Pinging Bruce for Clarification

On Mon, 10 Sep 2007 15:44:11 -0500, Ignoramus2883


If it has a centrifugal unloader that will not start pumping till the compressor comes up to full speed and the oil pressure comes up, like the higher end units from I-R and Quincy, yes the motor is essentially starting unloaded - well, except for getting the rotating mass of the motor and compressor moving.
You will still see a current spike at start, but not as big and it will ramp down faster because the motor isn't trying to produce work before getting up to speed. And for that, a start controller or VFD would be even easier on the motor and your power bill.

That your Bridgeport is manually started when you are standing right there, and if something goes seriously wrong you can kill the power.
Most compressors are designed to a price point (keep the mfg. costs as cheap as practical while meeting the specs for capacity and durability) so they won't spend for a soft-start. Unloaders cost more, so they are only built into the higher end units. And the compressor is expected to run unattended and start itself reliably every time air is called for, for decades, without anyone needing to run up and slap the power switch off if it stalls.
So the K.I.S.S. Principle says leave the electronics out if you don't really need them.
A VFD will work if you just set it at 60.0 Hz, but the whole idea behind it is Variable Frequency. The only reason I'd install one on a compressor is if you want to play around with Logic Controllers and adjusting the motor speed to the air consumption.
You can install one if you have one laying around and you want to (Play) experiment. But I still stand by "If it ain't broke..."
--<< Bruce >>--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
After a Computer crash and the demise of civilization, it was learned
-0700 in rec.crafts.metalworking :

    Sounds like he'll get to do it some more. Pay well, and on time. Good to have customers like that.
pyotr

-- pyotr filipivich "Quemadmoeum gladuis neminem occidit, occidentis telum est. " Lucius Annaeus Seneca, circa 45 AD (A sword is never a killer, it is a tool in the killer's hands.)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I just have a Bridgeport mill clone and a lathe in my garage, pure hobby stuff. The machines have built in 440 volt switchgear.
David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mastic wrote:

That isn't switchgear, it's machine controls. The switchgear is the meter socket and distribution panel for the 440V delta service, both of which cost significantly more than the equivelents for 220V delta service, which those machines will happily run on. I'd never consider 440V service until I had at least 6 large CNC machines.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sorry everyone.... for some unknown reason... I didn't get the original post or the original responses. I know they made it through, cause I saw them on the Google newsgroups at work (but I'm not set up to post there). I didn't get them at home, but I did get the posts under the header RE: Wondering how I can get Google to "send" the original headers and posts to my home computer.... any help here??? Thanks. Ken.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
To send the replies to your home computer, you could copy & paste the contents of the replies to a text document, while viewing the Google RCM group on any machine, then save the text file and attach it to an email, then send it to your email address and access it from home.
I just looked at some Goog RCM messages, and they have a Forward link at the bottom of each message, but it only works if you're signed in as a registered Goog member/subscriber.
This is yet another reason to have a couple of unimportant free Yahoo email addresses. Then you can join/subscribe to something useless like Goog Groups with a Yahoo email address as your username, and not have your ISP email address used at numerous places, attracting spam and nasties. Then, with a Goog username, you can forward those Goog Group RCM messages/replies from Goog Groups to your Yahoo email account (which you can access from anywhere), or to your other email account.
There are lots of worthwhile websites that offer access to good information, which require registration of users, so having some Yahoo email addresses will also likely come in handy later on.
WB ......... metalworking projects www.kwagmire.com/metal_proj.html
"Ken Sterling (Ken Sterling)" wrote in message

--
Posted via a free Usenet account from http://www.teranews.com


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Probably a regional thing. Shrug
Gunner
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Gunner wrote:

120 * SqrRoot 3 (1.73)= 208
Hmmm I did the math, then I stuck the probes of my Fluke on the 3 phase into our shop, and almost every other large distro I've ever had to work in and found 208/120. If your little corner of the world is different, it ain't my fault.
But then again, so much of your little world doesn't agree with reality, why should this be different.
Stuart
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 07 Sep 2007 17:46:59 -0400, Stuart Wheaton

Well...shrug..it is California. The 7th largest economy in the world.
You did say you live in the Rust Belt, right?
Gunner
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<Ken Sterling (Ken Sterling)> wrote in message

If your three phase power is 220/230/240 volts phase-to-phase, which is common, you get normal 220/230/240 volts single phase between any two phases. So your machine will not only work, it will be connected to its proper power.
This topic generally starts a really long and involved thread, so stand by. There is quite a bit more that can be learned about the voltages, currents, and phase angles and there is some disagreement about the terminology involved.
Don Young
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You question is really "can I run a 3 phase motor on single phase?" Answer is a qualified maybe: since you will be running only 2 of the 3 phases, you can only get 2/3rds of the rated power. Plus you will need to run some capacitors to pick up the 3rd leg to get it to start in the desired direction. This is the approach used by a static phase converter. Real answer is to run a rotary phase converter or a VFD.
Ken Sterling wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No his question was the reverese, "can I run a single phase load from a 3 phase source" THe answer of course being yes.

jk
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
RoyJ wrote:

Re-read his question please, it's the exact opposite of what you indicate.
The short answer is that yes, a 220V single phase machine will generally run just fine on power from a three phase service.
In some rare cases the fact that the typical three phase supply in a commercial environment is 208/120V wye service and therefore only provides 208V phase to phase can be an issue and the machine may have a transformer with adjustable taps to account for that, or you can use buck/boost transformers to compensate. In industrial environments you may have 220V three phase delta service where you actually get 220V phase to phase and there isn't a voltage issue. The 120 degree phase angle has no practical effect generally.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"RoyJ" wrote ...

