AC fridge on a small inverter.

[Naartjie AKA Duck Hatch]

It's no good reinventing the wheel, so has anyone tried this before.

DC fridges are rather dear. I'm looking at running an AC fridge on a small 12v inverter. Plan to switch the inverter on/off using the fridge's thermostat. I don't want have the inverter permanently on.

Any advice would be appreciated 

 

Edited June 20, 2025 by Naartjie AKA Duck Hatch

[nicknorman]

No direct experience but the fridge motor startup current is quite high, so you will likely need a larger inverter than the fridge spec might suggest. I believe around 1kw has been mentioned.

[GUMPY]

You will need at least a 1kw Inverter, I tried this a while ago and failed to find a small inverter that would start the fridge. In the end I got a 1600va Victron inverter and used it's sleep mode to save battery drain.

However this will only work with "mechanical" fridges as the electronic ones won't bring the inverter out of sleep mode.

[AJLElectronics]

Why are three way 'fridges not used on boats, like they are on caravans?  Running on Propane works very well.

[GUMPY]

As for switching it's far easier to use an external stat running on 12v with the probe fed up the drain hole of the fridge rather than messing with the internal stat. Just turn the internal stat to maximum and use the external stat to control the fridge.

Something like This

 

 

 

3 minutes ago, AJLElectronics said:

Why are three way 'fridges not used on boats, like they are on caravans?  Running on Propane works very well.

They used to be but regulations on sealed flues stopped installation of new ones.

Edited June 20, 2025 by GUMPY

[nicknorman]

Just now, AJLElectronics said:

Why are three way 'fridges not used on boats, like they are on caravans?  Running on Propane works very well.

If you look at a typical caravan installation the back of the fridge has a cavity ventilated to outside via a low level and high level grillle. Low level holes in narrowboat hulls don’t work very well…. (glug)

 

There are some gas fridge installations on older narrowboats using a single higher ventilation system but long since obsolete.

[blackrose]

9 minutes ago, AJLElectronics said:

Why are three way 'fridges not used on boats, like they are on caravans?  Running on Propane works very well.

 

They are used on boats - I used to have one. Apart from the ventilation issue that Nick mentions they don't work particularly well on 12v and are also fairly inefficient in terms of energy if used on mains. They do work well on LPG and for occasional use I found that was fine, but they will go through a lot of gas if you were running it on gas permanently.

 

I have a 2Kw inverter and leave it on all the time. The quiescent load is 0.6a x 24 hours = 14.4ah/day which is no big deal if you have a decent battery bank & solar panels.

16 minutes ago, GUMPY said:

 

They used to be but regulations on sealed flues stopped installation of new ones.

 

By boat builders? I think you can still install them DIY?

[GUMPY]

7 minutes ago, blackrose said:

I think you can still install them DIY?

There was at one time something in the BSS about sealed flue units which also hit instant water heaters.

[robtheplod]

31 minutes ago, AJLElectronics said:

Why are three way 'fridges not used on boats, like they are on caravans?  Running on Propane works very well.

Solar is used more on boats i suspect.... easier than propane, and its free....

[AJLElectronics]

32 minutes ago, robtheplod said:

Solar is used more on boats i suspect.... easier than propane, and its free....

 

A small refridgerator pulls a continuous 8 Amps, quite a load for solar to supply.

[Alan de Enfield]

54 minutes ago, AJLElectronics said:

Why are three way 'fridges not used on boats, like they are on caravans?  Running on Propane works very well.

 

1) The manufacturers state they are not suitable for boat usage (so the likes of insurance companies and the BSS get twitchy)

2) The 12v side is not thermostatically controlled so use something like 160Ah per day as they run continuously and draw 8amps ( the manual actually states that for a caravan it should be disconnected / switched off) if you park the car (go to services etc) as you may be unable to start the car on your return.

3) The latest BSS regs  ban their use on petrol engines boats (see section 8:2)

 

 

 

[David Mack]

1 hour ago, AJLElectronics said:

Why are three way 'fridges not used on boats, like they are on caravans?  Running on Propane works very well.

Manufacturers advice is that they cannot be used in boats. So you cannot install them in accordance with the manufacturers instructions, and that could be a problem if you ever have to claim on your insurance.

