fridge power consumption?

[jeffryscott]

So, I had this brilliant idea for a built in fridge in my truck - a Waeco CD-30. I compared its power consumption, 40 watts to a similarly sized stand alone unit, the CF-35, which uses 45 watts. But then I get to looking at this:

Average power consumption: 40 watts
Average running time:
20% at 68°F ambient temperature,
40% at 86°F ambient temperature,
both at 41°F interior temperature

For the CF-35:

Average power consumption: 45 watts
Average running time:
15% at 68°F ambient temperature,
19% at 86°FC ambient temperature,
both at 41°F interior temperature

Power consumption: Power input x average running time

The CD-30 appears to run 40% of the time to keep the temp low, but has a lower average power consumption. I'm a bit confused. Would the CD-30 be a battery killer?

Thanks,

jeff

 

[Robthebrit]

You really have to make sure you are comparing apples to apples. The first thing to be sure about is the wattage rating, is that power consumed while running or is that power somehow amortized over a period of time (this would typically result in an amp/hour or watt/hour rating).

I have an engel MT45 and an MT35 and they both consume the same power on paper. I did play around with the 45 and it seems the amount of current taken is directly related to where you position the knob, this is basically setting how hard it works when its running. The parameter you cannot control is how long it runs for and it does not appear as there is any smart logic in these fridges, at some ambient temperature the fridge will reach 100% duty and if that is still not enough cooling the internal temperature will rise. You can compensate by using a higher setting on the dial. Using the same settings over night as you do during the day in direct sunlight would turn your fridge into a freezer.

The numbers I saw was the MT45 takes just under 1amp at 12.6V (comes out to about 10w) when on number 1 on the dial. When the dial is on five the power consumption increases to about 3.1amps (39W). However, at such a high setting it will freeze in pretty much any ambient temperature, even in direct sunlight. Typically I have the dial around #2 and it holds just around freezing. I drove thorugh death valley in July with the fridge outdoors and did not have to run it at full power. Unless you want a freezer you probably never will need to use full power.

My measured numbers are slightly higher than the published numbers. If I get a chance this weekend I'll measure the consumption of the MT35 to give a comparison.

I hope that helps..

Rob

 

[hoser]

Just wanted to mention the CD-30 is only a fridge while the CF-35 is a fridge/freezer... if that matters to you. To me that would be a deal killer.

 

[VikingVince]

Jeff,

I have a Waeco CF50...have had it about 2 years...works great, no problems, and I love it.

Re your question above: I believe you have to figure out amps. I went through all that before I bought mine and now I can't remember the whole watts/voltage/amps formula. But what I do recall is that my unit draws about 3 amps/hour when running. The longest I've sat in one place is 5 days with an average temp of 70-75 degrees and no problem with frig performance. HOWEVER, I have a 120 amp hour auxillary battery. Obviously that is key if you intend to park in one place for several days without the vehicle running. My battery is a AGM (absorbed glass mat) Concorde Lifeline. Be sure to check the amp hour capacity on whatever aux battery you're considering. (no doubt you know that)

A couple other comments: Personally I would not want anything smaller than what I have. It fills up faster than you would think. Also, I bought a reconditioned unit from the waecousa website for $375. I see they have my same unit (reconditioned) for $600 now (bummer) and the CF40 is $450. I really think the extra bucks is worth the larger unit. I would guess their reconditioned units have become more popular...hence the price increase.

hope this helps...

 

[jeffryscott]

Thanks for the replies. Vince, I'm going to get a bigger battery, or a second battery, or both, and am looking at the Odyssey and I'll look at the Lifeline as well.

I'd like to go bigger, but because of the size of my vehicle and the realistic opportunities to go for more than a day or two, the 30-35 liter range should be fine.

I'm not too concerned, at least not now, with the lack of freezer.

I'm mostly concerned about if it runs 40 percent of the time what kind of draw that will be on the battery system. I don't know enough about vehicle electric to know if this thing, the CD-30, would drain a battery overnight or in three days with the figures I posted. I'd like to keep with the drawer type for my Suzuki as it would fit nicely and give me a nice clean install in the rear, but I could move up to the CF35 for about the same money if it is much more efficient.

