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Old 27-04-2015, 07:11   #1
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Unhappy 12v Fridge power use

I have a new Isotherm refrigerator for my small boat. It runs 24/7 and I am in the bahamas. The list power consumption is supposed to be very good. I think .6 -1 amp per hour. That would put my use at around 24 amps per day. I have 250 watts of solar plus a wind gen charging into a 270 amp bank of flooded cells which are also new. A typical day of charging gets me 60-70 ah of total charge plus maybe another 12-24 ah from the wind gen.
The issue is I never seem to get caught up to trickle my batts. My voltage will sometimes get to 12.2V by morning. Not bad but lower than I would like. I am very conservative with other usage. LED lights, I rarely turn on my fan and dont have AC or Radar. MY water pumps kicks on for seconds at a time a few times a day. I guess my laptop would be the #2 consumer.
So my question is in the heat here what is the actual consumption of the fridge? Would it be closer to 50-60 ah per day? If that is the case I am probably pretty close to my total usage and am just breaking even every day.

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Old 27-04-2015, 07:17   #2
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Re: 12v Fridge power use

Our isotherm fridge uses roughly 35-60 ah per day depending on climate, and our icebox insulation sucks. In Belize in July we were just shy of a break even with 130 watts of solar. The laptop isn't doing you any favors either.


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Old 27-04-2015, 07:28   #3
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Re: 12v Fridge power use

Hate to tell you this but I do believe your fridge is actually drawing between 2 and 3 amps when running. what model is it? if built in think more insulation, if portable unit think more insulation. ( at two amps and if the fridge is running all the time 48 ah and if at 3 amp you are right at the 72 ah point and loosing the power battle). What is the model of your fridge?
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Old 27-04-2015, 08:14   #4
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Re: 12v Fridge power use

A refrigerator will have a thermostat that has the compressor start and stop to maintain the temperature that it is set for. The compressor does not run constantly unless it is unable to keep up with the thermostat setting.

What this means is, it's impossible to determine the actual power used per day because of variables including heat loss through insulation and door opening and ambient temperature.

There are devices that can be used to determine power consumption of appliances but I've only seen these in 120 volt AC models. There may be 12 volt DC models available.

But; What you have is what you have. You can minimize power consumption by limiting the amount of time the door is opened and trying to pre-chill food before putting it in the refrigerator. You might be able to add insulation and you might be able to improve ventilation to remove excess heat.
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Old 27-04-2015, 09:22   #5
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Re: 12v Fridge power use

To save power, also make sure the place where the heat exchanger and compressor are installed is well ventilated.
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Old 27-04-2015, 09:44   #6
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Re: 12v Fridge power use

There are so many variables affecting refrigeration consumption; the type and amount of insulation, direct sunlight, ventilation of the compressor, the selected temperature, how full the unit is (the fuller the better), hwo cold the contents are when loaded and after 24hours, how many times the door gets opened, whether the door seal is effective, whether it is top opening or front opening.......etc etc. If you select to run at minimum temperature then just about every unit shall run continuously. The factors are significant. Good luck.
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Old 27-04-2015, 09:46   #7
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Re: 12v Fridge power use

I have had two IsoTherm's and noticed that the power converter mounted to the back used some power. You can test yours by checking the 12v input to the power converter and compare it to the output going to the refrigerator. Mine had about a half volt of loss. I eliminated the converter from the 12v side and had significant improvement on battery run time.

The problem this creates is the converter is what switches you from 12v from the batteries to 120v when you have shore power. (oddly the 120volts is converted to 24v not 12v) So I put a 3 way switch in that allowed it to switch between battery and shore power.
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Old 27-04-2015, 09:51   #8
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Re: 12v Fridge power use

Thanks for all the comments. I have the cruise 130 isotherm. The manual is telling me .6-2.5 amps. X 24 hours that 2.5 really adds up.
It has fair ventilation to the compressor but it could be better. More insulation sounds good but I can't see where I would use it as my installation is already tight.
Good to know it is likely just a power hungry device rather than another issue of my system.

