Beating Heart of the Shop (compressor)

[Ansimp]

desertrefugee » Wed Dec 04, 2019 12:57 am[/url]":32p48b96]
3 phase at home? Wow. Australia. What a country!

We are on acreage and when we built the property I elected to use our electricity supply company to do the installation on the property. Instead of 15 poles they were able to use 4 to go 700 meters to our “A” pole because it was run in high voltage (11KV with a 20KVa transformer) then we had to run underground 150mts down to my shed and 150mts up to the house. Even though we paid for the supply it is now part of the grid so it is fully maintained by Energex. They inspect the base of the poles, trim the trees and even fly the helicopter down the lines to do a video inspection. :good:

 

[DaveKamp]

I get lots of inquiries about my 3-phase conversions, many are from down under. From what I understand, Aussies get their own flavors of power, and if you have 3-phase, you're really lucky. Getting the HV mains closer to your doorstep is a good thing... keeps the line losses low. Having 3-phase means you present a more-balanced-load for them, too.

My farm has a single phase feeder, but a vast majority of my machinery is 3-phase. I have variable frequency AC drives on all but a few tools, and I've built rotary converters for testing the rest (before converting).

 

[Ansimp]

As you are probably aware Dave our standard voltage is 240v which can run some pretty heavy duty motors. I wanted 3phase because all the good second hand shop equipment was 3phase and also commercial air conditioners/ ducted. We never went that way just ceiling fans throughout and two bedrooms with split systems (his and hers). At the moment it would be nice as it is currently 44c :heat:

 

[DaveKamp]

Yes, I am... single-phase 240. My house fits the USA typical 120/240 system. My milling machines, radial drill, lathes... they're all 240v single phase... I feed that (through an appropriate control contactor) to two of the three input leads of a 3ph to 3ph variable frequency drive. The VFD rectifies it's incoming AC to DC, then has a microprocessor-controlled 3-phase inverter feeding the drive motors.

My Monarch 10EE lathe used to have a motor-generator type variable DC drive system ('Ward-Leonard' design), about six years ago, I converted it to 3-phase VFD. I used a 7.5hp 480v 3ph motor, a 10hp 480v VFD, and a 7.5kva 240/480 to 120/240v dry transformer wired backwards (240v in, 480v out) to yield 480v single-phase to feed the VFD. It works GREAT... and weighs almost 3 tons... but it sure does cut metal nicely...

Sounds like a great day to ride the motorcycle down to the harbor, and jump on a friend's boat for a while.
(the only thing better than having a boat, is having good friends with boats...!!!) :yahoo:

 

[pidjones]

When my house was being built, the utility tried to talk me into a three phase system. I stayed with just two. The extra copper cost didn't bother me, but the panels were much higher and I never envisioned the need for three phase. Meh, I'm Ok with two. Wish I had power out in the shed, but there is a 14' wide 8" thick concrete drive in the way. I should have buried a few conduits before it went in.

 

[joedrum]

If your crafty like me ...you can make a caveman phase converter making three phase out of single phase power ..I made one that would run some big machinery ...some had 80hp in electric motors ...

 

[saganaga]

pidjones » Today, 5:14 pm[/url]":1uis47lb]
When my house was being built, the utility tried to talk me into a three phase system. I stayed with just two. The extra copper cost didn't bother me, but the panels were much higher and I never envisioned the need for three phase. Meh, I'm Ok with two. Wish I had power out in the shed, but there is a 14' wide 8" thick concrete drive in the way. I should have buried a few conduits before it went in.

You could try to rent one of those "point and pray" horizontal drilling machines. Those are good for destroying anything you don't know of in the way. I've seen them go through a large concrete storm sewer pipe.

Don't know if you can rent them though.

 

[DaveKamp]

directional underground boring machines are really cool... steerable spade bit that can be articulated in all sorts of ways to get around obstacles underground... I've used them on several occasions for everything from pulling fiber to 3-phase underground power.

