My $45 homemade 10 HP phase converter is WORKING!!!

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| I do not mind installing an overload relay, as such, except that it is | a cost issue. Fuses are cheaper. (unless I can find something at that | junkyard). Realistically speaking, the idler is not going to bind. If | contacts to capacitors break, yes, I could have a stall issue, which | would be addressed by properly sized fuses. | | A relay is more exciting and possibly a little more convenient (it is | resettable, I do not need to buy new fuses when a fuse burns out), but | in reality will provide about same protection. | | Am I mistaken? |
Your 220V home circuit breaker has two poles, but each pole is connected so that if one leg has an overcurrent, it will trip, taking the other leg out with it. Otherwise, one leg will still be hot, presenting a very ugly hazard. Fuses cannot provide this protection, and as such, are a single shot deal. Overloads, on the other hand, have various trip conditions that can be selected for, and they take all three phases out at the same time, which is the safety you need.. Ask your supplier for assistance in picking them, I don't have that information at hand anymore. While motor starters have the contactor and the overload physically attached to each other, electrically they're pretty much the same so one brand ought to be usable with another even if you can bolt them together. Just for the sake of the record, a motor starter consists of a set of three large contacts, possible auxiliary contacts (usually clipped or screwed) and the overload. The overload has three fuse looking elements that are called heaters. When the heater gets to a certain point in its thermal cycle, it will bend and trip the overload, which actually just opens it's own auxiliary contact and the contactor opens up. The solenoid on the contactor is wired through this overload contact, so in order to reset it you usually have a reset button to push. To add a little more confusing information, starters are given sizes, according to NEMA, thus you have a starter for a given range of motor sizes. http://www.southlandelectric.com/Thermal%20heater%20elements.htm has a lot that info that might help you understand better. The overloads are sized to match as well.
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Thanks. That's very helpful!
i
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Arright, good to hear it.
John
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It looks like you're only using 1 contactor to switch the incoming lines, right? If that's the case, your converter will be imbalanced because, in order to start the RPC motor quickly, you have a large amount of capacitance permanently connected between L1 and L3. The correct way to wire it is using a start contactor to switch a big capacitor between L1 and L3 and have permanently connected smaller capacitors between L1 and L3 and also between L2 and L3 to balance the converter. I also agree with the other posters, use a No Volts Release circuit using a start and stop button and the spare or auxiliary contact on the main contactor to hold it in. Well done on getting the parts so cheap, those caps must be worth $40 a piece. Martin
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martin<dot here>whybrow<at here>ntlworld<dot here>com




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wrote:

yes.
the voltages between lines were 255V (utility power), 240V, and 259 V (IIRC). That's acceptable.

I will follow your advice regarding start and stop button. The guy selling these caps to me did not know what they were. That could explain things.
i
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Is there any way that I can rig up a phase converter such as shown below, and attach another power source (read gas or diesel engine) to the actual rotor, and come out with quality 3 phase eclectic power of 60 Hz?
thanks

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The amount of current that an induction motor draws depends on the amount of power being produced. A motor that has no load does not draw nearly as much current as one producing the horsepower listed on the nameplate. The neat thing is that if you put a little power into the motor it will draw even less current. More power in and the current drawn goes negative......That is the motor is generating electricity.
Note while an induction motor can be made to generate power when it is not hooked to the power grid, it requires some capacitors to do so and will not work well over a wide range of power out. But if one attaches another power source to the rotor and have single phase power connected to two of the wires, it will produce quality 3 phase power of 60 hz ( assuming 60 hz single phase power ). Can even be driven with a single phase electric motor, but must be driven at slightly over the synchronous speed ( 1800 rpm for a 4 pole motor ). So if doing this with a electric motor you need to belt drive and have one of the pulleys adjustable. Then measure the current drawn by the single phase motor and adjust the pulley ratio so that the current drawn by the single phase motor is within its rated nameplate current .
You can also use a induction motor driven with a gas engine to keep the rpms at a constant amount. This is used with the gasolene engines with variable compression ratio used to test octane of gasolene.
Dan
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that would be called a "generator". As far as I know, induction motors are not suitable as generating ends. In a rotary phase converter, the third leg is produced thanks to the magnetic field made by the utility supplied hot leg.
i

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On Fri, 29 Jul 2005 02:48:09 GMT, Ignoramus9394

Actually it is possible with some motors. It may require a short DC pulse to start it off. My understanding is that some motors work better than others in this application. But if you stay within the motors rating it will work (if the motor will generate at all). One key feature of this type of generator is that if you exceed the motors rating it will simply stop generating.
I recently scrapped a welder/generator with this same setup in it. They did have some extra windings wound onto the ends of the field windings to help it start up and stabilize it but otherwise it was just a 3 phase motor with a engine hooked to it. The welder was a Thermadyne but it was obvious from the components in it that it was made in Italy. In this case the touted cuts out if shorted rule seemed to not work and there was a short in the windings caused by a short in some internal leads of the welder. .
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On Fri, 29 Jul 2005 02:48:09 GMT, Ignoramus9394

Yes, it is well known that a pair of hot legs can excite a third leg.
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-john
wide-open at throttle dot info
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