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LtEngine10
11-25-2009, 05:00 PM
I am looking to replace the drum switch on a 3phase delta rockwell 10 inch lathe ( I believe it is causing a out of phase problem and over heating my motor) I know mcmaster carr and grainger have them I am just wondering if anyone has some advice on what to buy.

JMS6449
11-25-2009, 05:32 PM
Explain that!

LtEngine10
11-25-2009, 09:45 PM
I presume you mean the out of phase problem, that would be when one of the phases (legs) does not have the same voltage as the other two. 3 phase motors like to have the same amount of voltage going to them if one of the "legs" does not get enough energy the motor has to work harder and the motor will over heat. that would appear to be the problem that I am having, I have almost a 4.5% drop in voltage across the switch on one of the legs compared to less than a .14% drop for the rest of my machines. so I would like to replace the switch but since the switch is mounted in the cabinet I was hoping someone could point me in the direction of a replacement switch that would fit in the existing opening.

gda
11-25-2009, 10:06 PM
"out of phase" refers to the synchronization of the sine waves of your 3 power legs.

You are describing a voltatge drop problem that is more likey the result of some resistance in the switch in one of the contactor sets. Have you looked at the switch? Can you check the resistance across the differnt switches?

Are you getting 3 phase from the power company or using a converter. If you are using a converter the 3 legs will never be perfectly balanced, and will change slightly under load (according to the American Rotary converter literature I have)

JoeFin
11-25-2009, 10:37 PM
I'm sure you have already tried hoseing down the switch with electrical contact cleaner found at most any hardware store

Personally mine has inter-locked contactors and a selector swich. I ditched the drum switch (sold it on ebone) You could probably find 2 matching size 00 contactors on ebone for what you would pay for the switch new. The benefit of course is the added motor overload protection.

Of course it is a major PITA to set up and wire

http://cgi.ebay.com/Lot-of-Allen-Bradley-Contactors-Starters-OverLoad-Relay_W0QQitemZ110459659800QQcmdZViewItemQQptZLH_D efaultDomain_0?hash=item19b7e8a618

you could probably find better

http://cgi.ebay.com/TELEMECANIQUE-REVERSING-CONTACTOR-LC2D12004B6-NEW_W0QQitemZ230401461946QQcmdZViewItemQQptZLH_Def aultDomain_0?hash=item35a4ff4eba

john hobdeclipe
11-25-2009, 10:56 PM
Could you post a pic of your existing switch?

914Wilhelm
11-26-2009, 12:37 AM
Whoops Whoops

wooleybooger
11-26-2009, 12:52 AM
my late 60s era 14" rockwell has a furnas switch in it. very easy to clean up with contact cleaner or even file a little with an ignition point file. my lathe sat under a lean-to,under a tarp before i got it. the brass contacts were grossly green before i worked em over. works great now.

LtEngine10
11-26-2009, 04:22 PM
Thanks for all the help. I recognize that the condition I am describing is a voltage drop, however, I got the voltages off the other legs and then found the average voltage, subtracted the average voltage from the original voltages and then took the highest difference (8 volts) divided that by the average voltage then multiplied the answer by 100, the result is percent out of phase (I think).

I am using a rotory phase converter and it is preforming within spec and when I start any other machine in the shop I only have what would equate to a .14% out of phase.

But all that being said I removed the switch today conected all the wires together, than used the breaker to turn the unit on and i still have the problem... so I say Wisky Tango Foxtrot...:confused:

I now have turned my attention back to the motor but I still am not sure that is the problem...

doctor demo
11-26-2009, 04:44 PM
I am not a motor expert or an electrician but..... I do believe that voltage differences from leg to leg have nothing to do with ''phase'' .
I hope Jerry or someone else with more knowlege will jump in, but it sounds like a motor problem to Me.

Steve

JoeFin
11-26-2009, 05:25 PM
Thanks for all the help. I recognize that the condition I am describing is a voltage drop, however, I got the voltages off the other legs and then found the average voltage, subtracted the average voltage from the original voltages and then took the highest difference (8 volts) divided that by the average voltage then multiplied the answer by 100, the result is percent out of phase (I think)...

Phase differencial would represented in orintation to 360 degs. And no I'm not even going to attempt to regress to polar trig from 30 years ago

But we all understand what you are trying to describe.

Since your obviously taking measurements with a multimeter and you have the motor leads readily accessable, did you take any resistance measurements of the windings, and windings to ground?

LtEngine10
11-26-2009, 09:52 PM
No, I have not taken any resistance measurements from any place on the motor windings.:eek: I was lucky to figure out where I am so far. that being said (I should use this as my quote; how hard can it be?) can you give me some direction as to how to do this, a web link or something?

I would really appreciate the help

JoeFin
11-26-2009, 10:32 PM
http://www.ehow.com/how_4644429_test-electric-motor-windings.html

JoeFin
11-27-2009, 06:03 AM
Additionally - duesh the motor with contact cleaner as well. Be sure to select the non-flamable variety you can spray on the motor while it is running. Occasionally metalic grit will collect around the brushes and cause problems like you are describing.

Best if the motor is out and you can stand it on end (brush end up) so every thing runs down and out of the motor

Any electrician worth his salt is affraid to admitt just how often this works

LtEngine10
11-27-2009, 09:09 AM
Thanks Joe I will try that today.

As a side note (sort of a Ha Ha) I remember many years ago I was on an operation (I hope my screen name helps you figure that out) where this Lady's washing machine caught on fire. she needed a new motor, it turns out the motor would "not start". so what does any sensible person do? that's right she went to her husbands work shop and found a can of "starting fluid" (makes sense to me) anyway as you might guess it did not work. she was lucky though she did not burn her house down and she did not have to tweeze her eyebrows for a while I don't know what she did about her eye lashes though. (I guess it's cheaper that electrolysis) I would think that painting your eyebrows on every day would be a hassle though.

seemed like the story would fit into the "use a none flammable cleaner"...

Thanks again I will let you know how I make out

Tom