Buying a cool box to make a fridge out of

[Fr J Hackett]

So would 200W of solar for 9 hours a day keep up with that?

Domestic batteries are 230AH

- W

As I said it depends on the duty cycle which depends on the insulation but it looks like it should be OK during the day and will probably put some into the batteries, you will have to see how often it runs during the night and whether you need to switch it off then or it may over a few days deplete your batteries. Don't forget as I am sure you are aware it will be high 20°s even 30° when you use it and that will determine how long it runs for, the duty cycle.
Basically you are going to have to suck it and see, if you have an inverter then when in the marina you will be fine.

 

[AngusMcDoon]

So would 200W of solar for 9 hours a day keep up with that?

Domestic batteries are 230AH

Who knows? 270W in 24 hours is meaningless electrical-unit nonsense.

 

[AngusMcDoon]

I thought these things were measured in amp hours.

Ah per 24 hours is good if you known the voltage it's specified for, because some run at 12V and some at 24V and many others at either. Wh per 24 hours is also good.

 

[AngusMcDoon]

By no means an expert but it depends on the duty cycle of the compressor, I guess it is going to cycle on and off several times drawing about say 4 to 6 amps.

Values per 24 hours will take into account duty cycling, but the consumption figure given needs to be energy, not power, to be meaningful (or be able to calculate energy, like from Ah per 24 hour at specified voltage). A really decent specification will give a graph of energy consumption per 24 hours for a range of temperature difference between inside set temperature and outside ambient temperature.

 

[Fr J Hackett]

Values per 24 hours will take into account duty cycling, but the consumption figure given needs to be energy, not power, to be meaningful (or be able to calculate energy, like from Ah per 24 hour at specified voltage). A really decent specification will give energy consumption per 24 hours and also specifying inside set temperature and outside ambient temperature.

But it doesn't so Webby is getting the best guesses that can be made. Which may or may not help him to decide.

 

[BobnLesley]

So would 200W of solar for 9 hours a day keep up with that?

Domestic batteries are 230AH

- W

We were running our 30 or maybe it was 35 litre, Dometic unit along with everything else on that sort of panel output - we'd two 80W panels, plus a 55W panel that sat out loose on the deck when we were anchored for more than a day or two, though our battery capacity was 450AH which might've helped.

 

[Graham376]

So would 200W of solar for 9 hours a day keep up with that?
Domestic batteries are 230AH
- W

Are you still in Portugal? In early days with Algarve sun, we scraped by with 200W of solar. LED lights, computers to charge etc and BD50F fridge compressor drawing 7 amps in 170L badly insulated cool box, cold enough to produce ice in O ring evaporator. Winter sun, we need to top up with generator.

Bearing in mind our experience, I would guess you should be OK with a well insulated smaller box and smaller compressor, for most of the year.

 

[Elessar]

270w @ 12v = 22.5 Amps ?

If you're not familiar with Ohms law you can download an app that'll do the calculation for you.

I sure he knows ohms law. Amps is a nonsense measurement in this context.

 

[harvey38]

I sure he knows ohms law. Amps is a nonsense measurement in this context.

Refer to post #12, I was trying to be Helpful!

 

[Concerto]

You might find this article worth reading.
How’s your fridge? by Chris Blackman

At present I am have been using a Waeco coolbox, similar to this model. Waeco Tropicool TCX14 Thermoelectric AC/DC Portable Cool Box Formally TC14. I have been using this cool box for 7 years and ran this from a solar panel charging 2 domestic 105 amp batteries, when not using the engine or mains. This was used up to 3½ weeks at a time with no problems. However it had only limited capacity. Many other Fulmars have converted the fitted cool box with a fridge unit. So far I have increased the insulation using Kingspan, as per the link above, as this is very important I now have 100mm of insulation across the bottom of the fitted cool box. I am just about to fit a Dometic fridge compressor. Waeco Dometic Cold Machine Kit Evaporator VD-01 / Compressor CU55 This will treble my fridge capacity and should be even more efficient than the coolbox.

 

[Hydrozoan]

... I don't have the skill to fibreglass/gelcoat a custom made enclosure, let alone make a decent lid. ...

