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gnm109
09-11-2010, 11:59 PM
I have a 5 hp Rotary Phase Converter (RPC) that uses a 3,450 rpm motor. I bought it on eBay from the company in Phoeniz, AZ. It works great but I wanted to see if I could build one myself that is quieter at idle with no load, using a 5 hp, 3ph, 1,750 rpm motor. I've been told that they are quieter anyway.

My present RPC has a rather high pitched whine at idle but it falls silent when the mill is started. It's rather annoying if you want to let the RPC run while you are changing tools or doing a different setup. I'd like to be able to let it run without too much noise.

I scored a nice NOS 5hp 3 ph TECF motor on eBay recently. It was rather reasonable since it was a flange mount and they are somewhat harder to mount. I'm using the same schematic that the Phoenix machine has with a single 216-259 f, 370 V start capacitor and two 50 f, 370 V run capacitors in parallel. It starts automatically when single phase 240 V is turned on. I'm using a Steveco 90-66 potential relay that drops the start capacitor out after the motor starts. The balance is not bad on the 3,450 rpm model that I have. It's within about 5-10 V on all three legs. I'm hoping that the new one will be as good without too much swapping of capacitors. That's close enough for defense work anyway. LOL.

I'm also adding a three-fuse box on the new RPC. It also has single phase breakers in line to the RPC and three phase out to the mill downstream of the RPC. The mill has a 3 hp, 3 hp induction motor and runs nicely on the present RPC. The motor sits on four rubber vibration isolators and there are rubber feet on the legs of the stand. I did this on the original RPC and it helped a great deal.

I would encourage anyone who needs something like this to do one yourself. The first one that I bought was $375 with free shipping and I think I will be into this one a little under $200 including the motor, which is the big ticket item. The frame was made from scrap, including a 9" round 1/2" steel cutout for the mount and some steel 2" square table legs that I MIG welded together. I used a random ABS pipe fitting to cover the rotating shaft. The commercial companies often cut the motor shaft off at the bearing....a form of unnecesary mechanical mayhem, IMO.

Here are some pictures and a schematic, courtesy of a fellow who calls himself tcmptech on another site. It's similar to the schematic on my Phoenix machine and it works perfectly. Thanks!

http://i144.photobucket.com/albums/r188/gnm109/Machinery/RotaryPhaseConverter003.jpg

http://i144.photobucket.com/albums/r188/gnm109/Machinery/RotaryPhaseConverter004800x600.jpg

http://i144.photobucket.com/albums/r188/gnm109/Machinery/RotaryPhaseConverter005800x600.jpg

http://i144.photobucket.com/albums/r188/gnm109/Machinery/RotaryPhaseConverterMiller.png

wooleybooger
09-12-2010, 02:54 AM
good going. i live in a very small town with a non-existent supply of electrical components. i bought a motor,a pre-configured box,other odd things, wired it all up,plugged in my lathe and have been happily making a mess out of every piece of metal i can find for about 2 years. i am not an electrical wizard, this project was very intimidating at first. practical machinist has a whole section devoted to rpc,s. if i can do it,anyone can. i highly recommend building your own. greatest thing in the world is watching your 3 ph machine throw chips all over your 1 ph garage.

BadDog
09-12-2010, 03:19 AM
Not intending this as a hijack, but rather as an example of another who has done their own home brew. Both my idlers are 1750 rpm Baldors acquired from the scrap yard for between $30 and $45 or so. They looked like NOS other than the scratches from tossing into the pile at the yard. Likewise the NEMA enclosure cost me about $10, the Alen-Bradly switches and commercial grade contactors (and fuse block, transformer, etc) were stripped from scrap control panels for about $10, and I've still got over a dozen switches (push/pull, momentary, detent, etc) and maybe 8 contactors left. I pulled a bunch of the best looking (left several times that many behind), thinking some would be bad, but none were bad! I've gotten maybe 5 3 phase motors like that, all Baldor and looking almost unused, every one has been fine, though one did have a damaged wire box, and another a broken velocity plate (?) on the fan due to damage apparently received at the yard. Even the frame was built from scrap (as you can see). So all total I have maybe $250 in my RPC counting caps and all...

So here are pics of my shop built unit. In my case, I have it rigged to run in 5/10/15 idler hp modes. It starts on the 5, I can then use that to start the 10 for a total of 15, and then drop the 5 if I only want 10 (such as running my lathe on the low power windings). It also has permanent surface mount volt meters (cheap enough). Makes it easy to check balance on different loads and idler configs, plus I can see at a glance if things get "weird".

