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uWave ovens, was: 280V motor on 230V circuit
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uWave ovens, was: 280V motor on 230V circuit
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. 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. |
uWave ovens, was: 280V motor on 230V circuit
James Sweet writes:
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. [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.. -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
uWave ovens, was: 280V motor on 230V circuit
David Lesher writes:
James Sweet writes: 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. [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.. Never seen an FR uwave. :) Why would they use that when the basic circuit is adequate and reliable (more or less!)? --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
uWave ovens, was: 280V motor on 230V circuit
Sam Goldwasser wrote:
Never seen an FR uwave. :) Why would they use that when the basic circuit is adequate and reliable (more or less!)? Mostly less! :-) My Panasonic inverter unit just released the magic smoke. First the magenetron died, and then after I replaced that, an IGBT in the switcher shorted and did a fair bit of collateral damage. I finally did find a service manual...in spanish (which I read poorly,) but it did at least tell me what all the small resistors and diodes were supposed to be (before they melted.) So, $100 in parts later, I now have a working microwave again. And, if I get tired of it, I can sell it on Craigslist for at least $35! :-/ |
uWave ovens, was: 280V motor on 230V circuit
On Thu, 29 May 2008 22:19:09 +0000 (UTC), David Lesher
wrote: 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.. The transformer goes by several names, depending on where you are. Variable reluctance, leakage flux, stray flux, etc. It is exactly the same construction and operating principle as a neon transformer, some kinds of HID light ballasts and some series streetlight constant current transformers. The core is an almost standard "E" core (or "H" core if you prefer) with one exception. The center leg has an air gap. The windings are on the end legs of the "E" instead of the center leg. There are two magnetic paths around the core for the field set up by the primary to travel. Around the periphery and across the secondary and around the center leg and across the air gap. Field that travels along the center leg does not cross the secondary and induces no voltage. With no load applied, the bulk of the field travels the peripheral, very much lower reluctance solid iron path, inducing full secondary voltage proportional to the turns ratio. As current flows in the secondary, counter-MMF raises the reluctance of the peripheral path so that some of the flux travels through the center leg. With less flux traveling around the periphery and cutting across the secondary, the secondary voltage drops as the current remains about the same. At the limit, if the secondary is shorted, the peripheral path has so much reluctance that most of the flux travels the center leg and across the air gap. The same current as before flows through the secondary but at zero volts. When the dimensions of the core and gap are set up correctly, the transformer behaves as an almost perfect constant current device. That is, the secondary voltage varies as necessary to keep the same current flowing through a varying load. Just what the doctor ordered to keep the magnetron happy. The secondary current can be increased by opening up the air gap. This raises the reluctance of that path and forces more field through the secondary leg. Closing the gap has the opposite effect. The center leg is often called the magnetic shunt and frequently it is a separate piece of laminated iron stuck between the coils and TIG welded in place. It is a common trick for Tesla Coilers to open up a neon transformer and either knock out the shunt entirely or grind it down to open the air gap. This modification causes the transformer to output much more current than it is designed for - for a little while, at least :-) The same thing works with microwave oven transformers (MOT). This design in a microwave oven is a vital part of keeping the magnetron anode current within spec. The magnetron is electrically a diode. A diode that isn't emission-limited would draw destructive current if not externally limited. With this design, the filament can be heated good and hot for long life and not have the tube run away. The design also is vital for protecting the magnetron from potentially damaging conditions such as operating the oven empty, arcing, etc. It's popular to use several MOTs to build an arc welder. This works quite well specifically because these transformers are constant-current devices - exactly the characteristic stick welding needs. If they were conventional transformers, the first time the rod touched the work and shorted the secondary, fault current would flow and the breaker would trip or blue smoke would leak out. Along similar lines, one can cut off the high voltage secondary and replace it with a suitable number of turns of heavy wire, connect a bridge rectifier and have a nice constant current battery charger. Select the turns carefully and it'll do the bulk/absorption stages of the smart 3 stage charging algorithm. John -- John De Armond See my website for my current email address http://www.neon-john.com http://www.johndearmond.com -- best little blog on the net! Tellico Plains, Occupied TN In theory, there is no difference between theory and practice. In practice, there is. |
uWave ovens, was: 280V motor on 230V circuit
(Fiat Sparks) writes:
