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Phase converter


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  #1  
Old 10-26-2015, 01:51:18 PM
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Toesmack Toesmack is offline
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Default Phase converter

When it comes to choosing a phase converter, I see rotary converters are far more expensive than digital or solid state. This would imply the rotary is a better unit. Anyone wanna share their experience with each? Looking at a milling machine, probably about 3hp 3 phase. Very limited use. Which way is the more practical way to go?
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Old 10-26-2015, 02:18:17 PM
wmusta wmusta is offline
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Default Re: Phase converter

Factory built units are expensive. A friend built mine. Basically a 5hp 3 phase motor. Motor starter/stop switch, starting and running capacitors. All common parts that were salvaged or used. Works great. Cost me $50 bucks.
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Old 10-26-2015, 02:37:10 PM
pegasuspinto pegasuspinto is offline
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Default Re: Phase converter

Everyone Seems to be going with a VFD now. Very common. The rotary costs more because it weighs more! The VFD gives you infinitely variable speed and reversing, etc.

https://www.youtube.com/watch?v=ZqnfLHhuuUQ

Search for VFD for mill or lathe and a ton of stuff comes up.
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Old 10-26-2015, 02:53:24 PM
ronm ronm is offline
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Default Re: Phase converter

My son built a 5HP rotary for not much money, used a junkyard motor & bought the capacitors, etc. Used it for some project he had & sold it...My mill uses a static converter I got off ebay, but I have a VFD, if my son ever gets around to installing it on the mill. (He's the EE in the family)...Static converters don't cost much, but what they do is fool the motor into thinking it's got 3-phase until it gets started, then it will run on single-phase, but only produces 2/3 of its rated HP...I get by OK because I never have to take really heavy cuts & push the motor to its limit. If you need to work it hard, a rotary or VFD is better. Nice thing about rotary is that you can run more than one motor off it,if you don't start them all at the same time...converter needs to be rated for the total HP of all the motors.
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Old 10-26-2015, 08:03:16 PM
jpatrickc jpatrickc is offline
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Default Re: Phase converter

There is a rotary converter on Engineads.

http://www.enginads.com/classifieds/.../120709/cat/14
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Old 10-26-2015, 08:18:29 PM
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Default Re: Phase converter

Easy to hang on wall, no heavy converter to move

Shop direct mscdirect.com for many sizes.
If you have 1 hp Bridgeport 3 phase motor use 3/4-1 1/2 hp or 1-3 hp converter.
Do not use higher hp as it will cause slow or burn up motor buzzzzz
I have ordered one time for 3 to 5 hp converter box made 1 hp motor noise so I have to run my 3 hp 3phase Monarch lathe running when I want to use Bridgeport milling total 4 hp be fine. Msc catalog online will tell you the right choice. Has manual for wire diagram connection from single phase to 3 phase.

http://www.mscdirect.com/product/det...S_010=09521519

Hope this helps

Craig
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Old 10-26-2015, 10:50:08 PM
ChipTosser ChipTosser is offline
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Default Re: Phase converter

I have built a many rotary converters.
There is a lot of info. on building different configurations on the web.
I usually use a three phase motor, motor starter contactor, start capacitor, run capacitors, momentary switch.
This allows you to run more than one machine at a time.
Also, you can check the, Phazpak.com for many different options.
They are very helpful, lots of info there.
Static converters can be noisy, so can a rotary, depending on the fan on the motor. As mentioned, you have less power available with the static box units and have to be matched to horse power. They are not very flexible. As for VFD's, They are more expensive than building a rotary. If you cook a VFD, your not going to fix it, your buying another, unless you pay the big buck for a good quality VFD to start with.

Good luck
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Old 10-27-2015, 08:16:52 PM
Harvey Teal Harvey Teal is offline
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Default Re: Phase converter

Transient voltages produced by VFD's may exceed the insulation resistance of some older motors. Rotary convertors produce more of a sinusoidal waveform, which is much more friendly to motor windings. You can also install reactors between the VFD and the motor; this will render the VFD's output waveform less harsh. Also, VFD's tend to induce damaging eddy currents in the motor bearings. Kits are available for grounding the motor shafts to minimize bearing damage. If you are using a standard-frame commercially available motor, go ahead and use a VFD. But if you're using a vintage motor with a weird frame size that might be difficult to replace, think about using a rotary, even though the initial cost might be higher.
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Old 10-29-2015, 05:59:22 PM
dkamp dkamp is offline
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Default Re: Phase converter

While it's true that VFDs have the ability to generate switching transients, they're rarely found damaging older motors. A cheap imported motor, yes- where windings weren't properly wound (tight) with quality insulation, and proper binding. Even the oldest motors in my machines pass a 2kv hi-pot, and don't vibrate under switching frequencies. Of course, most VFDs allow programming the switching frequency. If the VFD is a 200-250v unit, you'll likely never see switching transients over 400v or any substantial energy distribution over 15khz, because the 60hz design simply squashes it... too much XL in the windings. A 480v VFD MAY have the ability to burn windings a bit, but I haven't managed. I haven't killed any motors with a VFD, and I've tried on many. I wasn't even able to kill railway tracton motors with their propulsion systems, and many of those were retrofits.