Getting underneath a driveway slab isn't too difficult if the circumstances are right. A trick that works well for me, is digging a hole on each side of the slab, then using a couple pieces of rigid metallic or stiff plastic conduit with a garden hose connected, flowing water. Push it into the side of the hole horizontally, and the water will saturate and push the soil out of the way. I've gone under 18 feet of 4" slab using this technique... and I even managed to hit the hole on the other side. If the ground is too gritty for water, then an old auger-type wood bit connected to sections of pipe with a sturdy collar, powered by a corded 1/2" drill will dig through.

 

[pidjones]

Actually, one side of the drive slopes away steeply. I could give it a go from there. Quite a bit of red clay, but also what goes with red clay? Limestone. I might give it a try next summer.

 

[DaveKamp]

If you run conduit for power to the shop, run an extra conduit and pull air line through it!

Back to the subject of air compressors... I used a term that may have gotten lost along the way- Adiabatic efficiency.

Adiabatic refers to the change of energy, and thermal circumstances. When a gas is compressed, a bunch of molecules are shoved into a smaller space. That means that all the energy in those molecules gets packed in WITH them... and as a result, the releative energy level in that smaller space, is proportionately warmer than it was previously. Boyle's Law (revised to Combined Gas Law) identifies that proportion mathematically. P=V/T where P is pressure, V is Volume, and T is Temperature (in degrees Kelvin).

The real-life application note here, is that a compressor gets hot, and the first reason, is because it's packing lots of air in a small space. The second reason, is because it's generating friction in the process, and that heat is radiating out of the parts, and SOME of that winds up being absorbed into the gases flowing through the compressor into it's outlet.

Once that air leaves the compressor, it goes through plumbing, and into a tank... and the heat is passing into the plumbing and tank, and escapes into the atmosphere.

Because the hot air is cooling, pressure in the tank falls short of what the pump was generating... and on the gauge, it's not greatly discernable, but if you compare the amount of electric energy going INTO the compressor, against the amount of work that the compressor's air volume yields, you'll see that some compressor systems can do a whole lot more work than others.

In the process of compressing air, everything thats IN the air gets jostled around. A little bit of dust gets through the filter, and whatever corrosion shakes free from the plumbing will go through, but the big number is moisture. The air we breathe carries substantial amounts of evaporated water, and as the wind blows, and temperature changes, the amount of moisture in that water fluctuates. it's actually DISSOLVED in the air, and like any other solution, a change in temperature or pressure changes how much moisture the air can hold. When air is compressed, that moisture precipitates out... it's squeezed out like squeezing a sponge. To complicate the process a little more, the presence of humidity in air changes the amount of force needed, and the velocity at which the air can be compressed, because the moisture takes up space inside the chamber.

Oil-less compressors run dry seals on their pistons, typically run shorter stroke, and much faster run speeds. Being oil-free, there's a basically-zero-chance of oil winding up in say... a paint sprayer... but that doesn't change the fact that moisture is falling out of the air.

So all compressors, in all circumstances, have to deal with moisture. The exit plumbing usually has a heat exchanger (aftercooler), and it's arranged so that precipitant moisture (and dirt, and oil, and crud) has some place to 'fall out' before winding up in the tank, or getting pushed onward into your air-wrench or sprayer.

And this is why an air compressor in Tucson or Scottsdale, or Tacoma will perform better than the exact same one in Jacksonville, Long Beach, or Portland. It also explains why a compressor in Davenport will run so much better in January, than in June.

Back to the term 'Adiabatic efficiency'... when a compressor runs fast, the gases are being compressed to a small space very quickly. Herr Diesel noticed that his laboratory compressor demonstrated some very high temperatures under certain conditions, and that geometry of the crank and rod, along with cylinder head volume caused the peak temperatures and the general temperatures to be quite different... the end hypothesis being that with different crank/rod geometry yielding higher piston speed, the peak temperature will be higher than with a longer rod geometry, and lower piston speed... and the rate of pressure rise was the key factor in achieving autoignition temperature of an injected fuel.

