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Question: switching vacuum pump from 3ph to 1ph

Started by Brad_S., February 23, 2020, 12:32:37 PM

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Brad_S.

I thought I would check with the collective knowledge of this group before heading out into the real world and looking like an idiot.

I recently bought this vacuum pump with 60 gallon reserve tank to use in vacuum forming. It has a 1.5 hp three phase motor which didn't bother me because I have a 40 hp rotary converter that I use to run the Logosol PH260. However, looking at the specs on the converter, it requires a 2 hp load minimum. I either need to get a smaller phase converter or switch this over to single phase which would be much easier to run in my shop.

 

My question is: is it as easy as swapping out the motor or are all the components such as pressure switches, contacts and the like designed for three phase use? 
"Life is what happens to you while you're busy making other plans." J. Lennon

btulloh

A VFD for that size motor is fairly inexpensive and has 1 phase input and 3 phase output. Might be the simplest and cheapest solution. Or build a smaller 3 phase rotary. Just depends on what you have laying around. 
HM126

btulloh

HM126

Southside

You would need a new contact starter to go along with the single phase motor, without seeing the pressure switch I am not sure but it would probably work fine.  That being said I agree a VFD would be the easiest and cheapest way to go.  Avoids a lot of - "whoops, didn't think about that"
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Brad_S.

 

 

 Thank you both for the replies, that settles it. It would've been easier to use it had of been single phase but there is a small converter available locally for not too bad of a price.

Thank you for the affirmation on the pump as well. I'm not a very mechanical person so it is good to hear that that is a good pump. I'm hoping to reproduce glass sign letters used in antique signs 100 years ago. I even picked up some of the original molds and what I don't have molds for I can create myself.
"Life is what happens to you while you're busy making other plans." J. Lennon

Ljohnsaw

Those are some interesting molds.  Looks like the glass is sucked down over a positive mold for the X and a negative mold for the S?  Wonder why.  Will you be doing glass or plastic?  You toss the mold and glass in a furnace and then into the machine or does the machine have a furnace as part of it?  Need to see more pictures! :)
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Brad_S.

On the original cast-iron mold, the glass is pulled down over the top. When I make reproduction letters, i use the plaster negative and pull the glass into the letter.
I will indeed be using glass. In researching the Flexlume company's original patent (thought to be the originator of the signs that these letters were used in) they would heat the glass on a flat plate and do the vacuum forming outside of the kiln. I haven't got everything hooked up to try the vacuum forming yet. The "S" was made by slumping the glass into the form using heat only. Melting into the form gives good sharp definition to the outside of the letter. If I don't use a vacuum on the cast-iron mold, the transition from the letter to the flat plate has a curve or a shoulder to it which doesn't fit well into the sign cut out.

This is the sign the "S" is being used for.


 
"Life is what happens to you while you're busy making other plans." J. Lennon

muggs

If you pull some of the run caps out. ( remove the wires) The converter  should then run your smaller motor OK.

luap

Add more load. Just run another motor in the circuit.

Al_Smith

I wouldn't think even with an over sized converter where it should make any difference .It just would  require more power for the converter than it would require just to power the small motor .So it's over sized .Using the idea an over sized converter would harmful by that thinking my home built unit which is 5 HP should not be used running a 1/2 HP Bridgeport milling machine but it does just fine .Am I missing something in the conversation ?

luap

I think it would be wise to define what makes it oversize. When I first built and used my rotary converter, after a half hour of use the motor on my milling machine would kick out from getting to warm. I used a clamp on amp meter and discovered an imbalance of amp draw between the three legs. After some experimenting with the size of the microfarad ratings of the capacitors I got the three legs more closely balanced and problem solved. I am not an electrician. The size of the rotary part has less to do with it than the capacitors.

Al_Smith

On 240 volts it takes about 7.5 microfarad per horse power run caps  on the converter .In my shop mine is 480 volts and it's within about 8-10 volts if I recall correctly .To get the 240 volt stuff I run it through a 480 to 240 volt transformer .The old Bridgeport mill is  the  only thing I have which runs on 240 volts . It's actually higher than that because my service has about 245 volts  coming in .
A converter's only job in life is to generate the third phase not to preform mechanical duties .Usually they only run on about half the normal running amperage .It might cost more to run a small motor like this vacuum pump but it's not likely to run all the time .So I'd think long term it would be something to consider .

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