bridgeport 3PH -> 1PH conversion

[Tony]

friend of mine owns a shop "just up a ways" and recently got a good deal on a bridgeport 2HP mill. great condition, DRO, power crossfeed, power quill, etc...

problem: 3 phase hook up required.

any way to run this machine on regular
2phase? (single phase out here is 220V,
50Hz)

tried an inverter today, but with no luck.
spindle would turn if not loaded. comes to a dead standstill if you hold it with your hand.

the xfeed is a DC motor about 400W but it doesnt say what voltage it runs at.

just changing the motor on the head wont solve the problem of the xfeed & DRO.

anyone done this before?
if so, is this cutting a great mill off
at the knees?

-knucklehead.

phaseconverter??

[SGW]

What do you mean by "inverter"? I would think a variable-frequency drive would be the way to go. If that's what you tried...is it the correct size for the motor, and is it designed to accept single-phase input?

[gizmo2]

went through this process jsut a couple months ago. Check out dealerselectric.com for their Teco/Westinghouse VFD's. I found the instructions somewhat confusing, but was happy with the results. Takes a 220 single phase input and makes it 3 phase, just buy the unit sized to your motor. By adjusting the frequency (normally stuck with 60 hz) you vary the motor speed, within limits, because the motors' internal fan is designed to spin so fast. The only thing I find odd about the unit is the motor is always under control. It speeds up slowly as the frequency comes up to target, then slows down slowly until the freq. reaches zero, instead of just coasting to a stop. This stuff is all programmable, and you can add braking resistors if you need to stop quicker. BUT, if you can live with about a five second delay while it starts and stops, it works pretty cool as is.

[steve schaeffer]

knucklehead,
a vfd would be very attractive on a step belt head bridgeport. you need an understanding of electrical/electronics. i am going to use one on my lathe project. however, motor heating is a concern when you run at slower speeds. but moreso on continuously run machinery versus a home machinist where it might only run for an hour at a time.

[steve schaeffer]

knucklehead,
a vfd would be very attractive on a step belt head bridgeport. you need an understanding of electrical/electronics. i am going to use one on my lathe project. however, motor heating is a concern when you run at slower speeds. but moreso on continuously run machinery versus a home machinist where it might only run for an hour at a time. a static phase converter is simple and cheap. i use this on my mill at home. a rotary converter gives you near 3 phase like power, and can be wired into your shop and sized to supply all of your machines. if you have any questions as to how each of these operate, please do not hesitate to contact me. just an fyi, a static phase converter does not actually convert anything, nor does it generate a third phase, (i know, what a ripoff) but its simplicitiy is to be desired. all it is, is a capacitor start system, with a voltage sensing circuit to take the cap out of the circuit once the motor is running. then the motor continues to run on two of the three motor windings (single phasing) if you would like to build your own static, or rotary, let me know i can give you some input. also here is another simple one, you can take a spare three phase motor,using a 110 v motor to get it spinning, then using it as a slave/rotary phase converter. this again works off the principle that a three phase motor will continue to run on two phases (if one is lost or shut off) but will not start on two phases,
any question?
steve

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extreme tractor racing

[steve schaeffer]

gizmo, have you tried adjusting the ramping/acceleration speed in your program?
or is the five seconds there to keep those unorhodox machining methods from flinging parts across the shop?? haha


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extreme tractor racing

[Tony]

sorry.. by 'inverter' i did mean VFD.
maybe the one we used was too small?

gizmo: you can change the amount of time the VFD takes to start/stop. set the DECELERATION to 0 and that'll be as close as you can get to making the thing "coast" -- or at least try to.

will the VFD screw with my other electronics? the 3ph input is wired to a MASSIVE transformer.. that feeds a DC motor (table feed) and a 120V DRO.. not to mention a 50W lightbulb.

also.. if anyone out there is right techy with these things.. i understand that VFDs output voltage = input voltage. sure, it'll change it to 3phase, but it wont make it 380V.

the motor on the head of this bridgeport reads 3Ph/2HP/380-420V

maybe that was the problem with my VFD? i was getting 3ph but not enough juice?

[SGW]

Heck, yes! You need a transformer to boost up the voltage, then an appropriately-sized VFD for that voltage to turn it into 3-phase at that voltage. And, at that point, I think you'd probably be better off replacing the motor as the cost of doing all this is getting "up there."

[ibewgypsie]

My bridgeport had a air brake on the spindle, until I got the controls to working and then air on it, my vfd kicked out too.. Check that..
Most inverters have a kick, high current boost to start a heavy load, I didn't need that with mine.

[Tony]

steve s--
run that by me again.. the part about the spare 3ph motor ...

intrigued,
-knucklehead

[mbensema]

SGW has it right, you can't run a 400v motor from a 240v VFD. You have to use a VFD sized to your motor and voltage. For the cost of a transformer and a new VFD, you could probably get a new motor at 240v. If you decide to go with the transformer and 480v VFD, you can adjust the parameters of the VFD to give you the voltage you need at the frequency you need.