Thanks all,

Jeff

 

[BajaTaco]

Jeff, I think you would probably end up running the CD-30 more than 40% of the time, because 41°F isn't cold enough. Also, that is at 86°F ambient temperature, which considering where you live and play, will fall short of the actual temps on many of your trips when you have your vehicle parked. Monitoring the interior temp of my fridge, I have found that I enjoy keeping it in a temp range of 30°F - 33°F for optimal chill. A few degrees more than that should be fine, but I would say not more than 37°F. Anyway, 40w/12V = 3.33A. If it is running at 40% per your example, that would average only 1.33 amps consumed per hour, which is not much. You could double that to 2.66 AH and still have a very conservative consumption number. So my concern wouldn't be so much consumption, as it would being able to maintain the desired chill while the suzuki is parked on a warm/hot day. Maybe you could locate some CD-30 owners for some real-world feedback, because having that drawer configuration sure would be nice for your setup. Unfortunately, I think the CF35 will be much more efficient, and you will get more chill for the amps.

 

[jeffryscott]

Thanks Chris. I have to decide if the tradeoff is worth it - built in or portable. I've got such limited space, I really like the built in idea. I was going to build a drawer system and this would fit perfectly.

If I go this route, what would a good battery recommendation be as to amp hours?

Thnks,

Jeff

 

[Redback]

I don't know if you have solved your problem but i thought this may help.


Mega Fridge Comparison
Author: Peter Pinto
Date: Wednesday, 9 November 2005

WAECO CoolFreeze CF-40 AC
BEST COMPACT FRIDGE
The test was done at the Australian Defence Industries facility in Western Sydney where the fridges were set to run at a few degrees above freezing.

The ambient temperature profile roughly approximates an outback summer's day. It started with four hours at 15°C, took six hours to climb to a peak of 55°C where it stayed for four hours, before descending over another six hours back to 15°C, where it remained for the final four hours.

"Among the smaller fridges... the WAECO CF-40 AC was the cheapest unit tested but still had it where it counted, producing a temperature graph that could have been sketched by a metronome and consumed a measly 22.5A over the full 24 hours".

Even at 55°C the energy consumption of the CF-40 AC was a class leading 2.2A per hour meaning more run time out of your battery.

Along with temperature and energy performance, the lowest retail price combined with extra features such as battery protection, internal light, sturdy handles, high power 'Turbo' button, and 240V built in earned it the "Best Compact Fridge".

"We were particularly impressed" states author of the article Ben Wickham, "... ran like clockwork, keeping its maximum internal temperature within about a degree throughout the entire 24-hour period. It also had the lowest energy consumption figures of the entire field, suggesting that even though it is sharply priced, it is still constructed with very effective insulation."

High Performance, Low Power Consumption
Current draw:
22.5 amps consumed over 24 hour test. No other product tested came even close. Average of other competing product in this class was 30.9 amps.

Temperature performance:
Never varied more than 1°C, even during the gruelling 4 hours at 55°C ambient.

Price and features:
Cheapest unit on test, and yet sporting features such as digital display, emergency function, 3 stage battery protection, internal light, sturdy handles, high-powered 'Turbo' button and 12/24/240 volts built in.

Acknowledgement
Acknowledgement is given to the Australian 4WD Monthly magazine for permission to use the contents of the article 'Cool Runnings - the 4WD Monthly mega fridge-freezer comparison' by Ben Wickham, issue #87, pp56-76

The Engel equivilent came second.

Real world testing is usually differant.

Baz.

 

[BajaTaco]

Thanks Chris. I have to decide if the tradeoff is worth it - built in or portable. I've got such limited space, I really like the built in idea. I was going to build a drawer system and this would fit perfectly.

If I go this route, what would a good battery recommendation be as to amp hours?

Thnks,

Jeff

Jeff, that will also depend on your available space and weight allowance that you want to afford the battery. I think that Lifeline or Odyssey deep cycle batteries will offer some of the best "bang for the weight" where amp-hours are concerned.

 

[Redback]

Thanks Chris. I have to decide if the tradeoff is worth it - built in or portable. I've got such limited space, I really like the built in idea. I was going to build a drawer system and this would fit perfectly.

If I go this route, what would a good battery recommendation be as to amp hours?

Thnks,

Jeff

As Bajataco has stated space will be the deciding factor as to what size you go, most battery site give the dimentions of the battery.

To give you an idea here are some Fullriver AGM batteries in various sizes, sorry about them being in metric, 300mm is 12" or 1 foot approx.

