will it?...will the small wire lead from the control box to large wire and then back to small wire at the arm create a voltage choke point leaving the control box?

thanks Gary...yea it will be stranded wire so maybe I will try doing that
The voltage loss occurs over the length it runs so increasing the wire size will alleviate the drop. Heat is also a concern if too much amperage is going through a small wire. At the final terminations if you trim a few strands so it can go into the block it should be a non issue.

GaryL
 

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there are sites on the internet where you can input your data , run length, amps etc, and they will tell you what gauge of wire to use. from looking at your drawing, I think you will have a hell of a time pulling that size of wire through a 3/4" conduit. maybe impossible. did you put sweeping 90's at the corners?
 

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Discussion Starter #7 (Edited)
there are sites on the internet where you can input your data , run length, amps etc, and they will tell you what gauge of wire to use. from looking at your drawing, I think you will have a hell of a time pulling that size of wire through a 3/4" conduit. maybe impossible. did you put sweeping 90's at the corners?
thanks...yea we used sweeping 90s...i have a 2 wire 14 gauge cable in there now so i plan to use that to pull the wire through...the trench is still exposed so i can always pull the conduit apart on each side of the driveway and snake it if need be...the conduit comes up to the gate posts and into junction boxes so i can get to the wire there as well...the length under the driveway is galvanized steel pipe and the rest is plastic pipe...i have a voltage drop calculator but i am not exactly sure what the voltage and amperage that the opener arm needs...it explains it on page 10 or 37 on the link i posted in the OP but it's a little confusing to me
 

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have you thought of putting a second battery on the far side and use the 14 gauge wires as a charging circuit. that would keep the wire size down
 

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Discussion Starter #9
have you thought of putting a second battery on the far side and use the 14 gauge wires as a charging circuit. that would keep the wire size down
not really...not too sure how to wire that and if i would fry something...i'm also trying to avoid putting anything extra outside with all the snow and cold weather
 

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I would think you will be able to put the 12 volt charging circuit ( 14 gauge wires) to the battery on the far side. then the accuator will draw it's amperage from the battery closest to it. it may solve a few problems in the long run. with a steady charge on the battery, it will stay warm in the winter and I think with a power source at both gates, they will open at the same speed
 

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Power = Voltage X Amps. Voltage doesn't cause voltage drop, amps cause voltage drop. Do you know what size the gate motors are, kW rating or horse? You should be able to look right on the motor. I will have a name plate with this data on it It will also have LRA or starting amps. That may be an issue too but there is an easy fix. This will tell us how many amps you have. I would not be too worried about the control circuitry. It will draw factions of an amp. What is the secondary voltage on your control transformer?

Devil, MSEE, PE, 30 Years Electric Utility Experience, RET
 

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Ryan, I believe your Mighty Mule might work satisfactorily as you describe. It is worth testing as you have described, may work well as well as Twilight's system.
Heavier gauge wire will lessen but not eliminate the voltage drop due to line impedance. Fewer and quality connections will also lessen total resistance. Should you elect to use Gary's fine 10 gauge stranded wire idea with some strands removed to neck down to 14 gauge ( avoiding the 14 gauge pigtails and connectors you mentioned) you might wish to solder the necked down transition. Should far gate open unacceptably slower than near gate you can always measure line impedance and add a ballast resistor to near gate's circuit to get matched impedance and thus hopefully matched operating speeds. Then at least you would have matched sluggish operating speeds.:p.
 

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Discussion Starter #14 (Edited)
Point37, I should have answered this first thing this morning, when I first read it, but.......I thought someone smarter than myself would come along and help you.

Question, is this system the Mighty Mule 500 ?

If so,. let me know, as I have a couple of them on my property, and the run from my transformer that is plugged in...inside the garage....to the main control box which also houses the back-up battery, is 110 feet, and I have NO problems at all, using the supplied 14 ga. wire. The control box itself has 10 ga. wire coming from it, to other controls within the box, and to the actuator arm, which is fine.

In YOUR case, you have the transformer in your garage...and very close to that you have the control box...in your garage...so the only external wires you have leaving your garage are the wires that feed the power to the actuator arms. Those wires should be 10 ga., and can easily carry that voltage, without any drop, across that length of wire.

