building rotary phase converter


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    The common type of "static converter" has a current sensitive relay (or perhaps a voltage-sensitive one, depending on connections) which switches the start caps in only until it is up to a self-sustaining speed. If you load it down enough, it will switch back in, and if you keep that much load on it, it can quickly burn out the start caps. This describes the relatively inexpensive ones such as those normally sold by Phase-o-Matic and others.
    From some earlier postings on this newsgroup, apparently there are some which use tapped inductances to achieve the phase shift, and maybe continue to feed that even when the load is up to speed.
    But you could achieve the same effect as the normal "static phase converter" with a momentary contact switch and the caps, and just hold it in long enough to spin up the motor. Some rotary converters are set up like this to start the idler. This is a royal pain without the idler, for a motor which you are starting and stopping frequently, as some of these days you (or someone else) will lean on that start button just a bit too long, and there goes the start cap. :-)
    I suspect that the torque available from single-phase operation may be a function of both the number of poles in the motor's design, and the amount of iron in both the rotor and stator. And it may be possible to get (for some combination of the above) more starting torque (as the earlier article suggested) than the rated running torque. This is in part because the motor is drawing a lot more current when starting. And IIRC, the cap array being used to develop starting torque was tuned for optimum starting behaviour. That cap will probably be a very poor value for normal running.
    So -- for normal operation, I think that *any* reasonable source of three phase (power company, VFD or rotary converter) will produce more power from the motor at peak than the same motor running from a so-called "static" converter.
    Enjoy,         DoN.
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wrote:

Eric
You might be overemphasizing the amount of degradation in power delivering ability of a 3 phase motor when running from single phase. The power and torque of a 5 HP 3 phase motor will be very little different for either single phase input or 3 phase input when the load is 3 HP or less. A major difference in the single phase compared to 3 phase is the smoothness of torque throughout each revolution. The instantaneous torque from a single phase motor (or a 3 phase motor spinning without the rotary) will go to zero within each revolution. That doesnt happen with the 3 phase power.
Rotary converters certainly make a 3 phase motor run smoother compared to running the same motor without the idler, especially when loaded heavily. When a 3 phase motor is loaded to less than 1/2 its name plate rated power, the power to the "tool" is very close to the same, with or without a rotary converter.
Big rotary converters are very noticeable in smoothing the 3 phase motor running from single phase power when the load motor is at or near full name plate rated load.
Jerry
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On Fri, 18 Jun 2004 04:58:24 GMT, "Jerry Martes"

Jerry, The motor behaved virtually the same at low loads. Instany reversing, such as when power tapping, was slower. But when taking heavy cuts the bridgeport would bog down when run off the static converter but be just fine with the rotary. I machined lots of stainless in the past and would take the machine to it's limits on a regular basis. The rotary converter saved me lots of money because of the time saved taking heavier cuts. Eric
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wrote:

the
the
delivering
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Eric
The data I recorded indicated that there will be virtually no difference in performance of a 3 phase motor loaded to 1/2 its name plate rated HP, when run from single phase, with or without the idler. Is that what you experience?
I also notice that, when the 3 phase motor is loaded to its full name plate rated HP, without an idler, the RPM drops 15 or 20 RPM below the RPM of the same motor *with* an idler. And, if the motor is loaded to 'over name plate rating', it will stall completely without an idler. But, with a big idler, the motor will deliver more than its name plate rating without stalling. Is that about what you experience?
Jerry
Jerry
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Any difference in smoothness between single-phase and generated 3-phase? - GWE
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difference
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GWE
Grant
I cant distinguish any difference of 'smoothness' *with* or *without* an idler when the 3 phase motor runs from single phase but loaded to 1/2 its name plate rated HP. When the 3 phase motor is loaded to its full name plate rated HP, the idler really helps smooth the Torque per Revolution. The bigger the idler, the smoother the motor runs, at high load. At low load, the motor runs the same *with* or *without* an idler.
I tried to build a sensor to monitor and record the "unsmoothness", but got distracted from that project when it got difficult.
Jerry
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Not an exact answer and maybe not even a close answer but when I changed the crap single phase motor on my mill drill to a leeson three phase motor and VFD, I could see a much smoother surface finish when milling.
chuck
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On 18 Jun 2004 18:26:47 GMT, snipped-for-privacy@w-sherwood.ih.lucent.com (Charles A. Sherwood) wrote:

The torque of a 1 ph motor (or a 3 ph motor run on 1 ph) goes to zero 120 times a second (100 times a second in Europe). The torque of a 3 ph motor run on 3 ph never goes to zero. So the 3 ph will always be smoother.
As others have noted, a static converter of the sort typically used is just a motor starter. It does not supply the motor with 3 ph power when the motor is running. However, a rotary converter does produce actual 3 ph power, so the load motor behaves as if it were operating on utility 3 ph power.
Gary
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3-phase? -

Chuck
Yeah, thats about the same subject. The theory indicates that single phase motors of this type do have a Torque per Rotor angular rotation that has zeros. So, the motor actually produces zero torque at some position, or positions, of the rotor shaft. Three phase motors's torque doesnt go to zero at any angular position, so they are much smoother.
Big idlers really improve the smothness of a 3 phase motor runing from single phase. But, that improvement is realized only when the tool motor is loaded well above1/2 the tool motor's name plate rated HP.
Jerry
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You will need a rotary phase converter of at least 1-1/2 times the HP of the load motor. There was a good article in the Nov/Dec, 2001 issue of "Home Shop Machinist" describing Rotary Phase converters. That article has good recommendations for start and run capcitance. Capacitors are available on the surplus market, and new from AC supply houses.
Bob Swinney

application.
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The size of your largest load motor will determine the size of the idler motor you need. The size of the idler motor will determine the amount of run capacitance. The rules of thumb developed on this NG over time are:
Idler motor: 1.5x the largest load motor's horsepower (e.g. 3hp load->5hp idler) Run caps : 12 uf (microfarads) per horsepower of idler motor Start caps : 70 uf per horsepower of idler motor
These numbers have been used many times and are reliable. When you're looking for 3 phase idler motors, take a good quality multimeter with you and check the ohm reading from L1->L2->L3->L1. All should be about the same, and very low readings, like 0.2 ohms. No open circuit. Then check each leg to the motor's case. All should look like an open circuit. Then spin the shaft and listen to the bearings. If you feel any crunch be ready to spend $40-50 on new bearings. Inspect the motor case closely. Many times motors are scrapped because of mechanical damage usually from being dropped. If the case is clean or at least undamaged, and the bearings are good, and the meter readings are OK, then consider the motor as a good candidate for an idler motor. The slower it spins the better in my opinion (less noise). Also, if it has sleeve bearings it will be quieter but you will have to oil them periodically.
There is a good source for used run caps in Seattle. I go there a lot. Email me if you want me to look for some.
Grant Erwin Kirkland, Washington To email me, see http://www.tinyisland.com/email.html
Charles A. Sherwood wrote:

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Is all the capacitance in one place or is it divided across legs? One set of plans used 5uf across L1:L3 and 12uf across L2:L3 Input is L1 & L2. Generated leg is L3.

All across L1:L3 right?

