Sizing Rotary Phase Converter Components

[cannuck]

I am finally getting around to using my new-to-me Cheng Ki Bridgeport clone. It is 3 phase, so need to build a 5HP phase converter (it has a total load under 3HP). Since we actually have an electrical forum on GJ, and a lot of sparkies who sure as heck know this stuff far better than I do, here goes:

I think I have enough information from many searches to be able to size the start and run capacitors, but I have a more esoteric question to get straight:

I am building around a 5HP idler that name plates out at 14 Amps @ 220V 3ph. If I assume to be loading up 2 windings to make 5HP that should in my relative electrical ignorance need/draw amperage of a 5HP single phase motor (28 @ 230V). Before I plunk down some cash for a motor contactor I want to be comfortable that this assumption is correct or at least close. Have wired it's supply circuit with 10 ga with 30A breaker and socket for twist lock. Expect to use Square D 8910DPA33V02 Definite Purpose Contactor rated a 30A and 5HP single phase and with 120V pull in coil.

Am I over, under or close on (or just missing the whole thing)?

 

[wyliesdiesels]

@Bert_

 

[Bert_]

I've never built a rotary converter. I have been around quite a few factory made ones. I am not an expert.

Are you switching the single phase power to the converter with that contractor?

A 30A contactor isn't much. For the price of what you linked you could have a 60A contactor and if nothing else it will last longer.

I wouldn't be surprised if you have nuisance tripping with a 30A breaker.

 

[cannuck]

I've never built a rotary converter. I have been around quite a few factory made ones. I am not an expert.

Are you switching the single phase power to the converter with that contractor?

A 30A contactor isn't much. For the price of what you linked you could have a 60A contactor and if nothing else it will last longer.

I wouldn't be surprised if you have nuisance tripping with a 30A breaker.

I try to keep things co-ordinated. Should only see 30A on circuit during startup, so very little part of run time. Probably should use a motor starter, though and move protection from panel down to the converter.

 

[cgrutt]

I had plans to build one about 5 years ago based of a 7hp Baldor motor but never completed it. Still have a bunch of caps that I bought for it but never used. If you're interested LMK I'll take some pics.

 

[Sumboodie]

Vfd

 

[Bert_]

I don't think you can really overload an idler. The hardest part is when no machinery is running and the idler has to absorb all the capacitor current.

The ronk rpc's I've installed never had any more protection than a fused disconnect.

 

[American Locomotive]

Your starting gear should be sized for the idler motor, and yes, you probably would want a motor starter to protect the idler in case something bad happened.

However, you really probably should just sell the idler and get a variable frequency drive. For $200 you can get a 3HP rated drive that accepts single phase input power. It's more compact, much quieter, and gives you infinite speed adjustment which is super useful on a mill.

https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/micro_vfds/gs11n-23p0

 

[dave*99]

I helped 2 of my friends buy and set up Bridgeport mills. One used a RPC, the other a VFD. I programmed the VFD. It was easy. Small, light weight, nice speed control and ramped start up and stop speed.

I'm thinking it you have a shop full of 3 phase equipment and want to use a big RPC to power all, perhaps that's a good reason to use one.

The VFD was economical, offers great control, and has been working well for 20 years now. There are some good threads on GJ showing how to use the switch on the Bridgeport to control the VFD etc.

You must hardwire the Bridgeport motor directly to the VFD and use the VFD controls. The Bridgeport switch gets connected to the control inputs (after some rewiring) of the VFD if you like. Otherwise you can use the buttons on the VFD or add your own remote buttons on the mill.

 

[cannuck]

I had plans to build one about 5 years ago based of a 7hp Baldor motor but never completed it. Still have a bunch of caps that I bought for it but never used. If you're interested LMK I'll take some pics.

I would appreciate any and all information, experiences and opinions, as I expect anyone reading this will as well.

 

[cannuck]

Vfd

VFD can only run one motor at a time. Using PRC all 3 on the mill are operative.

 

[cannuck]

I don't think you can really overload an idler. The hardest part is when no machinery is running and the idler has to absorb all the capacitor current.

