Converting a Bridgeport from 3 phase to single

[MattKParticipant @mattk47317]

Hi,
I have bought a Bridgeport mill with a J head and although I won’t get the machine until the end of the month I am trying to understand what I need to do to convert from single to 3 phase. I understand from other sources that I needed a 240V to 415V converter if I use the dual speed motor as apparently it is not easily reconfigured to work on 3 phase 220V. The documentation on the converter states that it must be connected directly to the motor with no switches or contactors in between. Looking at a circuit diagram from the BP manual it looks like I need to wire the outputs direct to the motor and the controls (forward and reverse) to the converter inputs. The main power switches the single phase input.
My questions are, Am I on the right track?
Also the machine has the early (not 6F) power feed on X axis which I know works but I can’t figure out a simple way to drive this easily. Would be interested to know anyone else who may have solved this. Thanks

[MattKParticipant @mattk47317]

[Des BurnettParticipant @desburnett83896]

Matt. I had the same situation with the addition of a Colchester Bantam to wire in also. I researched the digital route and could see the possible advantages of controlling the spindle speed and direction via the digital unit. You are correct in that these systems require to be wired in directly between controller and motor which poses a further problem when there is a coolant pump on the same machine. I could have rigged up a switch box to run either machine (not both) or purchaseud two digital units. My decision was to purchase a 3 phase rotary converter. This was based on its "plug and play" and if I add more 3 phase machines which I only run one at a time then the one converter (suitably sized) will be all I need. One other factor that had an influence on my decision was due to the non reply to enquiry emails sent to a prominent advertiser of digital drives on this web site.

Regards Des.

[Bill DawesParticipant @billdawes]

Hi Matt, if I have read it correctly your heading seems to contradict your text.

As I understand it, if you have a 1 phase motor / 1 phase 230v (ish) supply and you want variable speed you need to change it to a 230v 3 phase motor to work off an inverter, many small industrial 3 phase motors are dual voltage 400/230v (ish) as standard.

If you already have a 3 phase motor and it is 400/230v then no problem.

I have a 0.75kw WEG inverter (they sell for about £80 trade price) on my lathe for such a purpose, it is amazing what they can put into such a small box of electronics these days.

Bill D

[MattKParticipant @mattk47317]

Thanks for your replies.Sorry I can see how my heading is confusing. It is the supply that is changing not the motors. I did initially consider a rotary converter but wanted something small to fit in the cabinet. Actually I’m not that interested in controlling the speed via the converter. Also not thinking of using suds pump mainly due to the mess. Maybe I am looking at another small converter for the table motor.

[John Stevenson 1Participant @johnstevenson1]

First off you mention a two speed motor but is it ?

They did do a two speed motor as well as the single speed. Where the confusion arises is the single speed motor has a three position switch marked l – 0 – ll and everyone assumes the l and ll are two speed when in fact it is forward and reverse.

The Bridgy needs reverse on the switch because when the backgear is engaged the drive is revered.

A true two speed motor has a 5 position switch marked l – ll -0 – ll – 1 or For L – H – 0 Rev L – H

or other variations of the same layout depending on where they bought the knobs that week.

The two speed needs a phase converter to run correctly or one of those bodged up inverters that take 240v in and put 440v out.

The single speed motor which is a stupid Yankee 9 wire motor can be rewired in the terminal box to mimic one of the normal 6 wire dual voltage ones that can run off a 240v single phase in and 240v three phase out.

The table motor can be run off single phase with a capacitor across the dead leg, it will be down on power a bit but these hardly take any power anyway.

John S.

[Nigel RiceParticipant @nigelrice73086]

Matt. I ran a Bridgeport with J head for many years off a single phase 240v supply by use of a phase converter. The same converter ran a 3hp compressor and a rather complex variable speed motor on a Holbrook 17 lathe.

The phase converter uses a transformer to up the voltage and capacitors to start the motor, which when running, generates the third phase. This is probably why you are advised to bypass contactors.

