how much power do my fridge use

[LadyInBed]

Ploys that I use in 'managing' my top loading fridge:
When the boat engine is running, turn the thermostat to coldest setting, remember to reset it when engine goes off.
Put cool bag freezer blocks next to fridge element. I don't know the veracity of this but my logic says that the freezer blocks help the fridge stay colder longer.
Take the lid off the fridge slowly, to stop the bellows effect sucking cold air out.
My normal setting for the thermostat is at the warm end of the acceptable range. I lay a thermometer in the bottom of the fridge to keep a check on temperature.

 

[pcatterall]

Fit a battery monitor then you will know the answer after a few days averaging out, same goes for the rest of the on board kit.

I second David's suggestion. I thought a battery monitor was unnecessary but after fitting the NASA model would not be without one. I think the other figures quoted will give you an idea of consumption 6 amp hours may be right but the way you use it is the big ( unknown) factor how full what temp setting, how many times/how long is it open, insulation, ambient temp etc.

 

[dilly]

thanks guys

 

[Bosun Higgs]

thanks guys i was wondering how meny keep there fridge on all the time or do thy just stop/ start and run them when needed. i have new batteries and hooked up to shore power and a good batterie charger and wanted to work my batteries rather than them just sitting there.

Why? Batteries have a finite life which is measured in cycles. Cant imagine you help them much by running them down and then up again if you can avoid it.

Anyway my 1996 boat fridge consumes 5 amps when running and the duty cycle is typically 60%. So say 3 amps average. If you run it for 24 hours that 72 aH. My alternator is 60 amps but I've yet to see more than 45 amps out of it and even that drops fairly quickly to 10 amps or less. So at a guess, and one thing is for sure your boat will be different, 24 hours of fridge is maybe 3 hours of engine. In fact my Sterling digi regulator doesnt seem to drop back to float voltage when charginf 50% depleted batteries until at least 5 hours has passed on my 200aH domestic bank.

 

[johnalison]

The current usage of a fridge depends on the insulation as much as the efficiency of the unit. We have a top-opening box in our HR34 and leave it on continuously as a rule, on a low setting. This will keep meat almost frozen in the cooling section. On average, in fair weather with our 36w solar panel, we lose about 0.5v per day in our 200Ah of service batteries. Before we fitted the panel, we could still manage for several days off charge. I know other people do much less well, and you need to check your own system. Friends of ours sold their Bav largely because of difficulties with the fridge.

 

[nimbusgb]

Bit of drift ...

'Storing cold', running the fridge as cold as possible when he engine is running and theres lots of power available is simple if you fit an electronic thermostat. I added a small voltage dependent circuit to my dixel thermostat. When battery voltage is over 13.5v ( alternator charging ) the setpoint drops to lower value, alternator off setpoint normal.

Result is a nice cold fridge with low battery power consumption.

 

[charles_reed]

I allow 40ah per 24 hours for my unit in Greece.

It draws 5.5 amp on start up - 4.3 on supercool and 3.8 in eco mode.

Unfortunately determining your actual usage will require a lot of experimental research as no two installations are similar - I know of one unit fitted to an AWB as standard equipment which used all the output of a 25amp charger (or so the owner averred), in the S of France, during an heatwave - he had to borrow a battery to start his engine.

 

[Chalker]

Vyv
Nigel Calder used to push the 'cold air out of a front loading fridge' problem. In his latest big book he explains that he changed his mind when he did your calculation and now suggests that it has only a very small impact. Less effect the fuller the fridge of ourse.

 

[charles_reed]

Ploys that I use in 'managing' my top loading fridge:
When the boat engine is running, turn the thermostat to coldest setting, remember to reset it when engine goes off.
Put cool bag freezer blocks next to fridge element. I don't know the veracity of this but my logic says that the freezer blocks help the fridge stay colder longer.
Take the lid off the fridge slowly, to stop the bellows effect sucking cold air out.
My normal setting for the thermostat is at the warm end of the acceptable range. I lay a thermometer in the bottom of the fridge to keep a check on temperature.

It's interesting that a full fridge uses less power to keep cold, than an empty one, once you've got down to operating temperatures. I'd hesitate to go along with your use of the warmest end of the acceptable range - OK for northern latitudes but suspect in the Med.
As one of the main heat leaks is through the lid, covering that with a towel (or aluminium backed polystyrene) and not opening the lid drastically reduces power-consumption.
But, the single most important factor is the efficiency of the insulation - I've been quoted 6" of closed cell or 3" of special insulation (Cyano-acrylic board) is ideal, assuming sealing door, giving about 90% efficiency. The last 10% is hostage to the law of diminishing returns.

Lastly, the efficient cooling of the refrigerant plays a major part in keeping down power use - many swear by water cooling and certainly this method is universal in larger installations. The least one can do is to ensure the airflow is effectively ducted from start to finish with air-cooled devices - I've replaced the original 75mm fan on my unit with a 140mm one for a server enclosure - as the fan only works when there is a voltage of over 13.8 in the system this comes into operation when the batteries are under charge or the PV panels are close to going onto float.

 

[vyv_cox]

Vyv
Nigel Calder used to push the 'cold air out of a front loading fridge' problem. In his latest big book he explains that he changed his mind when he did your calculation and now suggests that it has only a very small impact. Less effect the fuller the fridge of ourse.

Thanks for the update. Nice to know that science is of some use!

 

[Chalker]

Regarding insulation thickness - take a look at Nanopore UK. Vacuum Impregnated Panels. 1" = 6" of expanded polystyrene. But difficult to use it for 100% of the panel area so you get perhaps an overall equivent of 4-5"

Looks expensive at first but when you look at the total price of compressor unit, keel cooler and evaporator it seems more reasonable.
Only way I could fit a freezer. 6" or even 4" of a better foam would have left me with enough volume for a packet of frozen peas!!