The ronk rpc's I've installed never had any more protection than a fused disconnect.

I am letting the 30A breaker be the primary point of protection, but wondering if going from simple relay to motor starter as main connection offers anything better.

 

[cannuck]

Your starting gear should be sized for the idler motor, and yes, you probably would want a motor starter to protect the idler in case something bad happened.

However, you really probably should just sell the idler and get a variable frequency drive. For $200 you can get a 3HP rated drive that accepts single phase input power. It's more compact, much quieter, and gives you infinite speed adjustment which is super useful on a mill.

https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/micro_vfds/gs11n-23p0

Thx re: motor starting relay. But, as I mentioned above VFDs will not work with multiple motors. I just need to get 3ph delta into the mill cabinet where it takes it apart to run single phase pump and variable speed electric feed drive.

 

[cgrutt]

I would appreciate any and all information, experiences and opinions, as I expect anyone reading this will as well.

Unfortunately I had all the parts but I never built it (situation changed and I had to sell an old lathe that I had intended to use it on. I did alot of research about it and settled in on a plan I believe I found at Practical Machinist forum. I had planned to use and purchased a Baldor 7.5HP motor. I still have 3 Dayton Start caps, 4 Proline 35/7.5 MF and 6 Proline 70/7.5 MF that I had sized based on configuration in the plan. I also have some bleed resistors to discharge caps when not in use and a potential relay. I had purchased some other parts, a couple of contractors, magnetic starter switch and a good electrical enclosure but I had sold those. I'll see if I can track down a link to the plans. I had considered a VFD but decided on the RPC mainly due to size of the lathe I had (it was pretty large) IIRC.

 

[American Locomotive]

Thx re: motor starting relay. But, as I mentioned above VFDs will not work with multiple motors. I just need to get 3ph delta into the mill cabinet where it takes it apart to run single phase pump and variable speed electric feed drive.

It was unclear that your mill had three motors. However you say the pump and variable speed feeds are single phase, so I'm not sure what the problem would be? You'd just run 240v single phase directly to those components, while the spindle motor gets connected to the drive.

 

[cannuck]

I helped 2 of my friends buy and set up Bridgeport mills. One used a RPC, the other a VFD. I programmed the VFD. It was easy. Small, light weight, nice speed control and ramped start up and stop speed.

I'm thinking it you have a shop full of 3 phase equipment and want to use a big RPC to power all, perhaps that's a good reason to use one.

The VFD was economical, offers great control, and has been working well for 20 years now. There are some good threads on GJ showingow to use the switch on the Bridgeport to control the VFD etc.

You must hardwire the Bridgeport motor directly to the VFD and use the VFD controls. The Bridgeport switch gets connected to the control inputs (after some rewiring) of the VFD if you like. Otherwise you can use the buttons on the VFD or add your own remote buttons on the mill.

Yes, I have a lot of 3ph stuff, but most of it far too large for the measley 100A coming into the small shop at home. Power in back alley is unfortunately a single phase line and I did allow for a 200A service entry directly to shop, but in reality I need to concentrate on putting enough money aside to build full size facility on our farm. Then I can use the big stuff, but for now would be nice to be able to run some saws, grinders, the mill, etc. from small power supply.

 

[cannuck]

It was unclear that your mill had three motors. However you say the pump and variable speed feeds are single phase, so I'm not sure what the problem would be? You'd just run 240v single phase directly to those components, while the spindle motor gets connected to the drive.

I don't want to re-wire the mill or any other tool. If and when they move to new shop need to minimize hassles to get stuff up and running.

 

[niget2002]

I wish I could help. I cheated and bought mine from American Rotary. I bought an AR10F. Looks like it was just under $1k when I bought it a few years ago. My mill is only 3hp, but I bought the larger size in case I ever get a lathe. I'd only ever run one at a time, but not sure what size lathe I'd end up with.

 

[American Locomotive]

I don't want to re-wire the mill or any other tool. If and when they move to new shop need to minimize hassles to get stuff up and running.

Is the idea to use this RPC on multiple pieces of equipment, or just the mill?

