115ltr Bar Fridge on inverter

Submitted: Tuesday, Jul 22, 2014 at 22:11
ThreadID: 108843 Views:3687 Replies:10 FollowUps:17
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For interest only, as I have an idea what the response would be. Trying to work out what size inverter would be needed to run a 115ltr bar fridge, and roughly what current it would drag(including inverter).
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Reply By: oldtrack123 - Tuesday, Jul 22, 2014 at 23:21

Tuesday, Jul 22, 2014 at 23:21
Hi
Best tell us the fridge Watt rating ,that should be on the model plate .
Then we can give some useful advice.


PeterQ
AnswerID: 536442

Reply By: SCUBADOO - Wednesday, Jul 23, 2014 at 05:30

Wednesday, Jul 23, 2014 at 05:30
FWIW and standing back for the usual flack. (-;

In our campervan I use a 230VAC 70l chest freezer with the thermostat adjusted for use as a fridge. I also use an Engel 80l upright 12VDC fridge alongside. Wall thickness is near double on the freezer.

I'm in NZ so the usage figures will not apply to tropical areas of AUS.
Current draw is 10A including inverter losses @ 12.6VDC. Duty cycle here is typically less than 12% or about 7 minutes per hour - measured. It also cools from ambient to 4C twice as fast as my Engel.
The Engel draws 3.6A. Duty cycle is around 30%.
You can do the maths.

You will almost certainly require a PSW inverter. A MSW on mine caused so much compressor motor rumble noises that it was simply not an option.

Start-up surge current is a major issue. Expect to purchase a 1000W inverter. My converted fridge JUST starts with my 500W PSW inverter. It then cruises @ c130W while running without the inverter cooling fan even operating.
AnswerID: 536447

Follow Up By: kevmac....(WA) - Wednesday, Jul 23, 2014 at 23:04

Wednesday, Jul 23, 2014 at 23:04
Difference between MSW &PSW inverter is ?????
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Follow Up By: SCUBADOO - Thursday, Jul 24, 2014 at 04:03

Thursday, Jul 24, 2014 at 04:03
Google "pure sine wave vs modified sine wave".

Wave output & $$$ (-;

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FollowupID: 820626

Reply By: Ross M - Wednesday, Jul 23, 2014 at 08:52

Wednesday, Jul 23, 2014 at 08:52
Bar fridges have abut the worst insulation of any fridge/freezer type and so even if run off a suitable inverter, PSW being the one which will cause less heat in the motor, the fridge itself is going to run more often than other types.

Wall thickness and insulation is you friend if running off batteries as the power source or in fact any source.
AnswerID: 536454

Reply By: Honky - Wednesday, Jul 23, 2014 at 10:20

Wednesday, Jul 23, 2014 at 10:20
Not sure if this is of assistance but it may be a worthwhile option ( maybe not a safe one)
Talking to a friend that had a friend of a friend go on a "boys" week away.
As a lot of beer was going to be consumed keeping it cold was an issue and camping fridges to small.
What they decides was to purchase a cheap chest freezer and small two stroke generator. All up just over a couple of hundred dollars and spread among a number of participants , even cheaper. Cheap compared to the value of the booze. They set it up on the back of a ute and ran the generator all day which used about a tank (4 litres ) of fuel. By the end of the day icy cold beer. Turn it off at the end of the night and start it up the next day.
I cannot see any issues with hidden 240 volts as reasonably obvious risk in a rescue situation, if required.

Honky
AnswerID: 536459

Follow Up By: The Bantam - Wednesday, Jul 23, 2014 at 18:06

Wednesday, Jul 23, 2014 at 18:06
"Hidden 240v" obvious in a rescue situation...hmmm
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Follow Up By: Honky - Wednesday, Jul 23, 2014 at 20:31

Wednesday, Jul 23, 2014 at 20:31
My comment might have been misunderstood as I was just comparing an inverter which may be still connected and producing 240 volts to a generator that has stop working. The generator could easily be seen and easier to hear if running.

Honky
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Follow Up By: The Bantam - Wednesday, Jul 23, 2014 at 20:55

Wednesday, Jul 23, 2014 at 20:55
yes a generator running on a trailer wound be obvious.

cheers
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Reply By: The Bantam - Wednesday, Jul 23, 2014 at 18:24

Wednesday, Jul 23, 2014 at 18:24
Interesting..at one time my sister and her husband where running a bar fridge as a travel fridge.

They where traveling couple or theree day trips to and from locations, and staying in motels over night.

SO...they would turn the fridge right up and hook up to power when they pulled up for the night...... some icecream containers in the freezer provided self refreezing ice blocks.

They threw a blanket over the whole shebang during the day to improve insulation.


