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04-02-2011, 04:06 PM #1
Wiring a push-button stop start switch.
I have got myself an old IXL Capitol lathe a while ago and I just recently got around to removing the old gigantic three phase motor, and making a pedestal up to mount a modern single phase motor so I can have the thing running in my garage.
Anyway at the moment there is no switch wired on, to make the machine run, you just have to plug in the three pin socket, which is a less than satisfactory arangement, as it is quite dangerous.
Anyway my friend gave me a proper stop start push-button switch, but opening it up, I cannot figure out how to wire it up! Inside, it just has two momentary switches, each with a normally open side and a normally closed side. Does anyone have any idea of how to wire this up, so that it will keep going even if I remove my finger from the start button?
04-02-2011, 04:24 PM #2
You will need a motor starter, contactor or relay to use the start/stop push button.
04-02-2011, 04:27 PM #3
First, glad to know that you've survived the catastrophe there and and are back to working in your shop. I hope all of your family is OK too.
Now, why would you go through some much trouble and expense to remove a perfectly serviceable 3 phase motor? You could have simply powered it up with an economical VFD unit and enjoyed the benefits of 3-phase power.
04-02-2011, 04:57 PM #4
It is a three phase motor from the 30's, is it so incredibly large and heavy that it requires a 2 person lift, and then it is only 2 horsepower. I don't know where I can get a VFD really cheap which runs off single phase, but I was able to buy a brand new 2 HP single phase motor for only $150 NZD if I recall correctly. I don't know if I can get a VFD for that much? I can use the old motor to make an induction generator for if we get any more power-cuts from big earthquakes.
So what you are saying, is that to make the start/stop button work, I need to get a relay, and wire it up so that when I push that start button,wired through the normally closed open it will feed the solenoid to close the switch inside, and there is a wire coming from the switch which keeps the solenoid energised to keep the switch closed. This will keep working until I push the stop button which has the circuit wired through the normally closed button which will break the circuit and the relay will open and the motor will stop.
Other option is originally on the lathe there was a magnetic three phase switch, can I just use that, but only use one of the switches inside, as the other switches will not be doing anything? Or should I just have it so that the electricity is running through all the switches in parallel?
04-02-2011, 05:10 PM #5
My house is in one of the worst affected areas, being quite close to the epicentre in Lyttleton, but doesn't have very much damage, just internal cracking and such like. Was a HUGE mess inside though with everything on the floor. The house has moved a couple of inches however, but just as one integrated unit. I have a little more land now, so that is good news.
Workshop was a BIG mess, with lots of stuff tipped over, and a LOT of stuff on the floor. My bandsaw was tipped over and my drill press was hanging off a ladder which was hanging off a vice!
Have just recently got it mostly tidied up, and am getting back to work in there.
04-02-2011, 05:18 PM #6
A drum switch is often used with a single phase motor to provide off-forward-reverse switching on lathes.
The pushbutton station you have is typically used with a magnetic starter. You'd have a set of normally open auxiliary contacts on the starter which would feed power to the coil and keep it latched in when you push the on button. The leaving side of the auxiliary would be wired thru the NC side of your off button such that pushing the button breaks the circuit to the coil, allowing the contactor to open. The auxiliary contacts work in sync with the main contactor, so when the stop button breaks the power to the coil, the auxiliary contact opens as well to interrupt the control power circuit.
One of the main purposes of a magnetic starter is overload protection. Single phase motors like yours usually have a built in thermal overload, so the overload protection provided by the overload relay section of the starter isn't necessary.
For your single phase motor, you could use a standard 2 pole relay instead of a starter. To use your pushbutton station, you'd still need to have a set of NO auxiliaries on the relay. Otherwise, you could use a maintained contact switch to provide control power to the coil. The drum switch is far cheaper and simpler to hook up, and provides a means of reversing. Reversing magnetic starters require both electrical and mechanical interlocks to prevent phase to phase shorts in the event one contactor doesn't drop out as it should when you reverse the motor. Way too much complexity and $$$ for control of a single phase motor.