 

[cannuck]

Is the idea to use this RPC on multiple pieces of equipment, or just the mill?

Mill for now, but need to keep available for several other machines (mostly saws and grinders)

 

[LukeOresk]

Hey, no experience with a phase converter but if this is on a residential property your utilities might not like it. This is a clip from hydro ones agreement.

And this is just me thinking, i know you don’t want to rewire to avoid hassles but unless the next ship is three phase and you can just use a transformer, wouldn’t you have the same problems there?

 

[Cruzan80]

Luke, I would be surprised if that was tightly enforced. With those rules, a 2-stage compressor that is actually 5HP (under 30A) would violate what you posted. Hard to believe nobody has more than a big box compressor in their residence...

 

[cannuck]

I have been running as much as 70A on one of my welders without any grief, but new shop will indeed be 600V service with 480, 415 and 208 coming from transformers (have them now) for various circuits/tools.

 

[cannuck]

Have been reading through a 2006 thread at PM and getting some good information. Ordered a 30A 2 pole contactor to energize box with and a 3 pole 25A to connect to 3ph plug outgoing. Salvaged a couple boxes from old equip and got one empty one that should hold capacitors and one with back plane and 2 push buttons/lights and a mess of equipment. I will only use the fuses, DIN rail and terminal strip in mine. I think I know enough of what I am going to do to make first drawing. Strangely about the best deal on caps seems to be Grainger - quite a surprise.

Have "ballpark" advice of 400uF for start cap and 70uF for run caps between L1 - L3 and L2 - L3 (i.e. L3 generated leg). What I still don't know is how to size the drain resistors for starting cap. Think I will rig up breadboard and test before selecting an L1-L2 power correction factor cap, or maybe try a trim of second run cap first, then select the 3rd.

 

[Ultradog MN]

I built two RPCs with kits from the company below.
First one was for my own shop = 7.5 hp idler.
Second one was for a friend = 5 hp.
I do a bit of scrounging around and know a couple of scrappers who give me a heads up on stuff so I got the 7.5 hp motor for $25 and the 5 hp for $50.
For both of them I bought a kit from below and had to buy the enclosures so have about $200 in each of them.
The kits came with EZ to follow wiring diagrams - and I ain't no electric guru.
My 7.5 rpc runs any of my now six 3 phase machines.
I can start my 1 hp band saw on a long cut and at the same time do heavy hogging on my 3 hp lathe. Or drill holes with the drill press while my 88 yo pal Kenny sharpens his Bush Hog blades on the big grinder.
I understand that VFDs have their advantages but I am happy to stick with One RPC.

Phase Converter kits ( Rotary Style )

phaseconverterusa.com

 

[cannuck]

I built two RPCs with kits from the company below.
r.
I understand that VFDs have their advantages but I am happy to stick with One RPC.

The prices shown in your link are mind boggling compared to what I have to pay up here! If I walk into an electrical wholesaler I can't buy one single contactor for the price of their whole 5HP kit! Fortunately Amazon can come to rescue to supply some PRC junk. I also have access to the junk bin at former EE customer, but most of what I have salvaged is not good match for this project. This may sound silly, but I am trying to puzzle through the design/build of this thing more or less on my own. Too many years of just writing up a list of requirements and handing to EE or CET for a design and seeing that given to the shop to build while I designed and built the mechanical parts. Time I learn to do a bit of sparky thinking on my own.

 

[American Locomotive]

Have "ballpark" advice of 400uF for start cap and 70uF for run caps between L1 - L3 and L2 - L3 (i.e. L3 generated leg). What I still don't know is how to size the drain resistors for starting cap. Think I will rig up breadboard and test before selecting an L1-L2 power correction factor cap, or maybe try a trim of second run cap first, then select the 3rd.

Some start caps have them built in, or attached directly at the top. Get something like a 1-watt 56kohm resistor. It will fully discharge the cap in about a minute.

 

[jar944]

Hey, no experience with a phase converter but if this is on a residential property your utilities might not like it. This is a clip from hydro ones agreement.

What they don't know..

If I followed that I wouldn't be able to run 90% of the machines in my shop.