Building an RPC and transformers.

[Matt Matt]

Has anybody built their own RPC? Care to show your build? How did you balance it? How do you start it? What size is the Idler?

On how do you start it, rope pull, delay timer, potential relay, regular relay, hold button start(like old dryer's)... maybe others can chime in how they do it.

Anyone step up with transformers? What kind a transformer did you use?

Add your wiring schematic if you'd like to.… Or just be shy and follow along.

The biggest reason for needing an RPC is for transforming single phase and three phase.

There's many ways of doing this through RPC's, VFD's, static converters & PP. Welcome to three phase Nervana.

 

[American Locomotive]

Built my own using a 15HP motor I got for $50. I use a delay-off relay to control a contactor that switches in a large bank of capacitors for starting. The relay engages immediately on power-on, then after ~0.5 seconds, it turns off and disconnects the start caps.

I had bought some run caps, and combined them with some I had to try and balance the voltages. My unloaded voltage is pretty high, but they're pretty much all perfectly balanced under load.

I have 3 pieces of 3-phase equipment: 1.5HP radial arm saw, 2HP table saw and a giant Lincoln MK-250 motor-generator welder. If it weren't for the welder having a 10-12HP motor, I would have skipped building the RPC and just used cheap VFDs instead.

 

[Matt Matt]

Sounds like a pretty cool build.

The Lincoln MK 250, is that the one that looks like an old floor polisher with a bullet head to it?

 

[American Locomotive]

That's the one

 

[matt_i]

Here's some info. Its 14 or 15 years old now, but some of it still applies, I don't use it any more due to needing better quality power for CNC machines.

http://www.metalwebnews.com/howto/phase-converter/3-phase.pdf

 

[larry_g]

Additional information to MattI is the Hanrahan write-up

http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

I followed this one many years ago and it is still working today. Realize that when you see a figure is blue that is a clickable link to the drawing.

lg
no neat sig line

 

[Matt Matt]

I think since RPCs have been around for 100 years, they're pretty hard to beat (except for in some CNC situations). Why is it so difficult to find an electrician that would know RPC's. I've tried household electricians, I've tried master electricians, I've tried industrial electrician's. I shot a whole bunch of zeros (about 12 before) I bumped into a technologist that had RPC field experience.

The first thing he told me was learn it or it will learn you! I think he meant it'll kill me. So I Learned. He gave me an educated capacitor unload. "Now you know what it's like to be tasered, Much more than this will kill you! Do you still want to play/learn?"

I guess I am either dumb or ambitious.

 

[Matt Matt]

Here's some info. Its 14 or 15 years old now, but some of it still applies, I don't use it any more due to needing better quality power for CNC machines.

http://www.metalwebnews.com/howto/phase-converter/3-phase.pdf

Is that your build? Very clean and I like it.

If you don't mind me asking what are you using now? Real three phase or PP?

 

[American Locomotive]

I'll try and get some pictures of my setup tomorrow for you.

 

[Matt Matt]

I'll try and get some pictures of my setup tomorrow for you.

Thanks. Out of 300,000 members it seems like there's only four of us. Why is there so many SPOB here?http://wiki.vintagemachinery.org/Sayings.ashx#SPOB_32

 

[matt_i]

Is that your build? Very clean and I like it.

If you don't mind me asking what are you using now? Real three phase or PP?

Thanks, it worked great for many years, thru a couple of moves. I had many machines hooked to it. But when I got the CNC machines I decided it was a worthwhile investment to upgrade. I realize many people use RPC & CNC together successfully.

I got a Phase Perfect, just in case I ever move. I didn't want to be locked in to a big dollar install by the utility only to leave it behind for someone who probably didn't even know what it was

That said, I also am relying on the integrity/longevity of the PP.

 

[Matt Matt]

Thanks, it worked great for many years, thru a couple of moves. I had many machines hooked to it. But when I got the CNC machines I decided it was a worthwhile investment to upgrade. I realize many people use RPC & CNC together successfully.

