LumberJocks

3 Phase in the wood shop

  • Advertise with us

« back to Power Tools, Hardware and Accessories forum

Forum topic by TopamaxSurvivor posted 01-25-2011 02:22 AM 2196 views 0 times favorited 5 replies Add to Favorites Watch
View TopamaxSurvivor's profile

TopamaxSurvivor

17669 posts in 3138 days


01-25-2011 02:22 AM

Topic tags/keywords: 3 three phase 120 208 240 480 y delta vfd variable frequency drive roto electronic converter

3 phase comes in 2 common models in the US for small motors. Delta, which is a triangle transformer connection with the power wires coming off the corners of the triangle. The other and most common, at least in the NW, is a Y. The transformer is connected with the 3 phases coming off the ends of the Y. The center of the Y is grounded so as to create a neutral. From each corner to the grounded center is 120 V. From any end to any other end is 208. All 3 ends make 208 3 phase. Any 2 corners are 208 single phase.

The delta gives 240 volts from any corner to any other corner. All three corners make 240 3 phase. Any 2 corners of the triangle is 240 single phase. You ground the center of any side of the triangle to get access to 120 volts. When you ground the one side, you have 120/240 single phase with those 3 wires. The 4th wire coming from the odd corner gives what is commonly known as a “high leg.” It is supposed to be marked Orange. The voltage to the neutral on the high leg is approximately 190 volts. If you see a panel with a 120 volt circuits and every third breaker is missing, it is 120/240 3 phase with a high leg. The high leg can only be used for 240 single phase or 240 3 phase connections. If it gets connected on a 120 volt circuit, it will probably cause the smoke to come out of the equipment. We all know, electrical devices work best with the smoke left intact!! ;-))

The other common 3 phase voltage is 480/277 Y. Most 3 phase motors will have 9 leads in the connection box for dual voltage connections; either 208/480 or 240/480. If the motor is marked 240, it will run on 208, but it needs a Service Factor (SF) of 1.25. Motors used to have SF of 1.15 or 1.25. I have seen them with 1.0 lately. The SF tells you how much of an overload the motor will handle without any damage.

Connecting 3 phase motors using single phase is much easier with the latest Variable Frequency Drive technology. Basically they erase the voltage coming in and give you anything you want out. A VFD is a much better option than an electronic phase converter. The converter just fools the motor into thinking it has 3 phase and is not very efficient. The other option is a rotary phase converter. It is much better that an electronic phase converter and will start motors under load such as pumps or compressors. The electronic versions will start no load motors such as table saws just fine. With the technology of drives, that is the method of choice today.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence


5 replies so far

View Dez's profile

Dez

1162 posts in 3540 days


#1 posted 01-25-2011 02:30 AM

My buddy at the cabinet shop used a 5 H motor and a “box” to create 3 PH for his drilling machine. While I have heard that this setup will not work for some CNC machines it seemed to work fine for his equipment. What is up with all that? (How does it work?)

-- Folly ever comes cloaked in opportunity!

View TopamaxSurvivor's profile

TopamaxSurvivor

17669 posts in 3138 days


#2 posted 01-25-2011 02:49 AM

The box has a capacitor or a few of them giving the three phase a direction when it is turned on. You can run a three phase motor with just another three phase motor connected to single phase power. You have to physically give the idler motor a spin in the right direction to get it started. It is not very efficient, but will work on low load. The capacitors are just giving it that spin.

A mechanic I used to know called me to connect his 3 phase compressor for his busy 5 bay auto shop. That 30 years ago. Electronic phase converters where being commercially offered, but I quoted him a price to use a real rotophase to start his compressor. He found someone to scab in an old motor in series with the compressor, complained about having to spin it every morning and bragged about what a good deal he got. Wasn’t too long before he called me wanting to know why his compressor would not run ;-)) The compressor motor was running overloaded continuously and burned up, that is why. If it had been a lathe or table saw, he would probably have been fine. If doing that, it is imperative to have proper overload protection. I mean a motor starter with overload heaters, not a circuit breaker. I seriously doubt if it would pass inspection in WA. But, if all the parts are UL listed, just not for the purpose.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Karson's profile

Karson

35035 posts in 3863 days


#3 posted 01-25-2011 03:37 AM

I’ve used 3 phase in my shop for about 30 years. The first 20 years was with a whole box of starting capacitors and running capisitors and single phase 220 volts. For about the last 10 years i’ve been using an electronic Phase Converter that creates the third phase as a starting kick and them lets everything run on single phase.

I’ve always ment to build a rotaty phase converter and had a line on a 10 hp 3 phase motor which the juck yard wouldn’t sell and then 2 weeks later it was trashed. It was almost a new motor hooked up to an hydraulic pump.

But my table saw and planer work fine with the 5 HP 3 phase motors that I’m using. So i’m getting about 3.3 HP out of the motors. But it will rip a 4 X 4 in one pass and not slow down.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware soon moving to Virginia karsonwm@gmail.com †

View TopamaxSurvivor's profile

TopamaxSurvivor

17669 posts in 3138 days


#4 posted 01-25-2011 03:51 AM

Intermit loads like saws work pretty good, running compressor all day every day is a different can of worms:-)) The only thing that would keep me from using a homemade 3 phase motor and a few caps is not being able to pass inspection. You know what happens to the last knowledgeable person to drive past within 5 miles of an electrical fire; and, all fires of unknown origin are electrical. I even heard of on electrical fire that started in a storage shed without power !! ;-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View TopamaxSurvivor's profile

TopamaxSurvivor

17669 posts in 3138 days


#5 posted 01-25-2011 04:15 AM

Dez Forgot to address the CNC issue. Most programmable controllers will require relatively stable and clean power. The way around it out in the “sticks” would be to power the controller off a 120 volt circuit. The controllers usually have a transformer to go from the input voltage to a control voltage for the servo motors, solenoids, ect. Then step it on down for the electronics if that power supply is not in the electronics.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com