Since these pics were taken, it was "gussied up a bit", and it now has surplus balance/correction caps pretty much filling the bottom of the box. These are connected so that they are brought in/out along with the motors, and it stays reasonably well balanced in all it's configurations/loads.

http://img4.pixa.us/89f/16993448_th.jpg (http://baddog.pixa.us/images/16993448/)

http://img4.pixa.us/201/16993451_th.jpg (http://baddog.pixa.us/images/16993451/)

http://img4.pixa.us/1a2/16993449_th.jpg (http://baddog.pixa.us/images/16993449/)

macona
09-12-2010, 06:58 AM
Supposedly the 3450 RPM ones are supposed to have a better quality output than slower motors.

gnm109
09-12-2010, 10:31 AM
Not intending this as a hijack, but rather as an example of another who has done their own home brew. Both my idlers are 1750 rpm Baldors acquired from the scrap yard for between $30 and $45 or so. They looked like NOS other than the scratches from tossing into the pile at the yard. Likewise the NEMA enclosure cost me about $10, the Alen-Bradly switches and commercial grade contactors (and fuse block, transformer, etc) were stripped from scrap control panels for about $10, and I've still got over a dozen switches (push/pull, momentary, detent, etc) and maybe 8 contactors left. I pulled a bunch of the best looking (left several times that many behind), thinking some would be bad, but none were bad! I've gotten maybe 5 3 phase motors like that, all Baldor and looking almost unused, every one has been fine, though one did have a damaged wire box, and another a broken velocity plate (?) on the fan due to damage apparently received at the yard. Even the frame was built from scrap (as you can see). So all total I have maybe $250 in my RPC counting caps and all...

So here are pics of my shop built unit. In my case, I have it rigged to run in 5/10/15 idler hp modes. It starts on the 5, I can then use that to start the 10 for a total of 15, and then drop the 5 if I only want 10 (such as running my lathe on the low power windings). It also has permanent surface mount volt meters (cheap enough). Makes it easy to check balance on different loads and idler configs, plus I can see at a glance if things get "weird".

Since these pics were taken, it was "gussied up a bit", and it now has surplus balance/correction caps pretty much filling the bottom of the box. These are connected so that they are brought in/out along with the motors, and it stays reasonably well balanced in all it's configurations/loads.

http://img4.pixa.us/89f/16993448_th.jpg (http://baddog.pixa.us/images/16993448/)

http://img4.pixa.us/201/16993451_th.jpg (http://baddog.pixa.us/images/16993451/)

http://img4.pixa.us/1a2/16993449_th.jpg (http://baddog.pixa.us/images/16993449/)



Very nice work! I see that you have a much larger unit that I have. It's also quite a bit more complex. I understand that with more than 5 hp you need to start adding contactors and various other items so I'm sure that the added complexity is needed. It's sort of out of my league, though.

I just wanted a simple unit with no frills. If I had a need for something larger, I'd build it just like you did.

As to motors, you don't have to have a new one, that's for sure. Anytime you can get a 5 hp Baldor motor for under $300 you are ahead of the game.

Macona: You know, I've heard that 3,450 may have some advantages over 1,740. I even started a thread once over on PM (under my alter-ego) trying to determine the benefits of 3,450 vs. 1,740/1750 and I was unable to get anything definitive. I heard from many there who get good results with either speed but no links to anything scientific.

I even called the rep. at Phoenix last year after I realized that the first unit was running at 3,450 rpm and asked him about the whine and why they use 3,450 (they don't on all of their machines, by the way, at least not on the larger ones). I was told "They are more efficient".......nothing scientific to show me the "why" part, though. In fact, he really didn't want to tell me anything, since I guess he felt it was proprietary. I had to "reverse engineer" a schematic myself, until I found the one on the internet that I showed above.

In that regard, I'm just seeking some peace and quiet in the shop. If it works even close to what I already have, I'll be happy.

I notice that BadDog is using 1,750 type motors....so I guess the jury is still out.

Thanks for the responses. I only wanted to encourage others. When I get the new unit done, I'll come back and report.

squirrel
09-12-2010, 11:42 AM
The best motors to use are the older pre 1970's non-energy efficient styles the have much more slip than the high efficiency types in current production. The only phase converter that is current production that has "good" characteristics uses the Baldor Gentec motor that was designed with high slip specifically for rotary applications. This type of motor/convertor is a "soft start" and quieter running due to the design. The only company I know of that makes one that generates quality power is American Rotary ( I AM NOT ENDORSING THEM just stating what I know about their design and use in my home shop)

If you are running just plain old 3 phase motors any of the converters will work. Running CNC machines requires much higher power quality, so it really depends on your application.

The Fixer
09-12-2010, 11:50 AM
So can you run a 3 ph wire feed welder using a RPC?

wierdscience
09-12-2010, 11:54 AM
Yes depending on how the welder is wired.

lakeside53
09-12-2010, 12:55 PM
I acquired a Lincoln RPC.. 5hp, 3450, "custom purpose- built motor". Works ok, but whiney... annoying, so... it's getting getting replaced with a 15hp 1740. I need more hp anyhow - 5hp won't start my lathe in the higher speeds.


