Fridges

[Colin Smith]

Tesco are offering this: A+ fridge for £79.97.

 

They quote 113 kWh per year consumption (240v). Two things spring to mind: Firstly, what would that consumption figure actually be if it was running through an inverter and equipped with cooling fans etc. and secondly, at about £250 for a Danfoss 12v compressor/electronics to convert it, you could have a 'new' 12v fridge for around £320 - almost half the cost of a Shoreline or similar!

 

Colin

 

Just thought I'd update this for anyone who may be interested!

 

I ended up buying one of the Tesco fridges that I mentioned above (just noticed that they've gone up £10). I am very pleased with it. True, it will hammer the batteries when running off the inverter but I've only done that once!

 

I filled the freezer box with those blue block things that you can get for coolboxes and plug it in when on shore-power,the engine or the genny is running to normally charge the batteries - leaving it un-plugged overnight etc. It is very well insulated and stays very cold inside. So much so, that I can confidently leave it up to 2 days without the need to switch it on. Even if I've had the central heating on all evening, it only needs a few hours running the next day to keep it cool.

 

So for less that £90 delivered I don't think you can go wrong - if you already have an inverter!

 

Colin

[nb Innisfree]

I reckon a good modern compressor 12/24v fridge and an identical 230v one will use approx the same power, so if you use an inverter just for the fridge then a mains one will cost more to run, on the other hand if you use an inverter 24/7 for other stuff then a mains fridge won't make any practical difference to a 12/24v one. It really just comes down to that.

[George94]

On paper the 12v ones are more efficient. Certainly my experience - 0and several other Forum members have said the same, is that the 12v Shoreline fridges generally consume even LESS energy than their datasheets suggest.

 

I am not arguing with your experience, but I am puzzled as to why a 12V compressor should be any more efficient than a 230V one. I wonder if the original research was based on old fridges made before we all became energy-conscious.

 

My 12V Shoreline is very obviously a cheap and nasty, old-technology, domestic fridge into which somebody has stuffed a Danfoss compressor. I should be amazed if a modern, energy-efficient, fridge wasn't MUCH less power-hungry.

 

I reckon a good modern compressor 12/24v fridge and an identical 230v one will use approx the same power, so if you use an inverter just for the fridge then a mains one will cost more to run, on the other hand if you use an inverter 24/7 for other stuff then a mains fridge won't make any practical difference to a 12/24v one. It really just comes down to that.

 

But surely the losses in the inverter will be proportional to load, so the fact that it is already in use by something else won't make much difference, if any.

 

Just thought I'd update this for anyone who may be interested!

 

I ended up buying one of the Tesco fridges that I mentioned above (just noticed that they've gone up £10). I am very pleased with it. True, it will hammer the batteries when running off the inverter but I've only done that once!

 

I filled the freezer box with those blue block things that you can get for coolboxes and plug it in when on shore-power,the engine or the genny is running to normally charge the batteries - leaving it un-plugged overnight etc. It is very well insulated and stays very cold inside. So much so, that I can confidently leave it up to 2 days without the need to switch it on. Even if I've had the central heating on all evening, it only needs a few hours running the next day to keep it cool.

 

So for less that £90 delivered I don't think you can go wrong - if you already have an inverter!

 

Colin

 

It's a fact that a fridge filled with beer is cheaper to run than one that is half empty. So that is my solution.

[nb Innisfree]

 

But surely the losses in the inverter will be proportional to load, so the fact that it is already in use by something else won't make much difference, if any.

 

That used to be my thought but after observing our Victron over a few years the efficiency (94%) seems to hold true over it's output range.

[George94]

That used to be my thought but after observing our Victron over a few years the efficiency (94%) seems to hold true over it's output range.

 

Precisely. Everything using it is losing 6%.

[smileypete]

I am not arguing with your experience, but I am puzzled as to why a 12V compressor should be any more efficient than a 230V one. I wonder if the original research was based on old fridges made before we all became energy-conscious.

Well, the 12V compressors have a variable speed DC brushless motor with permanent magnets, which is more efficient than a mains motor.

 

However the mains fridges can use better refrigerants, so the difference is not as marked as you'd expect. There are some that are equal efficiency to the Shoreline ones, but they're the A++ ones not the cheaper ones.

 

There are ways to squeeze a bit more efficiency from a mains fridge motor by getting it to do the same work for less power, but not very straightforward.

 

cheers, Pete.

~smpt~

Edited October 17, 2012 by smileypete

[George94]

Well, the 12V compressors have a variable speed DC brushless motor with permanent magnets, which is more efficient than a mains motor.

 

However the mains fridges can use better refrigerants, so the difference is not as marked as you'd expect. There are some that are equal efficiency to the Shoreline ones, but they're the A++ ones not the cheaper ones.

 

There are ways to squeeze a bit more efficiency from a mains fridge motor by getting it to do the same work for less power, but not very straightforward.

 

cheers, Pete.

~smpt~

 

One lives and learns. Thank you.

[Keeping Up]

That used to be my thought but after observing our Victron over a few years the efficiency (94%) seems to hold true over it's output range.

 

That is true for most inverters, albeit the actual number may differ, after you have deducted the static (no-load) consumption; the figure you get is called its "conversion efficiency". If you include the static consumption the efficiency is greater as the load increases.

[nb Innisfree]

That is true for most inverters, albeit the actual number may differ, after you have deducted the static (no-load) consumption; the figure you get is called its "conversion efficiency". If you include the static consumption the efficiency is greater as the load increases.

 

All I can say is when we turn one 20watt light on our BMV registers an 0.8A load (24v) turning on all 14 identical lights one by one increases load by 0.8A increments. Switching on a high load such as a 2.8kw instant boiler still gives a pro rata amp reading. It's actually 0.8 something, can't recall exact tenth of a volt but it still goes up incrementally.

 

Victron Multiplus 24-300-70.