Lister Engine Forum
How to / DIY => Generators => Topic started by: Eadie McCreadie on December 05, 2008, 07:52:08 AM
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And specifically, is the ST5 genny single phase?
Or is the phase unrelated to the model number or output, and merely something set by some other component inside the machine?
Thanks
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This is a bit of a challenge to describe but I shall try.
A single phase and a 3 phase alternator are vastly different in the way the internal poles are arranged and the number of coils and wires leading to the outside world. Basically a single phase unit will have two output wires and for every revolution of the shaft you will see either a single 360 degree sine wave come out (2 pole 3600 RPM head) or two 360 degree sine waves in the case of the more common 4-pole 1800 RPM heads discussed here. The single phase output winding is often center tapped to make 120-0-120 volts available from three wires.
The 3-phase head has three output windings instead of just one of the single phase head. Each winding of the 3-phase head will also make either a single 360 sine from each 'pair' of output terminals in a 2 pole 3600 RPM head, or two sines waves per rev in a 4 pole, 1800 RPM head, BUT the sine wave will be seen to begin on phase one winding, then 120 degrees of rotation later another sine wave will begin to be generated on the second set of wires and 120 degrees later yet a 3rd sine wave starts on the third winding. If you look at only one winding output it will resemble that of the single phase machine output exactly. In the three phase you have 3 simultaneously generated sets of sine waves that are each delayed or time shifted 120 degrees to the output seen on the other windings. The 3 separate coils create sinewave peaks can be traced back to coincide with 3 separate points, 120 degrees apart around the revolution of the armature in a 2 pole machine. This is repeated twice in a single revolution for a 4 pole machine where one 360 degree physical shaft rotation actually represents 720 electrical degrees.
Confused yet? ;D
Maybe this will help to form the image. You can generate 3-phase power IF you have three identical single phase heads and arrange their shafts to be phase locked to each other through a gear system or perhaps toothed timing belt. The keyway on each shaft can be used as a physical phase reference. The keyway on the first would be set at 12:00 o'clock. The key of the second would be set at 120 degrees later or say 4:00 o'clock. The key of the third shaft would be locked 240 degrees later or at 8:00 o'clock. As the prime mover rotated these three heads they would always have the same 120 degree phase or timing separation between their armature shafts. The six total single phase output wires from all three heads would give you true 3-phase power. Wire them all in series would give you 3-phase Delta. Wiring them all with one lead common makes a neutral and three live wires. This is three phase Y or Wye. In 3-phase Wye, the common 4th wire is used or not depending on the application.
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kind of like trying to write instructions on how to tie your shoe laces, isn't it?
Stan
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That's why I wear slip-ons.
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Well if someone wants to learn how to tie their own shoe laces by written instructions I'll let someone else tackle that challenge. I hope I didn't just go to all this trouble for Eadie just to keep my two typing fingers in shape 'cause I gotta tell ya', I had to clear out some brain cobwebs that maintenance hadn't dealt with properly composing that and in the process I had to fire some neurons. :D
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Great job rcavictim I solute you sir!!!!!
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rca,
I learned somthing today for a change!
Dave
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Rcavictim, my hats off to you sir.
So once the internal windings are wound as single or three phase they'ed have to be stripped out and re-engineered to convert the gen head. Right?
SteveU.
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Very nice primer on 3 phase, RCAVictim!
Yes, SteveU.
I'll add this:
The original purpose of three phase power was solely to drive three phase induction motors; the motors can be either more compact and/or have much larger HP ratings than single phase motors since those power pulses are now much closer together in time. The rotor can be smaller and lighter for the same HP. Single phase motors are limited to about 7.5 HP, max. No limits on 3 phase.
Three phase also has extra value when generating DC, as the rectified output doesn't swing all the way to zero since a new "hump" is starting just when the last was starting to fade. So there is much less ripple voltage on the DC. Auto alternators are set up this way for just this reason.
I hope this is somewhat helpful.
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Also, all three phase generators can be used as a single phase generator but a single phase generator can never be used by itself to generate 3 phase power. It could theoretically be done with a capacitor bank, but then it would be used like one of the homemade phase converters.
Another thing, if you look inside the single phase generator you'll see that all of the slots in the stator are not used. Due to the decreasing effectiveness of the chord spacing and span of the single phase skein winding it will on average only be 69% as efficient as a dedicated 3 phase winding, which will use all of the slots ensuring efficient use of the iron.
Just a note from an old motor winder....
Mike
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Thanks RCA - I've now established what I needed to know in order to obtaint the correct electricity meter - there are at least two types, single phase and three phase.
Thanks again for detailed post.
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all three phase generators can be used as a single phase generator
Not so.