It appears you decided to NOT go "under" your driveway slab...but go around it.
thanks TWilight...yes it is the mighty mule fm502 (i think the 2 just means dual openers) so basically the same as the 500...you can see the owners manual in my first post...the run between the transformer and the control box can be up to 1000' but that's not my issue...my issue is the run from the control box to the opener arm and the voltage drop since the control box just charges the battery and the openers run off the power supplied by the battery...my transformer will be in my basement and the control box will be in my basement right next to the transformer...control box to opener arm closest to the house is about a 15' run...control box to the opener arm farthest from the house is 115' run due to where i had to shoot the conduit under my driveway in the front yard (i couldn't go under my driveway next to my house, tried 2 times and failed so i moved to the front yard and got it through)...the wires to my control box and the connections (see photo below) are not 10 gauge and the connectors won't accept 10 gauge so i will either have to trim the 10 gauge stranded wire or use short pieces of 14 gauge to connect to the control box



Power = Voltage X Amps. Voltage doesn't cause voltage drop, amps cause voltage drop. Do you know what size the gate motors are, kW rating or horse? You should be able to look right on the motor. I will have a name plate with this data on it It will also have LRA or starting amps. That may be an issue too but there is an easy fix. This will tell us how many amps you have. I would not be too worried about the control circuitry. It will draw factions of an amp. What is the secondary voltage on your control transformer?

Devil, MSEE, PE, 30 Years Electric Utility Experience, RET
thanks Devils Advocate...the motors are housed in the opener arm and are about the size of a D cell battery so there is no plates on them...but that info is provided on the link i posted in the first post on page 9, i would paste the info but it doesn't format very well when i do and comes out all jumbled up...the ac power is only to charge the 12 V battery and the battery powers the system so i would assume the amperage on the battery would be the important part?
 

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Discussion Starter #15
Ryan, I believe your Mighty Mule might work satisfactorily as you describe. It is worth testing as you have described, may work well as well as Twilight's system.
Heavier gauge wire will lessen but not eliminate the voltage drop due to line impedance. Fewer and quality connections will also lessen total resistance. Should you elect to use Gary's fine 10 gauge stranded wire idea with some strands removed to neck down to 14 gauge ( avoiding the 14 gauge pigtails and connectors you mentioned) you might wish to solder the necked down transition. Should far gate open unacceptably slower than near gate you can always measure line impedance and add a ballast resistor to near gate's circuit to get matched impedance and thus hopefully matched operating speeds. Then at least you would have matched sluggish operating speeds.:p.
thanks Fred...good idea...i'll keep that in mind
 

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OK 680 ft. lbs motor. Lets use 700 just be sure we're safe. Starting requirements are up to five ties normal run but it only last for a second. 700 ft.lbs is is about 950 watts. At twelve volts you're drawing damn near 80 amps. That can't be right. The motors can generate that much torque but you will burn up 10 AWG wire.

What are the motor circuits fused at?

We can back into this and assume that the 10 AWG motor wire is 20% over rated draw. 10AWG is good for 30 amps so we could assume the circuits are fused at 24 amps. The resistance of 10 AWG is .999 ohms per 1000 feet. (Sorry, I work with power line stuff). V=I X R, or Delta V = 24 X .999 X 115/1000 or about a 2.75 volt drop. That's 22% V drop for a 12 volt rated motor and I wouldn't recommend it.

#6AWG copper is .395 Ohms/1000 foot, so now we're talking 24 X .395 X 115/1000 or a 1.09 V drop which is under 10% and acceptable. Now you have to look at conduit fill with that size wire. 4 #6 can fit in 3/4 inch conduit and meet code but you're going to play hell getting two of them around two sweeps.
 

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After looking at the picture you posted are both motors fed from a single pair of #10s? This could mean the draw of each motor is half of the 24 amps I assumed in with case the V drop would be half as well and then you would be close to 10% drop which would be marginal (probably work OK)
 

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The current draw of the motors depends on the load which I don't think will be too high. Just be aware that one gate will probably move at a different speed than the other. Most of these actuators draw less than 10 amps and that's under REALLY heavy load. Fire it up an see how it goes, you can only let the smoke out! :)
 

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It's not quite that simple. The limit switches, I would guess, sense current to determine when to open the power circuit. With a motor operating outside it's rated voltage it will not act linearly. At 20% under voltage a small variation in load on the motor would cause wide variations in current draw. It may cause the limit switch to interrupt the motor for just the swinging of the gate as it starts to move, that old harmonica thing of the mass of the gate not moving smoothly or uniformly as the motor draws it open or closed.

A more accurate guess could be made if we knew the expected current draw of the motor, like what the power circuit to the drive motor is fused for.
 
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