Portable Marine Refrigeration Test

One of the advantages of a compressor-driven portable refrigerator is that it can also serve as a freezer. And compared to thermo-electric coolers, they require fewer amps to do the job. Cruising boats need to be energy efficient, so amp consumption with a 12-volt power supply was one of the key factors Practical Sailor looked at in this test. As in any marine refrigeration test, insulation is a key factor in efficiency, so our comparison also tried to single out the best insulated units. Ultimately, the linear compressor system used in the Engel and Norcold refrigerator/freezers proved to be more efficient.

There are three solid reasons why compressor-driven, portable refrigerators and portable freezers have displaced and overwhelmed all other competitors in every arena where they are used: They are quiet, efficient, and effective. They’ve also proven to be long-lasting and low-maintenance. The major downside is the high cost. However, if you need the capabilities of one of these units, there essentially is no alternative. Your best bet is to pick a unit that fits your needs and budget. In the April 2007 issue, we covered thermoelectric coolers. This time around,

Practical Sailor takes a look at portable, compressor-driven units that can serve as either a refrigerator or a freezer.

What We Tested

We found four units with at least a 34-quart capacity. From Engel, we received the MT-35F, and from Norcold, the MRFT 40 and MRFT 60. Japanese manufacturer Sawafuji Electric Co. builds all three. Waecos CF-40 Coolmatic rounds out the field.

All of these plug into cigarette lighter outlets, a convenient but trouble-prone connection to have on a boat. Replacing the fridge plug with a marine-grade plug and socket is an option, but we recommend hard-wiring the fridge to the boats 12-volt system. In any case, it is important that the sockets wire size and the socket or connection are rated to carry the current these devices require. They should be sized so that there is no more than a 3 percent voltage drop in the circuit.

Both the Engel MT-35F and the Norcold MRFT 40 lighter plugs have thermal fuses designed to blow at temperatures higher than 160 degrees F or if there is an electrical short. The Waeco and Norcold MRFT 60 have common, fused lighter plugs. Regardless of the plug fuses, we recommend making sure the lighter sockets is also fused or protected with a properly sized circuit breaker.

How We Tested

Tests were conducted simultaneously on all four units indoors, where we regulated the ambient temperature to 76 degrees F using air-conditioning. During initial testing, each unit was set to its coldest temperature level. We wanted to see how fast theyd cool and how cold they would get. It was important to know if these units were really capable of achieving and maintaining freezing temperatures.

For power, we used our robust Astron VS-70M power supply regulated to 12.8 volts DC and the manufacturer-supplied DC cable for each unit. Testers monitored the output voltage using a Sperry DM-4100A digital meter. (We did not test the units using AC power.) DC-amp-draw measurements were taken with a Fluke 336 clamp-on ammeter. We took several measurements over the following three hours as the boxes cooled. Noise levels were measured in decibels using a Radio Shack sound level meter held 6 inches from the compressor end.

Temperature measurements were taken using a digital Fluke 116 multimeter with a thermocouple temperature attachment. The sensor, a long, thin wire with the temperature probe at the end, was placed into the box as near as possible to the center. (We only opened the lid enough to get the wire inside, usually no more than a 1/16 of an inch.) Once we had the reading, we opened the lid/door for a second and read the Taylor 5924 analog refrigerator/freezer thermometer we had placed inside each unit as backup. As long as the readings were comparable, we recorded the digital reading. All were. Past experience testing other types of coolers, refrigerators, and freezers led us to take temperature readings at one hour and again at two hours. After each two-hour reading, we opened the lid and placed a one-gallon plastic jug filled with 100-degree water into the box. Three hours later, we took another temperature reading to see how well the boxes had done cooling with the water jug inside. Once each one of these temperature readings was completed and recorded, we let the coolers run unattended for 12 hours. We measured the temperatures again, then shut off the electrical power. Five hours later, we recorded another reading to see how well the boxes were insulated. The next day, after letting each unit return to room temperature, we cranked them up again, but this time, testers set them to the warmest temperature level. After they ran overnight, we checked and recorded the temperature each box was maintaining.

We wanted to see how well each cooler held food and drinks, so we packed each with the following:

(2) six-packs of canned soda

(1) six-pack of bottled beer

(1) gallon of lemonade

(1) gallon of ice tea

(1) pound sliced turkey breast

(1) 1 pound boneless ham

(2) pound blocks of cheese

In the final analysis, we picked winners based on performance, construction quality, warranty, power usage, price, and load capabilities.

