# 3PH 480V for the home shop



## strantor (Jun 14, 2018)

Hello everybody. This thread will serve as a "build log" I suppose. I'm working toward having a 3ph 480V 25A service in my shop. My progress up to now is that I have 3ph 480V with enough current to satisfy a single 3hp VFD and motor that I'm currently working with.

A bit of background... I'm an industrial Automation/Controls guy. I design & build control panels for industrial machinery, and I like to play around with CNC machines in my spare time. I'm newly self-employed and scrambling to obtain all the resources that I am accustomed to having at previous employers. I'm accustomed to working with 3ph motors exclusively, in facilities with 3ph service. Single phase motors rarely come up in my line of work, so start caps, run caps, split phase, all these terms are a bit nebulous to me, but I'm learning (quickly). The inner workings of the Rotary Phase Converter were/are a total enigma to me, so rather than trying to build one, under the time crunch that I find myself in right now, I decided to buy one. I'm currently designing a large panel for a conveyor line that will have (12) 3HP VFDs in it. The first application for this 480V setup will be to power up and perform FAT on that panel once it is built. Thereafter, it will serve whatever purpose I find for it, most likely refurbishing CNCs and more panel builds.

Anyways, on to the good stuff... I found a used American Rotary ADX30 ($2,738 as configured, new) for sale on Craigslist. The asking price was $1,200. I went to look at it, and it was a strange setting. An Italian cougar driving new Mercedes Benz was selling it out of a storage building in a swanky area of Midtown Houston. She said she used to own an artisan pasta shop, and she had it installed to power a pasta dryer. I looked at the pasta dryer (which she was also selling) and the RPC was total overkill for the application, so I assume it's never been anywhere near its FLA. I offered $800 and after negotiations I took it for $950. It only saw 1yr of service and is in pristine condition. I aggravated my hernia loading the 382lb beast by myself, so any savings on the used unit are probably negated by what I'll have to pay to go down to Mexico for surgery (no medical insurance).

The 30kVA 3ph transformer I'm using was also a Craigslist find (GE 9T23B3872, $3,272 new). The guy was only asking $270 so I didn't even try to haggle. This is actually a 480>208Y120 transformer, not a 480>240 transformer, but some quick math on-site led me to believe that it would work regardless (because of a wide selection of primary taps), and that proved to be true in practice.

I plan to set this up on a portable skid with a control panel of my own design, including failsafe controls and volt/amp displays. I will post the details of all that once I've built it and have documented it. For now it's just sitting on a cart in my garage office, haphazardly wired together with a bunch of undersized SO-cord.

Below is a video of the beast in action. The purpose of the video, is I was trying to come up with a ratio of single phase input amps to 3-phase output amps, so that I will know what size my breakers and wires need to be. American Rotary provides this information in several places, but the information is inconsistent and/or unclear. Here's what I mean:

The dataplate on my ADX30 control box says 76A FLA @ 230V, and then further down it says "rated single phase amps = 3ph FLA * 1.6" which works out to 122A
This video by American Rotary states "single phase amps = 3ph amps * 1.6 * 1.2" which works out to 146A
The last page of the datasheet says "3ph load amps * 1.5" which works out to 114A
The 4th page of the datasheet says "Max Total HP(Amps) for optimal performace: 30(84)" and does not specify whether they mean single phase or 3 phase, but which matches neither the 3ph nor the single phase rating on my dataplate. The same chart recommends 1AWG for single phase supply, which per NEC is good for 110A, 130A, or 150A, depending on wire type, which they don't specify.
None of the values they provide adhere to my understanding of the conversion factor between single phase and 3 phase power, which is 1.73 (sqrt 3). If I use my own math it looks like this: 
rated 3ph FLA: 76A*240V*1.73= 31.56kW (42HP!, not 30HP!)......31.56kW/240V = 131A single phase amps
or this:
rated HP: 30 (22kW) / 240V =  91A single phase.... but on the 3ph side... 22kW / 1.73 / 240V = 53A

So I'm left wondering, have they de-rated the idler motor? Is this actually a 42HP motor that they're calling a 30HP motor, because 30HP more accurately describes what power you can get out of it as a generator? Or is this an honest-to-goodness 30HP motor that they're making all kind of wild claims about it's capabilities? Or am I under-estimating the extent to which power factor skews these numbers? I've selected a 125A breaker but maybe I need to shoot for worst case (2nd bullet above) and go with a 150A breaker.

Anyway, here's my video:






Feel free to chime in with any suggestions or clarification on the ratings. 

