power out put of a domestic fridge

[AstonHill]

Hi
I am the proud owner of a KENWOOD KUL55X23! fridge sold hear

https://www.currys.co.uk/products/kenwood-kul55x23-undercounter-fridge-silver-10248718.html

Sadly the technical description dose not state its power consumption
I wish to run it off of an invertor but I dont know what size invertor I will need to run it right?
Any clues please?
Thanks

 

[jj4091]

Small fridges use around 90- 100 watts.

 

[ericmark]

There are two main types of fridge/freezer, one uses a capacitor start single phase motor, the other a three phase motor powered by an inverter, the latter should be no problem, it has very little in rush, the highest load is normally when the auto defrost cuts in that will be around 150 watt, normal running as @jj4091 says around 60 - 90 watts.

However the single phase motor has inrush so start current is more like 5 amp, or 1000 watt, when running still 60 - 90 watts, but takes a lot more to start, I used a plug in energy meter to see the peak power. And the peak power varies a lot make to make.

To get around the inrush there are three options:-
1) Inverter controlled fridge.
2) Peltier solid state.
3) Absorption.
The latter two are not very economic to run, most caravan fridges are absorption and can run on 12 volt, 230 volt or gas, some times on 12 volt not regulated.

You can get dc motors, but the problem with any refrigeration plant is to get motor to running speed before the gas pressure builds up, so always a bit of a trade off. I would think likely a 750 watt inverter is about the smallest that will work, with an ability to cope with some overload for short time, I had a 3 kW running and 6 kW peak inverter most seem to be duel rated.

I looked at battery back up, but in the end went for combined solar array with battery and a back up system included. Not sure how long it will run freezers for, but should be long enough to arrange some other power.

 

[AstonHill]

fff

There are two main types of fridge/freezer, one uses a capacitor start single phase motor, the other a three phase motor powered by an inverter, the latter should be no problem, it has very little in rush, the highest load is normally when the auto defrost cuts in that will be around 150 watt, normal running as @jj4091 says around 60 - 90 watts.

I have tried my fridge today with an old 150W invertor and it did not power it! so i guess the fridge is a capacitor single stage starter

Should i just get a bigger invertor?

 

[ericmark]

I have used the energy meter with a series of fridges and although run current has always been under 100 watt, the start amps have varied hugely. Some need 1000 watt to start, and a 1000 watt inverter is not cheap. I am about to fit a 3.5 kW inverter and battery together with solar panels, but that's like using a sledge hammer to crack a nut.

It depends why you want to run it off an inverter, may be better to get an absorption fridge.

 

[AstonHill]

It depends why you want to run it off an inverter, may be better to get an absorption fridge.

Is that one of those 500 quid 12v fridges? then if so think the invertor will be cheaper

 

[ericmark]

Is that one of those 500 quid 12v fridges? then if so think the inverter will be cheaper

I have not bought an absorption fridge in years, no idea of cost today, and how it compares with a inverter drive fridge, I would suspect you are right a new inverter drive fridge is today cheaper than a multi-fuel fridge, but I did look on AOL site as they list "Fridge Freezers with Digital Inverter Compressor" and selecting cheap to expensive the cheapest was £449, OK it was a fridge/freezer not a simple fridge, but clearly the inverter fridge is more expensive to the single phase capacitor start type.

Battery voltage does make a difference, I note my app shows voltage as 53.9 volt, and the inverter can it seems supply quite a high output rated as 5 kW, and from that yes I could run the single phase capacitor start type fridge of freezer, but how small of an inverter is going to start them I simply don't know, as they vary, I could put my plug in energy meter on mine, but one it does not mean others will be the same, and I am not sure of the speed of the energy meter at recording peak power.

I bought an inverter 12 to 230 volt 3 kw for my sons narrow boat, and it failed giving out the black smoke of failure, and it seems it had an array of FET's and each one had it's own fuse, and they relied on the fuse resistance to balance to load to each FET, but there was nothing to tell one when a fuse had blown, so once one went the other FET's would be overloaded, a very poor design, so to get an inverter which is well designed is not cheap, it seems the narrow boat people go for pure sine wave as the whole inverter is better made.

