Mini 220v fridge

[Kelpie]

I know this has been discussed at length before on the forum, so sorry for bringing it up again!

Came across this with a quick google: https://www.amazon.co.uk/Inventor-Mini-Fridge-Silver-Small/dp/B01DY57IHA

Yes it is very small indeed, but it is 'A+' rated and draws only 70w.
I have read that your need to factor a five fold increase for the starting surge, so that makes 350w. I already have a basic 300w invert which is rated at 600w peak, so would hope that it could cope with this. If not, a better inverter plus the mini fridge still saves many hundreds of pounds over a proper marine 12v fridge (and the inverter is available for other jobs as a bonus).

Second question: would it be possible to dismantle a cheap 220v fridge and reuse its cooling system, akin to how the marine kits work? This would obviously be a lot of work but allow me to incorporate improved insulation and to fit it to the shape of an existing locker. I imagine the main restriction would be that I could not cut any piping as then I would lose all the coolant.

 

[ccscott49]

I use a mains fridge through an inverter, works fine. 600w should be ample to start it and if it doesn't, they are easily available larger ones, at very reasonable cost.

 

[superheat6k]

I know this has been discussed at length before on the forum, so sorry for bringing it up again!

Came across this with a quick google: https://www.amazon.co.uk/Inventor-Mini-Fridge-Silver-Small/dp/B01DY57IHA

Yes it is very small indeed, but it is 'A+' rated and draws only 70w.
I have read that your need to factor a five fold increase for the starting surge, so that makes 350w. I already have a basic 300w invert which is rated at 600w peak, so would hope that it could cope with this. If not, a better inverter plus the mini fridge still saves many hundreds of pounds over a proper marine 12v fridge (and the inverter is available for other jobs as a bonus).

Second question: would it be possible to dismantle a cheap 220v fridge and reuse its cooling system, akin to how the marine kits work? This would obviously be a lot of work but allow me to incorporate improved insulation and to fit it to the shape of an existing locker. I imagine the main restriction would be that I could not cut any piping as then I would lose all the coolant.

Yes you could extract the fridge system, and have recognised you must not breach the pipework. The three major parts are the compressor, the evaporator (cold part that goes inside the fridge) and condenser (hot part that is found on the back). Connecting the evap and condenser is a fine tube that looks like a silver wire, this is a capillary tube separating the high and low pressure zones of the system. It is critical not to damage this tube. If it folds the internal passage will become blocked and it will not work.

The final layout would have to be fairly similar to the original set up. Keep the compressor below the other vessels as this encourages proper oil return. Decent insulation around the locker is essential.

But yes a cheap fridge system for a suitable locker for the money.

 

[ShinyShoe]

Have I done my maths wrong?

70W of draw with 100% efficiency of inversion would drug 5.8 and a bit amps at 12V. Lets assume its 80% efficient thats 7.3Amps.

Clearly insulation and door opening affect efficiency. But my fridges at work typically cycle on 10minutes every 30minutes. so 1/3rd of time are on. So will be using 2.4amps / hour ~ 60ampH so my 120Ah battery would be crashing out after 1 day?

How would that compare to a standard boat one?

At least this one wouldn't need an invertor to be adding to the inefficiency...
https://www.amazon.co.uk/Reggio-Cam...90212452&sr=8-2&keywords=12+volt+refrigerator

And on an aside - when you buy a domestic fridge they tell you to let it "stand" often for 24hours after shipping to let the coolant settle. Why don't boat fridges need to settle? Or is it fiction?

 

[Kelpie]

Thanks for that, I wasn't aware of how fragile the piping would be.

I think the easiest thing might be if I can take the whole back panel of the fridge out as an intact piece- I assume the rest of it is just an insulated box. Would I be able to lie this back at a slight angle to match the back of a locker? Or would that cause problems with fluid flow?
I've read that you need to ensure a good flow of air at the back of the fridge; having it against the curved hull would ensure that there was an airspace and I could set up a small fan if necessary.
It might also be nice to make the whole thing able to slide out for easier cleaning as I know fridges become inefficient if the radiator gets clogged with dust etc.

 

[Kelpie]

Have I done my maths wrong?