P.S. Just turning this beast on causes brown-outs at all my neighbors which are on the same pole transformer. I'm going to move this to my new shop on the lot next door which is on a different transformer.


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## Karl_T (Jun 14, 2018)

You are going to have to SWAG this. Conflicting facts here.

I would suggest a three phase load center as a sub panel for this monster. They go cheap on eBay.

ASSUMING adequate wire gauge, I'd go 125 amp breaker to the load center (two hot wires here or 240 VAC.)

I'd put the converter on 100 amp 3phase breaker.

I'm not at all sure of the math on a 30 KVA transformer. Get another opinion, but looks to me like you could run it 60 amp breaker for sure, probably more if you really need it. Again, size the wire correctly.

This may be a code violation, but a second 3 phase  sub panel at 460 volts to each of your motors would be a good idea. You may need to put this all in machine panel and have it not be part of the shop wiring.

My two cents. I am experienced with this sort of thing, but NOT a trained expert.


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## strantor (Jun 14, 2018)

Karl_T said:


> You are going to have to SWAG this. Conflicting facts here.
> 
> I would suggest a three phase load center as a sub panel for this monster. They go cheap on eBay.
> 
> ...



Thanks for your input. I'm thinking along most of the same lines. I think I'm going to need to do a full load test at varying increments up to the 125A rating of my breaker, keeping an eye on idler & capacitor temperatures with a thermal camera. If it looks like I can go higher, make a decision whether to leave well enough alone or push my luck.

I thought the transformer was oversized (30kVA) with respect to the RPC (30HP (22kW)), but if the RPC really is capable of sustaining 31kW output as *some* of the ratings imply, then the transformer may become the limiting factor. 

I want as much of this as possible to be part of the RPC skid/cabinet that I build; not part of the building. For multiple reasons. I may want to move in the future and take this with me. I may want to rent it out. I may want to avoid conflicts between what well-established Engineering formulae say will work, and what NEC says is required for permanent installation. I will look into which/what code applies to the mounting of distribution subpanels on portable equipment, because if it's allowed, then you're absolutely right, it would be way cheaper than the DIN-rail mount high-amp breakers I had intended on putting inside my skid panel.


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## Bob Korves (Jun 14, 2018)

Did you look for a data plate on the RPC idler motor?


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## strantor (Jun 14, 2018)

Bob Korves said:


> Did you look for a data plate on the RPC idler motor?


The one that says Centech is the idler motor. The other is the dataplate on the RPC box


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## strantor (Jun 14, 2018)

I've been crunching the numbers and I think the missing link is power factor. I normally don't even consider PF in my back-of-the-napkin calculations because in my world of 3 phase motors, it's typically .9 or close to that, so I just lump it in with efficiency and give myself 20-25% headroom. I did not realize what bad power factor RPCs have. According to this page, RPC power factor is commonly as low as 0.65. So if I take the *entire formula* for single phase and 3 phase power, not leaving out anything, and rearrange solving for power factor, given the 76A nameplate 3ph amps and assuming 90% efficiency, I get a power factor of 0.77. Plug that back into the single phase (whole) equation and I get 132A. This makes a lot more sense now.

22kw/(240V*0.9*0.77*1.732) = 76.37A
22kW/(240V*0.9*0.77) = 132.27A

This would have been a lot easier to figure out if they had disclosed the info. I can't find efficiency or power factor mentioned on their site or in any of their documentation, other than the claim that they use a "high efficiency" idler. It's even got blocks for PF and EFF on the idler dataplate, which they (I have to assume) intentionally left blank.

I'm going to hunt for my current probes in the morning and see if they will work for these high amps. If they do, I will put this to bed real quick; read the actual power factor on the oscilloscope. Then I'll have a complete picture.


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## strantor (Jun 14, 2018)

...but giving it a bit more thought... That math treats the idler as a load, which it isn't. What if you connected its 3phase output to a purely resistive load, like a heater element? Then would you be able to get more power out of it? Or what if the load were something with an even worse power factor than that of the RPC? This is turning out to be more of a head scratcher than I anticipated. I need to put it on a shelf for tonight, go watch some Netflix, and decide in the morning if I want to venture any further down the rabbit hole to satisfy my OCD-like need for minute details, or just forge ahead with a 125A breaker, 1AWG wire, and trust that everything will be OK. I mean, I now have what _should be_ a sufficient number of indicators that single phase FLA will be around 125A, and if I'm going to get any closer to balls-deep in this, then I should have just built my own RPC. It's frustrating being obsessive, self aware, but still obsessive.

