Nova Kool RFU 8320 Refrigerator Installation

[dave macrae]

If this is a 2013 trailer should it not still be under warranty ? If so, would the logical step be to get it looked at diagnosed and repaired under warranty ? Jumping to the conclusion that a retro fit to another fridge that hasn't even been tested seems a bit harsh.

[hotfishtacos]

Originally Posted by padlin

According to the Nova Kool web site you'll use 125A a day (5.2x24). Using Vancouver BC for a location, an online calculator says you need 357 watts worth of panels. The 2 6v batteries will just manage.

This model shuts off when it reaches temperature then runs at about 50% duty cycle at normal ambient temps..longer when it gets hot. You must have it confused with another model..

[hotfishtacos]

Originally Posted by dave macrae

If this is a 2013 trailer should it not still be under warranty ? If so, would the logical step be to get it looked at diagnosed and repaired under warranty ? Jumping to the conclusion that a retro fit to another fridge that hasn't even been tested seems a bit harsh.

It is a 2012 model and I'm sure you'll get over it!..

[dave macrae]

Originally Posted by TRF18

We have a 2013 Escape 19 with the Dometic RML 8551, 6.7 cu ft. refrigerator. Worked well on AC prior to trip & when I returned from the trip. No access to AC during the trip. Set up the trailer at my campsite & set to propane, could hear propane burning well, no error messages from fridge electric panel. Just wouldn't cool. Has been "marginal" on propane in the past but this time, I may as well have had the door open - it was colder outside than in the fridge!

Sorry to not be clear . This was the post my response was to.

[padlin]

Hopefully I'm wrong on the power usage, 125A would put it out of my reach. They make no mention of it shutting itself down, just to multiply their Amperage spec by 24. It's down by the bottom. It'll be interesting to see what your bench testing reveals, hoping for the best.

http://www.novakool.com/products/two...al2013_001.pdf

[Brian B-P]

Originally Posted by padlin

They make no mention of it shutting itself down, just to multiply their Amperage spec by 24. It's down by the bottom...
http://www.novakool.com/products/two...al2013_001.pdf

What that page says at the bottom is this:

*Note: The amperage listed is while the unit is running. To determine 24hr consumption calculate the run time for 24hrs and multiply
this by the listed amperage.

If the unit is running 50% of the time, then the "run time for 24hrs" is only 12 hours; multiply that by the "listed amperage" of 5.2A, and you get 62.4 amp-hours (Ah).

This part of the note at the bottom is misleading:

Listed amperage will change with ambient temperature and unit door openings.

It should say that run time (not listed amperage) depends on conditions.

[alanmalk]

Thank you, Brian!

[dbailey]

Originally Posted by padlin

Hopefully I'm wrong on the power usage, 125A would put it out of my reach. They make no mention of it shutting itself down, just to multiply their Amperage spec by 24. It's down by the bottom. It'll be interesting to see what your bench testing reveals, hoping for the best.

http://www.novakool.com/products/two...al2013_001.pdf

"calculate the run time for 24hrs and multiply this by..." so not (<draw> x 24), but (<draw> x 24 x <duty cycle>). The duty cycle will depend on the amount of insulation, ambient temperature, how often you open the door, etc...

In a hypothetical fridge with perfect insulation (keeping perfectly spherical cow fragments cold), the compressor would run until the desired temperature was achieved and then shut off until somebody opened the door. The duty cycle is the percentage of the time that the compressor has to run to account for heat infiltration through the insulation.

(This is assuming that the compressor is either on or off. It's also possible to design a system that runs at different power levels, but the formula provided suggests this isn't the case for these fridges. Talking hypothetically, you might achieve a system that runs at exactly the right power level to compensate for heat coming through the insulation, and then kicks up the power to achieve the desired temperature after somebody opens the door.)

[Brian B-P]

Originally Posted by dbailey

(This is assuming that the compressor is either on or off. It's also possible to design a system that runs at different power levels, but the formula provided suggests this isn't the case for these fridges. Talking hypothetically, you might achieve a system that runs at exactly the right power level to compensate for heat coming through the insulation, and then kicks up the power to achieve the desired temperature after somebody opens the door.)

I agree. Refrigerators do not commonly have a variable speed compressor, but they do exist (including some from Danfoss, which supplies many of the mobile 12VDC refrigerator manufacturers). An on/off controller is cheaper.

[hotfishtacos]

Originally Posted by Brian B-P

I agree. Refrigerators do not commonly have a variable speed compressor, but they do exist (including some from Danfoss, which supplies many of the mobile 12VDC refrigerator manufacturers). An on/off controller is cheaper.

An experienced refrigeration engineer told me today that the reason my compressor drew lower amps as the refer cooled is because the head pressure on the compressor is reduced when the unit isn't drawing as much heat from the refer. It was drawing around 4.2 amps just before it shut off. My compressor also has a resistor wired in series with the compressor motor and different values are used to change the RPM depending on the application.

