Fridge Current Consumption

Submitted: Wednesday, Apr 24, 2013 at 23:19
ThreadID: 101859 Views:34015 Replies:7 FollowUps:17
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Ok Everyone, time to open a can of worms...
I am writing this to confirm my understanding of these matters.

How much current does a fridge pull?
Yes yes, it depends on the make / model, size, the temp and how many beers get pulled out!
Please advise the average draw and peak draw. I ask because for many of you, the fridge will be your biggest load, driving how much coin you put into solar, regulator and batteries, yet I am not sure this is well understood. Hey, I may be the one who has it wrong!
I'll kick it off. My Waeco CFX-65 pulls 0.85Ah average (25 deg ambient and 5 deg set temp) and 8 Amps peak according to the manual. A recent test in perfect conditions ( my shed) I got to 57 hours running and the 105Ah battery only got to 60% remaining capacity.

Cheers
Jason
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Reply By: pepper2 - Thursday, Apr 25, 2013 at 08:47

Thursday, Apr 25, 2013 at 08:47
plus 5 degrees is too warm to refridgerate food,try it at minus 5 degrees as it will be coldest at the bottom and warmer than minus 5 further up the fridge,closer to a practical setting.
AnswerID: 509713

Follow Up By: CampingTechAust - Thursday, Apr 25, 2013 at 20:17

Thursday, Apr 25, 2013 at 20:17
Thanks Pepper2,
I agree with your comment. I had only referenced the 25 and 5 degree setting as that what was mentioned in the Waeco manual for average power consumption. I am still experimenting but have run the fridge at 0 degrees very successfully but will take what you have said into consideration.
Thanks
Jason
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Reply By: Member - John and Val - Thursday, Apr 25, 2013 at 08:49

Thursday, Apr 25, 2013 at 08:49
Jason,

Let's start with basics. Your CFX-65 does NOT draw an average current of 0.85 Ah! Current is measured in amps (A), not amphours (Ah). Current (amps A) relates to the RATE OF FLOW of energy, not the quantity of energy. Since your fridge cycles on and off, and draws a few amps while running, the average current drawn may well be 0.85 A (NOT Ah!). The manual may be correct in stating 8 A peak, and that peak should only occur briefly when the compressor is starting. If your manual actually states that the fridge draws an average current of 0.85 Ah, I'd suspect it's either a typo or has been written by someone who doesn't understand what they are talking about. Either way I wouldn't rely too much on the manual. There are published tables (google) comparing the energy demand of various fridges, but these mostly rely on information supplied by salesmen rather than engineers.

There's a comprehensive article on fridges here on ExplorOz that's well worth a read, though it doesn't go into comparisons.

Sorry to rain on your parade, but as you say this is a can of worms, and one that has led to verbal bloodshed here in the past!

Cheers

John

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Follow Up By: Member - John and Val - Thursday, Apr 25, 2013 at 09:02

Thursday, Apr 25, 2013 at 09:02
Found one of the threads here, dealing with Waeco v's Engel that I refered to, and illustrating the sort of fights this topic can start!

Cheers

John
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Follow Up By: CampingTechAust - Thursday, Apr 25, 2013 at 21:30

Thursday, Apr 25, 2013 at 21:30
Thanks for your reply John,
As you said, the fridge cycles on and off over time. You would also know that the unit of time for power system engineering is 1 Hour. Therefore, a devices consumption that varies it's current draw over a time can most certainly be expressed as Ah. Yes, as you said, the devices instantaneous draw is only in Amps but this is not what the figure in the Waeco manual represents.
Also, I have found that the 0.85Ah figure is indeed correct, as my test shows, given that my fridge consumed 47.25 Ah of capacity (approx 40% of my 105Ah battery) over 57 hours. This gives 47.25 / 57 = 0.82 Amps Average consumption. Perfect world, yes, but still valid.
I have found the new CFX series fridges to be extremely efficient due to the new compressor and improved insulation. The Engel manual for a 60 Litre fridge indicates it will pull 4.2A average which is HUGE by comparison. This is why I purchased the Waeco. I get more than double the run time from the same battery.