Sorry for the monologue. Typing out what's in my head and reading it back to myself helps me be less stupid.


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## Blackjackjacques (Jun 23, 2018)

strantor said:


> I've been crunching the numbers and I think the missing link is power factor. I normally don't even consider PF in my back-of-the-napkin calculations because in my world of 3 phase motors, it's typically .9 or close to that, so I just lump it in with efficiency and give myself 20-25% headroom. I did not realize what bad power factor RPCs have. According to this page, RPC power factor is commonly as low as 0.65. So if I take the *entire formula* for single phase and 3 phase power, not leaving out anything, and rearrange solving for power factor, given the 76A nameplate 3ph amps and assuming 90% efficiency, I get a power factor of 0.77. Plug that back into the single phase (whole) equation and I get 132A. This makes a lot more sense now.
> 
> 22kw/(240V*0.9*0.77*1.732) = 76.37A
> 22kW/(240V*0.9*0.77) = 132.27A
> ...




Actually, there is sufficient data on the nameplate to determine pf since they give you the VA and W. The VA is 230 x 1.73 x 76 = 30240
So W/VA = pf = 22000/30240=0.73....but you were close enough.


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## strantor (Jul 15, 2018)

Here's an update. I've taken the components off the cart and made a permanent skid for them. The skid has forklift pockets sized for my pallet jack. Altogether I estimate the weight for the 480V skid to be 800-1000lbs. I have some load cells so I will weigh it later; my estimate is based on how the tractor behaves when I lift it. I have more that I want to do with it. I want to build a panel for it with Volt and Amp gauges for each leg of 240v and 480v, with single-button automatic startup sequence and imbalance alarm. That will have to wait. For now I just need the 480V so I can finish that panel I'm building in the background. I finally got the panel powered up this evening. Back to paid work tomorrow.











P.s. if anyone is considering doing something like this, my advice would be to put the RPC on the bottom. It's a good deal heavier than the transformer. Looks are deceiving.


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## Karl_T (Jul 16, 2018)

NICE!  You do quality work.


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## Blackjackjacques (Jul 17, 2018)

strantor said:


> Hello everybody. This thread will serve as a "build log" I suppose. I'm working toward having a 3ph 480V 25A service in my shop. My progress up to now is that I have 3ph 480V with enough current to satisfy a single 3hp VFD and motor that I'm currently working with.
> 
> A bit of background... I'm an industrial Automation/Controls guy. I design & build control panels for industrial machinery, and I like to play around with CNC machines in my spare time. I'm newly self-employed and scrambling to obtain all the resources that I am accustomed to having at previous employers. I'm accustomed to working with 3ph motors exclusively, in facilities with 3ph service. Single phase motors rarely come up in my line of work, so start caps, run caps, split phase, all these terms are a bit nebulous to me, but I'm learning (quickly). The inner workings of the Rotary Phase Converter were/are a total enigma to me, so rather than trying to build one, under the time crunch that I find myself in right now, I decided to buy one. I'm currently designing a large panel for a conveyor line that will have (12) 3HP VFDs in it. The first application for this 480V setup will be to power up and perform FAT on that panel once it is built. Thereafter, it will serve whatever purpose I find for it, most likely refurbishing CNCs and more panel builds.
> 
> ...



I know this post goes back some and may be moot, but looking back at your previous post:
 If I use my own math it looks like this: 

"rated 3ph FLA: 76A*240V*1.73= 31.56kW (42HP!, not 30HP!)......31.56kW/240V = 131A single phase amps"
I believe you are mistaken apparent power, "S" or VA for "W" or Watts.  76 x 240 x 1.73 = 31.6 kVA.  At 30 HP or 22.4 kW, the power factor is 0.71 PF, about what was figured in an earlier post.  This may help explain some of the unclear numbers.   However, your work is nice.  Good luck


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## Redmech (Sep 5, 2018)

Really glad to have found this. What I’m thinking of doing is exactly what you have done. Your video explained exactly what I was looking at doing. 

I purchased a Cincinnati Super Radial arm Drill that has a 15hp 480 3 phase motor on it. My plan is to buy a 30HP RPC and I’m looking at 30kVA transformers. Looking around online i saw one guy run 220 single phase into his transformer then ran the high voltage through his RPC. The way you are doing it makes more sense and your video shows the data to back it up. 

My current plans was to just have all my shop 3 phase motors wired to be 220. But buying this drill press that is 480 3phase only (not a high/low motor) has me thinking to run all my stuff at the 480 V thru the transformer I now have to own. 

I may hit you up with questions at some point.


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