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Inverter draw from battery for residential fridge

Campinfan
Explorer III
Explorer III
Does anyone know how many amps are drawn by an inverter to convert to AC for a residential fridge. My battery is rated at 175 minutes at 25 amps but I am trying to figure out how many amps are being drawn out. Or can anyone tell me how to figure it out.
______________________
2016 F 350 FX4 4WD,Lariat, 6.7 Diesel
41' 2018 Sandpiper 369 SAQB
Lovely wife and three children
23 REPLIES 23

JimmyG_The_One
Explorer
Explorer

AC = DC / 0.6360

Soooo...Probably not long.

MNtundraRet
Navigator
Navigator

You would be better off with 2 6-volt batteries. Two group 27 12-volt batteries would give less time. 

Mark & Jan "Old age & treachery win over youth & enthusiasm"
2003 Fleetwood Jamboree 29

Campinfan
Explorer III
Explorer III
voodoo101 wrote:
Consider using a kill-a-watt meter from P3. Inexpensive and you can plug your fridge into it for a day or whatever duration you choose. It will give you actual power consumed. Go from there rather than guessing.


Sounds like great advice. Thank you.
______________________
2016 F 350 FX4 4WD,Lariat, 6.7 Diesel
41' 2018 Sandpiper 369 SAQB
Lovely wife and three children

lenr
Explorer II
Explorer II
My residential fridge draws 1.3 amps, 120 volts, when running which is nowhere close to all the time. My battery monitor says my batteries are down to 55% in 8 hours when not plugged into shore power. However, driving down the road they only drop to 90% so I have to believe that the truck hot wire is supplying 80% of the fridge draw. No DC to DC converter is used, just a straight connection.

ScottG
Nomad
Nomad
Most new residential fridges use between 100 and 300 watts* (22cu/ft) and while the vehicle is running it will be putting out 14+ volts so the 7 pin would need to provide somewhere between 7~25 amps.

*Momentary start up current not withstanding.

Chum_lee
Explorer
Explorer
"Does anyone know how many amps are drawn by an inverter to convert to AC for a residential fridge. Can anyone tell me how to figure it out.


Look for the Manufacturers ID plate attached somewhere to your refrigerator. It will state the load in amps @ 120 volts. Convert that to watts. Watts = Volts X Amps. For example, if your refrigerator draws 6 amps @ 120 volts, the watts equal 6 X 120 = 720 watts actual load. Now add the power draw of your inverter (in addition to the energy required to run the frig) to convert from 12 to 120 volts. If you have a 1000 watt inverter, figure about 5%. So .05 X 1000 = 50 watts. Now add that to the actual load. 720 + 50 = 770 watts. Now convert to battery amps @ 12 volts. 770 / 12 = 64 amps. That's a lot, but it is not continuous. It's based on the duty cycle of your refrigerator.

64 amps @ 12 volts far exceeds what you could reasonably/reliably expect to run through a single pin on a standard 7 pin truck/trailer connector. Your residential refrigerator may draw less than 6 amps (@ 120 volts), but, if it's a high end model with all the bells and whistles, it could be considerably more.

Chum lee

voodoo101
Explorer
Explorer
Consider using a kill-a-watt meter from P3. Inexpensive and you can plug your fridge into it for a day or whatever duration you choose. It will give you actual power consumed. Go from there rather than guessing.

deltabravo
Nomad
Nomad
Campinfan wrote:
I did go buy a group 27 instead of the group 24 but now I am thinking I should have gotten the 6 volts or a second 12 volt but I am not sure another 12 volt will fit in the space.


One group 27 battery is not nearly enough capacity to run the fridge for more than a few hours.
2009 Silverado 3500HD Dually, D/A, CCLB 4x4 (bought new 8/30/09)
2018 Arctic Fox 992 with an Onan 2500i "quiet" model generator

deltabravo
Nomad
Nomad
wanderingbob wrote:
I am just curious since we are on the subject , Two inverters , hooked up the same , one is 1,000 watts , the other is 2,000 watts , both on idle , nothing plugged in . Is the 2,000 watt machine drawing twice as much current as the 1,000 watt one ?


Every inverter will have a different no load draw. Looks at the specs of the two inverters in question so see what their no load draw is.
2009 Silverado 3500HD Dually, D/A, CCLB 4x4 (bought new 8/30/09)
2018 Arctic Fox 992 with an Onan 2500i "quiet" model generator

deltabravo
Nomad
Nomad
The amp draw from the batteries via the inverter is dependent on what the AC amp draw of the fridge is. Look at the specs of the fridge to get the amp draw.
2009 Silverado 3500HD Dually, D/A, CCLB 4x4 (bought new 8/30/09)
2018 Arctic Fox 992 with an Onan 2500i "quiet" model generator

JRscooby
Explorer II
Explorer II
AllegroD wrote:
I would not assume that the 7 pin connection is providing charge or adequate charge. Get a voltmeter and check. Even if charging, some trucks have an undersized charge wire. This causes loss and therefore may not provide adequate charge.

Wiring diagram/reading


I have old absorption fridge, and have wired the trailer so the only power supplied to 12V side of fridge is from the 7 pin. And that is the only demand on charge circuit.
We only camp with power, the fridge runs 120 at camp, 12V when we travel. But you are right, need to know getting adequate power. Could there be a phone app to watch voltage of trailer battery and fridge temp?

pianotuna
Nomad II
Nomad II
It may not be double--but the larger the inverter the greater the idle draw.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

AllegroD
Nomad
Nomad
I would not assume that the 7 pin connection is providing charge or adequate charge. Get a voltmeter and check. Even if charging, some trucks have an undersized charge wire. This causes loss and therefore may not provide adequate charge.

Wiring diagram/reading

Campinfan
Explorer III
Explorer III
My rig is a fifth wheel so I do not have a tongue (on the trailer...lol) I figure the truck is helping to keep the battery charged as I am driving. I am exploring other battery options such as 6 volts wired in series (not enough room for 4 of them to run them parallel and in series. With Lithium Ion, don't I need to get a different converter to charge them. Every time I think I understand this stuff, I come upon something that makes me confused.
______________________
2016 F 350 FX4 4WD,Lariat, 6.7 Diesel
41' 2018 Sandpiper 369 SAQB
Lovely wife and three children