3 phase convertor options

[RichJ]

Hey guys, I am getting a lathe with a 5HP 220V 3 phase 2 speed 3KW motor. It comes with a huge transformer. The shop says it was to convert their 440V 3 phase down to 220V. Now I only have 220V single phase. I am completely new to 3 phase power. So I got a couple questions:

1. What type of phase converter do you guys recommend?
2. Will I still need to use the transformer?

I have already talked to a rotary converter company, they say that I would need a 15HP unit, due to the 2 speed motor 3KW motor. Does anybody think they are trying to upsell me?

On a side note: They said I shouldn't need the transformer. A rotary convertor will only add the third leg and does not increase voltage. Now I know I've seen plenty of stuff on YouTube and other places where guys are running pretty big stuff in their small shops off of a rotary converter. None mentioned using a transformer. I was under the impression that most 3 phase machines run off 440V 3 phase power. Am I incorrect, and is 220V more common? Also if I was to pick up something in the future that requires 440V, what is involved there.

Thanks in advance
Rich J

[lakeside53]

What your location, even county? Please put it in your profile.

Assuming USA...

You can use a Rotary Converter or a Phase Perfect type. 15hp Rotary will be fine (dual speed motors are generally pigs); 10hp Phase Perfect (smallest they make) also. VFD (I'm sure someone will mention it) is a possibility but not as simple to implement if you are electrically challenged.

3 phase is available in a number of voltages and configurations. You do not need the transformer. 240 single phase into the converter, 240 delta three phase out. Don't worry if you motor says "220" - it will just draw slightly lower current at rated output if you deliver 240 to the input terminals.

[Mcgyver]

You don't need a transformer....but hang on to it, if you get a 440V machine you'll be able to run....just hook it up in reverse (what I did to get 600V)

Three common ways to create 3P, Rotary phase converter, static phase converter and VFD

RPC

- not too much money if you DIY
- have to turn it on before using machines (can be a pita)
- can be used for multiple machines
- creates background drone that I don't like
- I built a 10hp RPC, and runs my shop very well - largest motor I run is 7.5

Static
- cheap and cheerful
- instant on
- loss of HP
- Most poo-poo them by I used one for a few years for both lathe and mill, I made a lot of parts, and it didn't seem to hold me back. Worth considering for the "get me going now at lowest cost" option

VFD
- quiet
- instant on
- gets expensive as hp goes up
- pretty much need one per machine
- some other advantages, breaking, soft start stop, speed control

I don't know about two speed motors, but if its 3kw, that's what, 4 HP? i wouldn't have thought it would tax a 7.5 hp rpc. Others more knowledgeable on 2 speed motors might have a better sense of it.

[lakeside53]

Hard starting (lathes in high gear with 2 speed motors) will be marginal with a typical "10hp" RPC with a 4hp dual speed motor. I owned exactly that type of lathe/motor until recently, and now have a 7.5hp dual speed.

I would never use a static converter on a lathe with such a motor. The lathe probably has built-in protection (which will nuisance trip at the wrong time) , but most (imagining what the OP has) are marginal at starting in high speed with three phases. During start up, the motor will attempt to draw as much power as it needs to get up to speed. All the static converter does it get it moving; the spool up time under load can be several seconds longer and running only on single phase during this time causes excessive current demand. A static converter does not "reduce hp". You have to limit the max hp (via current) by the motor protection device; if you don't have one - trouble, if you do it trips.

OP - what lathe are we talking about?

[RichJ]

I am in Chicago, Illinois and it is a Jingzhou 1440 lathe.

[J Tiers]

Lakeside is correct.

2 speed motors are typically pigs, and a 15 HP is quite reasonable for an RPC to run 5 HP. Starting in high speed is a high torque, extended time start. The RPC has to supply the current without too much voltage drop.

On top of that, some machines are even worse pigs in general. I understand that Brazilian WEG motors are obnoxious pigs, drawing more than most on start. It's common to hear of certain brands of machine that just will not start in high speed with an RPC unless it is well above the usual rating.

[Forrest Addy]

You don't need a transformer....but hang on to it, if you get a 440V machine you'll be able to run....just hook it up in reverse (what I did to get 600V)

Three common ways to create 3P, Rotary phase converter, static phase converter and VFD

RPC

- not too much money if you DIY
- have to turn it on before using machines (can be a pita)
- can be used for multiple machines
- creates background drone that I don't like
- I built a 10hp RPC, and runs my shop very well - largest motor I run is 7.5

Static
- cheap and cheerful
- instant on
- loss of HP
- Most poo-poo them by I used one for a few years for both lathe and mill, I made a lot of parts, and it didn't seem to hold me back. Worth considering for the "get me going now at lowest cost" option

VFD
- quiet
- instant on
- gets expensive as hp goes up
- pretty much need one per machine
- some other advantages, breaking, soft start stop, speed control

I don't know about two speed motors, but if its 3kw, that's what, 4 HP? i wouldn't have thought it would tax a 7.5 hp rpc. Others more knowledgeable on 2 speed motors might have a better sense of it.

Excellent bullet point list of attributes. You said in 25 lines of text what takes me three full screens

My preference would be permanently connect the two speed motor for high speed and run the motor from a VFD observing the rule about no contacts to be in the VFD line or load connections

[Danl]

Yep, I can confirm the 6 h.p. WEG motor on my Nardini 1440e lathe required a 20 hp RPC to get it to start at the highest speed.

Not sure if my neighbors lights dim when I fire the RPC up, but I am at the end of this particular power run, and I know the lighting for my mill dim for a second when I start the American Rotary RPC.

Dan

[RWO]

You can get a 3hp VFD that will run on 230v single-phase for about $350. It should run your lathe adequately as is since 3 hp is usually plenty for even a 14" HSM machine. You then will have all the advantages of variable speed which is a lovely thing to have.

RWO

[Danl]

Based on my experience with the 2 speed motors, and given that 3KW = over 4 hp, I'd suggest a 5 hp RPC.

Dan L

[J Tiers]

Based on my experience with the 2 speed motors, and given that 3KW = over 4 hp, I'd suggest a 5 hp RPC.

Dan L

out of curiosity, where do you get that?

RPC is normally at least 1.5 x HP of load, and that is for normal loads.

Did you perhaps mean "VFD" and not "RPC"?

[Danl]

Jerry,

I was just trying to be more conservative with the hp rating than RWO, who suggested a 3 hp RPC.

So, using your 1.5 x 4.02, I should have suggested 6 hp? (3KW = 4.02 hp)

Dan

[Mcgyver]

Jerry,

I was just trying to be more conservative with the hp rating than RWO, who suggested a 3 hp RPC.

So, using your 1.5 x 4.02, I should have suggested 6 hp? (3KW = 4.02 hp)

Dan

I'm lost too....you said you needed 20hp rpc to get a 6 hp two speed motor going? the OP's motor is a 4hp two speed....so based on your experience with the 6hp, wouldn't it need a 15 hp rpc?

[PStechPaul]

RWO suggested a 3 HP VFD, not RPC. A VFD, with ramp-up to speed, can probably handle most motors 3 HP or less. But for a 4 HP two speed motor, I think a 5 HP (or more) VFD would be best.

[Danl]

RWO suggested a 3 HP VFD, not RPC. A VFD, with ramp-up to speed, can probably handle most motors 3 HP or less. But for a 4 HP two speed motor, I think a 5 HP (or more) VFD would be best.

Arghhh.... sorry. My ignorance or at least inability to read and comprehend !!!

Dan