[hotfishtacos]

I now have some bench testing data from the Nova Kool refrigerator while hooked up to two 6 volt Interstate batteries in series while sitting on a work bench in my garage at between 75F and 80F ambient temp. I loaded the refer with a room temperature case of wine and the unit cooled it down in about 6 hours to 6 in the freezer and and 36 in the refer with the control knob set at 4, about half way. After the refer stabilized for about 24 hours I measured the amp draw over the next 24 hours. I measured 84.6 total amps at a 75% duty cycle. This was higher than I expected but will be very manageable with my system. I plan to go camping on Saturday then when I get back a week later I will move the refer outside next to my 19' and cable it to the batteries which are being replenished by two 95 watt solar panels on the roof. I plan to also turn on some other loads to try and simulate the real world while camping at this latitude. Stay tuned!

[rbryan4]

Originally Posted by hotfishtacos

I now have some bench testing data from the Nova Kool refrigerator while hooked up to two 6 volt Interstate batteries in series while sitting on a work bench in my garage at between 75F and 80F ambient temp. I loaded the refer with a room temperature case of wine and the unit cooled it down in about 6 hours to 6 in the freezer and and 36 in the refer with the control knob set at 4, about half way. After the refer stabilized for about 24 hours I measured the amp draw over the next 24 hours. I measured 84.6 total amps at a 75% duty cycle. This was higher than I expected but will be very manageable with my system. I plan to go camping on Saturday then when I get back a week later I will move the refer outside next to my 19' and cable it to the batteries which are being replenished by two 95 watt solar panels on the roof. I plan to also turn on some other loads to try and simulate the real world while camping at this latitude. Stay tuned!

Steve, that draw and duty cycle does sound a bit higher than the earlier estimates, but I think you're right -- your setup can more than handle it. It'd probably work with a single 160w panel and dual 6v as well. Looking forward to your next result.

[hotfishtacos]

Robert, I was speaking today with a close friend I work with that owns a solar business and he told me he can get me a new 250 amp panel with the same voltage output as my existing panels for about $200 that I could add to my system if I wanted to. This would take my total to 440 watts. I told him about the other tread discussing experiments with solar panels and he suggested that if I buy this panel I consider mounting it on customized bracketing on either the front tongue or rear hitch of the trailer depending on the sun angle while camping and angle the panel to generate the maximum output. This mounting would be highly efficient, stable, fairly secure and not blow over in the wind. Interesting conversation!

[padlin]

Steve, Have you determined the highest amperage you can generate in 24 hours with your existing panels? Best I've seen up here was 50A with the 160 flat mounted.

[Ron in BC]

Originally Posted by hotfishtacos

I loaded the refer with a room temperature case of wine

Yes, having the right provisions for camping is so important

Looks promising.

Ron

[Jubal]

Originally Posted by padlin

Steve, Have you determined the highest amperage you can generate in 24 hours with your existing panels? Best I've seen up here was 50A with the 160 flat mounted.

50A 12V from a 160W panel ?

"250 amp panel with the same voltage output as my existing panels for about $200"
3000 W panel for $200 or 250W panel ?
It is so easy to trip.
With a large wattage demand I have measured 15A output from two horizontal 95W panels at high noon in late July.

[hotfishtacos]

Originally Posted by Jubal

50A 12V from a 160W panel ?

"250 amp panel with the same voltage output as my existing panels for about $200"
3000 W panel for $200 or 250W panel ?
It is so easy to trip.
With a large wattage demand I have measured 15A output from two horizontal 95W panels at high noon in late July.

Yes, I tripped! It is a 250 watt panel. Thx!

[alanmalk]

Originally Posted by hotfishtacos

Yes, I tripped! It is a 250 watt panel. Thx!

Does this 250 watt panel provide 18-20 volts or 36-40 volts?

--
Alan

[padlin]

Originally Posted by Jubal

50A 12V from a 160W panel ?

"250 amp panel with the same voltage output as my existing panels for about $200"
3000 W panel for $200 or 250W panel ?
It is so easy to trip.
With a large wattage demand I have measured 15A output from two horizontal 95W panels at high noon in late July.

I knew exactly what I meant, darn keyboard has a mind of their own though.

50A total on an ideal summer day, sun up to sun down.

Best I've seen at any given moment was just over 8A in the summer, mostly it's mid 5's in the fall.

[hotfishtacos]

Originally Posted by alanmalk

Does this 250 watt panel provide 18-20 volts or 36-40 volts?

--
Alan

Alan, the 250 watt panel he offered has too high a voltage for me. I want to stay with the appx. 17 volt output so he is looking again. Good catch!

Steve