I got a Phase Perfect, just in case I ever move. I didn't want to be locked in to a big dollar install by the utility only to leave it behind for someone who probably didn't even know what it was

That said, I also am relying on the integrity/longevity of the PP.

If you have the blue one, you're in trouble if you have the white one might have many more good years.

 

[MushCreek]

Thanks. Out of 300,000 members it seems like there's only four of us. Why is there so many SPOB here?http://wiki.vintagemachinery.org/Sayings.ashx#SPOB_32

Maybe they don't know what an 'RPC' is. (I figured it out from context).

 

[Matt Matt]

Maybe they don't know what an 'RPC' is. (I figured it out from context).

A RPC, is a Rotary Phase Converter. It's just a motor/generator to create three phase power where single phase power only exists.

 

[matt_i]

If you have the blue one, you're in trouble if you have the white one might have many more good years.

Have the white one, fingers crossed.

The basic concept isn't hard, the homebrew version works very well with manual machine tools which typically have spindle motors that don't draw anywhere near the rated hp.

The problem I've experienced with it from back when is that one can balance the voltages really well at one load point, using run caps. But change the load and the voltages start moving. Also on the generated leg, very little current flows. The reason I know this is trying to run a 3ph hoist that had a number of relays in it, the relays would chatter like mad (hinting at not enough current to keep the coils energized) until I rewired to put them on the "utility phase". Then no more chatter.

I feel certain the "CNC rated" RPCs have better adaptive circuitry to maintain the balance and promote more equal current flow.

But, the classic 3ph AC motor is a rugged device. The idler motor runs on 1ph for quite a long time without complaint or damage. It just can't start on 1ph only without some other external impetus.

 

[wyliesdiesels]

Has anybody built their own RPC? Care to show your build? How did you balance it? How do you start it? What size is the Idler?

On how do you start it, rope pull, delay timer, potential relay, regular relay, hold button start(like old dryer's)... maybe others can chime in how they do it.

Anyone step up with transformers? What kind a transformer did you use?

Add your wiring schematic if you'd like to.… Or just be shy and follow along.

The biggest reason for needing an RPC is for transforming single phase and three phase.

There's many ways of doing this through RPC's, VFD's, static converters & PP. Welcome to three phase Nervana.

Just an FYI- step up transformer would have to be on the line side of the RPC because the generated/stinger leg on an RPC is the only thing that is used.

This means using a 480v idler motor.

 

[86turbodsl]

Adaptive circuitry has got me thinking. Has anyone ever put together a RPC with adaptive cap banks that can be switched in or out depending on high leg voltage to try and balance? I am thinking a PLC could be setup to pull caps in or out depending on a measured voltage. If this is too far off-topic, let me know and i'll start another thread.

 

[wyliesdiesels]

Adaptive circuitry has got me thinking. Has anyone ever put together a RPC with adaptive cap banks that can be switched in or out depending on high leg voltage to try and balance? I am thinking a PLC could be setup to pull caps in or out depending on a measured voltage. If this is too far off-topic, let me know and i'll start another thread.

Thats not off topic. Great idea.

There is a guy on youtube that did a 480v RPC with transformer and caps. Dont think he used PLCs though.

I will look for the video.

 

[Bert_]

Just an FYI- step up transformer would have to be on the line side of the RPC because the generated/stinger leg on an RPC is the only thing that is used.

This means using a 480v idler motor.

I'm not sure I follow this? I can't thing of any reason a transformer couldn't be wired to the 3 lines that are present after the RPC. I would guess it might even help with voltage unbalance problems if you used a delta wired transformer.

 

[86turbodsl]

Thats not off topic. Great idea.

There is a guy on youtube that did a 480v RPC with transformer and caps. Dont think he used PLCs though.

I will look for the video.

Awesome. I keep trying to refine RPC design to avoid the phase perfect route.


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[matt_i]

Awesome. I keep trying to refine RPC design to avoid the phase perfect route.

My free opinion is a phase perfect is a good idea for 1) you have servo drives that have to sink power back into the grid depending on how they decel and brake. 2) have a very heavy starting torque or load, like an air compressor, or 3) you have a 3ph welder that needs to draw current on all 3 phases.

