Do you run the fridge after sunset?

Our fridge consumed about 18Ah per day when first tested in Orkney - but we use a hull mounted cooling plate as its so much more efficient than the usual air cooled coil. We pobably uses a bit more power in warmer water but fridge remains on 24/7. With solar panels plus wind turbine we are self sufficient for electricity both at anchor or sailing at night.
 
The compressor always runs but thermostat is turned off most of the time so no power will be used. But that is not why the thermostat is turned off (inside the fridge locker) it is because if the thermostat is not turned off everything freezes! Fridge only needs to be run 4 or 5 hours a day to keep everything good. When it gets very hot in the summer I will keep it on all the time when I am in the mood for ice... I will keep a large container of water at the bottom of the fridge (it's American and you can sit in it its so big) and this will freeze nicely then I use a screwdriver and hammer to chip the ice. Once ice is made I can still turn off fridge overnight and ice will mostly not melt. When invited over to other boats for drinks bringing a bucket of ice always gets the aperitifs flowing more readily ?
 
We keep our fridge at no more than 6degC. Its 2degC at the bottom. This gives us an average of 4degC fridge temperature as recommended for commercial fridges.
We had a period recently when our fridge developed a fault. We had to buy large bags of ice each day to keep our food cool. It came as a surprise how much warmer the fridge was with the bottom full of ice compared to a proper working temperature controlled fridge. The top of the fridge was at 10degC. Our fridge is insulated with 150mm of PU foam insulation but it still want ideal for keeping food cool.
 
Your ice was at 0 deg when melting and your evaporator plate would be at about -10 deg, that’s quite a difference from ambient temp, that’s why it struggled
 
Akestor said:
As said in a Danfoss PDF, the compressor will consume around 40Ah/24 hours with a 100-liter cooling box installation. That is around 1, 6Ah per hour. Assuming that when it is working it consumes 5Amps, it works around 20 minutes scattered every hour on and off by the thermostat.
If we have a 100w solar panel, it can produce 100w/18v= 5amps lets say for 6 hours every day that will be 30Ah. So running only the fridge the battery will lose 10ah every 24 hours. That simple conclusion makes me think that I will have to shut off the fridge at night, but I will be glad to hear your installations.
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Your figures aren't far out but it isn't as simple as that.

In central med. you might get around 40Ah per day from a panel mounted flat on deck, probably falling to 30Ah in March and September in an average year.

Your figure for the fridge usage is a reasonable starting point at 40Ah (5 x 24 / 3 ) in a 24 hour period. I'm assuming a moderate summer with temp. under 30C. Usage actually increases hugely when it gets hot and temp. hits 40C but that's only for short period and I'll ignore it just now. Temp. can also remain quite high overnight in the med.

Sounds OK and breaks even making it better than your original estimate. Unfortunately, you need to put back a lot more than 10Ah if you take out 10Ah from flooded lead acid batteries if you want to stay at 100% SOC.

If we assume the 100W panel is producing 5A for about 6 hours each day it will produce 30Ah when fridge has used 10Ah, giving a 20Ah excess.

Unfortunately, that could well be enough to just put 5-10Ah back into the battery before the fridge is using more than the panel can supply.

This means that you take 40Ah out each day, using 10Ah directly from the panels and 30Ah from the battery. But the battery only get the benefit of about 5-10Ah towards increasing SOC. This means that the battery actually loses 20-25Ah each day.

You are generating 40Ah and using 40Ah which seems as if it balances but poor charging efficiency loses a lot. Of course this assumes you are trying to get back to 100% charge every day with a flooded battery, not something more exotic.

Most people used to be content to get back to 80-85% SOC each day and 100% once every couple of weeks. That's not too hard to achieve as charge efficiency is better at that level. Not ideal for battery life.

A bit rambling but I hope that makes sense that it is likely to work out worse than you would expect from the initial figures.

Fitting extra solar panels is a game changer. Output at least matches usage for much more of the day with the result that discharge doesn't start until late evening. The excess also gets the battery back to 100% during daylight hours. I leave the fridge one from mid-April to late October and temp. is in mid.-high 30s for a lot of the time. I have 345W solar and laptops etc. probably use as much as the fridge.
 