[pete.i]

1 hour ago, AJLElectronics said:

Why are three way 'fridges not used on boats, like they are on caravans?  Running on Propane works very well.

I had a 3 way fridge on my narrowboat. Mine was gas connected if I remember rightly. It was along time ago and  I no longer have that boat so I cannot remember any details.

[GUMPY]

3 minutes ago, AJLElectronics said:

 

A small refridgerator pulls a continuous 8 Amps, quite a load for solar to supply.

No it doesn't 

A three way fridge draws that however a decent 230v will have an annual consumption of 90kWh  so the solar will only have to produce about 0.3kWh a day hardly onerous

[Alan de Enfield]

Just now, GUMPY said:

No it doesn't 

A three way fridge draws that however a decent 230v will have an annual consumption of 90kWh  so the solar will only have to produce about 0.3kWh a day hardly onerous

 

 

A 3-way fridge on 12v does draw a continuous 8 amps according to the owners manual.

However a quality, designed for boats, 12v fridge only uses ~ 28-30Ah per day which is why I changed mine over.

[MtB]

52 minutes ago, Alan de Enfield said:

 

 

A 3-way fridge on 12v does draw a continuous 8 amps according to the owners manual.

However a quality, designed for boats, 12v fridge only uses ~ 28-30Ah per day which is why I changed mine over.

 

My fulI-sized Inlander brand 12v compressor fridge draws about 3A when running, which is about 30% of the time. Totally different kettle of fish from three-way fridges thqt work using the absorption principle. 

 

 

[nicknorman]

2 hours ago, AJLElectronics said:

 

A small refridgerator pulls a continuous 8 Amps, quite a load for solar to supply.

True, but no-one (with any sense) uses an absorption fridge on a boat on electric power. Boat fridges are normally domestic mains fridges retro fitted with 12v compressors and use a few amps intermittently depending thermostat duty cycle. So around 200Ah a day for an absorption fridge vs 30Ah for a compressor fridge  which gives an idea of the efficiency of the two different types of cooling cycle and why an absorption fridge running on gas uses a lot of gas!

[IanD]

Absorption fridges -- like the three-way ones -- are much less efficient than compressor fridges, which all electric-only ones are. So when running from a battery they consume much more power, not good for boats or caravans.

[MtB]

1 hour ago, IanD said:

Absorption fridges -- like the three-way ones --

 

Three-way fridges ARE absorption fridges. 

 

Three energy sources (gas flame, 12v element, 240v element), same cooling mechanism. 

 

 

[IanD]

33 minutes ago, MtB said:

 

Three-way fridges ARE absorption fridges. 

 

Three energy sources (gas flame, 12v element, 240v element), same cooling mechanism. 

 

That's what I meant, absorption fridges as opposed to one-way (electric compressor) fridges.

 

Because they only have heat as an input instead of electrical power which can drive a compressor, they're horribly inefficient when running on electricity so take about 4x the power of a compressor fridge.

[Lady M]

They are also silent and work well on gas or mains electricity.  We have found this a handy choice for cruising or in the marina.

[IanD]

3 minutes ago, Lady M said:

They are also silent and work well on gas or mains electricity.  We have found this a handy choice for cruising or in the marina.

All true -- but they absolutely hammer batteries when you're not in the marina, unless you use gas. For people using solar power and running them off (non-mains) electricity, they're a terrible idea.

[Tony Brooks]

1 minute ago, Lady M said:

They are also silent and work well on gas or mains electricity.  We have found this a handy choice for cruising or in the marina.

 

But also tend to react badly (stop cooling) if they go much out of level, which is why Electrolux used to supply a levelling spirit gauge with a new fridge. I understand the way the fridge is leaning has different degrees of effect. 

 

Says he, who had an email from France asking why the fridge had stopped working, and it turned out the son's motor home was parked on a slope.

[Alan de Enfield]

23 minutes ago, Tony Brooks said:

But also tend to react badly (stop cooling) if they go much out of level, which is why Electrolux used to supply a levelling spirit gauge with a new fridge. I understand the way the fridge is leaning has different degrees of effect. 

 

As explained in the owners manual ..........................

 

 

[rogher]

I wonder why DC compressor fridges are more expensive than mains ones?