size/type of invertor for small 220V fridge

[DeanS]

Hi all. Just getting my bits in a row so I can go cruising mid March. Fridge is one of those under counter ones you might typically buy for £100 at Curries etc. I need to keep it running permanently, off an invertor. Do I need an invertor larger than 1000Watts MSW ? Forgive me for being a bit lazy. I have an old invertor...600Watt somewhere, but dont think it would do? (or should I plug it in and try?)

 

Thanks.

[DaveC]

Hi all. Just getting my bits in a row so I can go cruising mid March. Fridge is one of those under counter ones you might typically buy for £100 at Curries etc. I need to keep it running permanently, off an invertor. Do I need an invertor larger than 1000Watts MSW ? Forgive me for being a bit lazy. I have an old invertor...600Watt somewhere, but dont think it would do? (or should I plug it in and try?)

 

Thanks.

 

 

Plug it in and try while you are still hooked up, just in case it doesn't work. i have a 1500 watt inverter and we run a small mains deep freeze 24 hours a day when we are out - usually for a 3 or 4 month trip.

 

 

Dave

[Keeping Up]

What you need is an inverter with a high "surge" rating to cope with the starting current of the fridge motor. Some smaller inverters actually have higher surge ratings than larger ones. Since the surge current taken by the fridge will be unknown, your best option is:

 

Step 1: plug it in and try it (preferably when the batteries aren't fully charged).

 

Step 2: depends on the result of step 1.

[Bobbybass]

Hi all. Just getting my bits in a row so I can go cruising mid March. Fridge is one of those under counter ones you might typically buy for £100 at Curries etc. I need to keep it running permanently, off an invertor. Do I need an invertor larger than 1000Watts MSW ? Forgive me for being a bit lazy. I have an old invertor...600Watt somewhere, but dont think it would do? (or should I plug it in and try?)

 

Thanks.

What is the continuous rating on the fridge ?

 

As long as the inverter is higher than the continuous rating...I would be 'tempted' (just my opinion) to just try it. ..although it may not work because of the sudden current draw during motor start.

Don't forget that for every 250 watt (only approximate) it draws while 'inverted' on 240 volts...it will draw about 20 amps from your batteries...at 12 volts.

I work out (roughly) 1 amp at 240 volts is 20 amps at 12 volts and find its about right.

[Serenity Malc]

Yello,

 

Having just taken delivery yesterday of a Curry's R5010B fridge to replace the huge fridge freezer in my barge, I thought I'd check out it's power consumption. Frustratingly the tech spec only says 175 kWh per annum. I worked this out at approx 20 watts at 240v per hour.

 

175 / 8760 x 1000 =

 

Could someone PLEASE check my maths out ?

 

Many thanks Malc.

Edited January 29, 2013 by Serenity Malc

[Chalky]

We had an 800W inverter that lasted less than 15 minutes when running a fridge. The current 800W one has lasted 7 years and has run a standard A rated domestic fridge (no freezer compartment) without problems. You need to look at the inverter spec carefully.

 

The initial one was a Nikai one from Maplin and was quoted as 800W however it was a bit like the peak music power on old car radios. What it said in the small print was 800W for 5 minutes at 20 degrees ambient temperature, 600W for 20 mins and 300W continuously. It had a surge capability of 1200W however the main output transistors failed due to poor cooling design. In effect this was a 300W inverter that had been bigged up by a marketing team. Read the specs carefully.

 

The existing inverter (Sterling pseudo sine) is specced at 800W continuously at 40 degrees ambient. It has the surge capability to cope with the fridge and is a a genuine 800W inverter. Some companies would sell it as a 1500W inverter...

[nicknorman]

Yello,

 

Having just taken delivery yesterday of a Curry's R5010B fridge to replace the huge fridge freezer in my barge, I thought I'd check out it's power consumption. Frustratingly the tech spec only says 175 kWh per annum. I worked this out at approx 20 watts at 240v per hour.

 

175 / 8760 x 1000 =

 

Could someone PLEASE check my maths out ?

 

Many thanks Malc.

 

Yes, that is an average of 20 watts per hour, however the motor will be running for some of the time, using a lot more than 20w, and stopped for some of the time, using zero. Therefore this figure is not useful to determine the inveter power required, only the overall battery drain. There should be a label on the back indicating the motor power consumption when its running. However the startup current is likely to be much more, maybe at least twice that figure for a second or so, therefore the inverter needs to be able to supply that surge current every time the motor starts up. You don't want a marginal situation where the inverter can only do that with batteries fully charged!