HGL45-12 12V 45A/H 198mm Long 166mm Wide 174mm High @ 15.00Kg and priced at $139.00.

HGL60-12 12V 60A/H 229mm Long 138mm Wide 212mm High @ 18.30Kg and priced at $170.00.

HGL80-12 12V 80A/H 260mm Long 170mm Wide 215mm High @ 28.50Kg and priced at $220.00.

HGL90-12 12V 90A/H 307mm Long 169mm Wide 215mm High @ 30.60Kg and priced at $250.00.

HGL120-12 12V 120A/H 331mm Long 175mm Wide 240mm High @ 35.00Kg and priced at $300.00.

HGL200-12 12V 200A/H 530mm Long 209mm Wide 218mm High @ 65.50Kg and priced at $495.00.

HGL260-12 12V 260A/H 521mm Long 269mm Wide 224mm High @ 89.00Kg and priced at $595.00.

And have a look at the info on this site, this is an aussie site and prices in the US will be cheaper, this is just good info on how AGM batteries work and the miths about them.

http://www.fridge-and-solar.net/agm.htm

Baz.

 

[jeffryscott]

Thanks all. Right now I have an Optima Red Top and am thinking of either replacing it or adding, as a second battery, this battery:

http://www.odysseybatteries.com/battery/pc1200mjt.htm

It only has 44 ah though, so judging from Chris' estimate of 1.33 amps/hour to 2.66 this would give me somewhere less to somewhat more than a day idle? Is that the correct way to figure that?

Is that about the minimum I'd look at for this application?

I also just looked at the Optima yellow or blue - they are both 55 ah reserve. Would one of these, with my existing red top as my starting battery be sufficient?

Just trying to get some guidance, this is all new territory for me.

Thanks,

Jeff

 

[Redback]

If a day at idle is what you want then 44ah is the absolute min, 55ah would be better, don't forget you must have power in reserve, draining them below a certain % is not good for any battery and doing it day after day is even worse.

My auxillary battery for my fridge is 60ah and i'd say from the few times i've been away with this setup i could safely go 2 days running the fridge, without adversely affecting the battery, i'm talking just running it overnight then charging during the day, with a drive for a couple of hours it will last alot longer.

All conventional deep cycle battery manufactures say that their batteries are designed to be cycled to 50% of their rated capacity!

So each and every time you take these batteries below this 50% you are shortening their lives, and if you do it regularly and deeply you will even more dramatically reduce their lives.

The Odyssey is a good choice as it is an AGM TYPE deepcycle battery.


Baz.

 

[jeffryscott]

Thanks Baz, you are giving some helpful advice. I think I might start with one Yellow or Blue Top and add another as money allows. Now to figure out how to wire the two together and make sure I don't get stuck someplace.

 

[Redback]

Like you i went down this road only 12mths ago, i made the mistake of draining too much from my auxillary battery as i had no idea about all this myself, i'm not electricly minded so lots of reading of sites like Fridge and Solar was what i did, i went with the Fullriver because the Odyssey over here is $400:Wow1: :Wow1: wereas the Fullriver is $160.

Baz.

 

[Robthebrit]

Even though the fridge takes 1.33 to 2.66 amps while running, it does not run all the time so the total amp/hour draw is effectively lower. Baz's review a few posts back said 22.5 Ah for a 24 hour period: 0.93Ah, lets say 1 amp per hour for the sake or argument.

To work things out properly you need to use Peukert's equation (C=I^k.T) which tells us how to convert a battery load into a battery drain, assuming you know some physical properties of the battery. It also tells us that there is effectively more capacity in a battery for a lower discharge rate.

For example 48 Ah could be 1 amp for 48 hours or 48 amps for 1 hour. As you'll see below the actual drain these loads put on the battery are significantly different. If we assume a Peukert constant (k) of 1.15 (typical for a lead acid battery is 1.1 to 1.2, lower for AGM, search the web for actual numbers) then we get the following:

for a 1 amp load over 48 hours: 1^1.15 * 48 = 48 aH
for a 48 amp load over 1 hour: 48^1.15 * 1 = 85.7 aH

for a 0.75amp load over 64 hours: 0.75^1.15 * 48 = 45.9 aH drain

Fortunately the fridge is a nicer load from the point of view of battery capacity and a 80 Ah battery would be about 50% discharged over a 2 day period.

The above vividly shows that all battery loads are not created equal.

Rob