280V motor on 230V circuit



Each mag has its own waveguide with a rotating antenna at the end that extends into the oven cavity. 2 of the waveguides are at the top of the cavity firing down and the third is at the bottom firing up. The HV transformer primaries are wired so that the top 2 mags fire on the positive alternation of the AC sine wave and the bottom mag fires on the negative alternation. The top 2 antennas are driven by a single timer motor with large plastic gears (complete with timing marks) so that they both are pointing the same direction at all times as they rotate. The HV transformers have tapped primaries so that the oven can operate on either 208 or 230 volts with no change in output power. Also there is a small 208-230 volt boost autotransformer that boosts the voltage for the cavity lamp, cooling blower, and antenna motors when the oven is plugged in to 208. When the microwave is first plugged in it sits for about 30 seconds to (I assume) to sense the supplied voltage and frequency so that it uses the correct taps on the 4 transformers. Oh yeah when the oven is set for less than 100% power the HV transformers are cycled on and off by 3 triacs (1 each) with arc snubbers across them and there is a relay that cuts the power to the triac/transformer circuits when the oven is off. Each mag has 2 thermal cutouts, 3 cut off the power to the respective transformer primary and the other 3 are wired in series and are connected to the logic board which makes the vacuum fluorescent display show HOT and also causes the oven to refuse to operate. There is also a thermal fuse in the oven cavity air discharge duct.
I think I have provided WAY more info than anybody wanted or needed.
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On Thu, 19 Jun 2008 03:38:43 GMT, "Daniel Who Wants to Know"

Perhaps more info, but intersting info, and appreciated. <g>
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In my other post I forgot to mention that Sam already has most of what I wrote posted on his site somewhere as I sent him the details awhile back.
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In alt.engineering.electrical Daniel Who Wants to Know
| Yes like my Amana commercial RadarRange which is 4KW in 2.2KW out and has 3 | HV magnetrons along with 3 each of the other necessary items (cap, diode, | etc.). It even has a current transformer that tells the control board via | current draw when the magnetrons are warmed up so that the timer doesn't | start counting down until it is actually cooking. It has a standard NEMA | 6-20 plug on it now and will pop a bag of popcorn in roughly 75 seconds | without scorching it. I can tell you it sure beats the hell out of regular | microwave ovens for most things. The only thing I still use the regular one | for are items that involve liquids as the Amana tends to make them either | boil over or boils out all of the water before the food is cooked.
Will it operate on single phase power, like I have in my home?
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wrote:

Considering a NEMA 6-20 plug only has the 2 hot prongs plus ground and the cord is a 14-3 AWG with one conductor being ground, yes it is single phase. :-)
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In alt.engineering.electrical Daniel Who Wants to Know
| wrote: |> |> | Yes like my Amana commercial RadarRange which is 4KW in 2.2KW out and |> has 3 |> | HV magnetrons along with 3 each of the other necessary items (cap, |> diode, |> | etc.). It even has a current transformer that tells the control board |> via |> | current draw when the magnetrons are warmed up so that the timer doesn't |> | start counting down until it is actually cooking. It has a standard |> NEMA |> | 6-20 plug on it now and will pop a bag of popcorn in roughly 75 seconds |> | without scorching it. I can tell you it sure beats the hell out of |> regular |> | microwave ovens for most things. The only thing I still use the regular |> one |> | for are items that involve liquids as the Amana tends to make them |> either |> | boil over or boils out all of the water before the food is cooked. |> |> Will it operate on single phase power, like I have in my home? |> | | Considering a NEMA 6-20 plug only has the 2 hot prongs plus ground and the | cord is a 14-3 AWG with one conductor being ground, yes it is single phase.
Don't be so quick to jump to conclusions. The NEMA 6-XX series gets used for both the 208 volt 120 degree and the 240 volt 180 degree 2-wire connections. Some devices work on one and not the other. You CAN derive three phase from one and not the other. A motor could be wired to use that angular difference (with the neutral) to achieve a motor starting direction instead of having a capacitor to change the angle on a shaded pole.
Also, if the supply is 208 volts then the maximum power available is 4157 watts (3326 under the 80% rule), whereas with 240 volts it is 4800 (3840 under 80%).
240 volts is a 15.47% increase over 208 volts. 277 volts is a 15.47% increase over 240 volts. Can either of those be substituted for 240 volts easily?
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In this specific application the third prong is used only as a chassis ground connection as everything including the light bulb is 230V. Also I am no expert here but I think intermittent loads can exceed the 80% rule hence the 14 gauge cord which would normally only be good for 15 amps but is protected by a 20 amp fuse inside the oven and a 20 amp double pole circuit breaker in the service panel. The NM-B (Romex) I used is 12-3 with ground and has the white neutral conductor simply capped but not connected at either end.
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Daniel Who Wants to Know wrote: >