Adiabatic efficiency in air compressors is all about PREVENTING the compressor from generating high pressure peaks. The fact that airless compressors must run faster in order to maintain effective sealing with short stroke, means they generate rather high pressure peaks in a small volume, and the result is high point temperatures, and much lower overall efficiency.

And they're loud.

So if you're ever wondering why big commercial and industrial compressors run so slow... that's why. ;-)

 

[dan filipi]

joedrum » December 6th, 2019, 3:56 pm[/url]":20gieghw]
If your crafty like me ...you can make a caveman phase converter making three phase out of single phase power ..I made one that would run some big machinery ...some had 80hp in electric motors ...

Caveman phase converter Joe?

 

[joedrum]

OK LOL ...yes caveman phase converter ...turning single phase power into three phase power ...ok follow the best you can this will be written in joedrum vocabulary....I once lived on a farm that had nothing but single phase power available ..the place had a huge barn basically three stories tall ...I turned it all into huge woodworking shop ...where I could make mounding ...tongue and groove flooring ..furniture ...kitchen cabinets...log cabin logs ...and could handle fresh cut logs to the finished products ....this involved many 3 phase wood working machines ...many lol....

I had 100amp service going to the barn...switch that breaker out to a 200 amp service breaker ...wire went about 100yrds to the barn ....where I had single phase service and box ...ok three phase power from single phase involves a three phase motor that. Will be known as idler motor ...the one I had was a 40 HP motor made in the thirties I’d say I bought for a 100$....this motor weight was over a thousand lbs my god it sat down never to move ..it sure never needed bolted down LOL....IN THE MOTORS WIRING BOX ..I hook the single phase service to two of the legs of the three phase motor ...leaving one not hooked up ...ok I’ll post some in a bit ...got some people here to deal with .....

 

[DaveKamp]

Dan- it's called a Fitch Williams rotary phase converter design... and they're extremely handy

The simplest, is a three phase motor, with single phase current powering two of the three, and spin the motor up by wrapping a rope around the shaft and giving it a pull. Once the motor is spinning, you'll have 3-phase power across all three legs, because the motor's 3-phase stator has now become a 'rotating transformer. It's referred to as an 'idler motor'.

The third leg is called 'generated leg', and will exhibit a bit of a voltage difference because of inductive phase shift... this can be 'balanced out' by putting capacitors from one of the line legs to the 'generated' leg, but balancing is a static function... meaning... it will result in voltage balance only as long as the load is constant.

There's a clever variation where a guy fitted the recoil starter from a Briggs 3hp to spin the idler motor.

There's a variation which uses start capacitors to 'kick' the motor into operation... this is referred to as 'self starting', and yet another that uses a smaller single-phase motor to initiate the spin... this is called 'pony motor starting'.

If you'd like a diagram of the complete thing, as well as my self-starting interlock controls, PM me an email address, and I'll send you a PDF of the one I built 20 years ago.

The next one I build will be using a 40hp Allis-Chalmers 480v motor, and instead of a rope, it'll use a pony motor and a centrifugal switch with some timer relays for self start and protection.

 

[joedrum]

Yah the rope thing sounds rather idiotic ...there’s only one way to set one up and that’s to have a single phase starter motor that spins the the tree phase motor to speed ..then hit the power to it ...when the motor is not up to speed it’s hard on everything and will burn things up ...on my set up I ran a complete wood shop ...the wild leg Dave is talking about is never a problem ...even regular power has differences ...just a bunch of BS to get people not to use it and buy static phase converters that are really junk and unreliable ...all high end phase converters use idler motor ...with transformer box to smooth wild leg ...I’ve tested them many times they don’t tame anything ...but they do burn out ...truth is there two types of three phase motors ...hmmm Wye power and dye power I’m sure the names are wrong ...but use the right motor and the so called wild leg is not wild at all ...

In my shop from the idler motor at the electric box on motor ...all three legs were wired up along with the single phase power hook up to legs ...went to a three phase distribution box ..where all things that ran on three phase were hooked up and had breakers ....

