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Old 05-12-2014, 05:02 PM   #1
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Duty cycle on Novakool fridge and freezers.

I went to the Novakool factory in Coquitlam BC to get a new gasket for my fridge door. $28 after taxes installed, which I thought was a good deal.

While I waited, I talked to one of the managers. He mentioned that the duty cycle on these is typically 50%, meaning that they run 50% of the time. That will go up to 80% of the time on hot days.

So planning electrical loads on my system, that would work out to 4.9 amps for the fridge and 6.6 for the freezer, 11.5 amps or 138 amp hours for the day. Probably conservative.
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Old 05-12-2014, 07:10 PM   #2
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Just curious, did the rep say they figured in a "typical" number of door openings in their calculations? and was the fridge empty or full?
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Old 05-12-2014, 07:58 PM   #3
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After installing a battery monitor I checked the amp draw on my 16 yo Norcold and determined it was about 150 amps per day, not too far off JDCAVE's calculations. Those measurements were taken is So Fl in March. My guess is the draw would be much higher in the summer.
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Old 05-13-2014, 10:08 AM   #4
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No, we didn't get into the details of how much food, door openings etc. I'm sure that humidity also comes into play.

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Old 05-15-2014, 06:53 AM   #5
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Quote:
Originally Posted by JDCAVE View Post

I went to the Novakool factory in Coquitlam BC to get a new gasket for my fridge door. $28 after taxes installed, which I thought was a good deal.

I ordered two door gaskets, one for each of our fridges, from them by phone. Very pleasant experience, including some tips on easing installation, etc.

-Chris
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Old 02-01-2015, 07:49 AM   #6
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I have a NovaKool refrigerator on my boat. It seems to run all the time. I checked the door gaskets and they seem fine. And seal fine. The temps are good, it just runs constantly. Is that normal? Is there anything else I should check?


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Old 02-01-2015, 08:09 AM   #7
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Quote:
Originally Posted by JDCAVE View Post
I went to the Novakool factory in Coquitlam BC to get a new gasket for my fridge door. $28 after taxes installed, which I thought was a good deal.

While I waited, I talked to one of the managers. He mentioned that the duty cycle on these is typically 50%, meaning that they run 50% of the time. That will go up to 80% of the time on hot days.

So planning electrical loads on my system, that would work out to 4.9 amps for the fridge and 6.6 for the freezer, 11.5 amps or 138 amp hours for the day. Probably conservative.
What compressor does it have, the Danfoss BD35F?

Two things, if it's teh above compressor, I was told that it is variable speed, in that it will vary depending upon load.

My Vitrifrigos are the pretty much the same, but the 50% was the max they would seem to ever run and in every day use, the average over 24 hours seems to be closer to 4.8 amps, or 115 amps per day.
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Old 02-01-2015, 08:41 AM   #8
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Wmiii, Do you have good air circulation?
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Old 02-01-2015, 08:57 AM   #9
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It looks like I have a RFS7501 (I think).
I'm not sure what compressor it has.
I does have good circulation vented at bottom and the top.
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Old 02-01-2015, 10:00 AM   #10
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When I had a Nova Cool

Quote:
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It looks like I have a RFS7501 (I think).
I'm not sure what compressor it has.
I does have good circulation vented at bottom and the top.
I had issues with the fan switch not turning off the pancake fan near the bottom of mine. Mine had a little pancake fan similar to a computer fan. Mine was built with freezer section on the bottom. I had problems here in the CA Delta with it keeping the upper section cold enough. Also had some freezing issues with refrigerant line icing up in the back of the box, Through it all Nova Cool was very helpful and responsive. I think the design in this case was not a good one for the summer heat we experience. I wouldn't go with the bottom freezer section again.
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Old 02-01-2015, 11:26 PM   #11
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""""""""I have a NovaKool refrigerator on my boat. It seems to run all the time. I checked the door gaskets and they seem fine. And seal fine. The temps are good, it just runs constantly. Is that normal? Is there anything else I should check?"""""""""""

It's possible the T.S. is goofy. Try running it set on low on a cool, not cold, day and see if it cycles.

If so, the odds are good that your passive ventilation simply is not good enough. It may not even be really working. Mine didn't.

If these things cannot vacate the heat removed from their interior they WILL NOT COOL properly. No different from the fridge at home in that regard.

Heated air does NOT turn corners willingly or travel horizontally readily. The cavity vents, I'll venture, are not really doing much.

Get and install a 4" muffin fan so it BLOWS the heated air OUT of the enclosure at the TOP. I like it to blow outside the boat but it does not matter that much as long as that heated air is evacuated. It could even be rigged so the same top vent that is already present is used. You would need some ducting or some type to ensure it leaves the enclosure or rig another opening at the cavity top.