RPCs are cheap and easy to build (I still have mine on-hand for testing), the most minimal is just a knife switch, motor, and piece of rope (to wrap-and-pull start) but all my day-to-day machines are running VFDs... all with single phase in, and either 240 out, or some are 480v VFDs, being fed 480 single-phase by virtue of a 480-240 dry transformer. Did I mention that my VFDs were all on-the-cheap? I bought a pallet of used pull-out Allen-Bradley 1305 and 1336 drives for about $40 each. Every one of 'em had been sitting for several years, and despite horror stories of blowing capacitors, I haven't had one die yet...
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Old 10-29-2015, 11:35:48 PM
Jim Kennedy Jim Kennedy is offline
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Default Re: Phase converter

RPC's are easy to build, I have built several, here are some pictures of one I built a few years ago. I wanted something simple and cheap. In Australia our 3 phase motors operate from 415v and our single phase is 240v. So I used an old choke welding machine which had a primary winding voltage option of 240v or 415v single phase so when the bridging jumpers are re-arranged it will input 240v and output 415v single phase so now this becomes an autotransformer, the secondary winding and the iron choke makes no difference. So I can connect this to the 7 1/2 hp 415v idler motor. I used 2 capacitors to balance the phases although not always required.
This RPC has a 3 phase socket outlet for it's output that is connected to the idler motor's 3 terminals. I wanted it simple so I attached a pull starter and it's driving dog from an old lawn mower to the motor and shaft. So to start this RPC it just needs a pull on the cord and then switch it on. It must be a lot easier in the U.S. where you don't need a transformer when it's 240v supply to a 240v motor, but everything else is the same.

Jim
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  #11  
Old 10-30-2015, 11:12:29 AM
Harvey Teal Harvey Teal is offline
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Default Re: Phase converter

I love that recoil/rope starter! This inspires me to build another rotary...... a good project for this afternoon......
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Old 10-30-2015, 12:37:44 PM
ronm ronm is offline
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Default Re: Phase converter

That's way fancier than the one the guy I got my mill from had...he just wrapped a rope around the pulley & gave it a jerk. It was a 3-horse 3-phase motor laying on the floor with about 100 ft. of Romex cable running all over the place. But hey, it worked!
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Old 10-30-2015, 11:46:44 PM
dkamp dkamp is offline
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Default Re: Phase converter

LOVE that recoil starter, Jim- that's precious! Needs a sticker that says "5HP" on it... and keep the CHOKE... modern machines don't have CHOKEs... at least, yours still has one...
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Old 10-31-2015, 11:24:35 AM
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Default Re: Phase converter

Jim Kennedy, what a neat job that is! And the idea of using the arc welder as an autotransformer, brilliant! But I have to say, I think it would have been easier to add a potential relay and a start cap than to make all the stuff to mount the recoil. I can't see your pics from this screen, but did you add bleeder resistors across your capacitors? That's an important safety feature.

RonM, a 3HP idler should be self starting with the properly sized run capacitors installed. Not too peppy, but it will self start. Mine does. 5HP and up, no joy. A start cap is needed.

To the OP, no one "converter" system can be considered BEST. There are too many variables to make such a judgement. Although as a sweeping generalization, the static "converter" can probably be considered worst, and in a perfect world where cost is no object, the Phase Perfect is best.

The static "converter", which, if commercially bought isn't a converter at all but rather a starting device that leaves the motor single phasing once it gets up to speed, is OK for intermittent use and low power requirements, OR for situations where the motor operates at a constant load and can be successfully balanced with run capacitors. Think of something like a blower.

VFD's are fine if you only run one motor, or if any of the VFD's many other features are needed. A slight downside is that the machine's existing switching devices have to be disabled when using the VFD, which acts not only as a phase generator but also as a starter and circuit protection. Major downsides are cost and the fact that the VFD's smoke is more loosely contained than other systems'.

So that leaves the RPC as the mainstream choice for probably most situations. Cheap if you build your own, and easy to build using information easily found online. Runs multiple machines simultaneously, and, within reason, the more machines you run, the better the line to line balance becomes. The biggest downside is that some motors that have to start under high loads MAY struggle to get up to speed. This is especially true if no other motors are running on the RPC at the time.

