You need a few lessons in electricity. Keeping it simple a battery developes a voltage potential. You want to use that potential to push electrons (flow is called current) through a wire to run a load (light bulb, motor, etc). So you connect the battery to the load with some wire. Now it gets a little more complicated. Wire has resistance and will consume part of the power you'd like to get from your battery to your real load (light bulb, motor, etc). The bigger the wire the less resistance it has and the less power you lose in your transmission wire and the more that gets to the load. The more power you lose in your wire, the hotter it gets, till, if you push too far, it will get hot and start a fire. With small currents/loads, the amount you lose in the transmission wire is small. The more current you try and push through a wire the more power you will lose as a result of the wire's resistance. Bigger wires have less resistance and will carry bigger currents, lose less power, and not get as hot as small wires. Fuses or circuit breakers should always be used to prevent too much current from flowing through a wire by blowing or tripping before the wire is damaged.
I think the book you are using is a little more conservative than necessary. House circuits use 14 gauge to carry 15 amps ( and 12 gauge for 20 amps) for a lot longer distance than any teardrop will, but there are some subtle differences between 120 volt and 12 volt power transmission.
Anyway, your wire is plenty big, as stated before you can get spade connectors that will fit your wire, and be ok. I think that the cigarette lighter type recepticles are rated for about 10 amps. I agree that the little white wire that came with your recepticle was a little whimpy but you can get away with short runs of small wires as the resistance is pretty low in a short small wire but would be too high in a long small wire. I have a number 14 or so wire that I push 300 (three hundred) amps through on a regular basis! It is, however, water cooled and if the water stops flowing, it will melt pretty fast!
Hope this helps.
Cheers,
Gus
Teardrops n Tiny Travel Trailersor t n ttt for short (tnttt.com) |
12 Volt Outlet Wire Question
31 posts
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You've asking for it now!
by eamarquardt » Fri Jun 04, 2010 8:29 pm
The opinions in this post are my own. My comments are directed to those that might like an alternative approach to those already espoused.There is the right way,the wrong way,the USMC way, your way, my way, and the highway.
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"You can't handle the truth!"-Jack Nicholson "A Few Good Men"
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"I'm impatient with stupidity. My people have learned to live without it." Klaatu-"The Day the Earth Stood Still"
"You can't handle the truth!"-Jack Nicholson "A Few Good Men"
"Some people spend an entire lifetime wondering if they made a difference in the world. The Marines don't have that problem"-Ronald Reagan
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eamarquardt - Silver Donating Member
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Wire Size 101
by Engineer Guy » Fri Jun 04, 2010 10:07 pm
I've dealt with this issue many times over my career, so let me try to un-muddy the waters...
My reference is always some version of the Chart linked below, and I've used 'ohms/1,000' for any given wire size. It's easy to get your head around that length and ohmage for mental math.
http://www.powerstream.com/Wire_Size.htm
Yes, 1,000' of #18 is >6 times the resistance of #10. While that's true of even short wire runs, it takes 1,000' of wire for this difference to be even a few ohms total. The short run of #18 wire likely will be inconsequential in the real world. Yes, a short bit of #18 will act as a 'fuse' relative to the #10, but only during long periods at maximum amperage [current] that #10 wire can carry, especially if the #18 run cannot air cool itself.
I used to advise folks making long, unwieldy wire/cable runs to run wires in parallel for any given size. You could do the same, and parallel another #18 or larger wire to the existing #18 wire. This trick would make the effective resistance of this short run ~half of what it was, or ~3 ohms [if it were #15 wire 1,000' long].
It's important to realize that resistance is evenly distributed along the length of any wire. That resistance difference is not all 'crunched' disproportionately into the short run you show in your very helpful pix. 'Run the numbers' to see #10 vs. #18 wire resistance in the relative lengths you're using.
The short length of wire on the connector ground side was because the expectation is that is goes to vehicle ground closely adjacent, or it grounds through mounting screws. This is not the case in a wood frame TD. It is assumed that the positive lead, +12 VDC run will be much longer, and more prone to resistance-related voltage drop, than a short ground connection made adjacent.
What you've got are called 'spade lugs' in the world of us 'sparkies'. You could buy a couple more spade lugs, and crimp on a larger size wire. It would then slip on the 'male' connector 'paddle'. Spade lugs come in various sizes, so take in what you have to match it in size [width].
