12 volt or 110 extension cord for small inverter?

How I wish I had my old reference manuals about electricity because I can't remember diddly without them. But here is my problem and question.

I use a small portable 400watt  inverter in my little old wheel estate. It plugs directly into the 12volt socket.  Sometimes I am boondocking and need this little inverter.  Most times it works fine where it is, but sometimes I wish I could use it outside or in my galley (neither have a 12volt socket)

So I need a  12 foot extension cord. 

What I am wondering, which would be less drain on the house battery:

a 12 volt extension cord
or
a 110 extension cord

Currently the only extension cord I have is a super heavy duty 35 foot 110 cord for when I am using 110 power to plug in my 30amp  in someone's driveway. It's almost as thick as the 30amp cord.

It seems to me this heavy duty cord would be overkill to use with a little inverter, that I might lose so much electricity pushing it through that heavy wiring, that it would kill my battery faster than I would like.

I can pick up a thin 110 extension cord and use that, but I was thinking the 12 volt extension might be better, but frankly I have no idea.

Any help from those in the know, would be greatly appreciated.

It's not a matter of drain on the battery.  The problem is that your inverter probably would not work at all (fail with low 12v source voltage) if you extend the 12v line very far.  It's always more efficient to extend the 110volt line.  35' of heavy cord is probably overkill, but it would actually help more than it hindered.

Let me put it this way, Current draw on the 12 volt leads is arund 11 times current on the 120 volt leads for most inverters.. So if you are drawing 100 watts at 120 volts, that is less than 1 amp at 120 volts.

But it's about 10 amps at 12 volts

More current means heavier wire, lots heavier..

Thus, extend on the 120 volt side.

Ok, use 110 volt cord.

Now would it be better to use the mammoth heavy duty cord or just buy a thin 110 extension cord?

DearMissMermaid said:

It seems to me this heavy duty cord would be overkill to use with a little inverter, that I might lose so much electricity pushing it through that heavy wiring, that it would kill my battery faster than I would like.

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You have it all wrong. The heavy duty cord would not be overkill it would be necessary. You lose electricity trying to push through thin wiring. The heavier the better, less voltage drop.

ok so on 110 volt cords you want super heavy

but on 12 volt the thinner ones are better

think I got it now

thanks

but on 12 volt the thinner ones are better

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No, no, for 12V you need even heavier wiring.  That's why you want to keep the 12V wires as short as possible.  For 120V a 12 or even 14 gauge extension cord should be sufficient for your 400W inverter.  You definitely don't need that heavy gauge 30A extension for this application.

The 120 volt extension would be better because the voltage drop will not be as critical or severe.

Let me see if I can clarify thing for you Miss Mermaid.

Pretend we have two theoretical garden hoses, each of which are 25 feet long. One has an inside diameter of 1/2 inch and the other has an inside diameter of 2 inches. It should be obvious that if you applied the same amount of water pressure to each hose you could get a lot more water to flow through the larger hose.

Electricity works the same way.

Lets say we have two wires, each one 25 feet long. One wire is large and and other wire is small. If we applied 110 volts to each wire we could push a lot more amperage through the larger wire than the smaller wire.

Multiply the amperage times the volts and you get watts, so therefore a larger wire will allow the passage of more watts than a small wire.

It works the same whether we are talking about 12 volts, 110 volts or 10,000 volts. However due to the fact that the wire has resistance some of the voltage will be lost along the way. When you start out with 110 volts you can afford to lose a few volts. When you start with 12 volts losing a few volts can be bad. So therefore keep the 12 volt wires as short as possible. Longer 110 volt wires won't hurt the final output as much as longer 12 volt wires will.

Ned said:

No, no, for 12V you need even heavier wiring. 

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Or put it this way.  For 12 volts you'd need wiring that's has ten strands of wire the same size as the 120 volts wiring to ensure the same low voltage drop.  That's a pretty thick expensive wire. 