I think his question was the other way around.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 07 Sep 2007 02:10:27 GMT, Ken Sterling (Ken Sterling) wrote:

Right. Figuring the sine wave overlap, it's more like six-phase power - every 60 degrees of an electric motor rotation one of the phases is at peak voltage, either negative or positive. That's why it's so darned efficient for running motors, since there's always smooth forward motion. It's the difference betweeen a one-lung hit and miss Johnny Popper and a Packard Merlin.
And vibration sensitive things like surface grinders should only run on real 3-phase, for the same reason. Try running it on a phase converter and the surface finish on the products can go straight to heck.

Residential style 120/240 single phase is one center-tapped transformer winding, with the center tap grounded for the Neutral.
The '180 degrees' is a convenient way to explain it because the polarity /appears/ to be opposite when viewed/measured from the center tap. In reality there's no differential at all.

Absolutely - you are going across one secondary core winding of the utility distribution transformer, and there's no worry about phase angle there.
Two times to worry: One is if you have 120/208V Wye power, because it is only 208V phase to phase. Most small motors are dual-voltage rated 208V/240V and will gladly run on 208V but at a higher current draw. But there ARE pieces of gear that do not take kindly to running on 208V - this is when you connect a simple 16V/32V Buck-Boost transformer between the utility and the load to kick 208V up to 240V.
The other: If you have 120/240 Open Delta or "High Leg" power - the High Leg (usually coded Orange and connected as B phase, but not always) is 208V to ground, not 120V.
When you run across Open Delta panels in the field, it is considerate to put a big note on the breaker panel to warn the less enlightened among us that 'The B Phase is 208V to ground, and connecting 120V loads to the B Phase is a Very Bad Idea.'
You can connect 240V loads between any two phases on Open Delta, but you can only connect 120V light loads between A-N and C-N. Try placing them on B-N and they won't live very long - but they glow really bright before they blow...
--<< Bruce >>--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 06 Sep 2007 23:07:32 -0700, Bruce L. Bergman

Indeed. Even if they dont have a light source..they can glow really nicely.
Then the magic smoke comes out.

Gunner, who has been putting orange tape on all manner of things the last few months......
Orange County is nearly all Open Delta and 240 vts
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 07 Sep 2007 02:10:27 GMT, Ken Sterling (Ken Sterling) wrote:

It may help to think of a "phase" as a pair of conductors rather than a wire. A pair of wires comprises a phase. With threephase, there are three wires, call them A, B, and C. (Ignoring ground for the moment). There are therefore three phases: AB, AC and BC. The sinusoidal voltages on these phases are 120 degrees apart. The voltages on each of these wires relative to ground will also be 120 degrees apart but line-to-ground voltage in a wye connection is .867 * line-to-line voltage.
Residential single phase power in the US is 120 volts relative to ground, or 240 volts line-to-line because one line has polarity opposite (180 deg phase shift) to the other w.r.t. ground. Household 120 volt power has one or the other of these lines on the black wire, and neutral (grounded somewhere) on the white wire. 240 volt loads like stoves are connected line-to-line, often do not use the neutral. Others have treated the various voltages found on each phase of commonly-found three-phase power distribution setups.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ken Sterling wrote:

Ken To visualize phase angles draw 3 parallel lines the same length, put a dot at the left end of the top line, and a dot at the right end of the middle line, and a dot in the middle of the last line. Now imagine those dots moving at the same time, the same speed from one end to the other. Their timing is 120 deg apart and if you look only at the top and middle lines, they are 180 deg apart. 120/208 is star or y just imagine each leg of the y is a coil of a transformer and the middle of the y is grounded. Each end of the y is a phase, the voltage is phase to ground 120, phase to phase 208. On a 120/208 bank all 3 transformers will be the same size. 120/240 is delta imagine a triangle, each side is a coil of a transformer, each point is a phase, in the middle of one side draw a ground. The transformer you ground is the lighting transformer. It has all the single phase load. The voltage is hot leg to ground 120, hot leg to ground 120, power,high,or stinger leg to ground 208, because it is a coil and a half away from ground. Between any 3 hot is 240v. In a 120/240 bank the middle or lighting transformer will be larger to handle the 3phase plus the single phase load. To visualize an open delta erase one side of the triangle. The only way you can tell if you have an open delta versus a delta is to look at the bank, 2 transformers is open delta, 3 is delta. Open delta is not very efficient. It is good for temporary repairs. I could rebuss a bank to open delta so a farmer could milk his cows and not have to wait 4hr for a crew to change out 1 transformer. The secondary coil of the transformers is not center tapped. It is two coils, you have them serialed for 240 and paralleled for 208. You can see some pages from a transformer manual at http://murrayranch.com/Electricity.htm
Don
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.