Rotary or static converter?

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: Harold_V, GlennW

User avatar
Richard_W
Posts: 1970
Joined: Fri Jan 10, 2003 1:00 am
Location: Molalla, Oregon

Re: Rotary or static converter?

Post by Richard_W » Fri Mar 19, 2021 11:12 am

I used a static converter on a Jet mill with a step head 2 speed motor. It worked fine because there wasn't a lot of mass to start moving.

On another note, I had a 14" Jet lathe that was a gear head with a 2 hp motor in it. The same static converter would only run the lathe at lathe below 500 RPM. I actually blew out the capacitor in the static converter after a few attempts to run at a higher RPM. It required a rotary phase to work.

On my present lathe a 16" Pratt & Whitney I am running what I think is 10 HP rotary phase converter. Its label is missing. Its a real old school converter from back in the day when 3 phase wasn't available. My lathe has a 7 1/2Hp motor under it. Under a heavy cut it wasn't the converter that had problems, but the 40 AMP breaker tripped. Still haven't upgraded the breaker to a 50AMP yet. The welder requires a 50 AMP but works fine so far with the 40 AMP breaker.

Richard W.

Harold_V
Posts: 19111
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Rotary or static converter?

Post by Harold_V » Fri Mar 19, 2021 3:01 pm

Richard,
Keep in mind, the breaker's purpose is to protect the wiring to the receptacle. If you replace the breaker and the wire isn't upgraded, you may find that the wire runs hot when you're drawing a heavy load. Switching to a larger breaker may not be a good idea.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

User avatar
Richard_W
Posts: 1970
Joined: Fri Jan 10, 2003 1:00 am
Location: Molalla, Oregon

Re: Rotary or static converter?

Post by Richard_W » Fri Mar 19, 2021 10:21 pm

Harold_V wrote:
Fri Mar 19, 2021 3:01 pm
Richard,
Keep in mind, the breaker's purpose is to protect the wiring to the receptacle. If you replace the breaker and the wire isn't upgraded, you may find that the wire runs hot when you're drawing a heavy load. Switching to a larger breaker may not be a good idea.

H
I have kept that in mind. I am running 8 Gage wire. I run the lathe and welder from the same cord, since being one person there is no danger of running both machines at once.

Richard W.

JackF
Posts: 1578
Joined: Mon Jan 26, 2009 3:56 pm
Location: Caldwell, Idaho

Re: Rotary or static converter?

Post by JackF » Sat Mar 20, 2021 11:39 am

I have a lincoln Idealarc Tig 300 That draws 100 amps at full power. I have 4 gage wire to the outlet but have only a 60 amp breaker in the box as that was all I had. I have never tripped the breaker but then I have never used it at full power :roll: . Maybe someday when I feel rich I will upgrade that breaker. :wink: :lol:

Jack

User avatar
Richard_W
Posts: 1970
Joined: Fri Jan 10, 2003 1:00 am
Location: Molalla, Oregon

Re: Rotary or static converter?

Post by Richard_W » Sat Mar 20, 2021 1:50 pm

JackF wrote:
Sat Mar 20, 2021 11:39 am
I have a lincoln Idealarc Tig 300 That draws 100 amps at full power. I have 4 gage wire to the outlet but have only a 60 amp breaker in the box as that was all I had. I have never tripped the breaker but then I have never used it at full power :roll: . Maybe someday when I feel rich I will upgrade that breaker. :wink: :lol:

Jack
That is my situation. I have a Miller Thunderbolt stick welder. I use 1/8" 7018 rod mostly. So I never crank the welder up to full AMP draw.

Richard W.

User avatar
BigDumbDinosaur
Posts: 1429
Joined: Tue Jun 28, 2011 9:19 pm
Location: Midwestern United States

Re: Rotary or static converter?

Post by BigDumbDinosaur » Sun Mar 21, 2021 2:05 am

Richard_W wrote:
Fri Mar 19, 2021 10:21 pm
I have kept that in mind. I am running 8 Gage wire. I run the lathe and welder from the same cord, since being one person there is no danger of running both machines at once.
8 AWG is too small for the current you are pulling.
——————————————————————————————————
Research is what I'm doing when I don't know what I'm doing.

Harold_V
Posts: 19111
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Rotary or static converter?

Post by Harold_V » Sun Mar 21, 2021 4:12 am

BigDumbDinosaur wrote:
Sun Mar 21, 2021 2:05 am
Richard_W wrote:
Fri Mar 19, 2021 10:21 pm
I have kept that in mind. I am running 8 Gage wire. I run the lathe and welder from the same cord, since being one person there is no danger of running both machines at once.
8 AWG is too small for the current you are pulling.
Depends on the insulation. If it's in a raceway and THHN (or equivalent), or in a cable, it's perfectly safe. Rated @ 50 amps. Even higher with open wires. That's assuming it's copper, not aluminum wire. If the wire is either aluminum or type TW or UF, yeah, it's not suited (rated @ 40 amps).

H
Wise people talk because they have something to say. Fools talk because they have to say something.