Just like people here our stay on 24/7 , AH used from when the panels stop charging till they come back to life is 29AH give or take a amp .
Our fridge is keel cool , I have also changed my thermostat to a electronic type set to come on at 5c and off at 3c
 
i used to keep several cushions on top of the fridge to help keep the cold in. Try it you will feel the cold under the cushons. Ive since heavily insulated the whole fridge and this works well in the Med. And yes i keep the fridge on 24/7 before i leave dock i leave the fidge on shore power on a very low setting to get everything cold
 
MAURICE said:
i used to keep several cushions on top of the fridge to help keep the cold in. Try it you will feel the cold under the cushons. Ive since heavily insulated the whole fridge and this works well in the Med. And yes i keep the fridge on 24/7 before i leave dock i leave the fidge on shore power on a very low setting to get everything cold
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Works well. We got some foam off-cuts a few years ago and made up sleeves from vinyl material with some reflective material on top of the foam inside. The reflective material came from a car window sunscreen. They cover the entire worktop above the fridge/freezer and look fine.

The worktop used to get extremely hot in the summer sun and is now cold to the touch under the cover. It is a cheap way to improve insulation and easy to make.
 
A lot of UK based boats have rubbish fridges which cannot be used 24 hrs a day unless you have a huge amount of solar or motor a lot or spend a lot of time hooked up to shore power. I've done a lot of cruises where we've basically not been able to rely on having a fridge. We buy a bag of ice when we can, we accept a pint of milk will go off before it gets finished, we eat according to what we can keep cool enough. We find a pub or sailing club for a cool beer.
Living like this, it's easy to get by with a modest electrical system.
Once you say that the fridge absolutely must stay cold all week, then you have to have the batteries and power source to make that happen.

It seems to me that some people on a typical South Coast cruise have just traded needing to plan where they'll get fresh food for needing to plan electricity production and use. It always seems to end up with running the engine to run the fridge.
 
lw395 said:
A lot of UK based boats have rubbish fridges which cannot be used 24 hrs a day unless you have a huge amount of solar or motor a lot or spend a lot of time hooked up to shore power. I've done a lot of cruises where we've basically not been able to rely on having a fridge. We buy a bag of ice when we can, we accept a pint of milk will go off before it gets finished, we eat according to what we can keep cool enough.
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All my holiday yachts have been like this. I never bothered with the fridge on narrowboat despite having a domestic one installed, had hatches into the bilge for a pantry and a countertop ice maker for gin. Have a chunky new Waeco in newboat and still assume I am going to need a lot more solar that the boat currently has to cope with it.

Vacuum insulation panels are vaguely affordable now, not sure if anyone has tried the for boat fridging What is a Vacuum Insulation Panel?
 
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Mistroma said:
Fitting extra solar panels is a game changer. Output at least matches usage for much more of the day with the result that discharge doesn't start until late evening. The excess also gets the battery back to 100% during daylight hours. I leave the fridge one from mid-April to late October and temp. is in mid.-high 30s for a lot of the time. I have 345W solar and laptops etc. probably use as much as the fridge.
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Our BD50F draws 7 amps when running, with a 170L badly insulated fridge with large O ring evaporator keeping food frozen. We just scraped by with 200w of panels in summer but early spring and late autumn weren't so good and batteries died early as never fully charged. Uprated to 320w and last year we had power to spare, no problem getting batteries fully charged, even with fridge running for long periods with temps down below up to 36 degrees at times.
 
Akestor said:
As said in a Danfoss PDF, the compressor will consume around 40Ah/24 hours with a 100-liter cooling box installation. That is around 1, 6Ah per hour. Assuming that when it is working it consumes 5Amps, it works around 20 minutes scattered every hour on and off by the thermostat.
If we have a 100w solar panel, it can produce 100w/18v= 5amps lets say for 6 hours every day that will be 30Ah. So running only the fridge the battery will lose 10ah every 24 hours. That simple conclusion makes me think that I will have to shut off the fridge at night, but I will be glad to hear your installations.
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I step on the boat in Portugal, the fridge goes on, I step off after a month to come home to UK the fridge goes off. In the marina my charger keeps up, on the hook, my 250 watts of solar keeps up the 330 amphr battery bank. Moral of the story, size your kit to suit the ancillarys?
 
Mistroma said:
Your figures aren't far out but it isn't as simple as that.

In central med. you might get around 40Ah per day from a panel mounted flat on deck, probably falling to 30Ah in March and September in an average year.
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Thank you all for your posts. Mistroma the detail about SOC was a good one!

