Inverter for fridge

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pcatterall

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We have decided to go down the 'mains fridge route' and seek advice on the pros and cons of various inverters. The fridge will be on mains more than on battery but it would be nice to have it on for short day cruises.
I guess that we will need a good sized inverter to cope with the start up ?
I understand that the inverter will waste a lot of power even when the fridge is not running? are there inverters which sense no load and shut down until the fridge decides to start up?
Any ideas on the current 'best buys' on inverters?
 
Possibly easier to buy a 12V mains power supply and install a switch to a 12V fridge? That way you achieve everything you want but without having to buy an expensive inverter. 12V supplies are very cheap indeed for the spec required to run a boat sized fridge.
Depends on the boat though, a 60' mobo might choose differently!
 
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pcatterall said:
We have decided to go down the 'mains fridge route' and seek advice on the pros and cons of various inverters. The fridge will be on mains more than on battery but it would be nice to have it on for short day cruises.
I guess that we will need a good sized inverter to cope with the start up ?
I understand that the inverter will waste a lot of power even when the fridge is not running? are there inverters which sense no load and shut down until the fridge decides to start up?
Any ideas on the current 'best buys' on inverters?
Click to expand...
They really seem to vary in standby from 0.25W to ten times that so usually much less than your fridge will take. Up to you whether you let the fridge take whatever it needs or fit a separate VSR to only connect the inverter when the batteries are above a certain voltage, or otherwise use it as a coolbox.
 
lustyd said:
Possibly easier to buy a 12V mains power supply and install a switch to a 12V fridge? That way you achieve everything you want but without having to buy an expensive inverter. 12V supplies are very cheap indeed for the spec required to run a boat sized fridge.
Depends on the boat though, a 60' mobo might choose differently!
Click to expand...
Not with you here. Boat fridges are stupidly expensive. So are 12V power supplies. Inverters and domestic fridges are cheap.
 
Power supplies are about £20. I agree 12v fridges are pricey, but are more efficient than running with an inverter. Obviously all depends on the boat though, my thinking was that OP might be considering pulling out a 12v one to replace with a 240v one because they run mostly on shore power. There wasn't much detail but I thought it worth mentioning the option.
 
lustyd said:
Possibly easier to buy a 12V mains power supply and install a switch to a 12V fridge? That way you achieve everything you want but without having to buy an expensive inverter. 12V supplies are very cheap indeed for the spec required to run a boat sized fridge.
Depends on the boat though, a 60' mobo might choose differently!
Click to expand...

Why on Earth would you do that ?

If you fit a 12v fridge it runs from the batteries, if you connect to shore power the battery charger keeps the batteries charged, whilst running the fridge.
 
Hi Peter good to see you planning Mediterranean again..looking forward to it myself..For what it’s worth.. Our 12v/240v fridge is ? great ..well pleased.Solar panels keep everything good during those hot sunny Med days???
 
All ball park figures, but good enough for a comparison:

Typical 12v fridge uses about 4a and runs 1/3rd of the time, so in 24hrs it would use 32ah.

Similar fridge, but 240v on an inverter would use the same 32ah, plus overheads and inefficiencies. For the 16 hours it isn't running the inverter overhead could be 1a or close to it, so add another 16ah. Whilst the fridge is running it will use around 10% more power due to inefficiencies in the inverter, so another 3ah. Total power for the same size fridge, 51ah instead of 32ah.

If you can spare the extra power, or as the OP states "The fridge will be on mains more than on battery " it doesn't matter.

Generally speaking, the bigger the inverter, the bigger the overhead and the cheaper the inverter, the bigger the overhead., but you'll need to look at the data sheets for what you intend to buy. I would suggest a 1200W Victron inverter. Will happily run the fridge and will also run a small microwave or a low power kettle (not at the same time).

There are a few ways to wire it all up (cue another inverter argument).

  1. You could just connect the fridge to it and leave it on all of the time, it would indirectly be powered by mains when the battery charger is on. This is a bit wasteful on power and usage of the battery charger and inverter.
  2. You could connect it to a changeover switch, so when on shore power you turn the inverter off and put the switch onto the "shore power" setting, when you put to sea, switch to "inverter" and turn the inverter on.
  3. You could install as per (2) above, but fit an automatic changeover relay. This would still need the inverter to be switched on/off, unless the automatic realy has secondary contacts that would be used to trigger the inverters standby setting, if it has one.
In all cases the inverter will need thick cables and be located close to the batteries, and fused at the batteries. It will also need an appropriate RCD and MCB or RCBO, exact details depending on the above options. In all events, appropriate Earthing must be provided.
 
The suggestion seems to be that domestic 240v fridges are more efficient than 12v fridges. I'm not disputing the idea but wonder where the data comes from. Frankly I worry (or think) about the efficiency of my 12v fridge and do whatever I can to make my 12v fridge as effective as possible - because we have a limited 12v resource. Our mains fridge has never crossed my consciousness - because even if its inefficient its power usage, alongside side everything else is simply not critical.

