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Rotary phase converter shopping list

J

jlmtb1

Plastic
Joined
May 19, 2017
Hey
I've since purchased a 7.5hp 3 phase lathe and looking at the best way to power it off 240v Australia single phase power
I've read pages of how to on them and there seems to be a endless variations of how people do it. From complex to basic.
My question is, what would the shopping list be to build a RPC to run a 7.5hp lathe. I want to work out the cost and availability of parts.
Thanks it advance.


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jlmtb1 said:
I've read pages of how to on them and there seems to be a endless variations of how people do it. From complex to basic.
My question is, what would the shopping list be to build a RPC to run a 7.5hp lathe. I want to work out the cost and availability of parts.
Thanks it advance.
Click to expand...

What is your plan? To build one of every possible "endless variation"? Basically, they ALL "work".

Shouldn't need much third-party / community help if you do the simplest thing FIRST.

PICK ONE of those "endless" variations. Ignore the others.

Order parts only for the ONE you picked.

How hard was that?

:D

PS: I happen to HAVE - under roof - the parts to build MOST of those "variations".

Also other demands on my time.

I cheated. Simply left the parts where they sat. Bought a new 10 HP Weg 3-P motor for idler. THEN - once I knew idler motor HP and RPM, and not BEFORE - bought an already "engineered" solution-in-a-box. A Phase-Craft spec'ed to work with the idler motor's characteristics.

Motor plus shipping was the larger part of the cost. THAT is worth seeking a bargain on. Or a used one. Do that part first.

THEN you know more as to what the "controls" need to be and do, whether bought OR built.
 
Plan is to build one that a. Works and does the job and b. Is cheap and parts are available.
I know the general parts needed but I was hoping someone could give me some specifics of parts so I can hunt down some prices and suppliers.


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jlmtb1 said:
Plan is to build one that a. Works and does the job and b. Is cheap and parts are available.
I know the general parts needed but I was hoping someone could give me some specifics of parts so I can hunt down some prices and suppliers.
Click to expand...

?? Why d'you think there ARE so many variations? One reason is that it just ain't that critical.

I say again - sort the idler motor FIRST. A 10 Hp should do yah nicely for a 7.5 HP lathe.

Shipping alone on the idler motor can be more than cost of a few capacitors, switch, and a relay or two. A "rated" (Australian rules, of course..) fused disconnect can also cost more than capacitors & c. Proper wire, outlets, cord, etc. are wotever they are for "Afghanistan", Australia (fix your location, willyah).
 
Yea I know I need to change that from Afghanistan haha
So I'll get a 10hp 3 phase motor first. Any specific specs or rpm of motor matter?


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jlmtb1 said:
Yea I know I need to change that from Afghanistan haha
So I'll get a 10hp 3 phase motor first. Any specific specs or rpm of motor matter?


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Click to expand...

RPM matters to the controls for best match. Otherwise, slower is quieter, has lower "windage" loss. 4-pole is cheap and common. Less-common 6-pole or 8-pole, the motor can get more expensive. Or maybe not - IF you find a decent used one.

No difference in the "quality" of the output, though.
 
Monarchist said:
RPM matters to the controls for best match. Otherwise, slower is quieter, has lower "windage" loss. 4-pole is cheap and common. Less-common 6-pole or 8-pole, the motor can get more expensive. Or maybe not - IF you find a decent used one.

No difference in the "quality" of the output, though.
Click to expand...


I highly recommend a motor with 1,750 rpm. The first RPC that I had was a Phoenix brand. I discovered that it had a 3,450 rpm motor that was over-rated by the seller. It also wailed like a banshee when in operation.

That might not make much difference if the unit is outside or in another room, but if it's anywhere near where you are working on the lathe, you won't like it.

There are variations as mentioned, but the one that I like is a self starting RPC with proper controls so that it won't restart if you are away when power is shut off due to some failure.

I like RPC's because I have only one 3 phase machine and it's a variable speed mill. Also, since I built my own RPC, I can fix anything on it if there is ever a problem. Good advice above on getting a nice 10 hp motor. WYE connected would be good.
 
Newman109 said:
I highly recommend a motor with 1,750 rpm. The first RPC that I had was a Phoenix brand. I discovered that it had a 3,450 rpm motor that was over-rated by the seller. It also wailed like a banshee when in operation.

.....
Click to expand...

For the OP that will be on the order of 1450 RPM, as he will be starting with synchronous speed of 1500 RPM (3000 for 2 pole).
 
jlmtb1 said:
My question is, what would the shopping list be to build a RPC to run a 7.5hp lathe. I want to work out the cost and availability of parts.
Click to expand...

1. 10 Hp 3 phase motor. 1800 or 1750 RPM. TEFC will cost more than open frame type.
2. Breaker for single phase power.
3. Motor starter with motor overload protection and push button switches for on and off. Or a Manual motor starter.
4. Indicator lamp(s).
5. Start capacitors.
6. Run capacitors.
7. Relay for start capacitor.
8. Fuses and fuse block.
9. Enclosure.
 
Thank you for all the help. So I'll get a 10hp motor first. As far as start capacitors it seems that it's a bit of a guessing game? Does 300uF for the start and 50uF for run sound like a starting point? As I'll be buying new and don't want to be buying to many to get the correct size.