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Old 27-04-2015, 09:54   #9
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Re: 12v Fridge power use

There is a spot on most installed 12 volt fridge compressor control boards to add a simple hour meter that will give you a better idea how long your refer is actually running per day do a week long read and average it for a better idea. Then go from there
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Old 27-04-2015, 10:05   #10
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Re: 12v Fridge power use

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.
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Old 27-04-2015, 10:10   #11
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Re: 12v Fridge power use

It sounds typical to me. Both my boats in the Caribe had very small boxes. (<2cu ft) Both used at least 70 AH a day for the fridge. Usually about 100 amps a day total usage for everything. With a Wind gen and 100 amp alternator was running the engine 1 hour twice a day typically.
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Old 27-04-2015, 12:08   #12
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Re: 12v Fridge power use

Lots of good info/suggestions above, but I'll add a little more:
  • Check the voltage of the power feed for the fridge - when we found that wiring was corroded (or if it was undersized, had partial breaks etc.) so that voltage reaching the fridge was low, that decreased the efficiency and significantly increased power consumption.
  • If you have, or install, a battery monitor (we have a Victron BMV 602S: BMV-600S series - Victron Energy ) you can use it to see the actual drain you're experiencing. If you shut off everything but the fridge, you can see amperage it alone is using (you can also see what happens when you turn it on and off) at a given time; or you can use the cumulative energy function to see what is consumed over a period of time.
  • You might also check to make sure that if you leave the fridge OFF, your batteries will charge up fully - to make sure your solar, wind & battery configuration is functioning as it should.
With an older isotherm model (I think a something or other 80), and not great ventilation and degraded wiring, ours was using in the vicinity of 6 amps - so if your installation and usage is anything less than optimal it's entirely possible you're drawing an average of well over 2.

Before we replaced our old array of 2x75 + 2x80 watt 12v panels, our batteries never fully charged up unless on shore power (we eventually found big voltage drops from a couple of them, and some wiring problems). When we installed 4x185 watt 36v panels with new wiring and an MPPT controller, we found batteries fully charged most days by midday, even with a freezer and fridge drawing a combined amperage of well over 10!



So....lots of things to check......good luck!


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Old 27-04-2015, 12:23   #13
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Re: 12v Fridge power use

What are the most efficient refrig/freezers on the market? How much foam in inches would you recommend. My unit needs replacing and my box needs a remodel. I have a top load with the existing unit in a space alongside. Would a low amp draw fan that would run with the compressor unit make sense?
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Old 27-04-2015, 12:39   #14
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Re: 12v Fridge power use

Quote:
Originally Posted by captainwireman View Post
What are the most efficient refrig/freezers on the market? How much foam in inches would you recommend. My unit needs replacing and my box needs a remodel. I have a top load with the existing unit in a space alongside. Would a low amp draw fan that would run with the compressor unit make sense?
That my friend is a question that will invoke many personal answers
On our boat in Seattle we have 2.5 cf freezer at 15 f and a 7 cf fridge spill down at 38 f ( its a front loader) with a stock technautics holding plate system with the cubigel compressor uses just under 24 ah per day. YMMV
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Old 27-04-2015, 17:46   #15
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Re: 12v Fridge power use

Isotherm 2013 Compact Classic Air Cooled Refrigeration Component System
Maximum Box Volume (cu ft): Fridge: 14.1 / Freezer: 4.7
Power: 12 / 24 Volt DC, Fan-Air Cooled, Max Draw: 6 Amps

I have 2 of these units, one for Frig and the other for Freezer. And they each draw 5 to 6 amps as shown by my Battery Controller and Power Management System.

With 2 x 140 watt solar panels and a Stealth Wind Gennie provides sufficient energy for Frig; Freezer, Laptop and TV majority of time. Can also boil a kettle of water for tea using Inverter. Once/day run main engine for 2 hours and occasionally run Honda 2000w generator.
Never short of battery power.
Needless to say I have good Frig/Freezer insulation.
Also have 12v Fans wired in parallel with compressors and cooling compressors.
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