I found a good 10HP motor. Seller claims it runs on real 3ph power, so I think that means its good. Using your formula I would need a 120uf of run caps and 700uf start caps. Will these caps cost a lot?
I think a 10HP idler is way overkill for a 1.5 HP grinder and 1/2HP dust collector. I am concerned that I will need massive contactors and wiring. I am also concerned that the caps will cost me a small forturne.
chuck
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I'm about to assemble one for myself (3 hp idler). Grainger has starting caps at a decent price ($10 for the one I need), but www.surpluscenter.com has run caps at about 1/4 the Grainger price.
I also bought the HSM issue that Bob Swinney mentioned, and it has some good information in it. Also check out some of the old threads at www.practicalmachinist.com (see VFD and converter topic area). Then, if you really want more information, there are a number of good r.c.m articles from 3-6 years ago that you can find by a bit of google searching. Look for Bob Swinney and Fitch Williams as authors. There were many other contributors, but google will get you to the threads and you can move back and forth from there.
Pete
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Buy new start capacitor(s) because those are electrolytic and dry out. You can scrounge run caps safely. Split the run caps about half between L1-L3 and other half between L2-L3. As you've seen, some guys get way into tweaking these things and add a little more on one leg or the other. The big reason to use run caps is they make the converter run much more quietly. As long as the load runs smoothly and the converter isn't buzzing you're fine. Mine has half/half. All the start capacitance goes L1-L3, yes. And you do have to do something to take the start cap out of the circuit. I use a potential relay, but you can also use a regular relay wired for momentary contact, plus a pushbutton. The relay has to be rated to break the full starting current, which can be much higher than the full load amperage.
A 10 hp idler is way overkill. Loud, big, wasteful. OTOH a buddy of mine dragged over a real nice Toshiba 15 hp motor the other day which we started up in my shop and it ran real quiet. I'd look for a 3hp idler. - GWE
Charles A. Sherwood wrote:

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On 14 Jun 2004 17:12:09 GMT, snipped-for-privacy@w-sherwood.ih.lucent.com (Charles A. Sherwood) wrote:

Starting surge on a 10 hp idler is substantial. I built a 20 hp rotary, and starting surge was horrific. To avoid that, I eliminated the self- start feature (and capacitors) and simply spin it up with a modest 1 ph motor before applying power. Starting surge is negligible that way, and I only need permanently wired run caps for phase balance, no starting caps or cap start circuits required.
The control circuit uses a spring loaded DPDT center OFF switch. In one position it applies power to the little 1 ph motor to spin the assembly up. In the other position it closes the contactor to throw 240 to the idler. Note that this removes power from the little pony motor once the rotary is started. It then just freewheels along for the ride.
Start procedure is to hold the switch to the pony side until the motors come up to speed, then flip it the other way momentarily to close the contactor and throw 240 to the rotary.
You could use two NO push button switches if you don't have a spring loaded DPDT center off switch, just make sure you don't hold them both in at the same time. If you do, and the two motors' synchronous speeds are different (they will be slightly), the little pony may overheat and fail. The spring loaded DPDT center off switch avoids this possibility.
A safety relay's coil is wired to be held in by L2 (the manufactured leg). Its NO contacts are in parallel with the start switch. So once the rotary starts making L2 (this occurs in a fraction of a second after you hit the rotary with 240), the relay pulls in, holds the contactor closed, and you can release the start switch.
If the power is interrupted and the idler stops, the safety relay drops out, the contactor opens, and will remain open until you work the start switch again. This prevents the idler from attempting to restart on its own (which it can't do), and burning up its windings after restoration from a power failure.
The stop circuit is just a NC push button wired in series with the contactor coil. Push it, the contactor drops out. Let the rotary wind down, then release. The converter won't restart until you operate the start switch again. Safe, simple.
On the subject of sizing breakers and wiring for this project, they only have to be rated slightly heavier than the *load* you're going to put on the converter. If the converter is properly balanced and power factor corrected with capacitors, it won't have high circulating reactive currents through the primary wiring and breaker. The only parasitic power draw is the small amount needed to overcome windage and bearing drag. All other real power will be consumed by the load(s), and so the primary wiring and breaker only need to be sized to accommodate load consumption.
For my converter, I actually sized everything to handle a 20 hp load, because I might run several large motors from my converter at the same time. But that's not necessary if you're only going to have a max load of 2 hp on the converter.
Gary
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This is a multi-part message in MIME format. --------------070608010307050404090303 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit
Up here in the great white north, the average house wife not only can change the engine on the family Buick, but can also come up with ways on how to save cash with the bat of an eye lash.
First, your values are a good ball park figure on your caps, of course you'll have to do some tweaking for balancing the the phases. The actual values to balance the phases actually vary between different makes, models and winding, so line balancing is a must.
I presently run a 5 hp rotary phase, home built to power the shop equipment . I run a Machine shop, and it is a legitimate business, up here where Poly Phase is no where to be found. To run a branch from the nearest city was quoted to me at $ 27,000.00 + $ 4000 per pole. Cost of my rotary converter: $ 25.00 I have a couple of schematics for a rotary PC that might be of some help. P.S. I've been running mine steadily for 4 years now, and not even a whimper! contact me
Charles A. Sherwood wrote:

--------------070608010307050404090303 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1"> <title></title> </head> <body text="#000000" bgcolor="#ffffff"> Up here in the great white north, the average house wife not only can change the engine<br> on the family Buick, but can also come up with ways on how to save cash with the bat<br> of an eye lash.<br> <br> First, your values are a good ball park figure on your caps, of course you'll have to do<br> some tweaking for balancing the the phases. The actual values to balance the phases<br> actually vary between different makes, models and&nbsp; winding, so&nbsp; line balancing is a must.<br> <br> I presently run a 5 hp rotary phase, home built to power the shop equipment . I run a <br> Machine shop, and it is a legitimate business, up here where Poly Phase is no where to be <br> found. To run a branch from the nearest city was quoted to me at $ 27,000.00 + $ 4000<br> per pole.<br> Cost of my rotary converter: $ 25.00<br> I have a couple of schematics for a rotary PC that might be of some help.<br> P.S. I've been running mine steadily for 4 years now, and not even a whimper!<br> contact me<br> <br> <br> Charles A. Sherwood wrote:<br>
<blockquote type="cite"> <pre wrap="">Run caps : 12 uf (microfarads) per horsepower of idler motor </pre> </blockquote> <pre wrap=""><!----> Is all the capacitance in one place or is it divided across legs? One set of plans used 5uf across L1:L3 and 12uf across L2:L3 Input is L1 &amp; L2. Generated leg is L3.
</pre> <blockquote type="cite"> <pre wrap="">Start caps : 70 uf per horsepower of idler motor </pre> </blockquote> <pre wrap=""><!----> All across L1:L3 right?
</pre> <blockquote type="cite"> <pre wrap="">These numbers have been used many times and are reliable. When you're looking </pre> </blockquote> <pre wrap=""><!----> I found a good 10HP motor. Seller claims it runs on real 3ph power, so I think that means its good. Using your formula I would need a 120uf of run caps and 700uf start caps. Will these caps cost a lot?
I think a 10HP idler is way overkill for a 1.5 HP grinder and 1/2HP dust collector. I am concerned that I will need massive contactors and wiring. I am also concerned that the caps will cost me a small forturne.
chuck
</pre> </blockquote> </body> </html>
--------------070608010307050404090303--
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If you already have some VFD's in your shop, why not use some of those relays to switch the output of a vfd to the grinder?
The reason that the various plans don't agree on the run caps is that different motors require different values. So the values are a starting point for something that is not very critical.
Try looking at places that do air conditioning work. Most single phase airconditioners use run caps. And a three phase compressor might make a reasonable motor.
Dan
snipped-for-privacy@w-sherwood.ih.lucent.com (Charles A. Sherwood) wrote in message

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My machines are not physically all together. The mill and lathe are in one room and the grinders are in a different room. The grinder needs a big VFD which are on the machines in the other room.
The bench grinder is right next to the surface grinder because I want to use the dust collector for both machines. The surface grinder has a 208V motor so the VFD needs to be configured for a lower voltage output. Too many variables for changing things around.
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