Thanks for the link to the fridge article. I look forward to reading it soon.

Cheers
Jason
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Reply By: Peter From Vic - Thursday, Apr 25, 2013 at 09:43

Thursday, Apr 25, 2013 at 09:43
I have a Waeco CFX50. Average current draw is .7 amps per hour. Talking to Waeco they rounded up to 1 amp which is about 24 AH per day rule of thumb for my fridge.
Peter
AnswerID: 509724

Follow Up By: Member - Frank P (NSW) - Thursday, Apr 25, 2013 at 10:16

Thursday, Apr 25, 2013 at 10:16
Here's another one of those frequently used, nonsensical terms dreamed up by salespeople and often quoted in specifications and brochures. Amps per hour. There is no such thing, but it seems to have caught on.

As John said, Amps is the rate of flow. It already has time built in (1 Amp is actually a flow of 1 unit of charge per second), just like one Knot is one nautical mile per hour. Saying amps per hour is rather like saying kilometres per hour per hour, or if you're a boatie, knots per hour.

You can have an average current draw of .7 amps, which averages out the on and off cycles of the fridge.

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Follow Up By: Member - Frank P (NSW) - Thursday, Apr 25, 2013 at 10:18

Thursday, Apr 25, 2013 at 10:18
Oh for an editor!

Add to the last "but you can't have .7 amps per hour"
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Follow Up By: Alloy c/t - Thursday, Apr 25, 2013 at 11:31

Thursday, Apr 25, 2013 at 11:31
But u can have point 7 of an amp usage......
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Follow Up By: ExplorOz Team - Michelle - Friday, Apr 26, 2013 at 15:34

Friday, Apr 26, 2013 at 15:34
Frank there is a Forum post edit function but you must go to PREVIEW to use it and you can only edit it before you finally decide to click the SUBMIT button ;) We cannot allow posts to be edited after they're posted because people would abuse it.
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Follow Up By: Member - Frank P (NSW) - Friday, Apr 26, 2013 at 19:50

Friday, Apr 26, 2013 at 19:50
Thanks Michelle.

Sometimes it's just an error, but sometimes, despite the Preview, I think of a better way of saying something or think of an additional point to make some time after posting.

I can see where that could be abused after someone has replied or followed up so I totally see your point.

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Reply By: Ross M - Thursday, Apr 25, 2013 at 12:07

Thursday, Apr 25, 2013 at 12:07
CampingTechAust
Jason, never sell that fridge, it is a beauty and is one of the most efficient I have heard of.
How did you tell the battery only got to 60% of it's charge after 57 hours? Because the battery can't speak and you have to rely on something to interpret a voltage level as charge capacity it is rarely, if ever, accurate.

The test situation, in a shed, isn't representative of portable use which a portable fridge is designed for, so in a shed means it is ok in a shed, now for the real world.

If the internal power controller can vary the amps and it goes up to 8amps peak, that means it can draw 8amps for an hour, therefore, in less than favourable conditions and asked especially if asked to freeze unfrozen produce it will be churning through power, in hot areas most likely running at near maximum for long periods. This will mean the fridge will easily flatten a 100ah battery in a day or far less.

If you have more batteries and think you have the solar capacity worked out to cover this usage then you probably will require double the solar to begin to make it all possible.

Ross M
AnswerID: 509738

Follow Up By: CampingTechAust - Friday, Apr 26, 2013 at 15:38

Friday, Apr 26, 2013 at 15:38
G'day Ross,
Mate, I couldn't agree with you more! The efficiency of the CFX series was the primary reason I bought a Waeco. And no, I DON'T work for Dometic!
With a sealed battery the only way you will be able to check the State of Charge on your battery is to measure the open circuit or no load volts. Do a google search and you will find many sites that with give you a table that links battery volts to its SOC.
At the 57 hour mark, I was reading 12.15 volts which roughly equates to a bit less than 60% remaining capacity in my 105Ah battery. In my case, I have found this to be quite accurate as I got very close to the rated consumption.

