The Naked Scientists

The Naked Scientists Forum

Author Topic: When should you replace a microwave?  (Read 7996 times)

Offline thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • Posts: 511
  • Thanked: 12 times
    • View Profile
When should you replace a microwave?
« on: 07/12/2015 19:50:02 »
Pamela Coates asked the Naked Scientists:
   When should you replace a kitchen microwave unit? Ours is about 14 years old, works fine and has a small rust spot on the plastic frame of the  interior window door. It's a Panasonic the Genius NN-S578WA.
P. S. we love listening to you on Radio National Friday morning here in Perth,  Western Australia.
What do you think?
« Last Edit: 07/12/2015 19:50:02 by _system »


 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4119
  • Thanked: 245 times
    • View Profile
Re: When should you replace a microwave?
« Reply #1 on: 08/12/2015 10:37:01 »
If the door seal is torn, or doesn't sit straight when you close the door, microwaves will leak out. This isn't good for anybody standing nearby, so that is a good reason to replace it. You can buy little detectors that can tell you if microwave energy is escaping around the door (but I don't know if I would trust the calibration very much).

If the fan is making scraping noises, or the rotisserie plate is broken, those are other good reasons to replace it.

Microwaves are so cheap today, that "I don't like the color any more" is often enough reason to replace them.

Otherwise, if it defrosts your dinner, it is working, so keep it!
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4708
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: When should you replace a microwave?
« Reply #2 on: 08/12/2015 14:45:20 »
Given the choice, I would scrap any "domestic" microwave with a rotating plate, and get a commercial one with all-stainless construction  and a "stirrer" (no moving parts visible). Much easier to clean, cooks quicker (usually 1 - 1.5 kW compared with a domestic 800W) and more evenly, and easier to use.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8665
  • Thanked: 42 times
    • View Profile
Re: When should you replace a microwave?
« Reply #3 on: 08/12/2015 21:59:44 »
"When should you replace a microwave?"
Either when it stops working or in the January sales.
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5338
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: When should you replace a microwave?
« Reply #4 on: 08/12/2015 23:08:06 »
"stirrer" (no moving parts visible)

How do these work? i.e. how do microwaves without turntables achieve even heating of food?
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4119
  • Thanked: 245 times
    • View Profile
Re: When should you replace a microwave?
« Reply #5 on: 09/12/2015 08:45:24 »
Quote from: chris
how do microwaves without turntables achieve even heating of food?
There is a device like a fan blade that turns in front of the microwave source.

This deflects the microwaves in different directions around the inside of the microwave, hitting the food from all angles, wherever it is sitting in the microwave cavity.

So instead of having a static microwave beam and move the food, you have static food and you move the microwave beam. In a well-designed system, they will achieve similar results.
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Re: When should you replace a microwave?
« Reply #6 on: 10/12/2015 08:18:17 »
Microwaves will leak out. This isn't good for anybody standing nearby, so that is a good reason to replace it.

What exactly would this do?
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4119
  • Thanked: 245 times
    • View Profile
Re: When should you replace a microwave?
« Reply #7 on: 10/12/2015 10:13:26 »
Quote from: SorryDnoodle
What exactly would (a leaky door seal) do?

The main risk from low-level microwave radiation is from heating.

Most parts of your body have a good blood supply, and will carry away small amounts of excess heat, such as from a leaky door seal.

However, the front of the eye must be transparent, so it has a very poor blood supply; if it heats up it can cause the lens to turn opaque (like boiling an egg). This is called cataracts, a condition mostly seen in the elderly.

See: http://en.wikipedia.org/wiki/Microwave#Effects_on_health
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Re: When should you replace a microwave?
« Reply #8 on: 10/12/2015 18:22:22 »
Nah, microwave ovens essentially never leak any significant amount of microwaves.

The only things you need to be careful of; the hinges must be in good condition, and make sure the door seal is reasonably clean, and makes sure there's no big holes in the metal work. Oh yeah, and the door mechanism that cuts off the oven has to be working- if it doesn't turn off when you open the door- shut it again, and then unplug immediately!!

The physics is fairly benign, a hole smaller than the wavelength blocks the microwaves; you get an evanescent standing wave a few times the hole's diameter outside the oven but beyond that, there's no radiation. That's how you can see through the door, it's got lots of tiny holes in it, and the door has a thickness which is a few times their diameter.