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jlmtb1 said:
Thank you for all the help. So I'll get a 10hp motor first. As far as start capacitors it seems that it's a bit of a guessing game? Does 300uF for the start and 50uF for run sound like a starting point? As I'll be buying new and don't want to be buying to many to get the correct size.
Click to expand...

It isn't so much a "guessing game" as simply a not overly critical item as to start. Larger ones start faster or start a larger motor, but cost more and put a larger shock load on the upstream feed. Makers & DIY builders each make the compromise they are comfortable with. Rope-start or pony start RPC may not use a start cap AT ALL.

"Run" capacitor right-sizing depends on percentage load or how variable the load(s). Some folk experiment to see what works best for their loads or provide for switching "extra" capacitance in and out.

Switch and relay selection is another "choice". Some folk don't mind a manual hold-til good switch - we are talking anywhere from a few seconds to under half a full minute, usually. Others want flip and go, local and/or remote, with or without meters or indicator lamps.

Enclosures, wire and fuse or breaker size is another.

Akin to choosing a meal, actually.

Should be safe food, not poisonous, also affordable, and nutritious.

Otherwise? What do YOU, your loads - and/or your local electrical codes - need or want optimized?
 
Hi jlmtb1,
I am assuming you live and want to operate this 7.5 HP Lathe in Afganistan, and you made reference to 240v Australian single phase power. So I am assuming Afgantistan has the same power supply as in Australia, which is 240v/415v or by our electrical standards 230v/400v.If so you will need a transformer to change 240v to 415v. My advice would be to change 240v single phase to 415v single phase first.

Jim
 
Hey Jim
I'm in Australia too but for some reason it auto set my location to Afghanistan. (Trying to change it)



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jlmtb1 said:
Thank you for all the help. So I'll get a 10hp motor first. As far as start capacitors it seems that it's a bit of a guessing game? Does 300uF for the start and 50uF for run sound like a starting point? As I'll be buying new and don't want to be buying to many to get the correct size.
Click to expand...

If you buy oil filled AC capacitors then you can build a value for the start capacitance. Then any left-overs can migrate into the run capacitor selections. Two run capacitors is what I use. Oil filled cost more but won't likely explode one day. That happened to one of my motors a few days ago.

I use 210uF for starting a 5Hp motor. And then use a 50uF and a 90uF for my run capacitors. I switch a 120uF in parallel with a 90uF for starting, after the start the 120uF is switched out and the 90uF is left in circuit for the T2 - T3 run value. The other run capacitor of 50uF is always in circuit for the T1 - T3 value. I am not sure if you can simply double the values here for a 10Hp motor.
 
So I picked up a teco 1450 rpm 10hp motor to build the RPC. Hopefully it should do the job?
In Australia (and possibly everywhere else)we have a active, a neutral and a earth. So am I right in saying active goes to one leg and neutral to the second leg?


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I'm trying to get my head around the wiring so I tried to draw a simple wiring diagram but I apologise if it's completely wrong. Is this anywhere near what it should be like? I've picked up the 10hp motor and I'm ordering the capacitors and switches today. So I want to work out how it all goes together now.
I can't seem to find any correct relays to switch the start capacitor off, but if I wired it as shown with a momentary switch to power the start capacitor. Then when the switch is released it will just have the run capacitor in the circuit?
IMG_4339.JPG


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Hi jlmtb1
This drawing can not possibly work because you can not input 240v and output 415v with what you have shown. Could you please post a clear image of your 10HP motor rating plate so I can see what your Motor is. I said earlier you will need a transformer if you want 415v don't order any capacitors because if you are using 415v your capacitor values will be less. Most small relays are suitable to switch out the start capacitors using a heavier relay.
Where about are you?

Jim
 
jlmtb1 said:
I'm trying to get my head around the wiring so I tried to draw a simple wiring diagram but I apologise if it's completely wrong. Is this anywhere near what it should be like? I've picked up the 10hp motor and I'm ordering the capacitors and switches today. So I want to work out how it all goes together now.
I can't seem to find any correct relays to switch the start capacitor off, but if I wired it as shown with a momentary switch to power the start capacitor. Then when the switch is released it will just have the run capacitor in the circuit?
View attachment 211536
Click to expand...

- Do not "switch" (nor fuse, nor circuit-breaker-protect..) EITHER of the Protective Earth (Ground) or "Neutral" lines. If even you carry a Neutral. Which usually one does NOT on RPC or Phase-Perfect unless "re-deriving" a local Neutral with a Delta to Wye transformer between RPC or Phase-Perfect and the load.

Proper relays are needed for unattended start, may be useful for remote manual start, longish wire runs. With loads that cycle on a regular basis, such as air compressors, RPC "dedicated", yes, relays.

For a lathe or a mill, seldom needed, where one is "the activator in Chief" and in-person, hands-on, ELSE RPC not being used atall, a momentary switch is fine.
 
I think I've found a problem then. In Australia single phase power we have 3 wires. Active, neutral and earth. So what wires would go to the 2 legs if not using the neutral wire?


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