I agree that a fridge can pull max current for extended periods of time but I think this is when you first turn it on and the compressor is running constant to get the fridge from ambient to the set point temp. Once at temp, the duty cycle is around 15% for ideal conditions. I also agree this will increase quickly in not so ideal conditions! Have you seen your fridge run the compressor for an hour? I built in additional reserve to my system by allowing 1.5Ah -2Ah as the consumption for the fridge. What did you allow for yours?

As for solar, for my load and the autonomy I require for 3-4 days "off grid" in any location at any time of year, I need 2 x 125W panels. If I had an Engel, I may require a 3rd panel to recover the battery each day within the available sun hours.

Hope this answers your question.
Cheers
Jason
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Follow Up By: Alloy c/t - Friday, Apr 26, 2013 at 18:08

Friday, Apr 26, 2013 at 18:08
Your forgetting the first rule of maintaining a battery ; that being you never let it discharge under 50% if you want the battery to last ,,, IE: a 100 amp hr battery should never have more than 50 amps drawn from it , be that a 1amp light running for 50hrs or a fridge that draws 2.5 amp over an hr for 24 hrs =60 amp drawn ,,,,, 57 hrs ? your battery is bound to die a premature death , SOC is only a useful guide AFTER the battery has been rested from discharge / charging for a considerable period of time ,,,,,
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Follow Up By: CampingTechAust - Friday, Apr 26, 2013 at 21:03

Friday, Apr 26, 2013 at 21:03
Hi Alloy C/T,

My battery was rested for 12 Hrs following the test and was still 12.15V. 60% SOC it was. The battery manufacturers I have been speaking to (we have many come through our office) typically will feed you nothing but rubbish WRT Battery life of a deep cycle battery. They are all consistent however when they say a deep cycle can get below 50% SOC and survive. If it is deep cycled every cycle, your going to kill it (quarter to one third is common). If its once or twice and gets a good boost following, you won't experience too many down sides.

Have you had a different experience?

Cheers
Jason
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FollowupID: 787868

Reply By: Member - PJR (NSW) - Thursday, Apr 25, 2013 at 12:13

Thursday, Apr 25, 2013 at 12:13
Hi Jason

This is why you should use the correct terms. Even the Engel site 40 ltr specs have made a mistake,

Specs state "DC Power Consumption: Variable from 0.5 to 2.5 AMPS Maximum". Watts is the unit of power. So what hope do we mere mortals have. Sales people aren't usually mortal are they?

For our fridge test I turned it on in the car on friday evening. It was still good and the battery still started the car okay on monday morning, after three nights later. Thus the way we have it set up will do us two nights (4PM to 8AM) in one place without the car running. A total of 36 hours.

Then when we were setting up for longer stops we added a second smaller fridge to act as a freezer and a third battery. Leaving one bbattery as a main/cranking battery and the other two in parallel and linked to the main one and alternator through a 200 amp Redarc isolator.

Same test. Both fridges running all weekend and temps all fine.

Both times the outside temps grew to 30+. Fridge running at 4 degrees and the freezer at -6 degrees (I think). Car locked so it got damned hot in there.

Worked fine for the Vic High plains and Simpson and Gulf drives when we stopped for a day or two. Meat frozen and beer cold.

Not very scientific but we should be okay for the Canning.

Phil
AnswerID: 509739

Reply By: Member - eighty matey - Thursday, Apr 25, 2013 at 14:25

Thursday, Apr 25, 2013 at 14:25
I don't know about watts, amps or other stuff, but I know my 11 year old Waeco 70 litre parked with my 100 watt solar panel hooked up keeps everything cold for as long as I'm parked.

Driving the alternator keeps it ok in the day and my battery pack keeps it all good overnight.

It's worked form the High Country to Kalumburu.

I tried to figure out the numbers but I got dizzy and had to have a beer, Lucky the fridge was working.

