My wife thinks that our 10 year old 800w microwave is losing it’s power so I put a cup inside with 250ml of water and ran it for 1 minute and the temperature of the water raised 28.5C. According to my calculations this means that it has delivered 7125 calories in one minute or 427,500 cals/hour.
Now it says 800W on the front of the machine so that is equivalent to 800 joules/sec or (dividing by 4.2) 192 cals/sec or 685,714 cals per hour.
On this basis the microwave oven is delivering only 62% of it’s rated power. However I am assuming that the 800w stamped on the front is the actual microwave power deliverable. Any comments or suggestions before I have to shell out for a new one? 3 x FL1 2 manual + 1 auto
5 x FL2 4 manual + 1 auto
Now Discovery Sport P250 MHEV SE

Yes your wife's micro wave does lose power over time/use.

This is due to the magnetron tube weakening on each used.

Depending on use, a good manufactures magnetron should last 8-10yrs.

PS. if you do scrap it, take out the magnets, as they are very powerful and have many uses
.At your own risk

Stop messing around and buy a new one. You could make it a delayed/anticipated birthday present. 11 GS Bali Blue
07 GS FL2. Usually muddy. Gone
Numerous LRs since 1963

All good wives deserve a new microwave, especially today, which is International Womens Day.

Not to forget to read the specs on the back of the microwave, it uses a lot more than printed on the front!

We haven't used a microwave for about 15 years. Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 3xARB air compressors After cooler Air tank On-board OCD pressure air/water cleaning Additional 50L fuel Carpet in doors ABE 2x1kg Waeco 28L modified fridge Battery 4x26ah Solar 120w Victron MPPT 100/20 DC-DC 18amps 175amp jumper plug Awning 6x255/60R18

If the 800w figure printed on the front is its input power, then I would think 600w actual microwave power would be expected.

From what I remember 65-75% is about the normal efficiency, the rest is emitted as heat and other radiations including X-rays.

Please bear in mind that my experience is in high powered military radar (a long time ago), and not cooking microwaves, but perhaps some things never change.

PS I have just dug out my original course notes from 1959. The quoted efficiencies (then) were between 30 and 60%.
These notes refer to high powered pulsed use.

From google, modern microwave magnetrons are about 65% efficient.

https://www.google.co.uk/search?sxsrf=ALeK...2s6sVH62NQ FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 77k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Last edited by IanMetro on 8th Mar 2020 11:14 pm. Edited 1 time in total

My .02 Cdn, appliances/electronics made today have a short lifespan. While they are likely more energy efficient, they simple don't last. If it ain't broke, ................

Our unused microwave 900w output 1400w input. I am sure a new one is a lot more efficient. Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 3xARB air compressors After cooler Air tank On-board OCD pressure air/water cleaning Additional 50L fuel Carpet in doors ABE 2x1kg Waeco 28L modified fridge Battery 4x26ah Solar 120w Victron MPPT 100/20 DC-DC 18amps 175amp jumper plug Awning 6x255/60R18

Using

watts = (temperature rise X specific heat capacity X mass) / time

Where temperature rise in C
specific heat capacity = 4200
mass is in Kgs
time in seconds

W = (28.5 x 4200 x 0.25) / 60 = 499

So yes the microwave has lost efficiency, a lot, they do over time.
So you have two options, buy a cheap one if you just use it a full power.
Buy an inverter model if you use it for defrosting, and at lower powers.

The cheap ones only ever run at two powers, flat out or none.
So for 25% power it might be on for 5 seconds, and off for 15 seconds, great if it's on for several minutes, rubbish if it's on for less than a minute as you can only guess what the actual energy is. Tangiers Orange - gone, missing her
Replaced by Ewok what a mistake - now a happy Disco Sport owner

Sharp Carousel II. 1984 - 2003 Faultless until turntable drive failed and parts were long obsolete

Panasonic Inverter. 2003 - Present. Faultless as well, Magnetron changed in 2010, still going strong

The modern magnetron is a fairly efficient device. In a microwave oven, for instance, a 1.1-kilowatt input will generally create about 700 watts of microwave power, an efficiency of around 65%. (The high-voltage and the properties of the cathode determine the power of a magnetron.)

https://www.google.co.uk/search?sxsrf=ALeK...2s6sVH62NQ

We have a Sharp R959SLMAA Combi Microwave Oven. We use no other oven and are very pleased.
The turntable/oven size is quite large, and it does various combinations of Grill/Oven/Microwave. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 77k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Scrap the wife and live on takeaways delivered, it will definitely work out cheaper
Only kidding If you want to rob a bank buy a shotgun if you want to rob people buy a bank.

I seriously believe it is the way forward.

We shop on-line, delivered to our home.
We eat on-line , delivered to our home.
we don't need to go out, of our home.

They call it self-isolation !!

It might be self isolation but I can lock the wife in one unit and me in the other so I will survive the lock down! With all the quarantining there is going to be a jump in divorces, murders and suicides! Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 3xARB air compressors After cooler Air tank On-board OCD pressure air/water cleaning Additional 50L fuel Carpet in doors ABE 2x1kg Waeco 28L modified fridge Battery 4x26ah Solar 120w Victron MPPT 100/20 DC-DC 18amps 175amp jumper plug Awning 6x255/60R18

Just use Talaq.

No one dies, no one goes to prison.
simples.