. The US NEC allows about any cord of 2 conductors (not including ground) to be used at 18A. Most (all?) cords with type starting H (hard use) can be used at 20A.
The 80% rule is for continuous loads - over 3 hours.
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| Daniel Who Wants to Know wrote: | > |> Also I am |> no expert here but I think intermittent loads can exceed the 80% rule hence |> the 14 gauge cord which would normally only be good for 15 amps but is |> protected by a 20 amp fuse inside the oven and a 20 amp double pole circuit |> breaker in the service panel. | . | The US NEC allows about any cord of 2 conductors (not including ground) | to be used at 18A. Most (all?) cords with type starting H (hard use) can | be used at 20A. | | The 80% rule is for continuous loads - over 3 hours.
Like a computer?
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"for short period and with limited lenght"

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A. K. SEPUT wrote:

. I see neither limitation in the US NEC. .

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Correct. #14 is the same as Europe's 4 mm^2-which we usually use here in Greece for the regular, 4 kW hot water heaters. It's rated for 20 A continuous duty when in a conduit with 1 live conductor (IIRC), we don't have extensions in that gauge. We usually protect it with an 20 A circuit breaker (single pole, aka automatic fuse) and a double pole circuit breaker (aka switch) which is not automatic, just to turn on off the water heater. There are 3kW heating elements, too, for older installations, which are quite incapable of sustaining a 4kW load.
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A Lucas snowblower? It would leak oil, not work when damp, and plow down the wrong side of the driveway...
And want 50Hz...
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Still thinking of the British Rail trains that wouldn't work because (to quote their PIO) "It was the wrong kind of snow"?

They'd be drooling over 60 Hz.
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Yes the inability to go to the nearest WallyWorld and buy a 240V 4kW cooker/microwave/whatever is a big problem. European appliance could be got, but I'd worry about anything with a motor (50 Hz), clock (do their electronic clocks operate off the line frequency like some in the US?), microwaves (don't they use frequency-dependent constant voltage transformers?).
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wrote:
|
| |>>| I envy EU houses. If we had regular 240V/30A+ outlets, I'd be able to
| |>>So put one in. | |>The issue is not the outlets available in my house [but I sometimes wish |>for 3 phase..]. | |>Rather, it's the ready market of consumer appliances that would take |>advantage of them. That would require many houses to have them. | | Yes the inability to go to the nearest WallyWorld and buy a 240V 4kW | cooker/microwave/whatever is a big problem. European appliance could be | got, but I'd worry about anything with a motor (50 Hz), clock (do their | electronic clocks operate off the line frequency like some in the US?), | microwaves (don't they use frequency-dependent constant voltage | transformers?).
It's all chicken and egg.
People don't usually go to the added expense of installing a 240V outlet when there are hardly any (and none at WallyWorld) 240V appliances.
Appliances are not generally made at power levels requiring 240V, at least for homes, because there is nowhere to plug it in by default.
BTW, one appliance I am interested in is an electric induction wok. Normally a wok just doesn't work right used over an electric burner surface. So most wok cooktops are gas based. However, the induction technology with the right kind of work actually does work fine on electric power. The catch is it needs a lot of power. Only the smallest version can run on 120V. All the rest need 240V. Here is the smallest 240V version:
http://www.selectappliance.com/exec/ce-product/ck_mwg-2500
And from this, it indicates world plug options for the 240V versions, which suggests to me the lowest wattage unit isn't marketed outside of 120V parts of the world (and hence is probably considered a wimpy model intended to at least work where 240V isn't available).
http://cooktek.com/product_info.php?c=3&s $&p
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snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) writes:

I don't know if microwave ovens still use ferroresonant transformer supplies. I'd heard that they'd moved to switchers but have not worked on any with same. It would make sense: good transformer iron & copper ain't cheap... and a switcher would also save shipping weight.
And yes, the clock would run fast.
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Some use switchers, they'll be much lighter and say "Inverter" prominently on the front of the unit.
I've never seen one with a ferro-resonant transformer. They use a standard laminated core power transformer with a pair of magnetic shunts to regulate the current. Every one that I've ever worked on has exactly the same circuit, 2KV RMS transformer feeds a charge pump doubler consisting of a diode and capacitor, feeding 4KV pulsed DC to the magnetron. Heater voltage is obtained from a tap at one end of the secondary, usually physically it's several turns of much heavier wire next to the HV winding wired in series with it.
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[Johnny Carson voice] "I did not know that...."
All I've ever had to a u-w power supply was to replace the rectifier stack; or junk the oven because it was clearly smoked...
Someone one mentioned they were F-R, and a casual look seemed to confirm that, so I never questioned it. A F-R is also current limited; short the output and it delivers rated current, period..
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Never seen an FR uwave. :) Why would they use that when the basic circuit is adequate and reliable (more or less!)?
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