You'd need a gap that is bigger than 9 cm to let the microwaves out.
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4119
  • Thanked: 245 times
    • View Profile
Re: When should you replace a microwave?
« Reply #9 on: 10/12/2015 20:32:45 »
I agree that microwave leakage is normally very low.

Quote from: wolfekeeper
You'd need a gap that is bigger than 9 cm to let the microwaves out.
That is true, but it doesn't mean a 9x9cm gaping hole.

It can be a 1-dimensional gap, 9cm long, eg along the door seal. That's why broken or damaged door seals are a good reason to discard the microwave oven.

As you say, a dirty door seal is a reason to clean it.
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Re: When should you replace a microwave?
« Reply #10 on: 12/12/2015 03:08:26 »
I agree that microwave leakage is normally very low.

Quote from: wolfekeeper
You'd need a gap that is bigger than 9 cm to let the microwaves out.
That is true, but it doesn't mean a 9x9cm gaping hole.

It can be a 1-dimensional gap, 9cm long, eg along the door seal. That's why broken or damaged door seals are a good reason to discard the microwave oven.
Although in theory a thin 9cm long gap would certainly allow one of the polarizations to escape, actually, from the googling I've just done, it looks like there's a sneaky hidden 1/2 wave arrangement around the edge of microwave oven doors, that stops the microwaves escaping, and so a small gap has no significant effect.

Makes a lot of sense if you think about it, if it was as simple as not cleaning the seal properly, virtually all ovens would be leaking like a sieve!
« Last Edit: 12/12/2015 04:16:52 by wolfekeeper »
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4119
  • Thanked: 245 times
    • View Profile
Re: When should you replace a microwave?
« Reply #11 on: 12/12/2015 05:33:15 »
Quote
a sneaky hidden 1/2 wave arrangement around the edge of microwave oven doors
That sounds clever - like a soap bubble of a certain thickness blocks light of a particular wavelength, the microwave door doesn't let through microwaves of the wavelength used by the oven.
 

Offline wolfekeeper

  • Neilep Level Member
  • ******
  • Posts: 1092
  • Thanked: 11 times
    • View Profile
Re: When should you replace a microwave?
« Reply #12 on: 12/12/2015 18:06:02 »
Yeah, I only just found this out, and it explains an observation I made a while back- if you put a cell phone in a microwave oven (with it switched off), and shut the door, and ring it from another phone, it will often ring.

That didn't make sense, how could it be in what was obviously a sealed Faraday cage, and yet still receive the radio signal???

The answer is the door seal, the 1/2 wave trick only works correctly at 2.4 GHz, so the phone signal still enters!!!
 

Online syhprum

  • Neilep Level Member
  • ******
  • Posts: 3819
  • Thanked: 19 times
    • View Profile
Re: When should you replace a microwave?
« Reply #13 on: 12/12/2015 22:26:25 »
One of the possible reasons for replacing a microwave cooker is if the motor that rotates the plate fails.
It is difficult to find a correct motor listed on the internet so one has to guess from pictures of what motors are available, I was lucky but buying unsuitable ones and trying to fit them with the work involved could be a wasteful exercise.
Another reason is if the glass plate is broken but with any luck you might find one thrown away with a suitable plate.
I grew up during the war when everything repairable had to be fixed and the thought of scrapping anything with a minor fault horrifies me.
A better test for the Faraday cage efficiency would be Bluetooth speaker that operates on 2.4GHz 
« Last Edit: 12/12/2015 22:34:26 by syhprum »
 

Offline marthaapodaca83

  • First timers
  • *
  • Posts: 5
    • View Profile
Re: When should you replace a microwave?
« Reply #14 on: 15/01/2016 06:16:00 »
Pamela Coates asked the Naked Scientists:
   When should you replace a kitchen microwave unit? Ours is about 14 years old, works fine and has a small rust spot on the plastic frame of the  interior window door. It's a Panasonic the Genius NN-S578WA.
P. S. we love listening to you on Radio National Friday morning here in Perth,  Western Australia.
What do you think?

Hey, I think the best time to replace any of the electrical appliance is when it stops working and thus you are sure that there is not any other solution which can make you keep working with it.
 

The Naked Scientists Forum

Re: When should you replace a microwave?
« Reply #14 on: 15/01/2016 06:16:00 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums