Our Panasonic microwave is about a year and half old. Its ability to heat things has dropped off by about 50%. We wonder since we now have to have it on for twice as long, does this in fact mean it uses twice as much electricity? Or since it's at half rate power, does it also use half the electricity at any given moment? In other words might it pay to buy a new one, since it could be *costing extra* to use, due to what might be inefficiency somewhere?
Unfortunately, some Microwaves use cheap Magnetrons which do lose output. It is probably still using the same as before to do half the work. Radar systems suffer from this as well, and you need to send back the magnetron to the makers to have it refurbished. I doubt the likes of toshiba or Hitachi off er that service. Of course it could be that the drop in power is due to the control circuitry being faulty or indeed the system now being more prone to the vswr mismatches.
Was it an expensive one? I bought an expensive one and its been very stable in the heating department. It just shuts off if its unhappy with the vswr.
That presumably protects the magnetron from damage from reflected RF. Most machines these days tend to not have power settings, just duty cycle controllers, ie the power is on for some time, then off for some time to allow the thermal transit through the food. It would take some big controllers to vary the power output even if it could be done. some magnetrons just go and stop with no control at all. Brian
Loss of magnetron output is down to loss of emission. That means the anode, which consumes most of the power, is only taking half the current. Filamen t power & other parasitics stay the same, but are a very small percentage o nly. So its lost close to zero electrical efficiency.
I don't know how practical is is to add another turn on the transformer to boost the emission. It certainly works well with almost all valve-like devi ces. I'd measure Vf first, nuke transformers put out very high volts per tu rn, so a quarter of a turn might be all that's needed.
NT
Seems like a warranty claim to me. Panasonics often use an inverter power supply to vary the power level so the inverter may be the problem. (magnetron current levels are varied to reduce power.)
Both the first microwave oven I ever owned, a huge beast, and our current standard one, used varying the time that they generated waves as the power is set, so 100% power for differing time periods is what I see.
Perhaps surprisingly magnetrons are widely available for £40-50.
What's a quarter of a turn going to do? No fractional turns, now...
Thomas Prufer
Same with ours. Its a Panny, at least 20, possibly 25 years old and still going strong (Model NE-662/662, 600W max power, one of these
I believe what you snipped addresses that
He's talking about filiment (heater) voltage, not HT. Ever counted the secondary turns of that Weller soldering gun you had in the 70s?
At some point they changed the way output power is calculated, so your
600W oven would be sold as 800W now. Good eh?
Domestic microwave oven transformers run saturated in normal operation, so I wouldn't expect much reduction in primary current as a result of an ageing Magnetron.
I don't know whether it's using more electricity or not - but even if it is, the economics may not be in favour of replacing it.
How much did it cost? How much do you use it? If we assume that it uses
1kW when running and that you use it for 30 minutes per day (which seems a bit excessive unless it's your main way of heating/cooking stuff), you'll use about 180 units p.a. which as (say) 15p per unit will cost about £27. If it's only running at 50% of the proper efficiency, you may be spending £54 on electricity instead. So, if you save £27 p.a.by buying a new one, the pay-back time will depend on the cost of the new one - could be quite a few years if it's an expensive one, or maybe only a year if you buy a Lidl "special".Mind you, if you *do* use it for 30 minutes a day - which has now become an hour - a new one might be worth it in terms of the time you'll save not having to hang around for things to heat up.
Our 40 year old microwave uses magnetron current limiting to vary the power. That way, the food can't boil over on a low setting.
Even so you can't add a 1/4 turn! either the winding passes through the core or it don't
Pah! Hi tech new fangled thing compared to our Toshiba. 35 years old and still going strong. Mechanical timer that goes "ping" just like a proper microwave should. ;-)
Tim
No But the OP does not pay for primary current only real power consumed so less anode current = less cost to run.
Valid point, but it doesn't keep pinging if you missed it the first/only time it did it.
Our old 'beast' of a machine was still working when we gave it to our neighbour in 2010, as we moved home. So it was about 24 years old, not as much as yours.
So what? It picks up mag. field all around the outside as well
In message , john west writes
You can measure the input power using the domestic electricity meter, but of course you need to switch everything else off , or take it into account.
Run it for a minute and see how many kWm it consumes ( or the change in kWm) and see how that stacks up with rated power.
Brian
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