The capacitor values above - as you likely know, take those as best guess and as a place to start. It depends very much on your motor and load. Adjust as required to achieve a voltage balance of better than 5% between L1 and L3, L2 and L3. Test with all your typical loads for best compromise. Also.. try it without any caps - my 15 hp is pretty much spot-on with nothing (to my suprise..). Even at 5%, derating is significant at (you can only achieve 70-80% of rated power), and serious derating required above 10%. Luckily most HSM lathe and mill operations don't use max hp for long (if at all).

Effects on voltage unbalance:
The simple explanation http://www.joliettech.com/voltage_unbalance.htm
For those that care, here's a very technical paper on the subject : http://people.clarkson.edu/~pillayp/12.pdf - Skip to Fig. 9 if you don't like math :)

gnm109
09-12-2010, 01:14 PM
I acquired a Lincoln RPC.. 5hp, 3450, "custom purpose- built motor". Works ok, but whiney... annoying, so... it's getting getting replaced with a 15hp 1740. I need more hp anyhow - 5hp won't start my lathe in the higher speeds.


The capacitor values above - as you likely know, take those as best guess and as a place to start. It depends very much on your motor and load. Adjust as required to achieve a voltage balance of better than 5% between L1 and L3, L2 and L3. Test with all your typical loads for best compromise. Also.. try it without any caps - my 15 hp is pretty much spot on with nothing (to my suprise..).

In a thread a few months back I posted the table of required load derating when the voltages are unbalanced - significant at 5%, and serious derating required above 10%.


It's nice to know that I'm not the only one bothered by the whine of a 3,450 rpm motor. I wonder, does yours fall silent like mine does when you turn on your load? Mine gets very quiet at that point.

I agree that it's good to correct your lines to as close as possible. In that regard, I asked my professional machinist friend down the road about line balance. He has Delta-wired three-phase from the local utility company that he put in about 30 years ago. He told me that he checked it from time to time when he first had it installed and one of the legs was really wild, close to 300 volts! Go figure.

Nonetheless, he runs two Bridgeports, two Monarchs and a large CNC milling center and a Mazak lathe with no trouble and does beautiful work. I presume that the machines themselves must have some sort of protection built in.

My original Phoenix RPC specifically states that it is not balanced for CNC. That's fine with me, since that's in another league.

.

lakeside53
09-12-2010, 01:20 PM
sorry, I was editing my post when you quoted it...

yes, mine quietens down under load, but but I can still hear it.


The "not rated for CNC" is an interesting issue... although cnc can be "picky" about it's power, I think it's mainly to dodge any liability. A great deal of the CNC machines have a vfd-like "power converter" right at the input, so whatever you feed it gets converted to dc anyhow.

My latest acquisition is an Acurite cnc conversion on a BP. I that case, the DC servo motors run at 167 volts, which is 117 ac directly converted to dc. I imagine under-voltage would just make them run a big slower, but over-voltage may present a problem to the drivers. The BP motor has it's own vfd, so no issues there.

gnm109
09-12-2010, 01:43 PM
The first paper mentions one symptom of excessive unbalance would be heating of the motor. Just considering that element, I'm probably OK on my first RPC since it never gets more than just perceptibly warm.

I recall checking it once and the third leg was high, something like 255 V but I never got around to checking it under load, which would be more significant, I would think. That's a test I'll be making soon on both RPC's just for fun.

As I mentioned earlier, I have two 50 f run caps in parallel simply because those values were in the unit when I got it. That's the same as shown in the schematic I posted earlier. I don't have room in the box to add any capacitors to each leg to get the perfect balance anyway....It could get expensive, too, just fishing around trying to get finite with the values. Have you noticed the prices of capacitors lately?

Like Yul Brynner said to Debora Kerr in 1956 in "The King and I"......"Is a puzzlement!".

lakeside53
09-12-2010, 02:01 PM
Maybe I misread you, but they mean the load motors, not the rpc, but in any case, it's pretty hard to use a HSM machine (or a BP/clone) at full hp for more than a few 10's of seconds at a time. The "nose" is a better indicator of danger - the smell of hot windings is easily identifiable and occurs way before the case gets hot!

You can find new run capacitor on ebay for a couple of $ each, and maybe $4-10 at Grainers. I use a random section 8, 12, 20, and 25's. All from various aquistions. I just gave away a box of HUGE 1940's army surplus 33ufd 400v oil filled caps - great for rpcs, which is where they went.


I recently had a problem on an rpc with the value of the equivalent of your C3 -the starting cap in series with the potential relay. One 5hp motor (like my Lincoln) was "easy starting", and only needed approximately 190 ufd; the other needed 300- 350ufd. The later has a nasty habit of welding the contacts on the relay and evaporating the caps in a cloud of white "smoke". I experimented and $30 of start caps later found the lowest value (about 270) that would reliably start the rpc, and it seems to be running a few weeks later. Starting caps have a wide range - often as much as 30% from their nominal values, so maybe I had a few on the high side.