For motors and stop-start controls, an RPC is just great. I wouldn't have the PP without the VMC and the turning center.

Also, the advent of lower cost VFDs makes it fairly easy to solve the same problem and get variable speeds at the same time.

 

[wyliesdiesels]

I'm not sure I follow this? I can't thing of any reason a transformer couldn't be wired to the 3 lines that are present after the RPC. I would guess it might even help with voltage unbalance problems if you used a delta wired transformer.

I dont remember the reasoning as I read it online.

I will have to ponder it some more.

 

[86turbodsl]

My free opinion is a phase perfect is a good idea for 1) you have servo drives that have to sink power back into the grid depending on how they decel and brake. 2) have a very heavy starting torque or load, like an air compressor, or 3) you have a 3ph welder that needs to draw current on all 3 phases.

For motors and stop-start controls, an RPC is just great. I wouldn't have the PP without the VMC and the turning center.

Also, the advent of lower cost VFDs makes it fairly easy to solve the same problem and get variable speeds at the same time.

And they are ridiculously expensive for a non business case. My opinion.


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[American Locomotive]

Transformer shouldn't have any problem on an RPC. They generate real 3-phase. Transformers don't work on the output of static phase converters.

 

[rburke65]

I thought a RPC was like a RMS. I stand corrected.

 

[Matt Matt]

Just an FYI- step up transformer would have to be on the line side of the RPC because the generated/stinger leg on an RPC is the only thing that is used.

This means using a 480v idler motor.

I'm not sure I follow this? I can't thing of any reason a transformer couldn't be wired to the 3 lines that are present after the RPC. I would guess it might even help with voltage unbalance problems if you used a delta wired transformer.

Any reason why you can't use "A" three phase to three phase transformer after the output? (Keep in mind you're not measuring hot to ground.) You're measuring between hot and hot (somewhat text book teachings). How come you're taking the stinger(wild, generated) leg into account? What are the subsections for the rules?

So what would be the best transformer? And why?
Y Y autotransformer? Or
D Y isolation transformer? Or
Y D isolation transformer? Or
2 single phase transformers with corner tap?

Some more questions are, how do you protect yourself? How do you protect leakage to ground using an isolation transformer(as any leakage to ground would show up on your single phase system)?

I have 600 V in my garage shops. And it's all being fed through a 60 amp 240 V single phase line. I even have a portable RPC generator that will plug into a 40-50A welding plug that deliver 240 or 600 V three-phase.

 

[Matt Matt]

I dont remember the reasoning as I read it online.

I will have to ponder it some more.

interesting. I await your expertise on my questions.

 

[wyliesdiesels]

Transformer shouldn't have any problem on an RPC. They generate real 3-phase. Transformers don't work on the output of static phase converters.

Transformers don't generate electricity. Thats what a generator is for. They transform electricity from one voltage to another. You cant use a 3 phase transformer to generate 3-phase electricity with a single phase supply.

Any reason why you can't use "A" three phase to three phase transformer after the output? (Keep in mind you're not measuring hot to ground.) You're measuring between hot and hot (somewhat text book teachings). How come you're taking the stinger(wild, generated) leg into account? What are the subsections for the rules?

The problem with stinger legs is that they can fluctuate depending on loading. This usually only applies to line to neutral/ground. But IIRCC, its an issue with output on RPCs since the generated leg is the stinger leg. Thats why capacitors and PLCs were brought up.

 

[Matt Matt]

The problem with stinger legs is that they can fluctuate depending on loading. This usually only applies to line to neutral/ground. But IIRCC, its an issue with output on RPCs since the generated leg is the stinger leg.

Thanks for your input, that's been a big help.

How often do you measure the stinger leg to ground(common) when working with three phase? I do always. But when performing three-phase tests and using oscilloscope, they only show up when I want them to.

How did you come to your findings? How do you set up your oscilloscope to show your findings after you step up transformer your RPC?

 

[wyliesdiesels]

Thanks for your input, that's been a big help.

How often do you measure the stinger leg to ground(common) when working with three phase? I do always. But when performing three-phase tests and using oscilloscope, they only show up when I want them to.

