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G4EBT > TECH 23.07.08 11:24l 102 Lines 3789 Bytes #999 (0) @ WW
BID : 678518G4EBT
Read: GUEST OE7FMI
Subj: Testing microwave ovens
Path: DB0FHN<DB0MRW<DB0ERF<DB0FBB<DB0IUZ<DB0GOS<ON0AR<F1ZNR<F4BWT<DK0WUE<
GB7FCR
Sent: 080723/0808Z @:GB7FCR.#16.GBR.EU #:10406 [Blackpool] FBB-7.03a $:678518G4
From: G4EBT@GB7FCR.#16.GBR.EU
To : TECH@WW
Now that just about everything in our homes originates from China, the
price of electronic goods from motherboards to microwave ovens, even in
"rip-off Britain" are so cheap that the cost of repairs almost always
exceeds the cost of a new item.
I'm always dismayed when I take garden rubbish etc to the household waste
centre, to see the huge piles of discarded electronic goods. Everything
from computers to hi-fi to plasma screen TVs and computer monitors and
printers, some probably no more than two or three years old.
In the UK, new microwave ovens typically start from œ30 GBP ($60) upwards.
A call-out charge, or even if you take an item to a repair shop for repair
will be twice that amount, plus parts.
Thus, repairing all but the most expensive models of microwave ovens
out of warranty is a thing of the past. New magnetrons at trade prices
typically start at œ30 ($60) upwards, so a repair is likely to cost
three times that of the cheapest new ovens with labour charges.
That said, back in 1998, when such domestic appliances were being repaired
rather than discarded there was an article in the now defunct TV magazine,
which covered the repair and testing of microwaves.
One aspect which I thought might be of passing interest to a few on here
was that of testing the power output. A magnetrons output can be simply
tested by measuring the temperature rise in degrees C of one Litre of
water over an 87 second period on full power from the magnetron.
(Don't ask me why!).
A magnetron usually reaches full power four secs after the clock button
has been pressed, so the timer should be set for 91 secs. The time lag
between switch-on to the magnetron reaching full power can be determined
by snipping the leads off a small neon lamp close to the pinch seal and
placing it in the oven along with a pot of water. Check the time it takes
to glow brightly, then switch off right away. That duration is the time
lag to full power.
The power output is determined by the temperature rise in degrees C
multiplied by 50.Thus, if there is a 14 degree rise in the temp of
1 Litre of water over an 87 sec period on full power, that equates
to 50 x 14 = 700 Watts.
The oven should be run on full power for more than one minute before
starting the test. Never run an oven without something in it such as
a jug of water.
The starting temperature of the 1 Litre of test water should not be below
17 degrees C, or in "old money" 63 degrees F.
Another test method, claimed to be more accurate, is to use two 500 Ml
beakers of water on full power for 30 secs, then check the temperature
rise of each beaker, take an average of the two readings, and multiply
this by 30.
The formula for this is P = (4.187 x V x temp rise)/t
Where:
P = Power in Watts.
V = Volume of water
t = Temp rise during which the magnetron is on full power.
This test conforms to IEC 705 (1988).
A suitable theme to end on:
Underground, Overground, Wombling Free,
The Wombles of Wimbledon Common are we.
Making good use of the things that we find,
Things that the everyday folks leave behind.
Wombles are organized, work as a team.
Wombles are tidy and Wombles are clean.
Underground, Overground, wombling free,
The Wombles of Wimbledon Common are we!
People don't notice us, they never see,
Under their noses a Womble may be.
We womble by night and we womble by day,
Looking for litter to trundle away.
We're so incredibly, utterly devious
Making the most of everything.
Even bottles and tins.
Pick up the pieces and make them into something new,
Is what we do!
We need more wombles!
Best wishes
David, G4EBT @ GB7FCR
Cottingham, East Yorkshire.
Message timed: 09:07 on 2008-Jul-23
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