Extension cords and generators

gonejeeping15

Adventurer
Would like to pickup an small emergency generator which I will carry on my trailer. I need to at least power my home fridge which is about 18 CU FT. It's my understanding that it consumes about 800 watts.

How many watts does a 12-2 or 10-2 extension cord consume per 25 FT ?

Thanks

Doug
 

frgtwn

Adventurer
Current limits on extension cords (AMPS)
Cord size 25 ft 50 ft. 100 ft.

18-Gauge 7 amps 5 amps 2 amps
16-Gauge 12 amps 7 amps 3.4 amps
14-Gauge 16 amps 12 amps 5 amps
12-Gauge 20 amps 16 amps 7 amps



http://www.machinetoolhelp.com/misc/toolsdata/extensioncordlengths.html



There is no 10 gauge on this chart, but you get the idea. A 12 gauge cord at 25 feet will safely supply over 2000 watts, if my math is correct.

Dale
 
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frgtwn

Adventurer
COPPER WIRE RESISTANCE (OHMS PER 1000' OF WIRE)

WIRE GAUGE (AWG)

12 10 8 6 4 2 1/0 2/0
1.588 .999 .628 .395 .249 .156 .098 .078


http://www.paigewire.com/volt_loss_formulas.htm


E = IR


E is the Voltage Loss, in volts
I is the current flowing through the wire, in amperes
R is the resistance of the wire, in ohms

Current loss is low, but let's figure it out. 12 gauge wire/1000 feet shows 1.588 ohms. Division will tell us that 25' wire is 25/1000 of that, or .0387 ohms.

Now, we multiply .0397 ohms X 6.66 amps (800 watts/120V)X 2 wires equals .5288 Volts. This means that our voltage drop will be somewhere about one half of a volt in 25 feet with 12 gauge wire. Not much.

Personally, given all this, I carry and use the heaviest cord that I think that I may need for all its possible uses. Seldom would there ever be a "need" for 10 wire in a 25' run. 12 is likely overkill, but I like that. Many would argue that 14 or even 16 is enough, and they are likely correct, but when I look at voltage drop, I'm happier with zero. (Now, zero is best expressed as the manufacturers recommended voltage range. If it is 112-120 volt, then anything supplied in that range is just fine.)

A more important consideration is the capacity of the generator. Likely you have addressed that, or you would have asked, but doing that part is essential to the success of the plans, but especially to the life of your frig.

Since I have not been conversant with this math for some time, I may have made errors, but point 'em out, and I'll just correct 'em. I know how to use the edit feature.

Dale
 
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JPK

Explorer
Don't forget start up draw. If the fridge takes 800 watts to run it can take, iirc, 2.5x that to start the compressor (and then there is the fan...)

So before you purchase a 1000W generator make sure it will start the fridge.

You may be able to find the start up requirements in the fridge specs. I have sometimes found them and sometimes not in various appliances specs.

JPK
 

gonejeeping15

Adventurer
I will also order a load meter to check the fridge before taking any chances. We have a lot of power outages and I usually just keep it closed, half the stuff is probably passed the expire date anyway and shoud be replaced.

Thanks for all the helpfull info.

Doug
 

dwh

Tail-End Charlie
How much power in watts or amps is sucked up by the cord itself ?

It's a sliding scale. The higher the load, the more the voltage drop per X feet of Y size wire.

As the voltage drops, the amperage goes up: amps = watts / volts.

So say your fridge draws 800w. If your wire size/length is sufficient so the voltage doesn't drop much, if any, then 800w / 120v = 6.66a load on the wire (and generator).

But if the wire size is smaller (or longer), and with an 800w load, the voltage drops to say 100v - then it'll be 800w / 100v = 8a load on the wire (and generator).


So, it's not like the wire itself consumed an extra 1.34a (8a - 6.66a = 1.34a). Instead, it caused the voltage on the circuit to drop, which caused the entire circuit (wire and fridge) to draw at a higher amperage - but the watts being consumed is still the same.

(Technically, it's not exactly the same, as there will be a few extra watts consumed to heat up the wire if it's being overloaded...but for a quickie explanation, we can ignore that.)


That same size/length wire, would have less voltage drop if the load were only 400w and more if the load were 1600w.


At some point, you reach the limit of the wire. Say an 1800w load and 12 ga. wire. #12 is good for up to 20 amps.

1800w / 120v = 15a. No problem.

Now lets make the wire longer so the voltage drops to 100v:

1800w / 100v = 18a. Getting close, but not there yet.

Let's make the wire longer still and drop the voltage to 90:

1800w / 90v = 20a. Ding!

If you make the wire any longer, the voltage will drop enough, so that an 1800w load would exceed 20a draw and now you've overloaded the wire.

(Not to mention, that quite a few electrical devices will gag and fall over on their faces if fed 90v.)
 
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gonejeeping15

Adventurer
I knew I could count on you DWH, I will put my figures in place of yours and calc this thing out!

Thanks for your expertise!
 

gonejeeping15

Adventurer
generator purchase

is it less than $899, which is one advertisers in the ARRL mag charges...

Thanks for the tip but I already bought within my needs, which is rare for me. Now I don't have to rework my trailer. It will also run 12 hours on a tank of fuel at 47 db.
 

bat

Explorer
Just go with a good 12 guage extension cord it is still over kill for your fringe and if you want to power something else down the road that has a bigger draw you still will be fine.
 
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Mike S

Sponsor - AutoHomeUSA
For about the price of a Honda 2000i generator you can buy a very good 6.9 CF 12V fridge that draws about 2.5 amps per hour. This will run off a single 12V batt that can be recharged while drving, by solar, by plugging a charger into a 110 AC source. Something to consider.
 

gonejeeping15

Adventurer
fridges

I decided not to mess with the fridges, after three days or so, I'm ready for a motel and hot shower. The gen. will mostly run my radio equip. and possibly a breathing machine, so quiet is a main concern and how long a tank of gas will last is the next.

The 1000watt should work out perfectly for my application.
 

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