04-02-2011, 05:55 PM #7
just remove the bridge rectifier and the diode and there is your diagram.. remove the jog switch also if you want
04-02-2011, 05:58 PM #8
Hi Metal Muncher.
Thanks for your advice.
I don't want to have any reverse option as the lathe has threaded on chucks, and in the event where reverse was inadvertently selected, the chuck could accidentally be undone, and this could be quite dangerous.
I believe that I may be able to use the three phase switch using one set of contacts, as I only have one phase to switch, rather than three. I will take it to my electrical engineer friend to have a look at tommorow I think.
I may also look at using the pushbutton switch using a relay as well.
04-02-2011, 06:28 PM #9
You have the idea, you can use the mag starter you have or any relay with the desired control voltage and current capability. On a relay or starter with out a latch and the same voltage for control and load, you can simply loop a leg through a contact to the coil. Once you close the relay it will remain latched until the stop push button interrupts the current.
04-02-2011, 09:18 PM #10
Normally a motor will not accelerate hard enough to unscrew a chuck that is properly tightened. I have a 14 1/2" South Bend with a threaded spindle and a 5 hp DC motor that has enough torque to slip the belt that I have used daily for 35 years and never had a chuck come loose. The reversing function is very useful, but I will not run a lathe with a single phase capacitor start motor and a reversing drum switch. When a motor has a starting winding and a centrifugal switch that disconnects it after the motor gets going, if you switch to reverse with it running forward, it will just keep running forward. If you have an emergency and slap the drum switch in a panic, it will go on over to the reverse contacts but the lathe will continue forward. If you are getting rolled up in the lathe, it will keep rolling you up. With a three phase motor, hitting reverse will make the motor come to a stop and then start backward. That takes long enough to realize your error and get the switch back to off. At worst, it will back up and unroll you. If you insist on having a single phase motor, a poor idea to begin with, separate the start/stop and reversing functions and put a big push button on the stop that you can slap without having to take careful aim.
04-02-2011, 10:41 PM #11
you should be able to reuse the old motor starter. Not sure is it a remote switch with a coil in the contactor box, or did you have to push a button on the relay box to turn the motor on and off. Also, if it has a coil, what voltage is the coil.
I would switch both lines going into the motor just a little safer that way. And as long as you have enough contacts why not?
Never ever switch the ground lead.
Personally I like to add a plug with a short cord on the motor and short cord out of the controls so I can plug/unplug the motor and check any wiring on the bench. Much easier then leaning over the machine and standing on your head while trying to hook up the motor.
PS with a contactor switch you can add as many stop/start switches as you want. Maybe one at the tailstock end?
04-03-2011, 06:25 PM #12
The Sheldon came without a drive, a long story, so we made one with a motor controlled three phase variac with rectifiers feeding a 15 HP DC motor. We made a panel for the normal spot, silk screen printed in case you are wondering, which works well, but I normally stand toward the tail for vision and dodging chips, so when the chuck picks up a load of swarf, spinning around spraying a rooster tail of coolant, I have to get past it to stop the lathe. It needs a stop button on the tail end.
04-03-2011, 09:28 PM #13
they make cable pull switches, as used on a bus. these would allow a rope across the front of the cabinet or maybe tied to a foot brake bar.
04-04-2011, 02:28 PM #14
I have attached a simple latching circuit diagram, your existing Contactor should be ok for this.
04-04-2011, 05:21 PM #15
Correct. Additional start switches are connected in parallel with the first one, added stop switches are in series with the original.
Bill D, a foot switch might be good. I probably will just put an extra stop button on the tail end. The controls on the Sheldon carriage are situated so that they are easy to reach from downwind so it would be easy to stop the feed to avoid breaking the carbide bit, then hit the stop.