Could you perhaps make a simple insulated ‘box inside another’ in ply with say 5 cm square wooden battens for the frame between the inner and outer ply layers? (I’m obviously just describing the principle: if your space has walls at sides and back, and a floor, you would not need a complete double box.) I think ply with a white laminate face, suitably sealed at the edges, would do for the inside - and, perhaps, a veneered ply for the outer front and lid. Having suggested that, I don't think you could sensibly get much better insulation than your proprietary box in the OP - see my response to Fr J Hackett below.

For an existing (and barely insulated) GRP box of ca. 70 litres I used a Waeco CU55/VD07, similar to Concerto’s. I used a few ‘bag’ panels from a hot water cylinder jacket kit as outside insulation, as it was easy to push into most (but not all) of the surrounding, awkward space, and less messy than loose fill or expanding foam. Despite that limited insulation, power use is modest and fine for my use: I have no detailed data but guess <100Ah for 2-3 days in UK summer (220Ah domestic bank). A smaller capacity and (say) Celotex panels should do better, but against that would be higher temperatures in Portugal.

Doubt it's insulation would be up to it and you would end up drawing a lot of current, can't you make one and maximise the insulation.

430x430x450 cm less 6 cm all round (2 layers of ca. 0.5 cm ply and 50 mm of Celotex or similar insulation) gives by my calculation ca. 32 litres to be refrigerated - similar to the proprietary box linked in the OP (33 litres capacity). If that were raised to just 9.5 cm all round (2 layers of ca. 0.5 cm ply and 75 mm insulation) the refrigerated space would be only ca. 15 litres.

I hope you and the OP will please treble check my calculations, as I might have got them wrong! But if they are correct, I'm not convinced that a custom-made box (though it might be neater, depending on location, and perhaps somewhat cheaper) would enable very much better insulation, for any capacity that I (albeit no expert on refrigeration) would think sensible for a compressor-based approach.

 

[Fr J Hackett]

Could you perhaps make a simple insulated ‘box inside another’ in ply with say 5 cm square wooden battens for the frame between the inner and outer ply layers? (I’m obviously just describing the principle: if your space has walls at sides and back, and a floor, you would not need a complete double box.) I think ply with a white laminate face, suitably sealed at the edges, would do for the inside - and, perhaps, a veneered ply for the outer front and lid. Having suggested that, I don't think you could sensibly get much better insulation than your proprietary box in the OP - see my response to Fr J Hackett below.

For an existing (and barely insulated) GRP box of ca. 70 litres I used a Waeco CU55/VD07, similar to Concerto’s. I used a few ‘bag’ panels from a hot water cylinder jacket kit as outside insulation, as it was easy to push into most (but not all) of the surrounding, awkward space, and less messy than loose fill or expanding foam. Despite that limited insulation, power use is modest and fine for my use: I have no detailed data but guess <100Ah for 2-3 days in UK summer (220Ah domestic bank). A smaller capacity and (say) Celotex panels should do better, but against that would be higher temperatures in Portugal.



430x430x450 cm less 6 cm all round (2 layers of ca. 0.5 cm ply and 50 mm of Celotex or similar insulation) gives by my calculation ca. 32 litres to be refrigerated - similar to the proprietary box linked in the OP (33 litres capacity). If that were raised to just 9.5 cm all round (2 layers of ca. 0.5 cm ply and 75 mm insulation) the refrigerated space would be only ca. 15 litres.

I hope you and the OP will please treble check my calculations, as I might have got them wrong! But if they are correct, I'm not convinced that a custom-made box (though it might be neater, depending on location, and perhaps somewhat cheaper) would enable very much better insulation, for any capacity that I (albeit no expert on refrigeration) would think sensible for a compressor-based approach.

I would say two things:

Nick seems to have no faith in his DIY abilities so no matter how much we recommend anything along those lines it's a no go and given where the boat is I doubt he has the tools and facilities to do the work to any great standard of finish even if he can find the materials.
I am not so sure about the quality of insulation in the original box, all it says is High efficiency PU foam

 

[Hydrozoan]

I would say two things:

Nick seems to have no faith in his DIY abilities so no matter how much we recommend anything along those lines it's a no go and given where the boat is I doubt he has the tools and facilities to do the work to any great standard of finish even if he can find the materials.
I am not so sure about the quality of insulation in the original box, all it says is High efficiency PU foam

Points taken, and I had noted your earlier encouragement to consider the DIY route.

