12v Fridge power use

[Dauntlessny]

Originally Posted by TacomaSailor

The Isotherm Cruise 130 manual says:
5 Technical data
Voltage 12 or 24 volt DC also AC/DC as an option
Power consumption when compressor is running: CR 42, 49 & 65: 2,5 - 2,7 A at 12 V (half at 24 V)
CR 130: 4,7 - 5 A at 12 V
CR 130 Drink: 5- 5,3 A at12 V
Average consumption: CR 42 & 49: 0,6 A at 12 V
CR 130: 1,2 A at 12 V
CR 130 Drink: 1,4 A at 12 V

AVERAGE consumption means nothing!

The BD35 compressor uses 5A (60watts) when running. How many hours a day does it run? If it runs 15 minutes out of each hour that would be 6 hours a day or 30 amp/hours.

Your solar panels should be able to power the compressor with no draw from the batteries at least 8-hours a day. Let us assume that the solar provides half the power needed another 4-hours a day so the BD35 only uses 2.5 amp hours of battery power during that time. During the 12-hours of darkness (no solar output) the compressor would run for 3-hours or so and would use only 15-amp hours of battery power. Those numbers look like they are saying the BD35 is only pulling 18 - 20 amp hours a day out of your batteries or less than 8% of the 270 amp hour capacity.

Something, other than the BD35, is consuming the power.

OR - if you know the actual run time / percentage you can get an exact answer.

Your laptop may use much more power than you realize. A typical 15" screen laptop will use about 60 watts (5 amps) with the screen on. If you use the laptop like I do it would be on for 12-hours a day or 60 amp hours. If you watch DVDs on the laptop the power would go even higher.

My Vitrifrigo, same size, but has external compressor (same one) averages about 2.6 amps/ hr at 12v over 24 hours for a total of about 60 amps or 720 watts.

Laptop uses about 60 watts per hour, plugged in only 12 hours, it will use 12 hr x 60 watts = 720 watts = 12 v x 5 amps/hr

[Scubatony]

Thank you Sternwake and Dauntless. This is really helpful. VEry creative and innovative work on the cooling channel. Unfortunately my space is way too limited to make that kind of modification so I am going to have to live with that.
I think my batts are fine. If I run my charger on the Eu2000 for an hour I assume I have bulked the batts to around 75%. I always do this in the morning and my Solar and wind top off the rest of batts during the day.
During this thread I have implemented several simple practices. I keep the Fridge full now and try to open the door less. I have also dropped the thermostat down to 4 of 7. Yesterday and the day before my solar controller went into float mode by around 1 pm and I turned off the wind gen. It stayed in float mode until dusk when I turned the wind gen back on. I assume my solar controller has a better system for controlling battery health than my wind gen which just has an internal voltage sensor. The amperage varies so much as it is charging I assume the solar is more stable. It is a morning star sun saver duo. It is just a PMW type controller.
I have been timing the compressor cycles as I don't have an ampmeter or battery monitor. It will run for 10-15 min then off for 5-10 then back on assuming I have not opened the door or added anything that needed cooling. So compressor is running about 75% of the time.
Laptop is a smaller Sony Vaio with a 13 in. screen but indeed it is big draw as well on my batts as well.
Excellent help all. I really appreciate it.

[onestepcsy37]

Originally Posted by maine50

I have an 15-20 yr old AB unit. With 450 amp/hr battery bank I can stay charged with a 130 watt panel running frig 24/7. I don't run computer much. Quit using computer for a day and see if it changes. Are you getting much shading on your panels and how old are the batteries? Tim

Nice. EXACTLY what I have, except my A-B is ten years old. If I had another 130 watt solar panel I could run the rest of the boat entirely with solar.

[Scubatony]

Yes. I do have some shading permanently. Which sucks cuz if they were clean I am sure I would get another 20-30 amps hours a day. The Previous owners had the davits built and put the pole and supports for the wind generator right in the middle of the panels. Which means no matter what the angle of the sun there is always some shading on my panels. The most I ever get out of the 2X130 watt panels is 11 amps. Unshaded I would guess more like 15 amps would flow at high noon. Considering I only average about 15-25 amp hours from my wind generator anyway I would just about break even by cutting that post down off the top of my panels. When the wind gen fails some day I won't replace it. Ill trim off the polls that it mounts too and just get clean sun on my panels instead.
Side note. Yesterday was a cloudy day and I got just over 21 amp hours from my panels and the wind died at night. So batts were down to 12.05V this morning. Running my generator now and 60 amp charger to get um back in the green. I also defrosted the fridge last night which I am sure didn't help my batts either.
ST

[SV THIRD DAY]

You mention the refrigerator defrost which is important because once the frost gets more than 1/4" thick you start losing efficiency. We did a test with two boxes side by side one had a scrapped off plate and the other has frost 3/8 of an inch thick. The frosty box was warmer and used 23% more power per day!!!! That's huge. So keep them evaporators defrosted and you will save power!

[Scubatony]

I wondered about the frost. That is a great hint. Hard to belive it makes that big a difference. Humid here so I do it about every 3 weeks. I guess 2 would be better

Sent from my SM-G7105 using Cruisers Sailing Forum mobile app

[newhaul]

Frost makes a huge difference in temperature holding and power usage with a 1/4 inch frost/ice on our holding plate we saw almost double the power usage for the same temp in the freezer. Keep it clean your batts will love you for it.