I crimp and solder everything and put heat shrink tubing around it. Alternatively, connections should always be mechanically sound [crimped or twisted] before you solder. Wires should be firmly twisted together well before a wirenut is put on to withstand road vibration. Old timers put electrical tape around secured wirenuts as well.
Last, I've had Cig Lighter plugs themselves overheat and melt. Resistance is proportional to contact surface area. The rounded end of the Cig Lighter tip is WAY too small to carry the amps req'd in many applications. In what is called 'the thermal runaway effect', the tip of the connector corrodes or degrades as it heats. The resistance of it then increases. More voltage drop thus occurs across it, generating more heat, which corrodes it more. And so on... This is why Honda and other Generators use 'blade' plugs at unique angles to carry even 8 amps @ +12 VDC. Blade plugs distribute current over more surface area, overcoming resistance and thermal runaway inherent to small contact area. My point: there's other safety 'weak links' in about any Cig Lighter connection used to carry 'high' amperage vs. worry over a lil run of #18 wire.
Plug a 'high' amperage draw Accessory into your completed plug and hold the #18 wire in your hand to see if it heats up 'excessively' to you. That real world test will trump all theory. I think the same way, so I appreciate your viewpoint. There is a hypen in A-R! ;-0
My reference is always some version of the Chart linked below, and I've used 'ohms/1,000' for any given wire size. It's easy to get your head around that length and ohmage for mental math.
http://www.powerstream.com/Wire_Size.htm
Yes, 1,000' of #18 is >6 times the resistance of #10. While that's true of even short wire runs, it takes 1,000' of wire for this difference to be even a few ohms total. The short run of #18 wire likely will be inconsequential in the real world. Yes, a short bit of #18 will act as a 'fuse' relative to the #10, but only during long periods at maximum amperage [current] that #10 wire can carry, especially if the #18 run cannot air cool itself.
I used to advise folks making long, unwieldy wire/cable runs to run wires in parallel for any given size. You could do the same, and parallel another #18 or larger wire to the existing #18 wire. This trick would make the effective resistance of this short run ~half of what it was, or ~3 ohms [if it were #15 wire 1,000' long].
It's important to realize that resistance is evenly distributed along the length of any wire. That resistance difference is not all 'crunched' disproportionately into the short run you show in your very helpful pix. 'Run the numbers' to see #10 vs. #18 wire resistance in the relative lengths you're using.
The short length of wire on the connector ground side was because the expectation is that is goes to vehicle ground closely adjacent, or it grounds through mounting screws. This is not the case in a wood frame TD. It is assumed that the positive lead, +12 VDC run will be much longer, and more prone to resistance-related voltage drop, than a short ground connection made adjacent.
What you've got are called 'spade lugs' in the world of us 'sparkies'. You could buy a couple more spade lugs, and crimp on a larger size wire. It would then slip on the 'male' connector 'paddle'. Spade lugs come in various sizes, so take in what you have to match it in size [width].
I crimp and solder everything and put heat shrink tubing around it. Alternatively, connections should always be mechanically sound [crimped or twisted] before you solder. Wires should be firmly twisted together well before a wirenut is put on to withstand road vibration. Old timers put electrical tape around secured wirenuts as well.
Last, I've had Cig Lighter plugs themselves overheat and melt. Resistance is proportional to contact surface area. The rounded end of the Cig Lighter tip is WAY too small to carry the amps req'd in many applications. In what is called 'the thermal runaway effect', the tip of the connector corrodes or degrades as it heats. The resistance of it then increases. More voltage drop thus occurs across it, generating more heat, which corrodes it more. And so on... This is why Honda and other Generators use 'blade' plugs at unique angles to carry even 8 amps @ +12 VDC. Blade plugs distribute current over more surface area, overcoming resistance and thermal runaway inherent to small contact area. My point: there's other safety 'weak links' in about any Cig Lighter connection used to carry 'high' amperage vs. worry over a lil run of #18 wire.
Plug a 'high' amperage draw Accessory into your completed plug and hold the #18 wire in your hand to see if it heats up 'excessively' to you. That real world test will trump all theory. I think the same way, so I appreciate your viewpoint. There is a hypen in A-R! ;-0
Last edited by Engineer Guy on Sat Jun 05, 2010 7:45 am, edited 2 times in total.
~Reality proceeds with or without your consensus~
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Engineer Guy - The 300 Club
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Confused?
It’s not about spade connectors or disconnects to use to connect a device.
Here is my question, singled out:
But, Don’t answer yet
Once again, I say, “Sorryâ€
Thanks a bunch for your reply! What you said makes a lot of sense. 