I doubt that the idea of running a bar fridge off an inverter would stack up these days.

By the time you account for the poor insulation and efficiency of bar fridges.....one or two start rated at best...bar fridges realy are the poor relation of the fridge market..and 240v fridges are in general far less efficient than good portable fridges.

then you look ot the economy of purchase...the fridge its self my be cheap ...but by the time you cough up $400 odd dollars for an inverter..the economics are not looking god against one of the better cheep and cheerfull second string portable fridges.

check this article
http://www.fridge-and-solar.net/fridgetest1.htm

cheers
AnswerID: 536472

Reply By: kevmac....(WA) - Wednesday, Jul 23, 2014 at 23:00

Wednesday, Jul 23, 2014 at 23:00
Thank you all for your input........as I said originally I guessed the response, but just had to see if there was a vain hope.......even if added 2nd battery would be pushing the proverbial up a hill.........Please enlighten me though on the difference between MSW & PSW Inverters!!!
AnswerID: 536502

Follow Up By: kevmac....(WA) - Wednesday, Jul 23, 2014 at 23:07

Wednesday, Jul 23, 2014 at 23:07
Oops didnt think this posted so asked MSW / PSW question twice.......
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FollowupID: 820618

Follow Up By: Member - Boobook - Friday, Jul 25, 2014 at 06:19

Friday, Jul 25, 2014 at 06:19
Your 230V at home is basically a sine wave. In other words it is a single 50 Hertz frequency with no ( or little ) other frequencies called harmonics mixed in. All mains equipment is designed to work on this.

When they make 12v to 240v inverters, it is difficult and expensive to simulate the sine wave, so the cheap ones cheat by making a square wave and modifying it's shape and sometimes filtering it. The result is an approximation of a Sine Wave. This is *generally* called a Modified Sine Wave - MSW. ( see below) The advantages are that it is cheap, generates little power and fairly compact. The downside is that it is electrically noisy and a lot of equipment does not work or can fail when powered by it.

Pure Sine Wave inverters - PSW are more sophisticated and put out a signal that is very close to the mains in your home. Almost all equipment designed for 230V will work on these if you size it correctly for the power. The cost to do this is dollars, size, weight and heat.

Actually while most manufacturers call MSW a Modified Sine Wave, this is actually a recent marketing term. MSW actually means Modified Square Wave. This square wave roughly approximates a sine wive.

Modified Sine Wave sounds better in the ads though.

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Follow Up By: Nomadic Navara - Saturday, Jul 26, 2014 at 23:19

Saturday, Jul 26, 2014 at 23:19
Have a look at this page - it takes more time to explain and shows some waveform diagrams for a better explanation.


PeterD
Retired radio and electronics technician

Lifetime Member
My Profile  Send Message

1
FollowupID: 820840

Reply By: kevmac....(WA) - Saturday, Jul 26, 2014 at 22:43

Saturday, Jul 26, 2014 at 22:43
OKAY>>>>
Now that I know my fridge I already had is allegedly 808 watts( checked over 24 hr period....manufacturer's claim) I calculate 240v current at roughly 3.6a.......if I am right in assuming a 30% load from an inverter that would make the current drain on my deep cycle battery 4.68a .
Correct me if I am wrong if you would please, but a 1000/2000 watt inverter would handle this???
AnswerID: 536651

Follow Up By: The Bantam - Saturday, Aug 02, 2014 at 21:26

Saturday, Aug 02, 2014 at 21:26
Remember, that 808 watts will mostly be consumed by a motor driving a compressor.....the start up current may be as much as 4 times the runnig current AND you have to consider the power factor.

many inverters will supply short term peaks...but the correction for power factor will be continuous....that 800 watt motor may infact present a 1000w pluss continuous equavalent load power factor corrected.

An inverter deliveing 1000 wats on the 240v side will be drawing somewhere arround 40 amps from the battery.

typical portable fridges like engel and wacko will be drawing innthe 3.5 to 8 amp reigion.....from the battery.

The three way absorbtion fridges runnig on 12 volts will typically draw about 15 amps....and that is considered inefficient and engine running only operation.

its a no goer mate.

