Refrigerator - A/C Load

ILFE

Greetings:

All current circuits on my system are DC, 12 volts, and need to remain that way if possible.

I need to purchase an AC refrigerator (and an inverter to power it). I want to buy it for my wife as a surprise.

I found a smallish one that I feel will work, a Sanyo SR-125PN. It draws, according to the label, 79 watts. This is at 220-230vac.

How do I calculate this load, to determine if my batteries (currently 480AH, at 12vdc) will be able to run this refrigerator 24 / 7 / 365? I believe I need to calculate it to run 14 hours out of each day, as well?

I am willing to upgrade, as necessary, with more panels and batteries. (I will also look at changing my system to a series array, 24vdc. That is, if I can retain my current 12vdc loads.)

mike95490

Re: Refrigerator - A/C Load

count it all in watt hours. fridge (80 watt hours) 50% run cycle 80 *12 = 960watt hours. [that's about what the daily draw for a 21cf energy star fridge is]

call it 1,000 watt hours daily usage, from batteries, you need to be able to harvest 1500 watt hours from your array, on a daily basis.

Changing array voltage won't do much, unless you add more panels. if you assume 3.5 solar hours in winter, 1500 wh needs at least 520watts of PV panels installed. Add a bit more to allow for some more system losses, or a light bulb.

Battery size depends on how many cloudy days you want to have power through, and backup generator so batteries don't sit discharged too long.

1,000w of power in a 12V battery consumes 83 amp hours, so the minimum size to support the fridge 1 day, would about 170aH, easily done with 2, 6v, 220ah golf cart batteries (in series)

This should get you started. But you will likely need a 800w pure sine wave inverter to start the fridge motor.

vtmaps

Re: Refrigerator - A/C Load

ILFE wrote: »

All current circuits on my system are DC, 12 volts, and need to remain that way if possible.

I need to purchase an AC refrigerator (and an inverter to power it). I want to buy it for my wife as a surprise.

I found a smallish one that I feel will work, a Sanyo SR-125PN. It draws, according to the label, 79 watts. This is at 220-230vac.

If you have no other need for AC, I think you should consider a DC fridge. They can be extremely efficient, but tend to cost more than AC fridges.

This is not the usual advice I give... usually I suggest an inverter and AC fridge because most folks have use for AC for other reasons. The money you save on an AC fridge will pay for some more panels and battery.

Even though your fridge draws only 79 watts, it probably has a high startup surge that requires a large inverter. A large inverter uses a lot of power just being on, and is not efficient when inverting only 79 watts. Some inverters have a 'search' mode where they only switch on when the fridge wants power, but some fridges start a defrost cycle every time the power is resumed... I'm not sure about that particular model of sanyo.

As far as whether your batteries can handle the load... you've got about 2900 watt-hours of storage before you hit 50% SOC. I don't know how much your other loads are, and I don't know what the energy consumption of the fridge is in your warm climate. One thing to count on... your inverter will consume 250 - 600 watthours per day in addition to what the fridge draws.

ILFE wrote: »

I will also look at changing my system to a series array, 24vdc.

One of the most common DC compressors is the Danfoss compressor used by Sundanzer, Sunfrost, Stecca, and many others. All of the Danfoss compressors work on either 12 or 24 volts... no switches needed, they self configure to which ever voltage you are using.

--vtMaps

ILFE

Re: Refrigerator - A/C Load

Thanks, guys, for the replies.

Mike, how I wish this refrigerator was a 21 cu ft unit. It is a LONG way from that. It is much closer to 6 or 7, honestly. But, maybe I will be able to find one that is much more energy efficient, by the time I actually expand the array. (I have never actually looked at the efficiency rating, or power usage of a refrigerator before.)

vtMaps, regarding going with a DC refrigerator, over an AC unit, this will not be the only AC appliance running off the inverter, I am quite sure. I will need it to run my electronic equipment, once we move into the house.

I tell ya, now that I am sitting here thinking of it, I know they sell multi-powered units in Phnom Penh. That is, LPG / 12vdc / 230vac. It may be more cost effective, for now, to buy one of those.

BB.

Re: Refrigerator - A/C Load

ILFE wrote: »

I tell ya, now that I am sitting here thinking of it, I know they sell multi-powered units in Phnom Penh. That is, LPG / 12vdc / 230vac. It may be more cost effective, for now, to buy one of those.

One thing to worry about with LPG/12v/230v units.

LPG units are normally "absorption" type units (using Ammonia as the working fluid). They are very "efficient" when used on LPG, but the typical LPG units just use electric heaters in place of the flame, and are not very efficient at all on electricity.

The true electric small refrigerators--They use some form of electric compressor and are very efficient when operated on electricity.

There are Peltier type refrigerators too (solid state thermal junctions that can heat or cool the box) too--These tend not be be very electrically efficient either (vs refrigeration types).

So--Be careful. (there may be mixed mode units that run well on both--I am not sure, I don't get into these small fridge discussions very often to keep up on the details).

-Bill

vtmaps

Re: Refrigerator - A/C Load

ILFE wrote: »

I tell ya, now that I am sitting here thinking of it, I know they sell multi-powered units in Phnom Penh. That is, LPG / 12vdc / 230vac. It may be more cost effective, for now, to buy one of those.

BEWARE! Those units are fine on LPG, but they are enormous energy hogs if used on 12 vdc or 230vac. Do NOT try to run one of those on electric power.

--vtMaps

edit: BB. beat me to it

zoneblue

Re: Refrigerator - A/C Load

+1 for danfoss compressor fridges. Check out the marine stores. One thing to bear in mind is that a smaller fridge doesnt really use less power. So dont necessiraily look for a smaller fridge!

ILFE

Re: Refrigerator - A/C Load

zoneblue wrote: »

One thing to bear in mind is that a smaller fridge doesnt really use less power. So dont necessiraily look for a smaller fridge!

No doubt. I learned that pretty quickly.

One problem with living in SE Asia is, many appliances are imported from neighboring countries. Having been manufactured in those countries, the labels reflect that. Labels become a bit of a challenge when printed in Vietnamese, Thai, or other Asian languages.