How did you come to your findings?

Not to often. Depends on whats going on or what the service call is.

We dont have much Delta left out here. And many existing delta services are being converted to Wye.

The local habitat store almost got converted from corner grounded delta to wye. Then, my friend(who is a lineman) and the PoCo engineer realized the customer would need to do a whole bunch of work on their end probably changing out the main service panel, so they cancelled the job.

 

[Matt Matt]

Not to often. Depends on whats going on or what the service call is.

We dont have much Delta left out here. And many existing delta services are being converted to Wye.

The local habitat store almost got converted from corner grounded delta to wye. Then, my friend(who is a lineman) and the PoCo engineer realized the customer would need to do a whole bunch of work on their end probably changing out the main service panel, so they cancelled the job.

So you have avoided most of my questions and post 26? I'm trying to be intellectual with you. There's many followers that want to follow, I am sure.

 

[wyliesdiesels]

So you have avoided most of my questions and post 26? I'm trying to be intellectual with you. There's many followers that want to follow, I am sure.

Boy you really are something.

I didnt avoid anything.

Its currently 10pm here. Im tired and on my way out the door(have been for 20mins) to go to the gym.

My brain shut off an hour ago so im not in the mood to think on a real deep level right now.

I will revist tomorrow or the next day.

good night...

 

[Matt Matt]

Boy you really are something.

I didnt avoid anything.

Its currently 10pm here. Im tired and on my way out the door(have been for 20mins) to go to the gym.

My brain shut off a couple hours ago.

I will revist tomorrow or the next day.

good night...

it's 1 o'clock in the morning here. Cheers. I'm just closing up the shop... My new day starts at customer shop, starts at 8:30. Enjoy your gym. maybe we'll talk on the other side of.

 

[American Locomotive]

Transformers don't generate electricity. Thats what a generator is for. They transform electricity from one voltage to another. You cant use a 3 phase transformer to generate 3-phase electricity with a single phase supply.

As someone who has an RPC, I'm quite aware, thanks.

I'm saying RPCs generate 3 real 3 phase, so a 3 phase transformer should have no problem being on the output of a properly balanced and loaded RPC.

 

[wyliesdiesels]

As someone who has an RPC, I'm quite aware, thanks.

I'm saying RPCs generate 3 real 3 phase, so a 3 phase transformer should have no problem being on the output of a properly balanced and loaded RPC.

your use of a pronoun in comment #24, is what threw me off..

 

[Matt Matt]

So you have avoided most of my questions and post 26? I'm trying to be intellectual with you. There's many followers that want to follow, I am sure.

Boy you really are something.

I didnt avoid anything.

Its currently 10pm here. Im tired and on my way out the door(have been for 20mins) to go to the gym.

My brain shut off an hour ago so im not in the mood to think on a real deep level right now.

I will revist tomorrow or the next day.

Did you get a chance to evaluate why you can't use a transformer on "your RPC", code or otherwise? You made a pretty pretty bold statement that it's not permitted as per stinger leg. Is this true or not under the Ul allowances? And why or why not?

Edit; do you own or actively use a RPC and/or transformer set up???

 

[930dreamer]

I've built three and currently run a 10hp with a 120v pony start motor.

 

[Matt Matt]

I've built three and currently run a 10hp with a 120v pony start motor.

I've built two. One I purchased the box from NARPC , The other one I built totally from scratch. Both of mine are autotransformers step up. One is a 5 hp with 6 kVA and the other is totally Homebuilt 20 hp with a 15 kVA transformer.

I'm glad there's others here, thet are actually using an operating!

 

[Matt Matt]

Well, here's my 20 hp build. I did personally machine up the whole copper/aluminum electrical distribution block, sourced and scavenged motor and pretty much all electrical pieces. My out-of-pocket, maybe $600-700 for the whole unit. It might not totally be UL, but it's pretty safe.

 

[930dreamer]

I need to go through my rpc setup some day, I have a pallet of good 3 phase motors and a 30 hp that I've started from a sub panel. I'll skip the pics.