I used a slave motor, (cannot remember size), which I would switch on for starting – this meant 3 phases to the machine, and no problems with wiring through normal control box. With the Bridgeport this meant the head with both speeds, coolant pump and DRO.

With the compressor and lathe I could switch off the slave once the machine was running, but with the Bridgeport I had to keep the slave running. I don't know why, but the head motor made 'orrible noises with the slave off. This combination ran for about 15 years with no problems.

Nigel

[MattKParticipant @mattk47317]

Hi John,

I think you may well be right but I don't have the machine to look at right now. This was niggling me but someone convinced me that it would have a dual speed motor. I already have the converter now so will probably use it but could have saved some money by not having to step up the volts.

I'll wait and see what the motor is and what's inside the control panel when I get the machine.

Another quick question though, I assume that the mechanical table feed doesn't have a fancy control board like the later 6f type feeds? Another forum user suggested that they ran their motor from a 110V tapping on the internal transformer but I think that was with a 6f feed and that theirs was not a 3 phase motor.

Any idea what size cap I would need to drive two phases in the feed motor? I'm assuming it would be wired in the same way as some of the static converter diagrams I have seen on the net.

Thank again for the wise words.

Matt

[Richie MParticipant @richiem]

Hi Matt

I have converted my Bridgeport to single phase, mine didn't have either a suds pump or an original table drive motor to worry about and my route to single phase was guided at the time with help and advice from John Stevenson over on Usenet at the time.

Step one for me was to rip everything relating to the original 3 phase setup off the mill (apart from the motor of course) I couldn't see any need to keep it..I have kept it all chucked in a dark corner of the workshop but I don't see that I'll ever need it again.

I bought my inverter/control station from Newton Tesla who I had used before when I converted my lathe (which was single phase but I wanted the speed control etc so went down the 3 phase motor avenue) anyway the inverter came from them pre-programed with the control station pre-wired, all I had to do was follow the diagram supplied to connect it to the inverter, simple enough after studying it for a day or so…..

I found NT very helpfull both times I have used them, I think I could have probably bought the inverter a bit cheaper, but I like their control station and it was really a turn-key package, with added back-up if needed, that has a value to me!

All I had to do was change the motor wiring to Lo-Volts as shown on the motor plate, all the wires are numbered so it was simple enough to follow through.

After that all I had was the supply from the inverter to bring in, again simple enough and ain't a sparkie!

It all worked first time and I havent had to touch the wiring etc from day one.

It gives great control, on the jog setting I can tap under power without having to go move into back-gear, the inverter gives 5hz (I think) in jog mode and with the mills speed wound down to the minimum 450rpm it's easily done and I haven't bust a tap so far!

I haven't had the need to mess with the programming of the inverter, the settings from Tesla seem fine and after 3 years use I haven't felt the need to alter anything.

I have the 110 volt "accessory" type drives on X-Y-Z axis they are powered from a single transformer bought from Screwfix, that's the only part of the setup that I have had problems with, when I switch on on it trips the breaker sometimes, seems that my RCD's in the workshop are not ideal for the "inrush" of the transformer, no big deal just a little irritating.

Hope this helps.

Richie

[MattKParticipant @mattk47317]

Hi Richie,

Thanks for the posting. It is helpful especially as most of the stuff I have read is from the US and of course their different voltage system. Always good to hear other people have attempted conversions without too much trouble. I will post my success (or otherwise) at the end of the month when I get the machine and I will no doubt be asking some other basic questions. I have done a bit on my lathe (Myford S7) but my milling experience is very low apart from a bit on the cross slide on the lathe. This forum is fantastic for me as machining is not my background and I don't know anybody who shares this hobby so although I have read quite a bit there is no substitute for the years of experience here. Thankfully electrics is something I am comfortable with.

[MattKParticipant @mattk47317]

Hi,

I have now got the Bridgeport in my workshop after a 7 hour marathon getting it from the gravel drive into the workshop. The motor is only a 0.75HP as can be seen here and can be wired in star as well as delta.

