Inverter install help

[tbax46]

I put in a household frig in my fifth wheel, but of course when I unplug to move down the road it's off line. I noticed the newer fivers have household refrigerators and an inverter on board for when offline.
Question is what size of inverter is needed for just this outlet and how do you wire it for part time use. Do you need a switch to allow the receptacle to go fro the inverter to shore power.
Not an electrician and could use some help and ideas.

[allbrandauto]

I just installed a res. ref. in my motorhome I used a zantrexs freedom xi 1000 watt pure sine inverter a little pricey at 495 dollars but had automatic transfer switch and a remote easy install and only needed inverter and batterys

[road-runner]

1 hp=745 watts. 1/2 hp = 372w. 372w/120v= 3 amps

That would be true with a 100% efficient motor with a unity power factor. In reality a 1/2 HP motor might be 70% efficient at optimum load, and have a PF of 0.75 (which varies with load). The math would be:

372 watts / 0.7 efficiency / 0.75 pf = 708 VA / 115 volts = 6.1 amps

The nameplate of a 1 HP motor I have says 13.6 A. A 1 HP motor is generally more efficient than a 1/2 HP motor. Motors of this size range generally do not have any PFC.

[2oldman]

larry cad wrote:
I still stand by my numbers.

You don't think something may be wrong with your measurements? It's hard to imagine the math being wrong by a factor of 3.

larry cad wrote:
A 1/2 hp, 1ph motor is rated to draw 9.8 amps at 115 vac.

Where do you find this rating?

[larry_cad]

2oldman wrote:

larry cad wrote:
My compressor is a 1/2 hp and draws 9 amps while running.

1 hp=745 watts. 1/2 hp = 372w. 372w/120v= 3 amps

You are talking math numbers, I am referring to National Electrical Code published ratings which are actual numbers obtained from real motors, including slip, and energy efficiency.

I still stand by my numbers.

[2oldman]

larry cad wrote:
My compressor is a 1/2 hp and draws 9 amps while running.

1 hp=745 watts. 1/2 hp = 372w. 372w/120v= 3 amps

[larry_cad]

MrWizard wrote:
larry the only time you could measure that much power is compressor startup
not even the defrost heating element in the door draws that much power
it would melt the plastic in the fridge

I stand by my numbers. A 1/2 hp, 1ph motor is rated to draw 9.8 amps at 115 vac. My compressor is a 1/2 hp and draws 9 amps while running. I don't see a conflict there. Perhaps you can clarify for me? The current I read with my ampprobe was just the motor, not the defrost heater which draws significantly less current.

Thanks

[tbax46]

Mr Wizard
I'm only looking for enough power to keep it running while driving from one spot to another. The closest I get to dry camp is electric only sites.

[MrWizard]

larry the only time you could measure that much power is compressor startup
not even the defrost heating element in the door draws that much power
it would melt the plastic in the fridge

[Searching_Ut]

When Heartland was putting the residential refrigerators in firth 2015 models there was a known problem with the inverters overloading and tripping off. They were using 1000 watt inverters for refrigerators drawing 8.5 amps AC. Interestingly during our last RV shopping we were asking about the main reason for going residential. Every dealer we talked to said cost. Evidently many folks don't dry camp much anymore and when you get to the 18cf refrigerators they were saying it's almost $3,000 dollars wholesale for the norcold units, plus baffles vents, fans etc. and much cheaper for the residential unit and cheap inverter. Of course they don't give you a big enough battery bank to do this for off grid camping, so the actual cost difference will be different once you take care of that issue.

[larry_cad]

Ivylog wrote:
A lot of bad info above... the 9 amps is times 12V not 120 so it's only 108W, not more than 1000W.

Ivylog, I'm sorry, but you are totally incorrect. I measured the 9 amps with my AC amp meter, while clamped around the AC power cord of the refer. The AC power cord is fed with AC power produced by the inverter. That is what an inverter does, it creates AC power. My calculation is:

Amps X Volts = 9 X 120 = 1080 watts.

If you were to check the DC amps from the DC battery at the input of the inverter, it would be 90 amps (plus losses)

[MrWizard]

tbax46 wrote:

Question is what size of inverter is needed for just this outlet and how do you wire it for part time use. Do you need a switch to allow the receptacle to go fro the inverter to shore power.
Not an electrician and could use some help and ideas.

around 1000w or more

the fridge will draw 100-200w while running
but its the compressor surge on start of cycle that will draw 900w or more

access to wiring dictates, whether you run a new circuit, and manually switch them by plugging and unplugging,
or if you can use an inverter with pass thru, that auto switches

even if you need to run a new circuit there are 'transfer switches' that can be installed behind the fridge to switch between the shore circuit and the new inverter circuit

battery bank & solar is another topic
do you dry camp ?
do you make frequent long stops 'over night' during the drive from one camp location to another ?

always use FHU campsites ?

No. No . yes, then you don't need solar, just enough battery power to get thru the drive time

a few more details will make for better answers

[RJsfishin]

ScottG wrote:
I noticed a much broader price range of RV's at the RV show this year that had resi units. When I could readily find the inverter, they were 1000 watt.

The MFGs figure most RV'ers don't "camp" anyhow, so why not stick a cheap res fridge in it, and keep the selling price down at the same time.
And then let it be a big and expensive surprise for those that really do go camping, and think that their fridge problems are over, when reality they've just begun

[ScottG]

I noticed a much broader price range of RV's at the RV show this year that had resi units. When I could readily find the inverter, they were 1000 watt.

[time2roll]

Generally you will need a sine wave inverter rated 1000 watts.

Usually best to install close to the batteries to keep the 12 volt connection short.

Small 15/20 amp transfer switch will allow you to wire the inverter to this single circuit.