Power Inverter

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 ...

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).

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

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.

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.

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)

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.

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

Gdetrailer wrote:

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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.

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

Absolutely

-Jeff