Jonathan

Paul posted as I was scripting this - apologies.
 
lustyd said:
Power supplies are about £20. I agree 12v fridges are pricey, but are more efficient than running with an inverter. Obviously all depends on the boat though, my thinking was that OP might be considering pulling out a 12v one to replace with a 240v one because they run mostly on shore power. There wasn't much detail but I thought it worth mentioning the option.
Click to expand...
All agreed. Depends on the boat, the size etc. A fridge freezer in a domestic size and you will be saving £1000+. Smaller sizes and you get down to caravan market so 12v ones are cheaper and the domestic ones get pricier.
 
Neeves said:
From memory many 12v fridges can be run direct from mains, though you would need to switch it over manually.

Jonathan
Click to expand...
mines got an external box that either passes the 12v through or converts the mains to 12v dc with automatic changover.

The box is £120 or so on top of the price of the fridge.

I've not seen (doesn't mean they don't exist) a dual voltage compressor fridge, but I have seen dual voltage (plus gas sometimes) evaporative fridges. I don't think you can have a gas one in a boat - caravan only AFAIK.
 
OK OP has decided to go a domestic 240vAC fridge mostly used on AC marina supply. But wants to be able to use it on 12v from an inverter. As said get a largish inverter but make sure it is "Pure Sine Wave" not "modified Sine wave" this is vital for the induction motor in fridge. Standby current for the inverter will as said be variable but not likely more than .25 amp. Sop I would suggest mostly not a concern compared to the operating current. Make sure you have very stout short cables for pos and negative to the inverter. I think most inverters will shut down with low battery voltage. (check) Often people report shut down because cables are dropping too much voltage.
As for switching of 240vAC to fridge. I would suggest a fool proof pull the plug out of the distribution board for marina power and plug it in to inverter. You can use relays and switching but dire consequences if you get inverter power and mains power connected together. (even momentarily)
I think in buying the fridge the efficiency rating will be most important.
Neeves said that he never thinks about domestic fridge efficiency because it is small use compared to every thing else. Well for me domestic fridge is the main user of mains electricity in my house due to it being running 24/7. Lights, all low current drain and heating/cooling only occasionally used. (only electric heating available) (perhaps due to latitude) ol'will
 
Elessar said:
mines got an external box that either passes the 12v through or converts the mains to 12v dc with automatic changover.

The box is £120 or so on top of the price of the fridge.

I've not seen (doesn't mean they don't exist) a dual voltage compressor fridge, but I have seen dual voltage (plus gas sometimes) evaporative fridges. I don't think you can have a gas one in a boat - caravan only AFAIK.
Click to expand...

I never said they were cheap :)

WAECO CoolMatic CRX 50 Fridge/Freezer 12/240v | Caravan RV Camping

That's about stg500.

Jonathan
 
Personally I don't know why you are considering a mains fridge ( though I fully understand your post that opens the thread).

Much depends on your yacht but most have fridge spaces designed round standard boat fridges, like the Waeco/Dometic range. A mains fridge is unlikely to fit. You now need to modify your galley to accept the mains fridge. Commonly mains fridges are deeper than 'our' fridges' and need decent air gaps all round. You are proposing to buy an inverter to run the fridge - given that Waeco/Dometic make a complete range of 12v/240v fridges of a decent range of sizes why not buy one 'off the shelf' that will do exactly what you want, negate the need to buy a new, another, inverter (which will only increase power consumption).

If you want to run the Waeco/Dometic fridge off either 12v or 240v is not difficult to wire it up to accept both and then simply switch from one to the other - as appropriate.


And in case it fleetingly crosses your mind - I have no association with Waeco/Dometic :)

What might influence my choice would be if I found that a domestic fridge was significantly more efficient than a 'recreational' fridge - no matter how it was powered. If the domestic, terrestrial, fridge was significantly more efficient - then I'd be prepared to consider ripping the galley apart to fit one. I am influenced as we seldom access mains power - so the advantage of dual power (we have recently bought one from the CRX range) is lost on us (and we have an option we paid for and do not use :(

Jonathan
 
Thanks all. Clearly the amount of usage on mains versus battery is very important. Thanks to PaulRainbow for his figures and suggestions. Out of interest I did read an 'article' suggesting that domestic fridges were, in fact, slightly more efficient than 12 volt but that this small gain was lost considerably when an inverter was used.
I dont think fridges were invented when our boat was built !! so we are having to create space somewhere! The fridge we are looking at is only around 46 L capacity and 50x50x70 outer dimensions, we will be able to add some insulation with the available space.
Pauls point about the 1200w Victron is noted, we do have a mains microwave rather than a gas oven ( too hot in the galley in Spain) the opportunity for a quick 5mins warm up when sailing would be handy.
Thanks all again.
 
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