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Old 11-24-2020, 01:33 PM   #1
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Extension cord for trickle charging

I have a 50amp class A and need to keep the batteries charged during the winter. The nearest outlet at the house is 100ft away and I have a 50amp to 15amp dogbone. I don’t plan on using any other electricity except for the battery charging. What gauge extension cord do you recommend?
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Old 11-24-2020, 01:37 PM   #2
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Extension cord for trickle charging

How long is your 50 amp cord? If it’s 25ft then you only need 75ft of extension?

I think you would be best served with a 12 gauge extension cord. Should be entirely adequate for 15 amp or less (at 120 volts) battery charging. Set your “shore max” parameter on your charger (most magnum inverter/chargers) to limit the amount of current it can draw. If your charger doesn’t have a programmable limit for current draw, make sure batteries are fully charged before plugging in using the extension cord, so current draw should be minimal.
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Old 11-24-2020, 01:42 PM   #3
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Quote:
Originally Posted by Fischse View Post
I have a 50amp class A and need to keep the batteries charged during the winter. The nearest outlet at the house is 100ft away and I have a 50amp to 15amp dogbone. I don’t plan on using any other electricity except for the battery charging. What gauge extension cord do you recommend?
My feeling is that 14 gauge will be fine. The thinner 16 gauge cord may work but for a few bucks more, why try.

Make sure you set your charge max down to 10 amps or so if you have an inverter/charger. If its a converter/charger, there will be no adjusting.
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Old 11-24-2020, 01:42 PM   #4
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I have 100 feet to go after I fully unwind the 50amp cord. Good call on setting the shore max to limit draw, didn’t think of that.
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Old 11-24-2020, 02:47 PM   #5
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Here is the calculation table to figure the gage of wire to supply your charging device. You will need to know the amp draw of your charging circuit.

The following calculator calculates the voltage drop, and voltage at the end of the wire for American Wire Gauge from 4/0 AWG to 30 AWG, aluminum or copper wire. (Note: It just calculates the voltage drop, consult the above table for rules-of-thumb, or your local or national electrical code or your electrician to decide what is legal!) Note that the voltage drop does not depend on the input voltage, just on the resistance of the wire and the load in amps.
Select Copper or Aluminum
Copper

Select American Wire Gauge (AWG) Size

30 AWG

Select Voltage

120 Volts 1-phase

Enter 1-way circuit
length in feet (the calculation is for the round trip distance)

Enter Load
in amps


Voltage drop

Voltage at load end of circuit

Per Cent voltage drop

Wire cross section in circular mils
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Old 11-24-2020, 02:54 PM   #6
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Agree with Twinboat that a #16 will do. I find 100' of #10, yes it's going to costs $100 (4 nights at a CG) as it's is handy when staying at friends with a 15A outlet. I can run one AC off it by shutting everything off other than the charger and refrigerator.
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Old 11-24-2020, 06:00 PM   #7
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Why don't you just use an extension cord for the battery charger only?
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Old 11-25-2020, 12:23 AM   #8
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I had the same problem at my house. I use a 100 ft 12 gage extension cord on our 30 amp MH when it is parked at our house. I also carry a 50 ft 12 gage cord for use when we stay at friends and relatives houses for a few days. It won't power every thing, but allows us to power computers, charge phones and run the TV without running the generator.
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Old 11-25-2020, 06:02 AM   #9
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14 gauge should be fine for the described usage.
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Old 11-25-2020, 06:20 AM   #10
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Quote:
Originally Posted by Fischse View Post
I have a 50amp class A and need to keep the batteries charged during the winter. The nearest outlet at the house is 100ft away and I have a 50amp to 15amp dogbone. I don’t plan on using any other electricity except for the battery charging. What gauge extension cord do you recommend?


This totally depends on what charging system your motor home has. Mine in floating stage it will draw maybe 1 amp but in bulk it can draw much as 14 amps. You need to figure out what will be your Max amp draw and go from there.
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Old 11-25-2020, 07:02 AM   #11
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Some have suggested buying a (possibly) $100 extension cord.

A 50 W solar trickle charger is around $60 on Amazon.
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Old 11-25-2020, 07:17 AM   #12
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Quote:
Originally Posted by Fischse View Post
I have a 50amp class A and need to keep the batteries charged during the winter. The nearest outlet at the house is 100ft away and I have a 50amp to 15amp dogbone. I don’t plan on using any other electricity except for the battery charging. What gauge extension cord do you recommend?
If you be sure you get the made in America cord this is the best buy out there.

https://www.amazon.com/Southwire-Ext...ef_=ast_sto_dp

Use the 12ga then if you need a little more you have the extra amps available - at this price you should smile.

JMHO,
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Old 11-25-2020, 07:22 AM   #13
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A 14 gauge extension cord should work just fine. But why not just disconnect the batteries when you park the coach. Then there are no worries if the charger fails or the cord gets unplugged.
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Old 11-25-2020, 07:50 AM   #14
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Lots of good advice above.

Some aspects of wiring code have not changed in a long time. Wire gauge code is one of them. However, the code is for permanently installed wiring. What you plug into the permanent wiring is not included. However, using the code tables for selecting extension cords can make life better for you.

Ampacity:
example: 14 gauge is good for 15 amps at 50 feet.
amp volt watt | volt watt gauge
15 120 1800 | 12 180 14
20 120 2400 | 12 240 12
30 120 3600 | 12 360 10
50 120 6000 | 12 600 8
75 120 9000 | 12 900
100 120 12000 | 12 1200


Ampacity means the wire can safely carry the current. It does not mean the appliance connected to the wire will work properly. To work properly one must increase the wire size to decrease voltage drop at the end of the wire. The above table will provide adequate voltage up to 50 feet from the service entrance. Any further requires bigger wire.

You can use smaller wire, but it would not be good to trust it if in contact with anything combustible like dry grass or wooden building.

A 100 amp battery charger (12 v X 100 = 1200 watts) will easily work with 14 gauge wire for up to 50 feet. However, fully charged batteries will only draw a few amps, maybe 5 amps (12 v X 5 = 60 watts). 16 gauge lamp cord will work. Voltage drop would probably be acceptable. Use a voltmeter to see if voltage is at least 110 volts AC.

There will not be circuit protection suitable for 16 gauge. If accidentally overloaded, a fire could ensue. Add a fuse or circuit breaker for safety. Some light cords have a fuse built into the plug for this exact reason.

I wish you good luck and happy trails ahead!
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