So a 500 watt modified sine wave may only cost £40, but pure sine wave type are £200. I am comparing same make. And 500 watt is at 230 volt only just over 2 amp, but at 12 volt it is 45 amp meaning heavy cables to stop volt drop, at 1000 watt you have about reached the limit for cheap isolation switches, we had to use welding cable plug in connectors on the narrow boat as an isolation method as with a 3000 watt inverter the DC isolator required was huge. We also had a problem running cables, so had to run two 16 mm² in parallel which still were not really big enough for that load for long, but only supplied from 3 x 120 Ah batteries so there was a limit on how long.

Better option is to use 24 volt, and even that is still a bit low, as one jumps to 48 volt then looking at special inverters, so again price goes up, today we seem to be leaning towards the same batteries as used with solar panels and EV's so my app is showing battery as being at 54.4 volts and 69% charged. But that battery and inverter is really going to cost way over the cost of a battery powered fridge.

The main problem is we want to use mass produced products as they are cheaper, it is not what is best, but what comes in at a reasonable price, narrow boats can't use gas, as drilling vent holes in bottom of boat would have an undesired effect, but caravans can use gas, so there are many options, but better asking on a narrow boat or caravan forum where people know what works.

 

[foxhole]

Aren’t all appliances required to have wattage/voltage requirement on them?

 

[AstonHill]

So based on cost, should I just go with the 100W invertor?

 

[ericmark]

Aren’t all appliances required to have wattage/voltage requirement on them?

Run watts yes, start watts no, which is the problem with a small power supply be it an inverter of generator.

So based on cost, should I just go with the 100W invertor?

Not really unlikely to work, and are you talking installation cost or running cost. Depends what you want it for. The absorption fridge is not very efficient so it can only be sold as a duel fuel, but likely a second had absorption fridge would be cheapest option to buy, but not to run, since no moving parts they can last for many years.

 

[AstonHill]

Run watts yes, start watts no, which is the problem with a small power supply be it an inverter of generator.

bit like my grinder rated at 700W but it needs about 3000w to start it

Not really unlikely to work, and are you talking installation cost or running cost. Depends what you want it for. The absorption fridge is not very efficient so it can only be sold as a duel fuel, but likely a second had absorption fridge would be cheapest option to buy, but not to run, since no moving parts they can last for many years.

im confused!
Which one is the absorbtion fridge, which one do i have?

 

[SFK]

Before buying a new fridge or inverter I would try measuring the inrush current (startup amps).

https://www.fluke.com/en-gb/learn/blog/clamps/how-and-why-to-measure-inrush-current

 

[ericmark]

My clamp meter does not have a max/min, my power adaptor socket does, I note this one does have max/min readings and at £20 a lot cheaper. I love my clamp meter it does what I want current AC and DC down to 0.001 amp so I can see what the earth leakage is, and the DC injected current needed to select type of RCD, but it is not suitable for what you want, the plug in monitor is.

 

[Harry Bloomfield]

I love my clamp meter it does what I want current AC and DC down to 0.001 amp so I can see what the earth leakage is, and the DC injected current needed to select type of RCD, but it is not suitable for what you want, the plug in monitor is.

I have an identical item, but I have never thought to test it for use as a reliable peak starting current monitor - I wouldn't really expect it to respond quick enough for that.

 

[Harry Bloomfield]

Which one is the absorbtion fridge, which one do i have?

Absorption fridges use some form of heat, to provide the cooling - heat from a gas flame, or an electric heating element. Many decades ago, mains gas powered fridges were quite popular, now the only absorption fridges I am aware of are the type used in caravans, and motorhomes.

The latter are usually able to run on 230v mains, or 12v - using a heating element, or via a propane/butane gas flame. Absorption fridges are very expensive to buy, and very inefficient to run, in regard to energy consumption, only worthwhile where there are no other options.