First thing in the morning spin up the idler motor with the single phase electric start ...hit power to idler motor ..turn off starter motor ...and then anything in the shop was ready to go ...the T G flooring machine had five heads and about 100 hp to run it along with dust collection ...had a four head sander that could sand 51” wide ...entire sheets of plywood could sanded continuously...it used about 100 hp to with dust collection...

I could make and cut log cabins ...most were small ..but people who came to the meet greets at my house seen the log cabin there ...I’m thinking those were made out of 5x6 logs that were milled through the Five head mounding machine ..right out the machine and into the truck to take where it goes ...Slabghost seen the shop one time where I did all this ...

 

[joedrum]

On a small scale basis ...say you had three phase lathe or what ever ...and you wanted to run it ...and not use a idler motor ...a really great spinner is a 1/2” angle drill ..they usually spin about 500 to 750 rpm ...it’s rathe easy to set up a vbelt drive system geared right most times 2 to 1 ratio ..you can spin the tool up to speed and hit the power to it and it will run at 2/3 of its rated power ..if the the single phase is hook up to two of the three phase power leads ...hope I explained that good enough ...so three phase power is rather easy to get if one wants it or a tool that has it and you don’t get it cause you think there’s no way to run it ..there is and it’s easy really ... :BigGrin:

 

[dan filipi]

DaveKamp » Today, 9:22 am[/url]":1h19wtz1]
Dan- it's called a Fitch Williams rotary phase converter design... and they're extremely handy

The simplest, is a three phase motor, with single phase current powering two of the three, and spin the motor up by wrapping a rope around the shaft and giving it a pull. Once the motor is spinning, you'll have 3-phase power across all three legs, because the motor's 3-phase stator has now become a 'rotating transformer. It's referred to as an 'idler motor'.

The third leg is called 'generated leg', and will exhibit a bit of a voltage difference because of inductive phase shift... this can be 'balanced out' by putting capacitors from one of the line legs to the 'generated' leg, but balancing is a static function... meaning... it will result in voltage balance only as long as the load is constant.

There's a clever variation where a guy fitted the recoil starter from a Briggs 3hp to spin the idler motor.

There's a variation which uses start capacitors to 'kick' the motor into operation... this is referred to as 'self starting', and yet another that uses a smaller single-phase motor to initiate the spin... this is called 'pony motor starting'.

If you'd like a diagram of the complete thing, as well as my self-starting interlock controls, PM me an email address, and I'll send you a PDF of the one I built 20 years ago.

The next one I build will be using a 40hp Allis-Chalmers 480v motor, and instead of a rope, it'll use a pony motor and a centrifugal switch with some timer relays for self start and protection.

Thanks Dave, but I know about these already. Was interested in how Joe did it.

 

[DaveKamp]

joedrum » Today, 1:07 pm[/url]":3r69yuy8]
the wild leg Dave is talking about is never a problem ...even regular power has differences ...just a bunch of BS to get people not to use it and buy static phase converters that are really junk and unreliable ...all high end phase converters use idler motor ...with transformer box to smooth wild leg

It is NOT 'wild leg', it is 'generated leg'. 'wild leg' refers to obsolete, but in some places still existing electrical services that use corner-grounded delta to provide other voltage choices.

The generated leg is generally NOT a problem if all you're running is electric motors, and in real life, the more motors you have running, the less the difference will be (and the stronger the generated leg will be) by virtue of the additional rotating XL of each motor. When I run my RPC against a very big load, I start a second machine and just let it spin (no load) to serve as additional idler. I have a Lodge & Shipley 26x200 lathe, a 17x50 Sidney, a Milwaukee #2, and a Cinci #2 horizontal mill, a 16" shaper, and a Cinci #5 vertical that all run just fine on an unbalanced RPC.

Where the generated leg IS a problem, is when there's controls on the generated leg, OR when the machine has motion control (CNC, etc) or a VFD on it with phase-loss protection. My MAHO MH600E will NOT run reliably on an RPC... even with plenty of idler behind it, the Phillips controls will not tolerate the drift that occurs when the spindle motor starts, as the generated leg dips, and then rises substantially as a result of the start. My MG plasma gantry WILL tolerate the RPC, but it's CNC control system MUST be wired across the two line legs.

