What guage wire for 120 foot 110V ext cord to 45 amp Iota battery charger? - Page 2 - SailNet Community

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  #11  
Old 09-18-2008
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An extension cord--and a GFI at the power post. Long extension cords in the rain or on damp ground can be a real shock danger without a GFI.
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Old 09-18-2008
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Sorry for jumping in late...as posted earlier, #12 wire size will be sufficient. You should also consider what the outer sheath of your extension cord is made of. Generally, like most things in life, you'll get what you pay for. If this is for long term usage, UV damage could be an issue. Will people walk on the cord or will it be subjected to physical damage? Will it be subjected to snow or ice? Just please don't buy the cheapest one you find at Home Depot. If I understand it correctly you are plugging two cords together...if that is the case, there are not a lot of very good ways to make that a good weatherproof connection.

Also be sure to not use something with Marinco 30 amp twist lock ends or it will require 100 more posts to figure that out.
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Old 09-18-2008
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I teach electricians for a living. There is voltage drop in AC. The max allowable voltage drop on a circuit is 3% according to Canadian Code. The 45 A is the dc side at 12 V. The AC side at 110 Volts will be less than (but very close to) 12 A if it plugs into a regular outlet. For 120 feet you should go #10. The maximum distance you can go with a #12 @ 12.5 A and 120 V is 14 meters. Max for #10 @ 12.5 A and 120 V. is 37.2 meters. All this according to the Canadian Electrical Code book.

That said, #12 would most definitely work, and probably be what I would use. After all, it's an extension cord, which by definition is a temporary installation, and so the rules can be bent a little.
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Sorry - should have mentioned - I do NOT have a fridge (just an ice box) but do have a force 10 6 gallon water heater, that plugs into shore power as well.
No A/C, or anything like that!

Does that change anything, or can I still get by with a #12. (realizing that a #10 would be better)
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I would highly recommend that you get a 10 AWG double insulated outdoor use extension cord if you can find it. Also, highly recommend using the GFCI on the end at the AC source... so you don't accidentally get zapped.

If you're going to be running the water heater and the battery charger at the same time, definitely upgrading to the 10 AWG cord is a good idea. BTW, I wouldn't recommend running them both at the same time on even a 10 AWG extension cord, which is really only rated for up to 20 amps generally.
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Running them both at the same time will trip the breaker anyways. I would seriously consider a different charger if I was you. Why do you need to charge the battery so fast?

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The charger wont draw anywhere near 11 amps if the boat is plugged in most of the time. Most of the time it will probably draw an amp or so just to maintain the batteries. Running that plus the water heater should be no problem. However if you run your batteries down a bit, then plug in the boat and flip on the hot water, you may end up tripping the breaker. Just wait the batteries come back up before turning on the hot water.

That being said, all this assumes you have a good power source. If you are plugging into a dock connection that is already a long run and is already being heavily used, you may be starting out at 108 volts or so. Adding a long cord would be a problem. Does your boat have a volt meter on the AC panel? Mine does, and I think it's a great idea. If it does, keep an eye on it for a while with whatever cord you choose. You can get a really good idea of the voltage drop by turning things on and off. You'll be able to see if your over taxing your setup.

Pay attention to your 12 volt system too. If you are pulling 20 amps from your batteries for a while your charger will be trying to put that much back, which is increase your charger load to almost half capacity or about 5 amps on the 110 volt system. You could operate totally safely on a #12 cord if you are careful and you have a good power source. A #10 cord would be better, but they can be hard to find.

Last edited by SteveInMD; 09-18-2008 at 09:09 PM.
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Look 12Guage is the minimum with JUST the charger running at 11 amps which is the MAX it can run at and this causes just about a 3% voltage drop which is the max you should allow.
Now if there are other big draws on that circuit like a heater then you could be drawing well in excess of 20amps with everthing going.
If you run 20amps of AC draw you are marginal even at 10 guage wire.
Just stick with standard dock cord all the way and be safe. You can get a couple of 50' cordsets for about $100 bucks and have no worries.
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Old 09-19-2008
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Can you please point me to where you can buy a 30 Amp 50' dock cord for $50???
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11 amps? That would imply only 41% efficiency on the part of the battery charger. Are they really that bad?

AllThumbs, how do you derive 12A at 120VAC from 45A at 12VDC? Battery chargers commonly have less than 40% efficiency?

I'm going to have fire-up the ol' Sears battery charger and take some measurements.

FarCry, there are many ways to make a good, temporary weatherproof connections. I do it every season with the outdoor Christmas display lighting. Perhaps the best way is self-vulcanizing tape, overlaid with 3M vinyl electrical tape. (I don't do that.) Done right, I'd probably trust that to be water-proof. (That is not a recommendation, but merely an observation.) What I do for the Christmas lights is a few snug wraps of Glad Press'n Seal wrap, with a few tight turns of 3M vinyl electrical tape at the ends. Quick and easy to put on, quick and easy to get off. Or sometimes I just go end-to-end, and back again, tightly, with 3M vinyl electrical tape.

Notice I've been explicitly writing 3M vinyl electrical tape? Just as with duct tape: Not all "black plastic electrical tape" is created the same.

Jim
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