There should be a fan drive output terminal on that Danfoss controller that will handle up to ~500mA. at 12VDC. A decent 4" muffin fan will use ~200mA. I recommend purchasing a fan with ball bearings. The sleeve bearing units are cheaper and more readily available but they often are noisier although that can be fixed with a really good oil and disassembly.

Fuse the fan, inline holder will be fine at something like 300mA or 400mA, and leave a good length of wire so you can install and remove the fridge as needed.
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Old 02-02-2015, 07:36 AM   #12
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I'm going to pull it out and see what I can see. I may need to clean the coils and see if that helps.
Other than that, possibly a fan to circulate the air would help.
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Old 02-02-2015, 11:18 AM   #13
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Quote:
Originally Posted by Wmiii View Post
I have a NovaKool refrigerator on my boat. It seems to run all the time. I checked the door gaskets and they seem fine. And seal fine. The temps are good, it just runs constantly. Is that normal? Is there anything else I should check?


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Wm

Just a few random thoughts -
  • Try turning the thermostat to (much) warmer so that it cycles on and off as it should.
  • Most, not all, boat fridges are expected by owner to cool as if they are in a house.
  • In a boat, the extremes of high humidity, higher ambient temperatures and sitting on top of a hot ER provide challenges.
  • I have found over the years a 20 degree freezer compartment is OK on a boat where in our house we expect 0 degrees.
  • Every two weeks or so we do a manual defrost which seems to help keep the Danfoss cycling as it should.
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Old 02-02-2015, 03:33 PM   #14
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I have done all the things mentioned by Clectric. I didn't get a huge gain but it's worth doing. Also, you should do regular defrosts. As mentioned above, you don't get the same type of refrigeration that you get at home. As mentioned in the original post, Novacool mentioned that a 50% duty cycle is normal under cool conditions but it goes up when the ambient temperature rises and they struggle with higher humidity. Also, important to do regular defrosts, freeze your food hard and well prior to filling the freezer.


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Old 02-02-2015, 04:05 PM   #15
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Are you the second owner of the FRIDGE?

You need to get the manual and read it. You should get it regardless.

Something I just remembered.

These Danfoss compressors are variable speed and can be set to run continuously. Apparently they are most efficient if run slowly and continuosly, no cycling at all or almost none.

From what I learned, set from the factory, they are set to cycle like a home fridge because that is what most people expect and they got a lot of complaints that , ""My fridge isn't working properly, it won't cycle"".

A knowledgeable owner who is concerned about total power useage can change that factory setting to continuous running by changing a resistor in the thermostat circuit. The manual explains and also gives a table for the resistors to be used.

Maybe, if you are the second owner, the previous owner has done that. If that is the case then the fridge MAY be doing exactly as it is told to do.

I will still push the fan so it blows out from the top of the cavity.
On my old fridge, a Norcold which actually worked well , the fan made a big difference in cycling time and thus power draw. This old unit was on or off so no slow speed. From no cyling at all to about 60-70% on a hot day. Even if it only improves cycling and heat removal by 10% it's worth it.
I cannot tell with my Novacool without disconnecting the fan which I will not do.
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Old 02-02-2015, 05:00 PM   #16
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I installed a 12v computer fan down low in the back of my refrigeration compartment to bring in cool air and another at the top of the compartment to exhaust the warm air. The fans are virtually silent. The ambient air temperature over the coils has a lot to to do with how cool the system can get.

My system is made by Vitrifrigo but probably uses the same compressor as your unit. Vitrifrigo tech support told me that the "thermostat" control on the unit does not actually set the temperature. I was told that the setting determined the run time on the compressor. The highest setting will cause the compressor to run almost continually without regard to the temp inside the unit. I keep my system set to the mid setting and keep ice-cream hard in the freezer, and meat at 38 in the cooler section. If I set the system to high, the compressor runs constantly, but the temps inside the unit stay pretty much the same. I don't know where you have your thermostat set, but you might find that a lower setting will reduce run time while still keeping things cold inside.
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Old 02-03-2015, 08:09 AM   #17
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I defrosted the unit Sunday and have set the thermostat to a higher setting. hen I got up this morning and checked, the unit was off!, the refrigerator side was 35 degrees and the freezer was 8.
Now I'm feeling better.
I will still clean the coils and see if that does anything.


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Old 02-03-2015, 08:15 AM   #18
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For most cruisers the fridge is the HUGE load that has to be recharged.

One key to successful cruising is coming up with 150+ amps per day to feed the beast.

Cutting the amps required by half would help, but really does not solve the task.
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