The difference you have seen in the past (0.1v difference causing damage in only a few hours) must be somehow different because like i said i've used other microwave ovens at lower than usual voltage for years and they all lasted at least five years.

The device in question was generating in excess of 25 KiloWatts! Ht was 8.6kV, heater 2.4 volts. Hence 0.1 volt was a large pecentage change.

 

The device in question was generating in excess of 25 KiloWatts! Ht was 8.6kV, heater 2.4 volts. Hence 0.1 volt was a large pecentage change.

Hi,

Oh yes ok, that is quite different.
So then the modern microwave ovens could be made differently then, in a couple different ways. Maybe that is why they work even at lower input voltages.

I dont have a definite answer, but i know they last for a reasonable time length.

Just cooked a piece of steak yesterday too with the oven at 500 watts input. Came out reasonable i guess. I can see that part of the evenness of the cooking of the meats is due to the larger cavity of the Panasonic. The oven i am trying now is a smaller one so i turn the meat over more often to get more even cooking. So part of the evenness of the meat cooking seems to come from the lower power and part from the size of the oven cavity. Still the experimenting is in it's early stages so i am still learning how to use this smaller oven as well as possible.

It's been interesting though and at first i wasnt sure if it would work at all to turn the input voltage (and thus power) down very low on a regular modern microwave oven. The one i am working with now is a regular one advertised as having 700 watts of cooking power with 1100 watts input power at 120vac.

 

Hi,

Oh yes ok, that is quite different.
So then the modern microwave ovens could be made differently then, in a couple different ways. Maybe that is why they work even at lower input voltages.

I dont have a definite answer, but i know they last for a reasonable time length.

Just cooked a piece of steak yesterday too with the oven at 500 watts input. Came out reasonable i guess. I can see that part of the evenness of the cooking of the meats is due to the larger cavity of the Panasonic. The oven i am trying now is a smaller one so i turn the meat over more often to get more even cooking. So part of the evenness of the meat cooking seems to come from the lower power and part from the size of the oven cavity. Still the experimenting is in it's early stages so i am still learning how to use this smaller oven as well as possible.

It's been interesting though and at first i wasnt sure if it would work at all to turn the input voltage (and thus power) down very low on a regular modern microwave oven. The one i am working with now is a regular one advertised as having 700 watts of cooking power with 1100 watts input power at 120vac.

As a point of interest, I just looked up my original design specs and the heaters had to be held within +/- 0.15 Volts that's 12.5%

 

From a Sharp training manual "three seconds to the heating time to allow for the magnetron filament to reach the correct temperature."

Power is applied for only one half cycle.

100%-- 27s-- on
70%-----21s--on--6 s off
50%-----15 s-o n--12 s off
30%-------9 s on---18 s off
5% --------5 s on---22 s off

The anode current is controlled primarily by changing the capacitor value.

 

From a Sharp training manual "three seconds to the heating time to allow for the magnetron filament to reach the correct temperature."

Power is applied for only one half cycle.

100%-- 27s-- on
70%-----21s--on--6 s off
50%-----15 s-o n--12 s off
30%-------9 s on---18 s off
5% --------5 s on---22 s off

The anode current is controlled primarily by changing the capacitor value.

Hi,

That's interesting, although i do want to remind readers that i am not turning the heater voltage down and trying to maintain full power, but rather turning the heater voltage down (presumably and coincidentally) and also cutting the total power getting to the magnetron. So although the heater is probably not as hot as it normally would get, the power getting to the tube is lower too so that may be the factor that allowed my ovens in the past to survive all that time.