Engel MT-35F

Engel is the worldwide brand name and distributor of a full line of portable fridge/freezers that range from 14- to 84-quart capacity. Engel refrigeration products, which are built by the Sawafuji Electric Co. in Japan, have been known for their quality since production started in 1962.

Our test model, the MT-35F, has a 34-quart capacity and its exterior is constructed of powder-coated and galvanized steel.

The Engel is designed to sit flat and open from the top. Its locking lid is removable for better access to the interior. Carry handles bolt onto the case sides, but we did not install them. The interior of the Engel is constructed of bright white, high-impact plastic for easy cleaning. A metal basket fits snugly inside and provides a means to hold or remove contents.

In our testing, we found the box temperature could be set between approximately 0 and 50 degrees F, making the unit useful as either a refrigerator or freezer.

The Engel held our full list of food and drink as well as three 1-pound packages of burger meat.

Bottom Line:

A top performer with an efficient compressor and low price. We rated it the Practical Sailor Budget Buy.

Norcold MRFT 40

The 40-quart Norcold is nearly identical to the Engel MT-35F. Both share a 25-inch x 14-inch footprint, but the Norcold is about 4 inches taller and uses the extra height to achieve increased capacity. Both are built in the Sawafuji factory, use the same compressor, and are constructed from powder-coated and galvanized steel outside, with high-impact plastic inside. The lid, lid lock, handles, and interior basket are the same, too, but the Norcold basket is a bit taller.

The Norcold performed well in testing and can be set to operate from 0 to 50 degrees.

We had no problem loading all of our groceries into the 40-quart Norcold. It had so much extra room, we were able to load 12 one-pound packs of burger meat, too.

Bottom Line:

A top performer.

Norcold MRFT 60

At 67 pounds, the bulky Norcold shouldnt be considered easily portable. Moving this big unit is a two-person job. It is another product of the Sawafuji Electric Co. and shares all the characteristics and features of the Engel and Norcold 40-quart. Everything is upsized here, with a larger compressor and interior.

The MRFT 60s top-mounted lid swings opens to the side and uses a chain stop instead of the rubber bumpers found on the smaller boxes. Two locks hold the lid closed tight.

This unit performed exceptionally well, taking a little longer to initially cool the bigger space, but it chewed up the hot water fast and remained colder than any other unit.

Divided into two equal-sized sections by a pair of metal baskets, the cavernous 60-quart Norcold swallowed up our provisions using only one basket. The other basket was empty and waiting for more stuff.

Bottom Line:

This brute will hold a ton of provisions, and it performed superbly.

Waeco Coolmatic CF-40

Waeco is a worldwide manufacturer and distributor of a wide variety of refrigeration systems. The Coolmatic unit we tested is constructed using a couple of different types of durable plastic. Even though its mechanical components are metal, its plastic exterior gives it excellent protection against corrosion.

The Coolmatic sits flat and opens from the top. The lid locks with two plastic latches and can be removed. It did not seem to shut as tightly as the other units we tested, in our opinion. Carry handles bolt onto the case sides, but as with the other units, we did not install them. A light is fitted to the interior; it switches on when the lid is open.

Though the Coolmatic generally performed as well as the others, it uses a less-efficient compressor, and in our test used significantly more power than the comparably sized Engel MT-35 and Norcold MRFT 40. Also, the temperature range setting did not seem to perform as advertised. When we set it to maintain a warm temperature, it shot right down to below zero.

The interior of the Coolmatic is divided into two sections, a main section with a metal basket, and a smaller, warmer section. We were able to load everything on our grocery list into the main section of the freezer, though it was a tight fit and filled the basket to capacity. We managed to pack four one-pound packages of burger meat into the small section that remained.

Bottom Line:

In our test, the Waecos Danfoss compressor was not as power-efficient as the best units tested. But we like the units completely plastic exterior and its price.

Conclusions

The compressor system used in the Engel and Norcold fridge/freezers proved to be far more efficient than the Danfoss reciprocating compressor used in the Waeco. In our tests, the Waecos amp draw was nearly 50 percent higher than a comparably sized Norcold unit. When coupled with the top-shelf construction and materials of the Engel and Norcold units, wed opt for one of these every time.

When shopping for a portable fridge/freezer, first find the right size, then buy whichever you can find at a cheaper price, Engel or Norcold. You may find only an Engel available in the size you seek as they market several more sizes than Norcold.