Mains Fridge via, Inverters?

[Kristian]

If one wishes to use a mains 240v powered fridge on a 12 system via an inverter hows does one calculate the inverter size needed?

The fridge draws 165kws per year, anyone any ideas? Heres the details, http://reviews.argos.co.uk/1493-en_gb/4857644/reviews.htm

Do I take 165kws divide by 365 (days) they by 24hrs?

Thanks Kristian.

[mrsmelly]

If one wishes to use a mains 240v powered fridge on a 12 system via an inverter hows does one calculate the inverter size needed?

The fridge draws 165kws per year, anyone any ideas? Heres the details, http://reviews.argos.co.uk/1493-en_gb/4857644/reviews.htm

Do I take 165kws divide by 365 (days) they by 24hrs?

Thanks Kristian.

A friend has a mains fridge running off a mastervolt 800 watt inverter with ease. I used to have a 2kw one which was obviously well on top of the job.

[Nickhlx]

If one wishes to use a mains 240v powered fridge on a 12 system via an inverter hows does one calculate the inverter size needed?

The fridge draws 165kws per year, anyone any ideas? Heres the details, http://reviews.argos...644/reviews.htm

Do I take 165kws divide by 365 (days) they by 24hrs?

Thanks Kristian.

 

Hi,

 

The annual consumption will not give you any help with the "on consumption" or the "surge to start"... The on consumption is likely to be around 50 to 75 watts, or well within the rating of any inverter you are likely to choose... The surge current each time the motor starts up ( and it is a bit of an assumption it has a motor as some don't) will be several times this... even so, even if it is 10 times this "on consumption", you are only looking at around a 500-750 watt inverter. To be sure and have a bit of spare for anything else you might want to run, I would look at at least a 1000 watt inverter. The other potential problem is the quality of the a.c. it is delivering ( waveform) so really it would be beneficial to try one out as some produce square wave or quasi-sine wave, whereas the best ones produce sine wave and won't be a problem. When we were being "advised" by our builder, he said a 12 volt fridge would be better in the long run, although now I know how we run the boat I would have probably gone for a (much less expensive) mains fridge too, but as it was "included in the price" and I didn't think he would have given a discount for a mains fridge, ( or made up the difference elsewhere) I didn't want to go there by rocking the boat...

 

Hope that forms part of the answer...

 

Nick

[ditchcrawler]

A friend has a mains fridge running off a mastervolt 800 watt inverter with ease. I used to have a 2kw one which was obviously well on top of the job.

Mine is 1500 true sine wave

Edited December 14, 2011 by ditchcrawler

[mrsmelly]

Mine is 1500 true sign wave

 

Ahh just reminded me for the OP a BIG consideration is the quality of the inverter. On my last boat I had a fab Mastervolt 2kw inverter that on standby used 0.6 of an amp so when fridge at rest was not wasting too much lectrickery. This boat has fitted a cheapo ( In comparison ) Sterling 2.5 kw inverter/charger and on standby it draws a humungous amount of lecktric so luckily this boat has a 12 volt fridge. Both inverters are pure sign.

[by'eck]

You will need to find the max wattage (power) requirement of the fridge. It should be displayed somewhere on device or maybe check the manual. If a max current is shown multiply this by 240 to get the wattage. The power consumption/year is no help whatsoever as its just an average indication using the unit in average conditions.

 

When you have found the wattage add at least 20% on to allow for compressor start up current & you have the answer to the minimum inverter size (wattage) you can use. I would buy one with considerable margins to allow for any other mains powered devices you may wish to use at the same time.

[Slim]

When my Mastervolt 2 kw pure sine inverter went belly up in the summer I ran on a Moore Power 1000w quasi sine inverter. This coped with my 230v Beko fridge and 230v TV playing DVDs without problem. On occasion I was also charging both my laptop and mobile phone.

 

 

 

Frank

 

 

 

Just realised I've 'Topped ' the ton on posts

Edited December 14, 2011 by Slim

[ditchcrawler]

Ahh just reminded me for the OP a BIG consideration is the quality of the inverter. On my last boat I had a fab Mastervolt 2kw inverter that on standby used 0.6 of an amp so when fridge at rest was not wasting too much lectrickery. This boat has fitted a cheapo ( In comparison ) Sterling 2.5 kw inverter/charger and on standby it draws a humungous amount of lecktric so luckily this boat has a 12 volt fridge. Both inverters are pure sign.

Mine is a Mastervolt, the overall efficiency seams good as well

[Kristian]

The boats already has an inverter, but for the ring main etc, Im going to get a smaller inverter just for the fridge only and wire it into the 12v cables

that supplied power the 12v fridge when its removed, 150watts tops?