Unfortunately in anticipation I purchased a 2HP inverter running at 415V after some misinformation from another source (not here).

What I want to do now is buy two smaller inverters at 230V and run the head with one and the cross feed with the other. At current prices I should be able to do this for less than the cost of the inverter I have already bought. I just need to trade the other one in.

Here is a pic of the cross feed (which I have seen working). A bit of the casting has been broken off but that is now JB welded back in place.

Inside the control panel are all the old contactors

The plan is to rip all this out and fit the inverters in there. What I do know is that the inverters need to be wired directly to the motors i.e. no switches or anything in between. I was therefore planning to run the On/Off/Reverse switch into the input of the inverter because there is an input for this. The one bit I am not so sure about is an emergency switch on the front which I guess is there to kill the supply power to the machine as a whole. I opened the front of it and it appears to be just microswitches wired back to a contactor in the control box. I am assuming I need to break the 230V supply power and will need to buy another contactor for that rated at 230V.

Would appreciate if you guys think my thinking is the right approach.

Thanks.

[David Clark 13Participant @davidclark13]

Hi There

The inverter forward, reverse and on off will almost certainly be about 10 volts.

Are you sure the feed motor is 440volts and not 240volts single phase?

The inverter manufacturers will almost certainly be able to supply control units that include an emergency stop.

I would contact Power Capacitors (Transwave) who advertise in Model Engineer and Model Engineers' Workshop.

regards David

Edited By David Clark 1 on 08/12/2012 19:36:55

[MattKParticipant @mattk47317]

Hi David,

Thanks for the reply. Yes the drive motor is a 3 phase 1/8 HP. I believe this can be run at a push off a single phase and a capacitor on a second phase.

Thanks for the link to Transwave.

regards,

Matt

[Sub MandrelParticipant @submandrel]

HI Richie,

Putting the 110V table motor transformer on the end of a long extension lead might help. I was given this advice for my arc welder (which tripped out every 3rd or 4th switch on) and it hasn't tripped once since.

Neil

[John Stevenson 1Participant @johnstevenson1]

Matt,

Working on my Bridgy at the moment doing roughly the same as you.

Mine is a 2J head, varispeed with 1.5 HP motor and it's sick. Sooner than replace the motor and repairing the varispeed which is showing signs of wear even though it had new bushings 18 months ago I am changing the top half over to the older step speed, replacing the 1 HP step speed motor to a 3 HP unit and fitting an inverter.

 

My take on this is that if cheap and reliable inverters were available 40 odd years ago then varispeed units would never have been invented.

I am going over to single phase for the spindle motor even though I have 3 phase with the idea that it will help it's resale value later. The old mechanical feed will still stay on three phase. I will keep the original electrical box because of the suds pump, power feed and slotting head but fit a new cabinet on the back for two inverters, one for the spindle motor and one for the knee feed which will be a future project.

 

This is where I am at the moment.

 

The motor on the right is the original one that needs to go back to the guy who sold me the step head.

 

John S.

Edited By John Stevenson on 08/12/2012 20:14:26

[MattKParticipant @mattk47317]

Hi,

I was actually looking for the J head because although I know the 2J is more desirable, I had read that it can get expensive if it goes wrong. Not sure if it is as simple as keeping the pulleys on a fixed speed and using the inverter to control the speed. Is there a trade off with torque?

Anyway, a bit slow going at the moment but I now have the correct inverters to drive the head and the table motor (Big thanks to the people at Drives Direct for real customer service and swapping out the wrong kit which I previously ordered with no fuss – recommended).

I have a quick question regarding an emergency stop. I have always thought these should be a mechanical mechanism rather than an input to a cpu controlled device or am I out of date?

Do I need a contactor and if so can somebody recommend one?

I also need to rewire the table drive motor but Ritchie's comments above make it a bit clearer as it is just a series of wires rather than jumpers but I think I can see which are pairs but I may have to come back on that one. Thanks.

Matt

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