User avatar
BigDumbDinosaur
Posts: 1429
Joined: Tue Jun 28, 2011 9:19 pm
Location: Midwestern United States

Re: Rotary or static converter?

Post by BigDumbDinosaur » Sun Mar 21, 2021 3:43 pm

Harold_V wrote:
Sun Mar 21, 2021 4:12 am
BigDumbDinosaur wrote:
Sun Mar 21, 2021 2:05 am
Richard_W wrote:
Fri Mar 19, 2021 10:21 pm
I have kept that in mind. I am running 8 Gage wire. I run the lathe and welder from the same cord, since being one person there is no danger of running both machines at once.
8 AWG is too small for the current you are pulling.
Depends on the insulation. If it's in a raceway and THHN (or equivalent), or in a cable, it's perfectly safe. Rated @ 50 amps. Even higher with open wires. That's assuming it's copper, not aluminum wire. If the wire is either aluminum or type TW or UF, yeah, it's not suited (rated @ 40 amps).

H
Except it's powering a motor, which is an inductive load, not resistive. Unless the motor's power factor is unity (which is unattainable without use of power factor-correcting capacitors), KVA will be greater than watts, resulting in higher than apparent current flow.
——————————————————————————————————
Research is what I'm doing when I don't know what I'm doing.

User avatar
Richard_W
Posts: 1970
Joined: Fri Jan 10, 2003 1:00 am
Location: Molalla, Oregon

Re: Rotary or static converter?

Post by Richard_W » Tue Mar 23, 2021 7:35 pm

Harold_V wrote:
Sun Mar 21, 2021 4:12 am
BigDumbDinosaur wrote:
Sun Mar 21, 2021 2:05 am
Richard_W wrote:
Fri Mar 19, 2021 10:21 pm
I have kept that in mind. I am running 8 Gage wire. I run the lathe and welder from the same cord, since being one person there is no danger of running both machines at once.
8 AWG is too small for the current you are pulling.
Depends on the insulation. If it's in a raceway and THHN (or equivalent), or in a cable, it's perfectly safe. Rated @ 50 amps. Even higher with open wires. That's assuming it's copper, not aluminum wire. If the wire is either aluminum or type TW or UF, yeah, it's not suited (rated @ 40 amps).

H
Its an 8 gauge SO cord all copper. It was made for the welder.

Richard W.

User avatar
Bill Shields
Posts: 7014
Joined: Fri Dec 21, 2007 4:57 am
Location: Somewhere in the World
Contact:

Re: Rotary or static converter?

Post by Bill Shields » Tue Mar 23, 2021 8:36 pm

Generally SO and SJ cords are copper...never seen any that is not.. .and I have used a lot of it in the last 50 years. => but there is a lot of stuff out there that I have never seen.

Just look at it...if it looks like copper when you cut the insulation off..then it is copper.
Too many things going on to bother listing them.

Harold_V
Posts: 19111
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Rotary or static converter?

Post by Harold_V » Wed Mar 24, 2021 1:43 am

This entire matter is a little tricky. The motor is reported to be 7½ horse, but the rotary is assumed to be 10 horse. Running from single phase 240 volts, the recommended breaker would be 90 amps (for a 10 horse motor), while it would be 80 amps for a 7½ horse motor. Wire size for the 90 amp would be #6, while wire size for the 80 amp would be #8. This according to the Motor Data Calculator published by Square D.

That is not to say that the setup won't work with a 50 amp breaker. It will, and it will be perfectly safe. If there are any issues, it will be with tripping the breaker, which would be likely to happen if the motor was cycled on and off regularly, or if it was subjected to a full load continually. Neither scenario is likely to happen. Go for it!

H
Wise people talk because they have something to say. Fools talk because they have to say something.

shootnride
Posts: 297
Joined: Tue Jun 05, 2012 12:31 am
Location: Sacramento, Ca.

Re: Rotary or static converter?

Post by shootnride » Wed Mar 24, 2021 9:33 am

Harold_V wrote:
Wed Mar 24, 2021 1:43 am
This entire matter is a little tricky. The motor is reported to be 7½ horse, but the rotary is assumed to be 10 horse. Running from single phase 240 volts, the recommended breaker would be 90 amps (for a 10 horse motor), while it would be 80 amps for a 7½ horse motor. Wire size for the 90 amp would be #6, while wire size for the 80 amp would be #8. This according to the Motor Data Calculator published by Square D.

That is not to say that the setup won't work with a 50 amp breaker. It will, and it will be perfectly safe. If there are any issues, it will be with tripping the breaker, which would be likely to happen if the motor was cycled on and off regularly, or if it was subjected to a full load continually. Neither scenario is likely to happen. Go for it!

H
I agree completely. These current ratings for conductors and breakers are for an assumed continuous full load. I suspect that most home shops aren't running a continuous 80 or 90 Amp load.
I have a single 240V, 50A single phase receptacle in my small shop that I share between my welders and my 10HP RPC. The receptacle is fed from a 50A breaker via #6 wire and I have never experienced a single issue in the 10 years it's been in service.

Ted
Some people raise the IQ of the room when they enter.........others when they leave.

Post Reply