Kristian.

[Nickhlx]

The boats already has an inverter, but for the ring main etc, Im going to get a smaller inverter just for the fridge only and wire it into the 12v cables

that supplied power the 12v fridge when its removed, 150watts tops?

Kristian.

 

A potential problem with the small inverters is the higher quiescent current they draw. Your existing larger inverter may well take less power, (be more efficient) and produce a better waveform than a cheap small unit which may not handle the significant switch on surge each time the compressor fires up ( every few minutes). I think you will need an inverter more like 500+ watts to cope with that ... Even my Victron 3000 watt inverter, now maybe 3 or 4 design years old ( old technology ?) takes well under an amp ( handbook not to hand) and I would imagine smaller units take a bit less - on a typical bank of perhaps 400 aH or more, it will last for a few days on a charge and if you are on board you will likely be running the engine for several hours a day to replenish other consumption. In winter, you may be able to do away with running a fridge and store the items in an outside locker when ambients are less than 5 deg C, thereby saving a shedload of charging time, diesel and wear and tear on the engine / genny.

 

Nick

[WotEver]

The boats already has an inverter, but for the ring main etc, Im going to get a smaller inverter just for the fridge only...

Why?

 

... wire it into the 12v cables that supplied power the 12v fridge when its removed...

Those 12V wires will almost certainly be too small. A 500W inverter (you wouldn't want less, in order to cope with the compressor start-up) will draw 42Amps at peak.

 

Tony

[ChrisPy]

If one wishes to use a mains 240v powered fridge on a 12 system via an inverter hows does one calculate the inverter size needed?

The fridge draws 165kws per year, anyone any ideas? Heres the details, http://reviews.argos.co.uk/1493-en_gb/4857644/reviews.htm

Do I take 165kws divide by 365 (days) they by 24hrs?

Thanks Kristian.

dear oh dear, where do these suppliers get their technical data from?

quoting 165 kilowatts per year is a nonsense statement, a bit like saying a car develops 2100 horse power per week.

[WotEver]

dear oh dear, where do these suppliers get their technical data from?

quoting 165 kilowatts per year is a nonsense statement, a bit like saying a car develops 2100 horse power per week.

Indeed. I assume they meant 165kWh which equates to about 38Ah/day at 12V, or 42Ah if you take into account inverter inefficiencies.

 

Tony

[mrsmelly]

Indeed. I assume they meant 165kWh which equates to about 38Ah/day at 12V, or 42Ah if you take into account inverter inefficiencies.

 

Tony

 

The manufacturers figures are an utter nonsense. Quoting how much consumption in a year is absurd we need to know what ampage is used just when the unit is running. The same fridge in 2 totally different houses will use hugely different amounts of lecktrickery depending for one thing how many times a day and for how long its door is opened.

[Chris G]

dear oh dear, where do these suppliers get their technical data from?

quoting 165 kilowatts per year is a nonsense statement, a bit like saying a car develops 2100 horse power per week.

 

But the Argos website says "Energy efficiency rating: A. Energy consumption: 165kWh per year based on standard test results for 24 hours.", which is a correct statement of energy consumption. Not that it's any use for sizing an inverter!

[Tony Brooks]

Why?

 

 

Those 12V wires will almost certainly be too small. A 500W inverter (you wouldn't want less, in order to cope with the compressor start-up) will draw 42Amps at peak.

 

Tony

 

If the 12V fridge was one of the gas/mains/12v types then I agree, but if it was a 12V compressor fridge and the inverter is just for the fridge then I think this statement needs looking at. Remember such a fridge 10m away from the batteries will need 10sq mm cable. However it does depend on inverter power.

[WotEver]

If the 12V fridge was one of the gas/mains/12v types then I agree, but if it was a 12V compressor fridge and the inverter is just for the fridge then I think this statement needs looking at. Remember such a fridge 10m away from the batteries will need 10sq mm cable. However it does depend on inverter power.

Agreed. If you're replacing a 12V compressor fridge with a 240V compressor fridge then the new fridge will only use slightly more power than the 12V one. (That's always assuming it was correctly cabled in the first place of course!)

 

I had assumed (and I have no idea why) that OP was replacing an absorption fridge.

 

Actually, I do know why I thought that... it's because that's what I did on Wot Ever a few years back

 

Tony

 

... Not that it's any use for sizing an inverter!