 

Hello there,

hello it is really a nice experiment ,i was just experimenting this a couple of weeks ago with the same technique ,and i found your idea while searching for some extra research on some of my doubts i got while experimenting,
my transformer input rating(Primary) is actually 220V ,and as you told i got an auto transformer(kind of a variac) lowering this line voltage from 220 up to 0V ,any value you want .i was just experimenting with a cup of water to see the effect of changing the line voltage on the heating and i can nicely observe the the temperature change of the water at any voltage from 160V to 220V,but if i go changing the line voltage below 160V i don't really get a change on the heating ,i just tried for 120V and waited for about 15 minutes to see the heating effect on the cup of water ,but nothing happens ,and i read some references it says as long the current in the secondary is in MA(mili ampere) and that starts when the secondary voltage is almost 2KV which is 4KV after the doubling circuit ,so from this i feel like if am changing the the line voltage below 2KV the current flowing in the secondary will be so small and nothing will go the magnetron anode ,it even stays 0 current in the secondary if the line voltage is small below the rating.so can you please share how it goes for you and suggest if you got some ideas .
thank you for sharing

 

Hi again,
hello it is really a nice experiment ,i was just experimenting this a couple of weeks ago with the same technique ,and i found your idea while searching for some extra research on some of my doubts i got while experimenting,
my transformer input rating(Primary) is actually 220V ,and as you told i got an auto transformer(kind of a variac) lowering this line voltage from 220 up to 0V ,any value you want .i was just experimenting with a cup of water to see the effect of changing the line voltage on the heating and i can nicely observe the the temperature change of the water at any voltage from 160V to 220V,but if i go changing the line voltage below 160V i don't really get a change on the heating ,which means for my case i can only vary from around 75% to 100% of the full power .i just tried for 120V and waited for about 15 minutes to see the heating effect on the cup of water ,but nothing happens ,and i read some references and it says as long the current in the secondary is in MA(mili ampere) and that starts when the secondary voltage is almost 2KV which is 4KV after the doubling circuit ,so from this i feel like if am changing the the line voltage below 2KV the current flowing in the secondary will be so small and nothing will go the magnetron anode ,it even stays 0 current in the secondary if the line voltage is small below the rating.so can you please share how it goes for you and suggest if you got some ideas .
thank you for sharing

 

Hi again,
hello it is really a nice experiment ,i was just experimenting this a couple of weeks ago with the same technique ,and i found your idea while searching for some extra research on some of my doubts i got while experimenting,
my transformer input rating(Primary) is actually 220V ,and as you told i got an auto transformer(kind of a variac) lowering this line voltage from 220 up to 0V ,any value you want .i was just experimenting with a cup of water to see the effect of changing the line voltage on the heating and i can nicely observe the the temperature change of the water at any voltage from 160V to 220V,but if i go changing the line voltage below 160V i don't really get a change on the heating ,which means for my case i can only vary from around 75% to 100% of the full power .i just tried for 120V and waited for about 15 minutes to see the heating effect on the cup of water ,but nothing happens ,and i read some references and it says as long the current in the secondary is in MA(mili ampere) and that starts when the secondary voltage is almost 2KV which is 4KV after the doubling circuit ,so from this i feel like if am changing the the line voltage below 2KV the current flowing in the secondary will be so small and nothing will go the magnetron anode ,it even stays 0 current in the secondary if the line voltage is small below the rating.so can you please share how it goes for you and suggest if you got some ideas .
thank you for sharing

Hi,

Somehow you put all that quote under my quote, which was not from me really but was your reply so i quoted it above.

The problem you are speaking of i think is the "bottom floor" problem where when you go too low in input voltage to the microwave the power goes too low to cook anything, and this point may be reached rather abruptly so that the power drops off fast after some lower voltage level. If i turn down just a little i get just a little power loss, but once i reach a certain point the power drops off fast and so it may take a long time to boil a small cup of water for example or it may only get luke warm at best.
I noticed this with another oven too when the line would go very low in the summer time. The oven would appear to stop cooking altogether although it may have been cooking so slow it was hard to notice any cooking at all.

The other problem is power line natural variation. The line varies a little bit on it's own as the other residents use power and so what we really need is a regulated AC power source which i do not have at present. I just have the variac, and that sets a certain ratio between power line voltage and oven voltage so if the power line goes a little lower (even 1 volt lower) then the oven voltage goes lower too, and that is hard to control without a circuit.
There are some variacs that have a motor control and you can use a circuit to have the variac constantly adjust itself to maintain a constant voltage output, but i dont have that kind and dont really want to have to add that to mine. An AC inverter might work too, where the AC output is regulated. I dont know if i want to be bothered with all that just yet though but maybe in the future some time.