Sam Goldwasser wrote: Never seen an FR uwave. :) Why would they use that when the basic circuit is adequate and reliable (more or less!)? Mostly less! :-) My Panasonic inverter unit just released the magic Sorry, I was referring mostly to the normal transformer/capacitor/diode circuit. :) smoke. First the magenetron died, and then after I replaced that, an IGBT in the switcher shorted and did a fair bit of collateral damage. I finally did find a service manual...in spanish (which I read poorly,) but it did at least tell me what all the small resistors and diodes were supposed to be (before they melted.) So, $100 in parts later, I now have a working microwave again. And, if I get tired of it, I can sell it on Craigslist for at least $35! :-/ :) --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
280V motor on 230V circuit
David Lesher writes:
(Michael Moroney) writes: I also asked about tap changers/regulators. Is this what these are, and if so, are they likely to be manual or automatic? http://tinyurl.com/534ffq (Google Maps street view of a set of 3 on a pole in upstate NY. You may have to click on street view and rotate to see them) Yes. Note the primaries are broken by insulators, and there is no secondary [240/120] service on the pole. [The lowest run is TV coax, then neutral above it.] I've never heard of such as manual regulators so I assume they are automatic. Earlier in this thread it was mentioned the automatic ones are expensive and only used for big substations, not for long runs of distribution systems like that one. Before I read that I assumed they must be automatic. It's somewhat unusual to see all three on one pole; it must be a BIG one. Generally I see them staggered on 3 adjacent poles; or two poles hold a platform between them. At that location there used to be 2 adjacent poles with 3 transformers on a platform between them, when the downstream was an older delta- connected system. I bet they just reused one of the heavy duty poles. I wonder why they simply didn't reuse the platform setup. I wonder what each of those puppies weigh, and how many MVA they can handle. |
280V motor on 230V circuit
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uWave ovens, was: 280V motor on 230V circuit
David Lesher writes:
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.. They look similar. Both transformers have magnetic shunts, and there's a big capacitor near the transformer. But the circuits are different. The FR transformer puts the capacitor across the secondary winding, or two secondary windings in series, and the windings plus capacitor resonate at the designed line frequency. This causes the voltage to rise above what you'd expect from the turns ratio alone, but the voltage is limited by the portion of the core that the secondary is wound on going into saturation. Sometimes the secondary voltage waveform looks pretty square because of this peak clipping, but sometimes there's a third winding that (somehow) reduces the second harmonic and gives something closer to a sine wave. There's a magnetic shunt between the primary and secondary windings so that the primary current doesn't go through the roof when the iron in the secondary saturates. It limits the shorted output current to about *twice* the rated current, not equal to the rated current. Still, the FR transformer runs hot with no load, dissipating about 20% of its full output rating as heat. In comparison, the capacitor in the microwave is wired as part of a voltage doubler; it doesn't resonate with the transformer secondary. The transformer iron is not designed to saturate (though, as an intermittent-duty transformer that is fan-cooled in use, it is apparently designed to operate close to saturation to minimize the amount of iron). Dave |
uWave ovens, was: 280V motor on 230V circuit
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uWave ovens, was: 280V motor on 230V circuit
Neon John wrote:
see originsl post It's popular to use several MOTs to build an arc welder. This works quite well specifically because these transformers are constant-current devices - exactly the characteristic stick welding needs. If they were conventional transformers, the first time the rod touched the work and shorted the secondary, fault current would flow and the breaker would trip or blue smoke would leak out. Along similar lines, one can cut off the high voltage secondary and replace it with a suitable number of turns of heavy wire, connect a bridge rectifier and have a nice constant current battery charger. Select the turns carefully and it'll do the bulk/absorption stages of the smart 3 stage charging algorithm. Another use for defunct MOT's, even those with a bad HV winding, is using two as a line isolation transformer. Just remove the HV winding, and connect the two magnetron heater windings together. The normal line winding on the second transformer then supplies your workbench with power isolated from the line. (You might need to modify the "shunt" core.) With a Variac on the input, this is a handy for working on line operated devices that might have a line-to-chassis defect. -- Virg Wall |
uWave ovens, was: 280V motor on 230V circuit
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uWave ovens, was: 280V motor on 230V circuit
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280V motor on 230V circuit
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uWave ovens, was: 280V motor on 230V circuit
VWWall writes:
Neon John wrote: see originsl post It's popular to use several MOTs to build an arc welder. This works quite well specifically because these transformers are constant-current devices - exactly the characteristic stick welding needs. If they were conventional transformers, the first time the rod touched the work and shorted the secondary, fault current would flow and the breaker would trip or blue smoke would leak out. Along similar lines, one can cut off the high voltage secondary and replace it with a suitable number of turns of heavy wire, connect a bridge rectifier and have a nice constant current battery charger. Select the turns carefully and it'll do the bulk/absorption stages of the smart 3 stage charging algorithm. Another use for defunct MOT's, even those with a bad HV winding, is using two as a line isolation transformer. Just remove the HV winding, and connect the two magnetron heater windings together. The normal line winding on the second transformer then supplies your workbench with power isolated from the line. (You might need to modify the "shunt" core.) With a Variac on the input, this is a handy for working on line operated devices that might have a line-to-chassis defect. Do you actually use a setup like that? I'd think that for any sort of current, the filament windings would be melting down even though they are made of fat wire. For example, at 300 VA of output, you're looking at ~100 A in the filament winding. --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
uWave ovens, was: 280V motor on 230V circuit
With a Variac on the input, this is a handy for working on line operated devices that might have a line-to-chassis defect. Do you actually use a setup like that? I'd think that for any sort of current, the filament windings would be melting down even though they are made of fat wire. For example, at 300 VA of output, you're looking at ~100 A in the filament winding. Connecting the HV windings together would probably work a lot better. Would want to knock out the magnetic shunts too, that can be tricky but I've done it on several without damaging the windings. |
uWave ovens, was: 280V motor on 230V circuit
James Sweet wrote in news:HT%%j.670$BV.298
@trndny05: With a Variac on the input, this is a handy for working on line operated devices that might have a line-to-chassis defect. Do you actually use a setup like that? I'd think that for any sort of current, the filament windings would be melting down even though they are made of fat wire. For example, at 300 VA of output, you're looking at ~100 A in the filament winding. Connecting the HV windings together would probably work a lot better. Would want to knock out the magnetic shunts too, that can be tricky but I've done it on several without damaging the windings. I wanted some heavy copper wire to wind a coil with so I tore xxxx started to tear up an old microwave transformer. Found out that pretty copper wire was aluminum with a copper colored layer on top of it. :( -- bz 73 de N5BZ k please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. remove ch100-5 to avoid spam trap |
280V motor on 230V circuit
Ο "danny burstein" έγραψε στο μήνυμα ... In writes: In alt.engineering.electrical Tzortzakakis Dimitrios wrote: | A shame that Tesla won the infamous "battle" and we don't have DC:-() But | then, we would be having a power plant at each neighborhood, instead of the | 300 MW ones. And the latter make easy terrorism targets, too. And so does that 20 gallons of gasoline parked in front of your house. And that 500 gallons of diesel fuel in your basment. And that 20,000 or so gallons in the nearby gas station. Good that terrorists are brain-washed lunatics, and haven't access to incendiary rounds:-) Yawn. -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr -- __________________________________________________ ___ Knowledge may be power, but communications is the key [to foil spammers, my address has been double rot-13 encoded] |
280V motor on 230V circuit
Ο έγραψε στο μήνυμα ... In alt.engineering.electrical Tzortzakakis Dimitrios wrote: | ? ?????? ??? ?????? | ... | In alt.engineering.electrical Tzortzakakis Dimitrios | wrote: | | | Professional washing machines. One of my very first days 'in the field' | was | | to connect some of them. They have a large heating element, you can | connect | | it single phase, or 3 phase, it just heats up faster (of course) when | you | | connect it 3 phase. (they have a single phase motor, so it works also in | | pure 230 V). | | If it has 3 elements rated for 230 volts, with 3 separate connections that | would be to three separate phase for a three phase feed, and all connected | to the one phase for a single phase feed, then it should heat up at the | same | speed, while drawing three times the current (not accounting for the | motor). | | I don't know why it should heat up faster in three phase, or why you would | say "of course" about it. I would think it would heat up faster if you | took | it over to London and hooked it up to a 240 volt supply. | | Maybe you connected with single phase just one element? The rest two | remained unconnected? (3 230 volts elements, connected wye). I'm sure it | heated up faster, in 3 phase connection. You were the one who said "it just heats up faster (of course) when you connect it 3 phase." I would disagree. But the fact that you said "(of course)" seems you presume that to be the general case. Now your most recent comment at least acknowledges that if not all elements are connected, it won't heat up as fast. In the simple case, each of 3 elements is individually wired, so you have a total of 6 leads. When connecting to three phase, one lead of each is connected to neutral, and each of the other leads is connected to separate phases. When connecting to single phase, they are all wired in parallel. Both cases always involve one of the leads from each element connected to neutral, so those 3 leads can be pre-connected together. So you could have just 4 leads. The common neutral lead needs to be rated for all the current together for it to be rated properly for single phase. It should apply the same voltage (230V) to each element, and they should each draw the same current. How would you believe this would be slower to heat? If the 3 elements were wired _internally_ in star without a neutral lead, it would still work fine on three phase as long as all elements were equal impedance. But on single phase, you