[PaulJ]

I fitted a 1000W Sterling MSW a few years ago and that ran a normal domestic fridge happily. Would the inverter only be for running the fridge ? Would be worth connecting to fridge stat if so- remember reading a thread on here about it once...

[Serenity Malc]

Yello,

 

Ta Nick ..... I've already checked the back for labels and guess what .... 240v 50 / 60 hz only ! That's why I'm a bit frustrated. I've a Sterling 3 in 1 1500watt pure sine inverter /charger / solar jobbie that I'm going to try and run it from, but I was considering installing a smaller fridge specific inverter as I'm concerned of the Sterling's overhead for just a fridge, some 12v lights and occasional TV / PC.

 

Cheers Malc.

[nicknorman]

Yello,

 

Ta Nick ..... I've already checked the back for labels and guess what .... 240v 50 / 60 hz only ! That's why I'm a bit frustrated. I've a Sterling 3 in 1 1500watt pure sine inverter /charger / solar jobbie that I'm going to try and run it from, but I was considering installing a smaller fridge specific inverter as I'm concerned of the Sterling's overhead for just a fridge, some 12v lights and occasional TV / PC.

 

Cheers Malc.

I would be confident that the 1500w inverter will run it, and once you have connected it to that, you will be able to see at least the continuous draw of the fridge motor. That will give you an idea of the size of dedicated inverter you need.

 

ps I found this thread, eg post #9, might give you an idea of the inverter power needed. Of course the best answer seems to be to install a 12v fridge!

Edited January 29, 2013 by nicknorman

[OldGoat]

Fools rush in (that means me) - I try to stay away from threads where I don't have direct experience,

Oh well -

 

I'm tempted to say ash one of the hre boat companies. I have heard tell that at one time "somebody" fitted quite small inverters as dedicated units in their boats with some success. Indeed I think some 12v fridges had a 12v inverter as an option - and it wasn't a large beast - I found it on the web, but there were no useful details.

 

The logic is this - domestic fridges typically have compressors rated at between 60 ( small fridges 5 cu:ft) - 120 watts (girt big full height larder ones). However allowance must be made for the startup current and its duration. Good quality kit like Danfoss units are designed to minimise this surge power. Cheap chinese copies may not be so good.

Likewise good quality inverters will have quite a high surge rating - Sterling (used to) publish a graph - even for the less expensive range.

 

My feeling is that a 600w reasonable quality MSW unit should do the job.

[Keith M]

Hi all. Just getting my bits in a row so I can go cruising mid March. Fridge is one of those under counter ones you might typically buy for £100 at Curries etc. I need to keep it running permanently, off an invertor. Do I need an invertor larger than 1000Watts MSW ? Forgive me for being a bit lazy. I have an old invertor...600Watt somewhere, but dont think it would do? (or should I plug it in and try?)

 

Thanks.

 

Hello Dean,

 

I have installed many 230 volt AC fridges and freezers

To be honester I cannot reminder the last time I fitted a DC fridge into a boat.

As a rule of thumb take an average fridge around a 100 watts it will have a power factor of roughly 10 to 1 so for a 100 watt fridge I would be looking at 1000 watt inverters

 

I hope the above helps

 

Keith

[DeanS]

Thanks to all

 

eta - just hauled out my old 600Watt invertor with a 1500Watt surge. I'm going to give it a try while in the marina...and hopefully it'll do the job. It may need a good clean, so I'm taking it apart to see what the innards look like.

Edited January 29, 2013 by DeanS

[Chalky]

Thanks to all

 

eta - just hauled out my old 600Watt invertor with a 1500Watt surge. I'm going to give it a try while in the marina...and hopefully it'll do the job. It may need a good clean, so I'm taking it apart to see what the innards look like.

 

Make sure that you haven't powered it up for at least a day before you take the lid off. Inverters tend to contain large capacitors to help control the voltage ripple on the input and these can take some time to discharge. If you touch one that it charged you'll know...

[OldGoat]

Thanks to all

 

eta - just hauled out my old 600Watt invertor with a 1500Watt surge. I'm going to give it a try while in the marina...and hopefully it'll do the job. It may need a good clean, so I'm taking it apart to see what the innards look like.