Hoo roo,
Steve
AnswerID: 509749

Follow Up By: steved58 - Thursday, Apr 25, 2013 at 18:39

Thursday, Apr 25, 2013 at 18:39
Same here 2 100 ah batteries 120 watt solar 80 litre waeco running -12 plus the alternator over 80000kms in 4 trips all over oz and never a warm beer don,t care about the figures it works for me

Steve

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Follow Up By: CampingTechAust - Friday, Apr 26, 2013 at 21:39

Friday, Apr 26, 2013 at 21:39
G'Day Steve & Steve,
Sound like you have a good reliable mix between solar & alternator.
Could you advise how old you battery is, how long your typically away and how many days you run solar only?
You both obviously have a tonne of experience with these systems which would be very helpful.
Cheers
Jason
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Follow Up By: steved58 - Friday, Apr 26, 2013 at 22:16

Friday, Apr 26, 2013 at 22:16
Hi jason
Most trips are 2 to 3 months never stay more than 3 days in one spot with solar alone also have generator backup Most of the time we are touring and the battery is charge from the alternator When at powered sites the fridge is automatically on 240v as soon as plugged in and at the same time the charger tops up the batteries As we tow a caravan with a 3 way fridge installed I found this drained my batteries every time we stopped reducing the capacity of the alternater to put a good charge into the batteries so a fridge switch installed on the 3 way cuts it out of the circuit but allows the batteries to keep the waeco in the back of the 4wd going Heavy wiring mine is 13sq mm is a must from the battery isolator to the auxillary batteries I found this works very well for us but we do tour and very rarely camp in one spot without driving fof long I have just replaced one of my batteries the last one lasting 5 years and the other still going 4 years and yes I have on several occasions accidentely run them below 50% soc
Cheers
Steve
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Follow Up By: CampingTechAust - Friday, Apr 26, 2013 at 22:30

Friday, Apr 26, 2013 at 22:30
Cheers Steve,
That's really helpful and confirms the theory.
I couldn't agree with you more about heavy cable from your alternator to batteries. I have a dual cab Navara and camper with loooong draw bar. It's a long way for those 40 Amps (max) to run.

Cheers
Jason
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FollowupID: 787880

Follow Up By: Member - eighty matey - Saturday, Apr 27, 2013 at 11:29

Saturday, Apr 27, 2013 at 11:29
G'day Jason,

like Steve above, we don't often sit around for more than a few days but there have been times when the fridge has run off the solar panel only for four or five days.

We don't run much else except a couple of LED strips and occasionally an inverter to charge the laptop.

We had some trouble on the last big trip but it turns out the alternator was on the way out. Changed the alternator and the problem was solved.

We only have the cranking battery and a battery box in the back. We charge up the battery box first when we start driving, then plug the fridge into the vehicle for the rest of the day as soon as the battery is fully charged.

This works good for us.

Steve
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FollowupID: 787895

Reply By: olcoolone - Saturday, Apr 27, 2013 at 14:20

Saturday, Apr 27, 2013 at 14:20
Jason...... good post and easily understood.

Many will take advice but some will put on their white lab coats and start using formulas and industrial terms complicating it for the people who don't understand it in the first place.

The only criticism I would make is 5 Deg C. is not cold enough and when camping you open the fridge often and replace cold stuff with warm stuff (drinks)...... a fridge also will use less power when full to when half full or nearly empty.

The other thing to take into consideration is not every aux battery is charge to 100% SOC when charged of the vehicles alternator..... 70-80% is more realistic.
AnswerID: 509891

Follow Up By: Jason – Perth - Saturday, Apr 27, 2013 at 17:38

Saturday, Apr 27, 2013 at 17:38
Thanks Olcoolone,
I agree it is a challenge to write "tech" for the lay person. I have a long way to go before I would consider myself a guru in this area.
Yeah, the 5 degree comment has generated other posts but was only referenced because that's what Dometic had in the manual. It's also the reason why I posted this in the first place, what are the members fridges pulling in the real world?

I also agree with your comment RE: 100% SOC. I suppose I was locked in to my system setup as I have a Redarc unit that will boost the alternator volts to achieve 100% charge. Again, this is a manufacturers claim and I haven't yet confirmed this actually the case.

Thanks for the feedback. Much appreciated.

Jason
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