70W of draw with 100% efficiency of inversion would drug 5.8 and a bit amps at 12V. Lets assume its 80% efficient thats 7.3Amps.

Clearly insulation and door opening affect efficiency. But my fridges at work typically cycle on 10minutes every 30minutes. so 1/3rd of time are on. So will be using 2.4amps / hour ~ 60ampH so my 120Ah battery would be crashing out after 1 day?

How would that compare to a standard boat one?

At least this one wouldn't need an invertor to be adding to the inefficiency...
https://www.amazon.co.uk/Reggio-Cam...90212452&sr=8-2&keywords=12+volt+refrigerator

And on an aside - when you buy a domestic fridge they tell you to let it "stand" often for 24hours after shipping to let the coolant settle. Why don't boat fridges need to settle? Or is it fiction?

Sorry just saw your reply, must have cross posted.
The information for the fridge claims an annual power usage of 84kwh- which translates to 9.5w/hr, which intuitively seems about right to me. It is A++ rated after all, although I don't know how much of that is down to the insulation, and how much is inherent to the electrics.

Edit to add: the 12/240v fridge linked to looks considerably less efficient. The blurb says it is a 'D' rating, and draws 29.5w/hr.

 

[Rum Run]

I know this has been discussed at length before on the forum, so sorry for bringing it up again!

Came across this with a quick google: https://www.amazon.co.uk/Inventor-Mini-Fridge-Silver-Small/dp/B01DY57IHA

Yes it is very small indeed, but it is 'A+' rated and draws only 70w.
I have read that your need to factor a five fold increase for the starting surge, so that makes 350w. I already have a basic 300w invert which is rated at 600w peak, so would hope that it could cope with this. If not, a better inverter plus the mini fridge still saves many hundreds of pounds over a proper marine 12v fridge (and the inverter is available for other jobs as a bonus).

Second question: would it be possible to dismantle a cheap 220v fridge and reuse its cooling system, akin to how the marine kits work? This would obviously be a lot of work but allow me to incorporate improved insulation and to fit it to the shape of an existing locker. I imagine the main restriction would be that I could not cut any piping as then I would lose all the coolant.

Hacking the works out of tabletop fridges is something I used to do a lot a few years ago when building prototype drink chillers. Angling the evaporator a bit isn't a worry and the other advice regarding keeping the compressor down and not mangling the pipes is sound. Good airflow across the condenser (the radiator on the outside) is key, and a 12v fan might be useful there.
If your donor unit has a gutter inside under the evaporator with a pipe leading to a plastic cup on top of the compressor, it it worth keeping that feature in some way as it is for dealing with condensation inside the cabinet.
It is the lubricating oil that has to drain back into the compressor after being rolled about, which is the reason for keeping it low and the pipes leading down to it.

 

[superheat6k]

Thanks for that, I wasn't aware of how fragile the piping would be.

I think the easiest thing might be if I can take the whole back panel of the fridge out as an intact piece- I assume the rest of it is just an insulated box. Would I be able to lie this back at a slight angle to match the back of a locker? Or would that cause problems with fluid flow?
I've read that you need to ensure a good flow of air at the back of the fridge; having it against the curved hull would ensure that there was an airspace and I could set up a small fan if necessary.
It might also be nice to make the whole thing able to slide out for easier cleaning as I know fridges become inefficient if the radiator gets clogged with dust etc.

I would expect it will be OK up to say 15degrees tilted. The critical thing is that the compressor is getting its lubricant to its moving parts, so perhaps set this level. I doubt dust will be an issue on a boat, and a small computer cooling fan will easily provide sufficient air flow to the condenser grid, but air flowing in requires air flowing out so a suitable grill or vent holes will be necessary. Simply blowing into a sealed space will not work. The curved hull if under water might be enough cooling on its own though.

The allow to stand after moving is incase the fridge has been seriously inverted, so the time is to allow the oil to run back to the compressor.

In terms of consumption, I would expect 80% is about as good as an inverter will get, bear in mind also that charging a battery is very inefficient, at best ~ 50%, so this will be ideal for use on shore power, rather than inverter. I would set the stat low when on shore power, and perhaps use a eutectic block, then wind the stat up when going over to battery power.