Static converters are totally different from rotary converters. A static converter is essentially the balancing capacitor setups and a start capacitor system that one would use to make a rotary converter, but it works as if the motor being driven IS the idler. Actually, if you add an idler motor to a static converter, it'll be a Fitch-Williams RPC... and for what it's worth, BOTH of my Behlen grain dryers have 15hp 230v 3-phase blower motors that are (eh, WERE) powered by 240v single-phase overhead feeders by virtue of a factory-made static converter panel... a box with a couple contactors, a timer relay, a potential relay, and about a dozen oil-filled capacitors.

There's many other ways to get three-phase power, and a Phase Perfect converter will do an excellent job of it... but a Phase Perfect is a 3-phase fixed-frequency inverter... there's no moving parts, and it doesn't require a start circuit... and the voltage balance is identical, and CNC machines run GREAT on them, just flip a switch, and it's on... BUT... They're also VERY pricey... so much that the 'caveman' solution is very well accepted by many.

But the stuff I use most often... namely, the Bridgeport J-mill, the Monarch 10EE, the Johannsen radial drill, and one tool grinder all run on variable frequency drives (VFDs)... single phase in, three phase variable speed out.

oh... and my 46" concrete trowel runs on a VFD too... I have a step-up transformer with a 250v plug feeding long extension cords that connect to the 480v VFD, and it's programmed to spin the 3hp electric motor to 5500rpm, with a 2:1 reduction to the gearbox where a 5hp Briggs used to sit... and I can dial those trowels down REALLY SLOW, or wind 'em up to burnish like a helicopter. :rocks:

 

[desertrefugee]

Amazing experience and rundown, Dave and Joe. Even an old electrical engineer (me) is humbled. But, my career has not focused on power, rather lots of things that use it. Sheesh, I never used (or needed) 3-phase outside the commercial world. And certainly didnt futz with conversion. Hadnt even thought about it for years.

Good stuff.

 

[joedrum]

No Dave it’s a wild leg period ...certainly not generated ..this is not a system of a generator ...it’s a phase converter peruiod ..you never get more power than what is coming in ....it’s a wild leg and proper name for it ...it is created by the properties of AC power that moves back and forth ..this ability happens in the idler motor and creates three third leg of power through the winding of the motor ..nothing is generated at all ...if your dealing with DC current this wouldn’t be possible at all ...and of course like true hreat inventors everything in modern life was made possible by a man that bankers and patent office stole everything from and died penniless and scorned by all ..kind of like how there treating Trump now LOL

 

[DaveKamp]

Joe... Look up 'wild leg'... it is an NEC electrical term. There's a great description of it, and a drawing, at en.wikipedia.org/wiki/High-leg_delta

Rotary converters are NOT a high-leg delta application, there is no neutral connection, and it doesn't matter wether the motor is delta or wye configured, there is no neutral possible on a rotary converter, as the neutral point is apparent, not actual.

On a rotary phase converter, you have three leads going to the idler motor- two driven legs, and one generated leg. Single phase line goes tot the two driven legs, the third, is generated. The idler motor becomes a 'rotating core transformer'. In NEC code, the third leg is referred to as 'generated', and when doing so, it is general industry practice to identify the driven leads with red and black, and the generated leg is 'blue'.

In a High Leg Delta configuration, the 'wild leg' is color coded orange.

And if you're refering to Nikolai Tesla, yeah- there's a movie out ("The Current Wars?") that I haven't seen yet, but would like to.

In my prior occupation, one of my clients was Knorr-New York Airbrake (formerly WABCO)... and they had a very nice private museum of George's history, and how electricity changed Westinghouse as a company.

BTW, if you want a really, really, REALLY nice, stout MIG welder, but live on a very low budget, look up "CP-200 on Single Phase".