Question about Coleman 5640B807 Compact Refrigerator

# Conecting to 120 volts AC

I would like to know how many AMPS is the consumption on 12 VDC to calculate the converter for 120 ac.

Thank you

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If you want to get more precise, figure out everything in terms of power (watts).

Basic electrical rule 1, 2 and 3:

voltage x current = power

or re-arranged:

current = power divided by voltage

or re-arranged:

voltage = power divided by current

For example, 12V X 2 amps = 24 watts.

or another example, 400 watts divided by 120 Volts = 3.33 amps

A 55W headlight that uses 12V would draw 55 /12 = 4.6 amps @ 12V

A 55 watt light bulb in a lamp at home would draw 55 / 120 = 0.46 amps @ 120V

As the previous post mentioned, inverters are not perfect when convertering 12V into 120V. If the converter consumes 1000W from the 12V battery, then a 90% effecient converter would generate 900W of 120V AC power best case. The other 100W is lost primarily as heat.

The other thing that gets tricky is that these ratings and the formula above are used for resistive loads, like light bulbs or hair dryers. Anything with a motor or transformer is considered an inductive load and can get much more tricky to calculate.

Consequently you need to give your self a safety margin when figuring out how big an inverter you need.

How does work in a practical sense?

Lets say you want an inverter for TV, DVD and Sat. Receiver. Look at the back of TV or in the manual. It should say how many watts it consumes. Lets say it is 400W. The DVD might be 100W and the Sat. receiver 50W - just as an example.

400 + 100 + 50 = 550 Watts. (just as an example)

You might think, well no problem, I'll use a 600 Watt inverter and have 50 watts left over. Depending on your inverter, that 600W might really be 600 x 90% effecient = 540 Watts of AC, less a 20% margin of error for the inductive transformers in the electronic of the TV, DVD and Sat. receiver 540 - 20% = 432 Watts.

Now you can see your 600 Watt inverter isn't big enough to do the job.

If we really need 550 watts of AC, add 10% to make up the effiency loss, then add a safety margin for inductive loads.

550 + 10% = 605 + 20% = 726 Watts.

Sounds more like an 800W inverter fits the job.

What does that mean in terms of wiring the 12V batteries to the inverter?

from the formula above:

current = power divided by voltage

In our example, we have an 800W inverter that runs on 12V

The current would thererfore be:

current = power divided by voltage
current = 800 watts divided by 12V
current = 66 amps.

That is important info because you can not use light gauge wire to carry 66 amps worth of 12V to the inverter nor could you use a 20A fuse to protect your inverter.

Now that's a lot of science for a guy who just wants to run a toaster on an inverter right?

800W / 120V = 6.66 amps

Using garryp's ratio 11:1, 6.66 x 11 = 73 amps.

That is a good ratio with a good safety margin.

This is all just MHO and should not taken as solid technical advise. In other words, don't blame me if you blow yourself up.

Posted on Nov 26, 2008

Hi,
A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
Good luck!

Posted on Jan 02, 2017

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Check the nametag on the fridge and take note of the total amperage draw of the unit. That that reading, and multiply it by 120 volts and the resultant answer will the the total wattage of the unit... If you want to get it precise, measure the applied voltage at the receptacle where it is plugged in. Your 120 volt circuit may really be supplying 125 volts or more and that will effect the calculation....though minimally.

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you are missing the voltage supply here to get an definitive answer
for 240 volts drawing 4.8 amps the required wattage is 1152
for 120 volts the wattage is 576 watts
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### What is the cprimary load on a 12volt to 240 volt 300watt inverter

Ohm's law tells us that: volts = amps x resistance and watts =volts x amps. Watts (300) = volts (240) x Amps (?); or 300 / 240 = 1.25 Amps That means the inverter can supply up to 1.25 Amps to a 240 volt load.

The primary is 12 volts, this is just 1/20th of the secondary 240 volt output. Since the best you can ever get is 100% efficiency -this means you'll need to supply 20 times the current. 1.25 Amps (at 240V) x 20 = 25 Amps (at 12V). As a check, from above Ohm's law that states Watts=Volts X Amps we get: 12VDC x 25Amps = 300Watts. Check!

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### Will not run only on gas but will not cool

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There is a 120VAV element a AND a 12VDC element. The chances of both of these failing at the same time is pretty slim.

There is a note in the manual:
If the gas only pushbutton is depressed the
lamp will illuminate green and the refrigerator
will only operate on the LP gas mode, even if q
120 or 12 volts are available.

Another significant change in the third
generation A.E.S. system is how the 12 volt
heating element mode operates. As with the
first and second generation series, the 12 volt
heating element circuit is energized by the
ignition lock terminal. This terminal receives
its DC voltage from a wire that runs from the
run side of the vehicle’s ignition switch to the
refrigerator’s ignition lock terminal. This
allows the 12 volt heating element to be
energized only when the RV is traveling down
When the ignition lock terminal is energized
by the ignition key, the printed circuit board
must see at least 13.3 volts DC for a period of
40 seconds before the system will activate the
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If 13.3 volts is not achieved in this time frame,
the electronics will light the LP gas burner and
the refrigerator will operate on the LP gas
mode.
LOWER THAN 13.3 V.D.C. =LP Operation

If the battery voltage remains low after the
delay cycle, the automatic controls will light
the refrigerator on the LP gas mode and stay
on the gas mode until the printed circuit board
sees approximately 13.3 volts DC to the
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For proper cooling on the AC mode, the AC
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each differently rated heating element will
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power range would be between 103.5 to 126.5
volts AC. If the heater is rated for 120 volts,
the acceptable AC power range would be
between 108 to 132 volts AC.

The unit to operate on either AC or DC must have 13.3 volts to the unit. I think this is where your problem lies in that the battery voltage is less than 13.3 VDC

If all of that checks good just repsond here and I will help you. There is still more that can be checked.

Thanks for choosing FixYa.

Kelly

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Here are a few ways to calculate your BTU's.
Get ready to use that algebra you thought you'd never use.
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