Inverter draw from battery for residential fridge

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?

It may not be double--but the larger the inverter the greater the idle draw.

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

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.

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 ?

I second this question. And assuming the 2 are on separate 120V circuits, would 3,000 watts be available?
How much more would be wasted compared to 3000 watt inverter?

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 ?

If you only have a single 12v battery I can't see that lasting very long without some additional charging the whole time it's running?

Look into the LI batteries out there now.

You say you don't have room for a second battery? Humm... 41 foot TT should have some room on the tongue for more batt capacity?

My little 26' TT has 2 batts from factory. I can add more if needed, but my needs do not require that at this point.

Good luck! Mitch

One of my favorite 120 volt tools is my Kill-A-Watt meter. it's about a thousand dollars worth of meters.. in a thirty dollar, give or take, box

You read the WATTS draw and divide by 10 (yes I know that's not the battery voltage but by the time you factor in the conversion loss in the inverter 10 works real good) so if the fridge draws 100 watts running the inverter draws 10 amps

Or you can read the amps draw. the Power factor (you can do things to improve that) and other stuff... Power factor is zero to one (one means you are using 100% of the power) and is the cosine of the relationship between voltage and current... Ideally it's ONE. It's also the difference between VOLT-Amps and Watts. It's possible to have something drawing say 150 Volt-Amps (Which is what you pay for) and only using 100 Watts. (PF .6666666)

Kill-a-watt on Amazon

I'm not a expert, or even very smart. But I think the bigger a inverter, the more it drains battery even when load on inverter. Considering that, and the fact the fridge cycles off and on, wouldn't it be better to have a inverter just large enough to power the fridge, left on all the time, and a second that can be turned on only when need other 120V loads?

Campinfan,


I'd go with a dc to DC charger that has enough capacity to power the fridge.