To separate the phases it will need to be a 4 wire generator. Three wire generators are 3 phase only - unless a deal of rewinding and modification is carried out......
The answer to the question is: The manufacturer.
Regards, RAB
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Very nice primer on 3 phase, RCAVictim!
Yes, SteveU.
I'll add this:
The original purpose of three phase power was solely to drive three phase induction motors; the motors can be either more compact and/or have much larger HP ratings than single phase motors since those power pulses are now much closer together in time. The rotor can be smaller and lighter for the same HP. Single phase motors are limited to about 7.5 HP, max. No limits on 3 phase.
Three phase also has extra value when generating DC, as the rectified output doesn't swing all the way to zero since a new "hump" is starting just when the last was starting to fade. So there is much less ripple voltage on the DC. Auto alternators are set up this way for just this reason.
I hope this is somewhat helpful.
Bruce,
You have added some useful notes about the advantages of 3-phase over single phase power systems. The fact that in a rectified 3-phase system the DC level never drops to zero, even when smoothing/storage capacitors are NOT employed is the reason that a rectified 3-phase welder (i.e. not speaking of any MG set welders here) makes such a much nicer DC arc to weld with and potentially less splatter. Some of us here may have noticed this.
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Regarding '3 phase welders'.
I think you will find they only use two phases. 'Three' phase ones can drive the meter backwards, I have been told by an electricity board electrician.
Regards, RAB
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Regarding '3 phase welders'.
I think you will find they only use two phases. 'Three' phase ones can drive the meter backwards, I have been told by an electricity board electrician.
Regards, RAB
RAB,
I have a ~350 amp, Miller 3-phase welder here and it is a real 3-phase power supply (transformer followed by three bridges). I have been into it and have the schematic so there is absolutely no doubt. The only way I can run it off the mains here however since my mains service is only single phase is to use a homebrew rotary phase converter (7.5 HP induction motor). I never saw my meter go anywhere except forwards at near light speed when I was running this equipment. I could only use the Miller on low range. I do not use the rotary converter anymore since I now have real 3-phase from my DIY VW generator plant. I can still only use low range but what an improvement!
I cannot see how a three phase transformer followed by rectifiers into a series reactor and electric arc (basically a resistor) as a load could set up a condition to run the meter backwards. If it could there are a lot of industrial and commercial power supplies that would be saving their owners money, including radio station broadcast transmitters!
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Regarding '3 phase welders'.
I think you will find they only use two phases. 'Three' phase ones can drive the meter backwards, I have been told by an electricity board electrician.
Regards, RAB
Uhhh.... I've been inside probably a hundred or more 3-phase welders, and they've all run on genuine 3 phase. I've NEVER seen a 2-phase welder. Single phase yes. but 2 phase... never.
How would a 3-phase welder possibly drive the meter backwards?
Your electrician friend is either pulling your leg or he's utterly clueless...
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That's the kind of welder I want, one that will run my meter backwards, I'll use it all day long. ;D ;D ;D
Stan
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That's the kind of welder I want, one that will run my meter backwards, I'll use it all day long. ;D ;D ;D
Stan
Of course we all would! Unfortunately I think it belongs in the category of urban legends like the alleged 200 MPG carburetor.
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funny you should mention the 200mpg carburator
it is no urban legend, it actually existed :)
i found the book down at the tacoma main library about 10 years ago,
it had the technical drawings and all the details
the inventor admitted the following from memory
"i don't think my invention will ever have practical application, because no one will want to drive a car
with such a carburator"
basically the engine he had it on, would make something like 150mpg, out on the flat highway, with a strong
tail wind, tires aired up to something like 80psi, etc etc.
the thing had no accelerator pump, no power valve and as such would take something over a mile to get up
to highway speed,, all the while the driver had to fiddle with remote adjustments of timing and other crap associated
with the carburation just to keep the thing barely running.
so it did exist, it just wasn't at all practical
the engine probably started out life as a 150hp plant, and after being retrofit with the supercarb probably didn't make 3hp
just thought i would throw that out there,, i was actually shocked when i came across the little paperback book at the main library
he probably made more selling the book than he ever made on the carb idea.
bob g
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funny you should mention the 200mpg carburator
it is no urban legend, it actually existed :)
I'll second that!
I have heard exactly the same info before.
Bob G knows his automotive history well!!!
regards,
matt
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I can't remember seeing anything that ran off of "2 phase" power except condominiums, they will bring 208 3 phase into the building & " split it up", using A & B phases' to run the first condo panel, B & C to run the second, A & C to run the third & so on, giving you 2 phases of 208 volts on each panel.
scott r.
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Lowspeedlife:
208 V is convenient because you have 120 V to neutral for small loads and 208 V for bigger loads like stoves, water heaters, etc.