 

[PuffTheMagicDragon]

At least this one wouldn't need an invertor to be adding to the inefficiency...
https://www.amazon.co.uk/Reggio-Cam...90212452&sr=8-2&keywords=12+volt+refrigerator

Am I correct in saying that this is not a compressor fridge but a Peltier?

 

[William_H]

Am I correct in saying that this is not a compressor fridge but a Peltier?

Yes Peltier type, no good on a boat at all.
Re original question,to drive a 240v compressor fridge make sure you get a pure sine wave inverter. (Not a modified sine wave) I think that domestic fridges tend to have less insulation than would be desirable on a boat. But it does seem a lot of trouble to remove the gubins intact from a small fridge and fit into a boat box. olewill

 

[Norman_E]

My boat has a mains fridge compressor, and that has no problems at all running on a Sterling modified sine wave inverter. I actually asked Stering Power whether I should buy a pure sine wave one and they told me it was not necessary for a fridge, and it was OK to buy the cheaper type.

 

[CAPTAIN FANTASTIC]

I have a 2 year old mains fridge from Argos running through a low cost 1000w inverter from Maplins.

 

[William_H]

Interesting that people have apparently no problem running domestic 240v AC fridges on modified sine wave inverters.
Most modified sine wave inverters produce a wave form not square wave but with as step so voltage rises square rapidly to a point about half way then remains at that voltage for a time then steps up again to full voltage for a period then drops half way and then back to zero. (as different to a sine wave which smoothly rises then falls) (50 times per second of course)
The reason that square wave or rapid switching is used is because transistors can be very efficient at full on or full off, so much less heat loss compared to incrementally turning on and off to emulate the sine wave. The problem is that each rapid switch on or off produces a large range of frquencies (harmonics). Some can be filtered out but still high frequencies appear in the output. These are not a problem in a brush type motor but in an induction motor the high frequency component is dissipated in heat in the coil and iron. Thus giving excess heating and inefficiencies. (as I understand it)
So it would be very interesting to measure and compare the DC current into both a pure sine wave inverter and a modified sine wave inverter to measure these theoretical inefficiencies. olewill

 

[Norman_E]

I just point out that my mains fridge on the boat is not a domestic fridge but a water cooled mains compressor driving a holding plate. I do not however see any reason why a domestic fridge would need a pure sine wave inverter, unless it had delicate elecronic controls.

 

[Kelpie]

Good to know lots of people are successfully running fridges on cheap inverters. Hopefully a cheaper fridge will have less fancy electronics in it anyway.

For my next question... it's crossed my mind that being able to freeze things could actually be more useful than having a fridge. Obviously it would take much more power, but availability of power on a yacht tends to be 'feast or famine'- if you have a really sunny day, or you are motoring, or you have access to shore power, then generally you end up with power than you can use. But if you could store it by freezing cool blocks, you could then maintain a cool box at fridge temperatures for several days.

I don't know if this is possible, but might it be an idea to 'hack' the themostat and controller on a mini freezer and have it cycle on and off to maintain fridge temperatures? So you can minimise your power consumption when away from power, but also store up ice blocks when you get the chance.

Probably more hassle than it's worth, but curious anyway.

 

[superheat6k]

Good to know lots of people are successfully running fridges on cheap inverters. Hopefully a cheaper fridge will have less fancy electronics in it anyway.

For my next question... it's crossed my mind that being able to freeze things could actually be more useful than having a fridge. Obviously it would take much more power, but availability of power on a yacht tends to be 'feast or famine'- if you have a really sunny day, or you are motoring, or you have access to shore power, then generally you end up with power than you can use. But if you could store it by freezing cool blocks, you could then maintain a cool box at fridge temperatures for several days.

I don't know if this is possible, but might it be an idea to 'hack' the themostat and controller on a mini freezer and have it cycle on and off to maintain fridge temperatures? So you can minimise your power consumption when away from power, but also store up ice blocks when you get the chance.

Probably more hassle than it's worth, but curious anyway.

Assuming you are not going below -10oC then most fridges will get that cold simply by lowering the stat right down, or fitting a lower range stat, but energy transfer is all about insulation efficiency, so you should check this is effective. Otherwise your idea of storing 'cold' is fine, and very practical. Filing the air space in your fridge with eutectic blocks will also improve the value of cold you can store.