Mike

[gizmo2]

Steve, the answer is no! It took a couple days of reading the manual, over and over, before it made enough sense to me to get things spinning. Yeah, I know the ramps are adjustable. But other than limiting the low end to 30 hz., I haven't tried to decipher the rest of the instruction manual. It is surely partly ignorance on my part, but I think the manual was translated into English by a Latin major in Hong Kong; not any form of English I am familiar with...

[JoelK]

Knucklehead,

it sounds like you've got several "show stoppers". If your connecting the VFD to the transformer, you've got problems. Most likly, it's a step down transformer. Your feeding 220 into a step down transformer, so your 380 volt motor is probably really low on volts. You don't want anything on the VFD output except the motor. I have no idea how a VFD would run with a transformer on it's output.

If the motor is 380, you'll need a 380 rated VFD or change the motor. You might be in luck though with that transformer. If it's made to power the whole machine, you might be able to reverse it and use it as a step up transformer to get 380 from 220. Even if it's 3 phase, you can probably use it to convert single phase to 380 for a 380 VFD.

I'll bet everything else is 120 VAC, the xfeed, DRO and lights. The transformer might have a 120 tap.

If the transformer is connected to a single leg or it's outputs aren't connected to the motor, it's probably just to supply 120 to the xfeed, DRO and lights.

Hmm, just noticed your comment that local single phase is 220, 50HZ. You're not in the US, so you may have a 220 VAC light, xfeed or other auxillary equipment.



[This message has been edited by JoelK (edited 03-01-2003).]

[steve schaeffer]

<font face="Verdana, Arial" size="2">Originally posted by knucklehead:
steve s--
run that by me again.. the part about the spare 3ph motor ...

intrigued,
-knucklehead</font>

you can use a three phase motor to generate three phase power when hooked up to single phase line. all you have to do is get it spinning. when you buy a rotary converter from the store, they have a capacitor start circuit,(basically the same guts that are in a static converter)what i was saying is if you do not have the electrical expertise to get that involved, you can do it the "mechanical way" let me explain that. if you have a 7 hp 3 phase motor for your slave, mount it on a plate. now you need a single phase motor, this can be very small. this would be mounted opposite your slave and able to be meshed shaft to shaft with the slave.this can be a coupling, belt and clutch or a drop out gear, whatever. the way it works: the single phase power line 1 and line 2 go to any two of your three leads on the slave. you also connecto your machine tool leads t1 t2 and t3 to the slave. this is a parrallel hook up. when you turn on your power switch to the slave , it should also turn on your single phase "starter" motor. this will get your three phase slave motor spinning. once its spinning it will keep running on single phase (l1 and l2) then you can take your "starter" motor out of mesh. the slave just sits there and runs by itself, its not hooked to anything mechanically. however it is now generating a lesser third phase on its third motor winding (the one thats hooked up to your machine tool) now you can turn your machine on. ok, so it sounds kinda mental, but its not.its just a bare bones way of going about getting a three phase motor spinning. let me rephrase one more time, if you take a three phase motor, hook it up to just two lines (single phase, two hots,)and turn the power on, it will just sit there and hum. on the other hand, (this is just to get the point across)if you had a pull rope wrapped to the shaft of the motor, turned your power on , it would hum, then if you yanked on the rope and got it spinning , it would continue to run on two of its three windings. yee hawwww
steve. and about your vfd, you have to match the vfd to the motor. it has a range though and will tolerate some under/over voltage. but you already have the vfd,

ok, lets get all of our facts straight about this vfd.
-we have a motor of 380 v three phase
-the motor is directly connected to the vfd's output terminals.
-we have single phase 220 to the input. eeeeeeeeee. wrong. unless the converter says on its nameplate that the input is 220 and outputs 380, you need a step up transformer on your line (input)side. garbage in ,garbage out.
looks like ya might need a new motor, and vfd, or just a step up transformer. what a pain. not that this helps, but i have 220 single phase, my motor was dual voltage, so all i had to do was buy a static phase converter.(i feel like im lying when i say static phase converter. that bothers me. it doesnt convert a darn thing, haha.)
sorry for being wordy with the rotary phase converter topic.

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extreme tractor racing

[Tony]

steve--
you've gotten me so excited that i hardly slept last night ... so before my girlfriend breaks up with me, clear something up:

are you telling me i can start USING 3 PHASE EQUIPMENT IN MY OWN SHOP if i get a rotary 3phase converter????

who came up with this magic box?? i've spent years now complaining about the cost of having 3ph power run to my shop and have been crippled (power & price) by my 220 line.

what are the limitations? what size converter do i need? how many machines will it run? (i can just plug them in in parallel??) how much do these things cost?
why didnt the guy get a nobel peace prize?