could only activate 2 of the elements, and that would be 2 in series fed with 230 volts. You'd only get 1/6 the power that way. Are you assuming the elements would be wired that way? That would clearly NOT be intended for single phase connection. The 3 elements could be wired _internally_ in delta. In this case, these would have to be 400V elements. Connecting 2 leads to 230 volts would still give you only 1/6 the power (but more evenly distributed in this case). So what is the situation that makes _you_ believe that 3 elements connected to single phase _will_ draw less power to heat the water than when connected to three phase? I have no idea, we didn't even open up the washing machines as they were under guarantee. I know that the landlady's electrician connected the wms single phase, and I connected (in the distr.box) all 3 phases. I suppose it has 3 elements connected wye, and single phase is 1 element, plus motor and automation. -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr |
280V motor on 230V circuit
? "James Sweet" ?????? ??? ?????? news:HKnVj.128$6D1.49@trndny02... The central air kicks on without my lights dimming, and I am in North Central Florica. Mine dim slightly for an instant when my 3 ton heat pump kicks in, it's only noticeable with the few incandescent lights left in the house though. The LRA on that thing is something like 90A. I think most of the drop must be in the 50' or so of 2/0 AL wire between the meter base and the transformer though as they don't seem to dim at all from any of the neighbors. That's because you have no bloody wind-turbines on your grid. We have here, and I had to include them in my thesis, and these things seriously harm the voltage quality in interconnected grids. In stand-alone residence installations, they work ok, probably with photovoltaics, but here they are a disaster, in whole Crete all the lights flicker every evening when the bloody wing stalls them and they convert momentarily from generating to motors. I prefer old-fashioned fossil-fuel fired power plants, after all smoking chimneys is a token of peace:-) -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr |
280V motor on 230V circuit
Tzortzakakis Dimitrios wrote: That's because you have no bloody wind-turbines on your grid. We have here, and I had to include them in my thesis, and these things seriously harm the voltage quality in interconnected grids. In stand-alone residence installations, they work ok, probably with photovoltaics, but here they are a disaster, in whole Crete all the lights flicker every evening when the bloody wing stalls them and they convert momentarily from generating to motors. I prefer old-fashioned fossil-fuel fired power plants, after all smoking chimneys is a token of peace:-) You need to move your politicians closer to the turbines, to maintain a higher efficiency. This detail os often overlooked in this type of installation. ;-) -- http://improve-usenet.org/index.html If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm Sporadic E is the Earth's aluminum foil beanie for the 'global warming' sheep. |
280V motor on 230V circuit
wrote in message
... 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. :-) |
280V motor on 230V circuit
"msg" wrote in message
ernet... Daniel Who Wants to Know wrote: snip 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.). Does this oven somehow injection-lock the magnetrons? Can you describe the (RF) plumbing? Michael 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. |
280V motor on 230V circuit
"msg" wrote in message
ernet... Daniel Who Wants to Know wrote: snip 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.). Does this oven somehow injection-lock the magnetrons? Can you describe the (RF) plumbing? Michael 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. |
280V motor on 230V circuit
On Thu, 19 Jun 2008 03:38:43 GMT, "Daniel Who Wants to Know"
wrote: 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. Perhaps more info, but intersting info, and appreciated. g |
280V motor on 230V circuit
In alt.engineering.electrical Daniel Who Wants to Know wrote:
| wrote in message | ... | 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? -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
wrote in message
... 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? -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | 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. |
280V motor on 230V circuit
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. -- bud-- |
280V motor on 230V circuit
In alt.engineering.electrical bud-- wrote:
| 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? -- |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance | | by the abuse department, bellsouth.net is blocked. If you post to | | Usenet from these places, find another Usenet provider ASAP. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |
280V motor on 230V circuit
"bud--" wrote in message .. . 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. "for short period and with limited lenght" The 80% rule is for continuous loads - over 3 hours. -- bud-- |
280V motor on 230V circuit
A. K. SEPUT wrote:
"bud--" wrote in message .. . 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. "for short period and with limited lenght" .. I see neither limitation in the US NEC. .. The 80% rule is for continuous loads - over 3 hours. -- bud-- |
280V motor on 230V circuit
? "bud--" ?????? ??? ?????? ... A. K. SEPUT wrote: "bud--" wrote in message .. . 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. "for short period and with limited lenght" . I see neither limitation in the US NEC. . The 80% rule is for continuous loads - over 3 hours. -- 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. -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr |
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