And one last suggestion. If you are building a rotary converter and plan to use a momentary switch to switch the start capacitors in and out of circuit, be careful! The currents and voltages involved place great demands on the switch. My 5HP converter (in the garage; the 3HP is in the basement) momentary switch failed shut (contacts welded together) and before I could shut it off it destroyed the start capacitors. Potential relays are inexpensive and readily available as a better alternative. I suppose a properly-sized manual switch would also be OK. I built mine with a chintzy switch as a "temporary measure" that became permanent. Sort of. You know how that works.
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Old 10-31-2015, 01:16:12 PM
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Default Re: Phase converter

[QUOTE=s100;1217597]Jim Kennedy, what a neat job that is! And the idea of using the arc welder as an autotransformer, brilliant! But I have to say, I think it would have been easier to add a potential relay and a start cap than to make all the stuff to mount the recoil. I can't see your pics from this screen, but did you add bleeder resistors across your capacitors? That's an important safety feature.

RonM, a 3HP idler should be self starting with the properly sized run capacitors installed. Not too peppy, but it will self start. Mine does. 5HP and up, no joy.

Hey, this was an old hippie VW mechanic that had the mill, it was in an old barn, far as I know there was no capacitor within 20 miles. ..he started it with a rope, that's all I know...
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Old 11-03-2015, 03:46:27 AM
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Default Re: Phase converter

Hi s100, Thank you for your kind comments, of the several phase converters I have built, this is the only one I did not use a voltage sensing relay because I wanted it simple and cheap. Just cutting some 3/4" bar and flat iron and threading, the motor shaft was already internally threaded, was not much work and I have plenty of time and I enjoy. I did not consider bleed resistors on the capacitors because the capacitors are connected in parallel to the motor windings.
I think you gave a excellent assessment of running 3 phase motors from single phase. I would like to expand on what you said about Rotary Phase Converters under heavy load, struggling to get up to speed. Well sometimes Rotary's just don't successfully get these motors started at all. I have used the higher voltage method using an autotransformer to achieve the higher voltage. Using this method I can start loaded motors just like they were connected to Supply Authority 3 phase mains. I think the best advantage of this method is the motor can be operated at full nameplate amps, delivering full power but the load has to remain pretty constant to achieve good results. Ronk Electrical Industries Inc. of Illinois use to market
Add-A-Phase Power Converter which is a commercial example of the higher voltage autotransformer method. I am not sure if they still exist but they probably do.
s100, are you familiar with this method and I would enjoy hearing your comments on it.
Hi Dave, next time I might just bolt the choke winding handle on so it looks the part but I will still remove the choke because they usually make extra noise when still in place.

Jim
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Old 11-06-2015, 10:51:00 AM
wmusta wmusta is offline
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Default Re: Phase converter

Also pay close attention to what wires you hook up to your equipment's motor starter/contactor. Make sure the generated leg is not part of the circuit. The Guru's can explain better than I can why.
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Old 11-06-2015, 07:31:41 PM
Harvey Teal Harvey Teal is offline
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Default Re: Phase converter

Good point. When using a rotary, the downstream motor contactor coils and misc controls will appreciate being connected to the "master phase"; that is, the
single phase source that supplies power to the rotary.
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Old 11-06-2015, 11:00:53 PM
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Default Re: Phase converter

Jim Kennedy,

I have no firsthand experience with the higher voltage start system. I am fortunate in that all of my really hard starting loads have single phase motors running them. If I did have problems with three phase motors starting under load, I might consider the autotransformer as a last resort (because I am too cheap; nothing wrong with the idea, it's me that's the problem). Before going that route I would try something that has already been mentioned, starting a second motor to improve the three phase before trying to start the heavily loaded motor. This might work OK but falls off the wagon when considering auto start loads, such as air compressors.

In some ways I have reached complication saturation. Static converters, VFD's, rotary converters, replacing three phase motors with single phase, Steelman patent connections, where does it all end? At some point, if one methodology (or possibly two) isn't the silver bullet fix, it may make sense to throw in the towel and get the Phase Perfect.

Steve
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Old 11-07-2015, 07:50:49 PM
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Default Re: Phase converter

We bought a Roto-Phase converter over 40 years ago. It is rated to run motors up to 5HP, with a total of 20HP at the same time. It has started a 5HP motor on a crank grinder with a 3 foot by 1.5 inch wheel with no problem, without any other motors running. That is a lot of mass to get spinning, but it has done it hundreds of times over the years. It seems that if a rotary converter is having trouble starting motors it is rated to run, it must be over rated or poor quality.
Just my thoughts.

PT
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