The only way that a 240V domestic fride is vialble is if you strap a generator to the drawbar and run it continously.

cheers
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Follow Up By: The Bantam - Saturday, Aug 02, 2014 at 21:28

Saturday, Aug 02, 2014 at 21:28
I notice further on that the figure is not 800 watts.
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Reply By: kevmac....(WA) - Thursday, Jul 31, 2014 at 21:54

Thursday, Jul 31, 2014 at 21:54
Back on my original thread....(sorry People)

Just back from a trip away with said new fridge, but alas only on 240v. Did do some checks on how long compressor runs and how long between runs, but wasn't done until had been home a while and fridge had been off for while also(probably close to a standard start up). First run from initial power up was about 9 minutes, a break of 8 mins and then next 2 runs were 3 mins, still with 8 min breaks between. JUst wondering if this sounds about normal? Presuming that if run purely as a fridge(no freezser function at all, that these break times would spread out? We normally run our Engel off 12v only when bush camping, so can afford to turn down the fridge setting down to save power. Unfortunately still waiting for fridge manufacturer to get back to me with true power details, unless someone has had experience with Euro 240v fridges?
AnswerID: 536925

Reply By: kevmac....(WA) - Saturday, Aug 02, 2014 at 15:14

Saturday, Aug 02, 2014 at 15:14
PLEASE HELP

Have finally managed to get to back of fridge and read compliance plate and found the following:-

Nominal wattage is 90w : 240volt input current is stated as 0.55a: and light wattage is 10w(insignificant really)

All I am trying to arrive at is what sort of current drain there will be on my 120ah deep cycle running the fridge thru say a 1500w inverter? Inverter I have looked at has an at rest drain of around 1a.

If I can get help on this , then this thread will be laid to rest.
AnswerID: 537007

Follow Up By: oldtrack123 - Saturday, Aug 02, 2014 at 17:07

Saturday, Aug 02, 2014 at 17:07
HI
OK, 240V x -.55A =132VA, indicates it has a PF of 0.606 which is around the figure for most frigs motors
The inverter will need to be capable of putting out THAT CURRENT continiously

That means min 150W pure sine wave inverter
But the starting current could well be6<8 times 0.5A. that for a short duration[A second or two]

So the surge or peak output required of the inverter would be near 1kVA
If you get an inverter with a 1Kw or 1kVA peak abilty you should be on the safe side.

PeterQ
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FollowupID: 821271

Reply By: oldtrack123 - Saturday, Aug 02, 2014 at 17:41

Saturday, Aug 02, 2014 at 17:41
Hi
A far as current drain from the batteries is concerned best use the make'/s annual figures Watthrs /365 /12 .= Average daily amp hrs used by fridge then add about another 30% for losses
I would expect a figure around 60Ahrs per day

PeterQ
AnswerID: 537015

Follow Up By: kevmac....(WA) - Saturday, Aug 02, 2014 at 18:13

Saturday, Aug 02, 2014 at 18:13
Your help has been most appreciated Peter & cant thank you and the others enuf. At least now I have a better picture of where I stand.
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FollowupID: 821278

Follow Up By: kevmac....(WA) - Saturday, Aug 02, 2014 at 18:32

Saturday, Aug 02, 2014 at 18:32
Presumably any 12v DC cable supplied with most inverters would be considered more than adequate for basic use? Either way, what would you consider a maximum distance from battery to input, so as not to cause any problems? I have a place to put said inverter in dropdown cupboard under where fridge is located. I also have an existing 12v feed there, that used to supply the old 3 way fridge(wild guess is that is 20a capable wire).

For an old PMG/Telstra Technician I seem to have lost a lot of headspace on what I learnt over the years with them(left in 1998).
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FollowupID: 821279

Follow Up By: oldtrack123 - Saturday, Aug 02, 2014 at 19:22

Saturday, Aug 02, 2014 at 19:22
Hi Kev
A 1500W intverter will draw around 150A @12V at full load
The better ones will work down to around 11V input but will then draw even more amps
This is when voltage drop becomes a problem
If you can give the proposed length of cable run , from the battery to the inverter,we can workout some sizes for you BUT it will be much heavier than that old fridge feed .

PeterQ
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FollowupID: 821284

Follow Up By: kevmac....(WA) - Saturday, Aug 02, 2014 at 19:40

Saturday, Aug 02, 2014 at 19:40
distance would be around 3-3.5m all up. Reason I chose the spot I did, is that it becomes the easiest place to modify for air flow and available free space. Then if worse comes to worse could place in front cupboard and install vents and have slightly longer 240v cord or even install a specific 240v inverter outlet??
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FollowupID: 821285

Follow Up By: oldtrack123 - Saturday, Aug 02, 2014 at 20:37

Saturday, Aug 02, 2014 at 20:37
Hi Kev
In that case I would use at least AWG orB&S #1
[copper core dia of 7.35mmm]
At 150A will give around 0.75V drop


PeterQ
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FollowupID: 821289

Follow Up By: kevmac....(WA) - Saturday, Aug 02, 2014 at 21:12

Saturday, Aug 02, 2014 at 21:12
You have been more than helpful Peter, so will leave you in peace now, along with everyone else too!

Take care and happy travels
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FollowupID: 821291

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