This puzzled me greatly the first time I heard this so I had to think about things a while myself.  This is also why long distance transmission lines are such high voltage, that is 69,000 or 115,000 volts.  They can move a lot more electricity this way using a relatively small wire.

I am thoroughly confused now.

Will buy a cord and cross my fingers.

Just keep on using the 12V source you have been. Get a decent extension cord at Lowes, Home Depot, ect... One of those orange ones will do nicely (probably in the 25 foot length). Save the super heavy duty one for the main power like you have been.


One like THIS should do nicely, but you can purchase from wherever you prefer. With only a 400W inverter, you shouldn't need more.


Joe

Don't be confused, Miss Mermaid!

Get any kind of 120 volt extension cord you want.  At 400 watts, anything you want to use on the 120 volt side is fine.  An orange outdoor extension cord, or even a plain old indoor extension cord will work.

The large cord you have now is perfectly fine, if a little inconvenient. The larger wire doesn't use more power than a smaller wire, if anything the larger cord will be slightly more efficient than a smaller one.  But I doubt you could measure the difference.

It's on the 12 volt side where wire length and size are critical.  Currents are 10 times higher at 12 volts, which which means you need wire that's 10 times thicker than you do at 120 volts.

That's why inverters work best when they're mounted close to the battery and are connected with short, fat wires on the 12 volt side.

Then extend the 120 volts to wherever you need it.  You could even get a 100 ft. extension cord and run power over to your neighbor's patio if you want (just kidding, but it could be done).

DearMissMermaid said:

I use a small portable 400watt  inverter in my little old wheel estate. It plugs directly into the 12volt socket. 

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Which socket?  A cigarette light socket or something else?  If a cig lighter socket then, as far as I know, they are limited to 10 amps DC which works out to about 1 amp on 120 VAC.

Thanks for bringing some sanity to the discussion Lou.

Thanks so much for all the help.

About the 12volt socket, my motorhome came with 3, installed by Fleetwood,  but 2 aren't really convenient for my applications.
One on the dashboard
One in the living area far from the kitchen and opposite the dining both table
One in the bedroom about 25+ feet from the battery.

I was planning a boondocking trip with a friend. I wanted to be able to type outside and recharge my laptop as needed with just the 12volt inverter, an extension cord would make this easier, as otherwise I have to sit at a weird angle and block the motorhome door.

Also, I use my 200watt crockpot almost daily, sometimes it would be nice to use it while driving on the road, as it's already cooking but not finished and I need to drive somewhere. I don't typically drive with the generator going, because I either drive with the windows open or  the dash air cools the driver and dog just fine if we are creeping in traffic. The fridge chills on propane. 

I would like to set the crockpot in the sink on a rubber mat,  for a safer voyage , but the 12volt socket is 10 feet away, hence the need for the extension cord.

I do sometimes run the generator while driving, just to exercise it and keep it happy, in that case, I let the fridge and sometimes the A/C draw on it, plus the usual stuff that is already plugged in like various battery rechargers for laptop and camera etc.

If I am boondocking, I typically don't use the generator much at all unless I need to recharge the house battery or run the microwave.

This proposed boondocking trip, we wanted to enjoy the peace and quiet with minimal use of generator. Normally I could go days without touching the laptop, except I take tons of photos, I need to download and crop for future use on a project I am working on. 

Also, having been through more than my share of hurricanes, disasters and the aftermath...  while I hope I never go through another disaster, I would like my motorhome set up for boondocking...  just in case...

I've worked as volunteer relief worker, so having a motorhome set up for boondocking in the event I volunteer again, would be a plus all around.

I am just thinking ahead. Heck, I haven't even been shopping in 2 weeks, I guess it's time to get on the road and at least shop for food and that dang extension cord. 

Sounds like a little indoor extension cord will work fine.  It did occur to me that one of  the 12volt sockets for the inverter is in the bedroom next to the compact washing machine. I suppose I could let the crockpot sit in the washing machine while underway. Then I wouldn't need an extension cord at all.

Again, THANKS for all the help!