[Thumbs Up]

The amp draw of these danfoss units (bdf35) entirely depends on the ohm rating of a resistor that is installed in the thermostat circuit. The compressor is variable speed. If you remove the resistor it can draw as low as two amps (depending on temperature). The slower it runs, the more efficient it is, and the less it will cycle (it will just stay running on a hot day but only drawing two amps). The drawback is that it won't cool quickly after you load it. With the 450 ohm resistor it will draw 3.5 amps and with a 1500 ohm resistor, closer to 6 amps. There are also "smart controllers" available that will vary the resistance according to conditions or you can wire a switch to bypass (or increase) the resistance for quicker cooldown. These Isotherm units have very little insulation which is what makes them inefficient.

[Stu Jackson]

2A x 24 hours = 48 ah

3.5A x 24 hours * say 50% duty cycle = 48 ah

6A * 24 * 50% = 60ah (BTW, to the OP, this has been the essential "gold standard" of making an energy budget for refrigeration for the past 4 decades UNLESS singificant and quality insulation has been installed)

In the larger scheme of things, 12 ah per day on a 400 ah bank shouldn't make that much difference.

[SV THIRD DAY]

Just to add some clarification to Thumbs Up's comments so a new round of Chat room myth isn't created regarding the variable speed of the Danfoss compressor. You know that saying, "a little knowledge is dangerous", so lets flush out this topic a little more. And besides I don't really want to start my final paint coat on the forward head yet...so this is called Boat Project Stalling 101.

For a Rolled Aluminum Evaporator:
The reason variable speed is nice and can save power is that it does you no good at all to run your compressor at a faster speed than your evaporator can remove Heat from the box. The evaporator surface area needs to be matched to the box heat load and compressor running speed. So if you run your compressor too fast...well you are spending Amps that don't remove heat...equals inefficiency. So on thin rolled aluminum evaporators, a variable speed controller WILL save you power at the end of the day. Sure you can swap out and play with resisters manually but at 3PM you may need one compressor speed when your boat temp is 90-degs F but at 4AM when it is at 80-degs you need another speed due to the different amounts of heat that are entering the box. Heat is only removed from the box when the compressor is running! So doing it manually just isn't going to give you the benefits as paying the little bit extra for a variable speed controller. They also make lots of after market add-ons to make your single speed controller into a variable speed.

For a Holding Plate type Evaporator:
This type of system is designed around the compressor being operated at a speed or we can say "heat pull out speed" faster than what the evaporator (holding plate) can pull out of the box. The point of this design is to freeze down the temperature of the eutectic liquid inside the plate in addition to pulling out heat. Holding plate systems continue to remove heat when the compressor is off, so you need/want to store up "cold" in the plate. So on holding plate system, you don't gain anything efficiency wise by varying the speed of the compressor to match your box heat load. You just set the compressor at the most efficient speed and you want it to be "mismatched"...or over-sized...for the real time heat entering the box. This is how you get the longer off cycles with a holding plate set-up.

What you use the speed control for on a holding plate system is control the length of the compressor on cycle, in other words how long it will take to freeze down the holding plate. While this will control your instantaneous amp usage the end of the day number will be about the same! For example if you use 2.5A at low speed and it takes 2hours to freeze down the holding plate that 5AH. Or if you run the compressor on high speed and it takes 5A but only needs to run for 1hour...bingo...you will use the same 5AH per day. Personally, I would rather go for the faster holding plate pull down and use more real time amps, that way when I load the box or put in a big Dorado it freezes faster.

I get this question all the time from folks wanting to add a smart speed to their holding plate system because their "dock buddy expert" told them it will save them 37.5% on their power usage, because he read it online......but not so fast. While automatic speed control is a good thing on a evaporation system, manual speed control is the best for a holding plate systems, set it and forget it.

Speaking of a Big Dorado....
45lb monster caught in the Cervalo channel sailing into Pa Paz.
It took me 45 minutes to get aboard and we had to douse sails and reverse the engine down on this guy...so yes that is sweat on my shirt...oh the Memories.

[newhaul]

Nice fish now get back to work

[1affiah]

Thanks again to Sternwake and Dauntless.
I also have a Cruise 130, and had done some of the mods to direct the airflow, but I made the mistake of wrapping the fridge box with mylar bubblewrap which condensed the water vapor. I'll redo with batt insulation, the surrounding cabinet is already insulated with foam.
The tip on the Noctua fans is great as well, the std fans are junk by comparison.
One question: How do you hack the interior light fixture to run the small fan?
The bulb only lasts a week anyway!

[Sternwake]

Originally Posted by 1affiah

One question: How do you hack the interior light fixture to run the small fan?
The bulb only lasts a week anyway!

My VF has LED lighting. The wiring is always hot, and a magnetic reed switch tuns the light on and off. So I just tapped the wiring before the reed switch to power the interior fan.

I would not want this fan to cycle on and off with the compressor anyway. Sunon, told me the fan would never work properly in such an environment. I imagine the hub Lube would get too thick if the fan cycled.

The fan adds a small amount of heat load to the cooling unit. For this reason I searched out the lowest amp draw fan I could find at 6.3cfm and 0.03a

Sunon MagLev-Vapo 40mm x 20mm Fan w/ TAC Sensor Wire - (KDE1204PKV3.MS.AR.GN) - FrozenCPU.com

My previous Sunon fan in my Norcold fridge started getting noisy in year 5 of 24/7 use. the Sunon fan I currently employ linked above will be 3 years old of 24/7 use in October.

I removed the 270 OHM resistor from my T stat circuit for a slower compressor speed. I don't require faster cool downs, it seems fast enough with the internal fan.