 

 

Do please come back if successful or not - and what happened.

'Tis the only way "we" know if we're talking rubbish or not...

[mrsmelly]

Thanks to all

 

eta - just hauled out my old 600Watt invertor with a 1500Watt surge. I'm going to give it a try while in the marina...and hopefully it'll do the job. It may need a good clean, so I'm taking it apart to see what the innards look like.

 

Yow Dean

 

If ya verter isnt any good my bro in law has a couple of mod sine ones kicking about somewhere. Ones a good make ( cant remember ) its 1200 watt though and I reckon I can prize it off him for a few squid.

 

Tim

[ditchcrawler]

My fridge Lec under counter with frezer compartment draws about 90w including the losses in the inverter as measured with a Sterling Battery management unit with a 0-200 Amp shunt. I.E. 3.5 Amps at 24V

[jonathanA]

Hello Dean,

 

I have installed many 230 volt AC fridges and freezers

To be honester I cannot reminder the last time I fitted a DC fridge into a boat.

As a rule of thumb take an average fridge around a 100 watts it will have a power factor of roughly 10 to 1 so for a 100 watt fridge I would be looking at 1000 watt inverters

 

I hope the above helps

 

Keith

10 to 1 !!! the oft quoted figure for motors is the start up current is 5x running. I assume this is what you mean when you refer to a 'power factor' although the proper use of the term power factor really refers to a completely different thing altogether...

 

As others have said the start up 'surge' whilst quite large is only very brief in duration.

[Bobbybass]

Do please come back if successful or not - and what happened.

'Tis the only way "we" know if we're talking rubbish or not...

 

Yes...do please come back..otherwise...we will wonder if those capacitors really were still charged !!

 

I did read 'once'..(actual reading may vary from description)..that buying a small chest freezer (240 volt) and fitting it with a fridge thermostat was a good option ?

The 'thinking' went..that you didn't let all the cold air out when you opened it...and that a freezer was designed to be better insulated than a fridge.?

 

Was this good thinking..or hooey by a manufacturer ?

Edited January 29, 2013 by Bobbybass

[DeanS]

ok..I opened up the old invertor...the outer case looked shocking (excuse the pun) but the innards all look clean. I havent used it for months, so just wanted to check it still came on etc. I'll dig out a spare battery, connect the fridge and see what happens....tomorrow perhaps...promise to give some feedback. I'm committing this invertor to run the fridge only, and everything else is going either generator or 12V.

[Chalky]

My fridge Lec under counter with frezer compartment draws about 90w including the losses in the inverter as measured with a Sterling Battery management unit with a 0-200 Amp shunt. I.E. 3.5 Amps at 24V

 

We get about 6A at 12V for a standard LEC under counter fridge with no freezer, so we're in the same ball park.

[Keith M]

10 to 1 !!! the oft quoted figure for motors is the start up current is 5x running. I assume this is what you mean when you refer to a 'power factor' although the proper use of the term power factor really refers to a completely different thing altogether...

 

As others have said the start up 'surge' whilst quite large is only very brief in duration.

 

 

You have to remember that you are not starting a motor but a compressor

 

I have measured many 100 watt fridges require over 1000 watts to start

 

Keith

Edited January 30, 2013 by Keith M

[nicknorman]

You have to remember that you are not starting a motor but a compressor

 

I have measured many 100 watt fridges require over 1000 watts to start

 

Keith

I suppose it depends on how much pressure remains in the system when the thermostat kicks in. Left to its own devices, the compressor will be off for a good while so pressure will be low when the pump has to restart. On the other hand, a power interrupt, or turning up the thermostat markedly just after the stat cuts out, would result in the compressor trying to start against high pressure - much harder. Obviously when you design a system you want it to work regardless, so I suppose the inverter has to be over-rated for what would be required for a normal start.

[jonathanA]

You have to remember that you are not starting a motor but a compressor

 

I have measured many 100 watt fridges require over 1000 watts to start

 

Keith

 

we are talking very brief (millseconds) surges here, the OP has said he's going to try it with his 600w unit, guess we'll have to wait to see what happens. So much depends on the actual spec of the inverter as opposed to the marketing fluff

[nb Innisfree]

Edited 'cos I repeated someone else.

Edited January 30, 2013 by nb Innisfree