freezer conversion to refrigerator question

dolcesails

Hi,
I have read about the freezer to frig article and I'm thinking of putting one together. I have a couple of questions. A few years ago I ran a 110v refrigerator in a motorhome on a 800 watt inverter modified wave type.We drove non stop for 3 days.It seemed like the frig was cold, but not as cold as it would be if it was plugged into city power. Was it because of the modified wave inverter? Now my question is.... will the conversion frig run better on a pure sine wave inverter. I am thinking of a smaller soft start inverter......how small? You will need to tell me. Is the conversion frig a good idea, any input would be great........I have plenty of solar power and battery to back this theory. P.S. it's warm here in SW Florida Thanks Nick

waynefromnscanada

Re: freezer conversion to refrigerator question

Can't see why the fridge was not running as cold as on grid - - - unless - - - the compressor, which would be running hotter on MSW than on pure sine power, may have been getting so hot it was cutting out from overheating until it cooled down again, therefore, especially if the location of the fridge was hot, or if it was enclosed in a cabinet and not able to get rid of it's heat. Other than that, yes, it will run better and use less power, and the compressor run cooler on pure sine than on MSW. But it should keep food just as cold, all other things being equal. I have a cousin who has installed his small fridge in an enclosed cabinet on his boat in spite of my recommendation to provide ventilation, and it runs non stop on his MSW inverter when he's at sea, and it too often doesn't cool as it should, and no wonder, it must be 110* inside that cabinet!

BB.

Re: freezer conversion to refrigerator question

An RV refrigerator can be different animals. The common fridge is an Ammonia Absorption type unit. They use heat to operate--Propane flame, or 12/120 VAC and electrical heaters. TSW vs MSW would not matter much to the heaters--But may affect electronics (MSW "sharp" wave fronts can cause excessive current peaks and circulating currents in transformers and overheat components).

If the RV Fridge is a compressor type system--Then there can be different types of motors. Induction motors (standard type of AC motor) tend to use upward of 20% more AC line power which is wasted as heat in the motor (can cause overheating/shorter motor life). There are other types of AC motors/motor controllers too--so it is hard to "generalize" the effects of MSW vs TSW without knowing the details of the design and/or testing.

With standard Energy Star refrigerators/freezer today--They are very low energy consumption and usually so much less expensive vs the "off grid" designed fridge/freezers, it is still cheaper to buy a TSW inverter and a bit more solar panels+battery bank than to buy an "off grid" refrigerator. Also, repairs tend to be easier/cheaper with standard residential units.

Another issue with many of the modern refrigerator/freezers is they use electronic timers for auto-defrost control. MSW wave forms can confuse timers (run fast or slow) if they run off of line frequency. And using low power "search" mode on inverters can reset the electronic defrost timers (when power is removed, the fridge will start another defrost cycle when the power is restored).

Lastly, even if you use a simple non-frost free chest freezer with a ~120 watt motor--The starting surge usually requires a 1,200 to 1,500 watt minimum inverter to provide ~5x the starting power (and poor power factor) needed to get the motor running.

One poster here (the famous Wayne from NS Canada:D) has figured out how to use a 300 watts (600 watt surge) TSW MorningStar inverter to run his conversions--But it took a bit of home brew hacking (auto transformers, a stash various values of motor start capacitors, several types of relays) to make it work.

The better option is usually to get a ~1,500 watt inverter, battery bank, and solar panels to run same--And use the extra power for other loads (lights, cell phone, laptop computer).

-Bill

dolcesails

Re: freezer conversion to refrigerator question

You fellas ask all the right questions.......1st the refrigerator is apartment size, it has no defrost cycle, it has plenty of air to circulate around it and the motorhome has AC so it was cooler than not having it. I can relate to a warm boat cabin. The drinks were cold but the things in the freezer didn't seem to be as hard as I thought they should have, it wasn't overloaded with stuff. I believed it cycled on and off. I've used the microwave on the inverter and doesn't heat as fast as city power and fans don't work as good either, and not all at the same time. MSW vs PSW ? The article I read about the freezer conversion uses a manual temp. control which the freezer plugs into and then on to the power source, setting the temp. at around + or - 40 degrees. Is it that easy? What is used for shelves in the box, how much water acculates on the bottom. Is it really that energy efficent. Any help would be great, I do have an E-bay special PSW 2000-4000 inverter, the cooling fan runs all the time, that's why I was thinking of a soft start PSW inverter. Thanks again Nick

BB.

Re: freezer conversion to refrigerator question

If the fridge compressor cycled--Then it should be getting as cold as "normal". You can have issues with the freezer--It is usually "uncontrolled" cooling--Freon goes there first, then the cold freezer cools the refrigerator--where the thermostat is.

In a cold envronment, the freezers tend not to get very cold as the refrigerator does not operate enough to keep the freezer cold... Hot envronments--Don't know--But perhaps the hot ambient conditions also warmed the freezer.

Microwave ovens tend to not heat as efficiently on MSW inverters. Known issue.

Regarding Chest Freezer Conversion--One person I read (may have been Wayne) used some plastic channel glued at a slope about 1/2 way down the wall of the freezer to catch condensation and direct it to a drain tube.

Chest freezer conversions are a pain and may not be acceptable to a spouse regarding food access.

Using a standard upright freezer may address that issue--but raise others (draining condensation, etc.).

Humidity in a chest freezer stays high compared to a fridge/freezer--great for vegetables.

-Bill