Here is the pdf by Danfoss.
http://files.danfoss.com/TechnicalInfo/Dila/06/application_guideline_bd_solar_09-2005_pa100a202.pdf
It's all interesting but especially on page 8 there is an example of running a bd35f unit solely on solar and ice packs( 150 lit box). As 1 kg of ice can store 30w of energy, the compressor will run 8 hours during the day with solar , and the remaining 16 hours will be maintained by 5 kgs of ice without operation. I guess the example can be realistic only with a very good cooling box.
 
We live aboard in Greece and the fridge stays on 24/7. Fitted a keel cooler to the standard Frigoboat set up a couple of years ago and that made a significant difference to power consumption. Insulation is not great I think but getting at it will involve a lot of furniture destruction so I'm hesitating. After a discussion with Penguin earlier this year I've improved seals around the lid and blocked the hole where coolant pipe and thermostat come in and another big step up in performance. We have 200W of solar and 550AH of service batteries so rarely need shore power from March - November. The only supplement to solar is when the engine runs and a small input from a Rutland 913.
I keep a close eye on the battery monitor, amps in / out and voltage but no interest in SOC. Occasionally voltage drops to 12.2 by midsummer morning when solar kicks in. Plan to increase solar to 300W, maybe 400, this year if we're allowed out of the marina to power the new 12v water generator.
 
Akestor said:
Thank you all for your posts. Mistroma the detail about SOC was a good one!

Here is the pdf by Danfoss.
http://files.danfoss.com/TechnicalInfo/Dila/06/application_guideline_bd_solar_09-2005_pa100a202.pdf
It's all interesting but especially on page 8 there is an example of running a bd35f unit solely on solar and ice packs( 150 lit box). As 1 kg of ice can store 30w of energy, the compressor will run 8 hours during the day with solar , and the remaining 16 hours will be maintained by 5 kgs of ice without operation. I guess the example can be realistic only with a very good cooling box.
Click to expand...

The ice will tide you over during the night and reduce battery use when solar isn't available. However, you need space in the bottom for 5 litres of ice overnight and the same amount of space in the freezer during the day to re-freeze the ice block. We go for a much less effective method. The fridge is kept full of water, wine and beer. All added early in the day when there's plenty of solar. There are also eutectic packs under the bottom of the freezer compartment. Every little helps and I have sometimes found it useful to always have 20 cans of cold beer and 5 litres of cold wine available. :D
 
Our fridge is linked to the "load" on the solar panel controller. Everything else is linked to the battery. The load is programmed to turn off below 12.8V, and on again at 13.5V (from memory, can't check now). So the fridge goes off at sundown and switches on around 9;30 on a Greek summer day. The stuff inside stays cold enough overnight.
 
Surprised: am I the only one to have installed a 12V weekly timer switch on my fridge? Chinese, of course, works perfectly. Off at 21.00 and on at 08.00. My custom fridge
(handcrafted) runs at 2 or 3 ° in the Med: overnight rises to maybe 6°. But lots of bottles in it... this is important!
 
Anchorite said:
Surprised: am I the only one to have installed a 12V weekly timer switch on my fridge? Chinese, of course, works perfectly. Off at 21.00 and on at 08.00. My custom fridge
(handcrafted) runs at 2 or 3 ° in the Med: overnight rises to maybe 6°. But lots of bottles in it... this is important!
Click to expand...
You say “maybe” have you actually measured it? Worth checking temperature at the top and bottom of the fridge. In my experience there can be a considerable temperature difference when there is no evaporator running. Cold air will sink to the bottom and top of the fridge can be quite warm?
 
Feeling very smug as I write this.

Our boat has two large side by side fridge/freezers with two Waeco compressors and separate controls, easy to make one a fridge and one a freezer.

Trouble is, one is far bigger than we need for a freezer and the other too small for fridge space required, so both are used as fridges.

We bought a Dometic 40 litre fridge/freezer box with the Danfoss compressor. This is now the freezer, set to minus 15c.

All left on 24/7 when we are cruising. Obviously no problem on Shorepower, and with 600AH's of domestic bank and 1 hour per day of genset running when without Shorepower the batteries rarely drop below 12.5v, normally 12.8 ish no load.

Nice to always have ice cream on board, ice for drinks and to be able to freeze cooked and uncooked food for later.

There are Chinese copies of the Danfoss compressor units available now at very attractive prices, Brass Monkey being one brand.
 
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