Power Inverter

[hellbird503]

I just installed an apartment type refrigerator and want to install a power inverter to run it while I am traveling. What I need to know is what size cables do I need to hook it up to my batteries. I will need about 12ft. of cable and the power inverter is 1500 watts. Thanks for any help, Dave

[brulaz]

CA Traveler wrote:

...
For starters 400KWh/364 days = 1098W per day/12.5V = 88Ah. And these are nominal figures probably at 77F. This seems just a little high for a smaller refer.

Yes, converting Energy Star's kWh per year to a Daily Ah or Wh is a better way of looking at it.

The Wiz above is using ~37Ah over 9 hrs at nite.
So maybe 100Ah per day? And his frig's Energy Star rating could be > 400.

That 400 kWh per year Energy Star rating was for a 10-11 cuft built-in LG frig. Not too small ...

[DrewE]

CA Traveler wrote:
The numbers you need are:
1. The running amp draw on 12V or at least the AC amps
2. The maximum startup amps
3. An adequate inverter for the above
4. Your battery Ah rating so you can check the sizing of the above

For starters 400KWh/364 days = 1098W per day/12.5V = 88Ah. And these are nominal figures probably at 77F. This seems just a little high for a smaller refer.

Dorm fridges are not very efficient in comparison to their size. They do use very nearly the same amount of energy as full-sized fridges, at least the smaller full-sized fridges. The dorm fridges have poorer (and hence thinner) insulation and are generally sold based on initial costs rather than running expense (electricity is included in dorm fees).

[MrWizard]

I know you said it
But the OP may not realize you are talking about an RV lp fridge using battery electricity for a 345 watt heating element
3 times the poorer use of the residential fridge he is talking about

[pianotuna]

Hi Time2roll,

I do run my absorption fridge on either 120 volt ac or 12 volt dc while trundling down the road. Both methods show a draw of about 34 amps. Even with the solar system pumping it some amps the end result is a slow discharge of the battery bank. I'm set up with dual #8 wire charging paths. Part of the issue may be the lousy duty cycle of the fridge. I guess the only way for the OP to find out is to try it.

[time2roll]

If you wire the 1500 watt inverter to produce 1500 watts all the amp draw calculations are mute.

Long term power consumption only matters if you will be camped off-grid. In transit the battery should receive plenty from the alternator.

[pianotuna]

It really comes down to what the duty cycle is. I'm fairly sure that the Energy Star testing may be done at STP 25 c (77f) or else at 20 C (68 f).

Duty cycle on the absorption fridge for my ride is about 2:3 (bad bad bad)

[CA_Traveler]

The numbers you need are:
1. The running amp draw on 12V or at least the AC amps
2. The maximum startup amps
3. An adequate inverter for the above
4. Your battery Ah rating so you can check the sizing of the above

For starters 400KWh/364 days = 1098W per day/12.5V = 88Ah. And these are nominal figures probably at 77F. This seems just a little high for a smaller refer.

[MrWizard]

That page has the math PROCESS screwed up

The logic is all wrong, the fridge Doesnt run non stop at 0.34 amps

The total kwHr is ok, but a fridge cycles on off
It uses about 1.2 amps when running and only runs 30~40 percent of the time

mine has a cycle duty time of about 40 percent

Something like 36~38 amp hrs during a 9 hours overnight sleep period of not being opened

[brulaz]

Gdetrailer wrote:

...
Energy star is an "average" of 365 DAYS of "usage".

So 400 Kwhr usage over 365 DAYS, but the compressor is not RUNNING ALL DAY. So your "math" is flawed by "assuming" 24/7/365 COMPRESSOR OPERATION..

In reality the 400 Kwhr is used 20-25 MINUTES per hr or 600 MINUTES per DAY (which is 10 HOURS MAX PER DAY).. or 3650 HRS PER YEAR..

As I stated, the REAL number is closer to .75A at 120V and not what you came up with (.38A at 120V).
...

No idea how you did your calculations based solely on an EnergyStar rating of 400KWH per year.

Here's how I did mine: http://www.mediproducts.net/blog/how-many-amps-does-a-refrigerator-use-over-time

And my apologies to the OP for the off-topic.

[Unyalli]

hellbird503 wrote:
So, you are saying I should mount the power inverter near the batteries and run an extension cord from there ?

Absolutely

-Jeff

[Gdetrailer]

brulaz wrote:

Gdetrailer wrote:

brulaz wrote:
Was looking at a 10-11 cuft LG frig that might be crammed into our trailer.

The Energy Star rating was 400KWH per year. Which I guess translates into only 46W or 0.38A at 120VAC?

Seems hard to believe ...

Your assuming the fridge compressor operates 24/7/356, it does not.

No, I'm assuming the Energy Star rating system takes all that into account and gives you an overall average. No idea if that's true or not.


In actual use the fridge compressor should run only about 20-25 minutes per hr.

The defrost cycles typically will run once for about 10 minutes per every 10 hrs of compressor operation.

You will find that your LG will actually be drawing about 80W-90W while the compressor is running or about .75A at 120V..

Many of the newer fridges are much more energy efficient, one way this is done is to run some of the refrigeration tubing (heat side) around the door openings. This replaces the older electric heaters used to reduce sweating at the door.

Energy star is an "average" of 365 DAYS of "usage".

So 400 Kwhr usage over 365 DAYS, but the compressor is not RUNNING ALL DAY. So your "math" is flawed by "assuming" 24/7/365 COMPRESSOR OPERATION..

In reality the 400 Kwhr is used 20-25 MINUTES per hr or 600 MINUTES per DAY (which is 10 HOURS MAX PER DAY).. or 3650 HRS PER YEAR..

As I stated, the REAL number is closer to .75A at 120V and not what you came up with (.38A at 120V).

As a reference, my 10 cu ft home fridge has a name plate rating of 1.1A at 120V, BUT my MEASURED draw was .8A at 120V..

[brulaz]

Gdetrailer wrote:

brulaz wrote:
Was looking at a 10-11 cuft LG frig that might be crammed into our trailer.

The Energy Star rating was 400KWH per year. Which I guess translates into only 46W or 0.38A at 120VAC?

Seems hard to believe ...

Your assuming the fridge compressor operates 24/7/356, it does not.

No, I'm assuming the Energy Star rating system takes all that into account and gives you an overall average. No idea if that's true or not.


In actual use the fridge compressor should run only about 20-25 minutes per hr.

The defrost cycles typically will run once for about 10 minutes per every 10 hrs of compressor operation.

You will find that your LG will actually be drawing about 80W-90W while the compressor is running or about .75A at 120V..

Many of the newer fridges are much more energy efficient, one way this is done is to run some of the refrigeration tubing (heat side) around the door openings. This replaces the older electric heaters used to reduce sweating at the door.

[MrWizard]

now you have the real info
And it falls In to line worth everything we have been saying
The 1500w inverter is that continuous or peak
I also have the trip lite 1250 power verter , very good inverter not a little chopper like you buy at the car parts store
It weighs 22# and has a big transformer inside, it is made to power motors, power tools, compressors etc..

[hellbird503]

Okay, looked at the compressor plate and the numbers are: 115-60hz,1 ph,lra,11a. I also found a service data sheet with the paperwork which says Amps(running) 0.8 to 1.5