But that's not to everyone's liking, or facilities, and on looking a bit further into the modest space I thought it might not offer significant capacity advantage anyway. I did wonder if the proprietary unit might have better insulation than, say, Celotex, but I've no more idea than you have on that.

 

[Fr J Hackett]

Points taken, and I had noted your earlier encouragement to consider the DIY route.

But that's not to everyone's liking, or facilities, and on looking a bit further into the modest space I thought it might not offer significant capacity advantage anyway. I did wonder if the proprietary unit might have better insulation than, say, Celotex, but I've no more idea than you have on that.

15 litres of well insulated space is a whole lot better than 50 of poorly or average insulated space My view is that I would sooner have a small volume that kept things that had to be refrigerated and didn't draw to much out of my batteries than a large box that was inefficient and struggled to maintain temperature.
I learned the hard and expensive way trying to make a silk purse out of the proverbial sows ear.

 

[Hydrozoan]

15 litres of well insulated space is a whole lot better than 50 of poorly or average insulated space ...

At that volume I wonder if a compressor system is best, but it's beyond my expertise to make any firm suggestion on that.

 

[AngusMcDoon]

15 litres of well insulated space is a whole lot better than 50 of poorly or average insulated space My view is that I would sooner have a small volume that kept things that had to be refrigerated and didn't draw to much out of my batteries than a large box that was inefficient and struggled to maintain temperature.

I agree. For best part of 20 years I've had a Waeco CF-18 18 litre compressor coolbox. It's enough volume for food for 2 people for a week with some squishing down. Taking food out of space wasteful packaging and putting it in plastic bags saves a lot of space. Also I see people putting stuff in fridges that shouldn't be there (nanas, bread, tomatoes) or doesn't need to be (eggs, salad, other veg). My ickle box uses 10 Ah per day at 12V in a typical UK summer set at 4C where the outside temperature is in the 20-30C range. My 50W of solar easily keeps up, even in soggy Scotia.

 

[AngusMcDoon]

At that volume I wonder if a compressor system is best, but it's beyond my expertise to make any firm suggestion on that.

It is as power consumption will be far lower than for a thermo-electric device, which is often even more important for a small boat that is likely to have a coolbox rather than a built in fridge. Downside has always been price as the western made boxes, for example from Dometic/Waeco, have cost hundreds of groats even in the small sizes. Now Chinese ones like Alpicool have brought the price way down similar to Chinaspachers. I've not heard any negative reports on their quality or reliability.

 

[Fr J Hackett]

At that volume I wonder if a compressor system is best, but it's beyond my expertise to make any firm suggestion on that.

Don't even think about thermoelectric That was my first of several lessons.

 

[Hydrozoan]

Don't even think about thermoelectric That was my first of several lessons.

I didn't consider thermoelectric myself, certainly, but I did have an existing coolbox of 70 litres. The cost of a compressor system for such a small capacity as 15 litres - with the extra insulation you suggested - was a thought in my mind, but Angus' point about lower prices covers that. I guess a remaining issue for the OP would be 30 litres capacity with ca. 5 cm insulation or 15 litres with ca. 7.5cm of insulation, if the latter can be found (or contrived) in a proprietary box.

 

[Fr J Hackett]

I didn't consider thermoelectric myself, certainly, but I did have an existing coolbox of 70 litres. The cost of a compressor system for such a small capacity as 15 litres - with the extra insulation you suggested - was a thought in my mind, but Angus' point about lower prices covers that. I guess a remaining issue for the OP would be 30 litres capacity with ca. 5 cm insulation or 15 litres with ca. 7.5cm of insulation, if the latter can be found (or contrived) in a proprietary box.

The sad thing is that a bespoke box could be made with a bit of laminated ply or perspex, a few screws and sikaflex plus insulation board from a builders merchant (Brico) Linked to a compressor unit or even as an ice box it would be a better option than the OP.