DIY Doctor UK DIY Forums

Hello all,

Having had power failures of several days in the past, what's the minimum sized genny that would start the fridge/freezer motor? The rest of the household can manage with minimal power requirements but I worry about the cold stuff...

Regards Ant

Much depends on how the generator is regulated. A fridge rarely draws more than 5 amp (1kw) but the start current is a lot higher and some generators will have a field fail with the start current other will take it in their stride most home steads on the Falklands could run on 1.5KVA.
Eric

Hi Eric,

A normal household fridge/freezer is likely to to need only around 100 watts when the compressor is running. I checked mine a couple of weeks ago and found the maximum power consumption to be 100watts +-10%. When the compressor was off it only needed 10watts, and the mean power consumption is nearer the 10watts than the 100. A generator is really inefficient at supplying this type of load because much of the time it will just be ticking over supplying the 10watts and wasting fuel. A better solution might be an invertor connected to a 12 or 24 volt battery, the genny could be used to recharge the battery if a sustained power outage happened. A 60 Ah 12V battery with a 150/300 watt invertor could happily keep a fridge/freezer ticking over for up to 12 hours as long as the door was not opened too often. A good quality 150W invertor could handle the compressor start up surge without tripping the overload sensor. A true sinewave output device is preferable to avoid the possibility of compressor overheating due to harmonics in the motor windings. I am going to test out a modified sinewave type (semi squarewave) on my fridge shortly to see if there are any problems. I am trying to get prepared for these types of problems because I feel the grid and other services are likely to be far less reliable in the future.

Hope this helps - Chris.

I do agree as to inverter supply but not knowing any sizes one has to be careful. I know the bigger ones now include an inverter so there is no problem if phases are wrong. And I seem to remember the walk in type reefers had Peters engines at about 5 BHP which is a lot bigger than domestic. But I have been caught out trying to run motors of generators and inverters and with one farm we had to run the shears sharping tool before starting the shears themselves because of inrush on a 1.5Kw generator but on another farm with a 1Kw generator it all worked without a problem all to do with the way the generator was excited.
As it is at the moment keeping lids shut in power cuts and good insurance seems cheaper option!
Eric

Hi Eric,

I must apologise for addressing my previous message to you instead of Ant, it made it seem like a criticism, which was not my intention at all. I was trying to give the discussion my own thoughts and findings with regard to household/domestic fridge/freezers. Yes I agree the first rule in a power cut is, don't open the lid/door, the second might be, throw an old carpet or some coats over it.

Regards - Chris.

I was also not in essence disagreeing with you.
But I have been caught out in the past and told a guy to run this motor you need this. Only to find the motor he has takes more than normal inrush or his generators field will collapse with any overload good fail safe but not so good with motors.
Best is a regulated power supply feeding a battery which feeds inverter so no change over required with power cut i.e. UPS. And some larger UPS units are now becoming available at reasonable prices.
But the main detail is missing. He has not said how big the unit is.
Eric

Hello all,

Thankyou for your thoughts; the fridge/freezer is an ordinary Candy-branded built-in domestic thing.

I already have a large tractor battery which served me well over Christmas a year or three ago with the computer UPS when I recorded all the Radio Three Bach, despite the power cuts! That supply is 365W from memory, I shall try it and let you know - it will probably not be for a few days...

Regards Ant