In industrial applications (in the U.S., at least) it is common to feed 208 V / 3-phase power to a breaker panel and then populate the panel with a variety of single pole, two pole, and three pole circuit breakers according to the needs of the loads.
For what it's worth, there actually was a 2-phase system developed way back in the early days of electricity. I believe it predated the 3-phase system. This system required four wires -- two for each phase, and the voltages in the two phases were 90 degrees out of phase with each other. The 3-phase system is superior in that it only requires 3 wires.
Best regards,
Andy Hall
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Your electrician friend is either pulling your leg or he's utterly clueless...
Spoke to him fleetingly over Xmas. He assures me that the power generators do not like 3 phase welders on the system for metering reasons.
Engine driven - fine - but fed from the mains is 'at least not encouraged'. He is a reliable and well-informed ex regional electricity board leccy (retired), so should know what he is talking about.
Regards, RAB
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Your electrician friend is either pulling your leg or he's utterly clueless...
Spoke to him fleetingly over Xmas. He assures me that the power generators do not like 3 phase welders on the system for metering reasons.
Engine driven - fine - but fed from the mains is 'at least not encouraged'. He is a reliable and well-informed ex regional electricity board leccy (retired), so should know what he is talking about.
Regards, RAB
Well, I can be fooled about a lot of things... but I've done serious time repairing welding equipment for a living and have the T-shirt and Lincoln and Miller ball caps to prove it, so I don't fool quite so easy on that one....
From 1980 -1984 I worked for a large fabrication shop in the SF Bay Area (Northwestern Equipment & Supply Co.) that in addition to having a rather large steel fabrication shop, also rented, sold, and serviced industrial welding equipment and supplies. We had over 200 welding machines in our rental fleet, plus dozens more in the fabrication shop. But no 2-phase machines in the lot.
During those years I serviced, installed, repaired literally 100's of welding machines belonging to us or our customers. Almost exclusively 3-phase or gas/diesel driven machines from 200 to 2000+ amps output.
I've worked on equipment in a huge variety of Bay Area industrial businesses... every oil refinery in the bay area, Pacific Steel Casting , TASCO valves, Mothers cookies (RIP), OAK and SFO airports, lots of work at Moffet field including the big wind tunnel and that enormous "hanger 1".
I serviced machines at the old Airco Welding Institute in Oakland (they had about 60 3-phase machine in the fleet for their students).
I've fixed machines in countless smaller shops that few folks have heard of. But in ALL of them, the welding equipment was genuine 3-phase. Never ever seen a 2-phase machine or a 3-phase machine that only used 2-phases.
I spent 4 days at the Lincoln Electric Co. Factory in Ohio, to become a "factory certified technician". In 4 days of class discussion about welding equipment no one EVER mentioned any 2-phase equipment, or any metering problems with the millions of 3-phase welders in the world.
I walked away from Lincoln with about 50lbs of books and service manuals for all of the then current Lincoln welding equipment. Any 2-phase stuff in there? Nope.
(Later, I consulted with Bill Urbanski and the senior designers at Lincoln and proposed several changes to the control circuitry of the LN23-P wire feeder and one of the large Sub-Arc welders that was new at the time. My suggestions were incorporated into the newer versions of those machines and my SJD initials appear on schematics in the service manuals for those machines.) ;D
From 1985-87 I worked for a smaller company in Hayward doing basically the same thing. Still never seen any 2-phase welders.
In the early 90's I did a lot of work for 2 large stainless fabrication shops that made wine fermenting tanks and equipment. I repaired dozens of genuine *3-phase* welders for those folks.
By '97 I'd pretty much moved away from the equipment repair scene, so my direct experience ends there.
I'm pretty sure that if 2-phase machines commonly existed (or 3-phase machines that only "use" 2 -phases) that I would have seen or at least heard about ONE of them in my lifetime...
Most 3 phase welders are just a simple 3-phase transformer that feeds a standard 6 diode 3-phase rectifier then regulates the current/voltage appropriately. There's absolutely nothing in there that's gonna "fool" anyones metering equipment.
Here's a schematic for a Miller DeltaWeld 650. 3-phase, 240/480 volt input. The genuine 3-phase input is clearly show at the left side...
http://www.weirdstuffwemake.com/sweetwatergems/geek/misc/deltaweld_650.gif
Please ask your friend to send me a schematic for any "2-phase" welding machine, or provide me with a make/model# of one so I can look it up for myself. Seeing is believing. :)
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Hi RAB, I would bet money that utility companies would really like to keep all their phases ballanced as close as possible so I don't understand the "not encouraged" coment :o ! Would you please ask your friend to explain the reasoning for his belief and share it with the list? Might be an interesting perspective! Leland