Well no, I guess they didn't envisage these Chinese fridges being fed from an inverter

Edited December 15, 2011 by WotEver

[ditchcrawler]

The manufacturers figures are an utter nonsense. Quoting how much consumption in a year is absurd we need to know what ampage is used just when the unit is running. The same fridge in 2 totally different houses will use hugely different amounts of lecktrickery depending for one thing how many times a day and for how long its door is opened.

True, but the manufacturers have to give a guide, just like MPG on cars, I am sure if you and me drive the same car over the same route we will get different mpg figures. No one expect the car to do 69.7 mpg because that is what it says in the spec but they do expect it to be more fuel efficiently than the one that is quoted at 43.4 mpg.

[smileypete]

A potential problem with the small inverters is the higher quiescent current they draw. Your existing larger inverter may well take less power, (be more efficient) and produce a better waveform than a cheap small unit which may not handle the significant switch on surge each time the compressor fires up ( every few minutes). I think you will need an inverter more like 500+ watts to cope with that ...

If a bit of DIY is OK, a way round that is to use a cheap 12V digital temperature controller to tell when the fridge needs to cool, then switch the inverter on and after a short delay switch the fridge on.

 

Probably cost £25ish in parts but would pay back quite quickly for a liveaboard.

 

For startup it's the surge rating of the inverter that's important, an 800W inverter with a 1600W surge is better than a 1000W inverter with 1200W surge.

 

cheers,

Pete.

[Kristian]

If the 12V fridge was one of the gas/mains/12v types then I agree, but if it was a 12V compressor fridge and the inverter is just for the fridge then I think this statement needs looking at. Remember such a fridge 10m away from the batteries will need 10sq mm cable. However it does depend on inverter power.

 

Hi Tony, yes the fridge to be removed is a 12V compressor fridge not a 3way job, and the new mains fridge will have its OWN inverter.

[Tony Brooks]

If the 12V fridge was one of the gas/mains/12v types then I agree, but if it was a 12V compressor fridge and the inverter is just for the fridge then I think this statement needs looking at. Remember such a fridge 10m away from the batteries will need 10sq mm cable. However it does depend on inverter power.

 

Hi Tony, yes the fridge to be removed is a 12V compressor fridge not a 3way job, and the new mains fridge will have its OWN inverter.

 

 

In that case get the power or amps drawn + 20% or so and use the cable calculator or voltdrop calculator to check your existing cable is large enough. Too large is fine but too small or sometimes only a bit small is not.

[Theo]

Ahh just reminded me for the OP a BIG consideration is the quality of the inverter. On my last boat I had a fab Mastervolt 2kw inverter that on standby used 0.6 of an amp so when fridge at rest was not wasting too much lectrickery. This boat has fitted a cheapo ( In comparison ) Sterling 2.5 kw inverter/charger and on standby it draws a humungous amount of lecktric so luckily this boat has a 12 volt fridge. Both inverters are pure sign.

 

My Sterling 1800W MSW has a quiescent current of 0.5A and a peak power of 2000W. It has proven fine for heavy 230V use: fridge, freezer, reading lamps, laptop, spin dryer.

 

Nick

[steelaway]

My Sterling 1800W MSW has a quiescent current of 0.5A and a peak power of 2000W. It has proven fine for heavy 230V use: fridge, freezer, reading lamps, laptop, spin dryer.

 

Nick

 

 

 

DITTO Nick

 

Mine has run a long list of 240V appliances quite happily for over 6 years.

Why would you have two inverters? More wiring, more loss's, more complication.

 

Alex

[WotEver]

Why would you have two inverters? More wiring, more loss's, more complication.

Yup, I asked why several posts ago - never got a reply.

 

Tony

[Nickhlx]

If a bit of DIY is OK, a way round that is to use a cheap 12V digital temperature controller to tell when the fridge needs to cool, then switch the inverter on and after a short delay switch the fridge on.

 

Probably cost £25ish in parts but would pay back quite quickly for a liveaboard.

 

For startup it's the surge rating of the inverter that's important, an 800W inverter with a 1600W surge is better than a 1000W inverter with 1200W surge.

 

cheers,

Pete.

 

Hi Pete,

Not quite understanding the connection here - surely the method you describe is to enable the inverter to cope better with the surge, not reduce the quiescent ( what it takes when delivering no output) current. My point is that if the mains inverter is drawing say 1 Amp quiescent ( even when the fridge is between cycles, i.e. it draws this 24/7) the power drawn by the inverter just being switched on is 24 Ah/day which is likely around 50% of what the fridge itself would take in 24 hrs ? That may not be a problem if the inverter has to be on anyway, although it can't help, but it is tantamount to "designing in" a problem, in my view...

 

Nick