motor starting and reversing.

On or around Fri, 22 Aug 2008 05:44:44 -0700 (PDT), houstonceng


hmmm. that's a point. The reversing switch on it now does the same as the setup in the latest drawing but is downstream of the main supply switch (with the overload cut-out), so there are no volts anywhere when the supply is off. Ideally, I need to get the start buttons to control the main switch as well, then.
Or perhaps I need another relay to make the L and N lines into the motor 1 and 4 pins.

yeah, needs more work... It'd be a damned sight easier if I could just buy the necessary box.

2HP high starting torque. I've got 30A relays on order...
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 22 Aug 2008 22:35:44 +0100, Austin Shackles

When I wired up my CNC mill the contactors had switches added to the sides which are used to prevent both forward and reverse contactors from being energised at the same time. The coil from one contactor is wired through the NC switch on the other contactor. When a contactor is energised the switch turns off so that even if the control tries to turn it on it can't because no power will flow. Why can't you do this with relays with moltiple contacts? To make the scheme work the motor will need to be turned off first which is fine for your situation because your single phase motor will not plug reverse. If you want I can make a sketch, scan it, and post it to metalworking.com. Or e-mail it to you. Maybe this has already been discussed and rejected. If so then of course just ignore this post. Eric
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Aug 22, 11:35 am, snipped-for-privacy@whidbey.com wrote:

Yes. That would work as well. Ideally, you'd need two 4-pole ST contactors each with Aux C/O contacts. You could get away with two 3- pole ST contactors with Aux C/O contacts if you wired one side of the motor run-winding permanently to Main N.
Andy
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
David P wrote:- "The type of motor that does what he describes is a sp induction motor with separate forward and reverse start windings. They can be switched by spdt switch and separate main contactor. Better to use dpdt with centre off position, then you can control the contactor to give forward-off-reverse control. Usually cheaper to do it this way than some relay switching to reverse one winding. Nothing special needed for the switch, I use toggle switches as the contactor does all the power stuff."
Yes. I'm aware of the type of motor that Austin has. I was thrown by his remark in an earlier posting viz:- "The forward and reverse on this motor is just a case of connecting it the other way around, and it can be done with a single DPDT switch."
That appeared to say that the complete feed to the motor was connected the other way giving reverse whereas, after I checked by asking, Austin clarified matters with a circuit diagram and words.
As his motor is 2hp (1.5kW), I doubt you would find a DPDT, centre off toggle-switch capable of taking the starting current. Austin was also asking how to use the Fwd-Stop-Rev pish-button set he'd sourced from e- bay and the only way of doing that is to use relays or contactors. Besides which, I cannot see how you'd control a single contactor with a DPDT, centre off toggle-switch to give Fwd-Off-Rev as you suggest, so I'd be interested to see the wiring diagram.
BTW. Many of the Taiwanese lathes sold in Anerica (and some sold here with control transformers) use 110v relays to do the interlocking, NVR and hold functions which then switch 110v coil contactors switching mains to the 220v (240v) motor. Jet and Grissly (sold in USA) lathes have 3-wire single-phase motors switched by two three-pole contactors. This type of motor has a 110v start winding connected to the centre-tap of the 220v run winding. The run winding connexions are, usually, U1 & U2 and the motor is reversed by connecting the free end of the start winding (Z1) to either U1 ot U2. With a three pole contactor you can connect the run-winding to 220v and Z1 to, say, U1. Then, with the other 3-pole contactor, connect run-winding to 220v and Z1 to U2.
For the motor that Austin has - usual separate run and start winding (ie 4 connexions) - you'd need two 4-pole contactors (assuming you interlocked, etc, using relays as per Jet/Gris).
I proposed a design using 3off DPDT relays, which provides interlocking, NVR and reversing from Austin's push-buttons. You could use a DPST, NVR/Overload contactor - with C/O Aux contacts - to do the main switching, but you'd still need two DPDT relays for the reversing (one to do the motor switching, one for the interlock) OR 1-off QPDT relay.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On or around Fri, 22 Aug 2008 17:05:03 -0700 (PDT), houstonceng

OK, nother rethink (and annoyingly, I just ordered 2 relays - might be able to add to the order if they haven't dispatched it)
http://www.roman-road.co.uk/temp/DSC00201.JPG
I reckon this one works. Assuming that 240V ac relay coils work the same regardless of L/N connection, and I can't see how they don't.
does that equate to the design you proposed, out of interest?
it doesn't make the main relay 'til after the forward/reverse, but I don't see that as an issue, it's only a few milliseconds.
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In article
wrote:

It doesn't need to take the starting current, that flows thro' the main winding (and is switched by the contactor). All the switch is doing is, on one pole, selecting which starting field is to be used, and on the other pole, taking the coil current of the contactor. If it's for a battleship, RS 316-642 is 15A, @240VAC A. (Making capacity not specified) . Or, as Austin almost says, a conventional motor p/b starter with all the trimmings and a separate dpdt switch to reverse the start winding. I like KISS!
Must admit, it was somewhat confusing as to exactly what he had and what he was doing.

Yes, you need to memorise the states of the p/bs.

Any clearer now? Obviously some misunderstanding when you refer to the switch taking starting current.

Same basic idea, consider the two starting coils to be a single, centre tapped coil. Or feed a single start winding from one side of a 240/240-0-240 transformer. We can choose to reverse either the start or the run windings. I'd choose the one with the lower current demand every time. (Unless it's a DC motor.)

Depends on what you want. Provided it's a machine under operator control, emulation of ye olde forward/stop/reverse gear lever is ok by me. I like to see what's selected. Don't see much need for interlocking forward and reverse, except via the switch. Worst that can happen is that the switch is flipped too quickly and it carries on in the same direction. No NVR release either. Not suitable for (say) a remote suck/blow fan in ductwork. Oh! Almost forgot,and just to placate the elf'n'safety stazi, a stayput emergency stop p/b in series with the contactor overload.
Regards,
David P.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Big SNIP
Sorry David.
It's the "English usage" in your explanation that threw me, viz :-
"They can be switched by spdt switch and separate main contactor. Better to use dpdt with centre off position, then you can control the contactor to give forward-off-reverse control."
The way it read was that the motor could be switched by the SPDT switch (between forward and reverse) with only the need for a main contactor.
You then went on to mention that a DPDT switch could control the contactor to give Fwd-Stop-Rev, so I assumed that the contactor referred to was the "main contactor", so I was interested to see how you could do that with it. My mistake. Shouldn't have read it the way it looked.
You then said :- "Usually cheaper to do it this way than some relay switching to reverse one winding."
Which implied that you used the DPDT switch to reverse one winding since, if you were using two contactors (One Main, One Reversing), that's exactly what the contactors would do - reverse one winding (ie the same as using two relays). So it also seemed that you were using a DPDT, switch to carry Start or Run winding current.
You reinforced the implication with :- "Nothing special needed for the switch, I use toggle switches as the contactor does all he power stuff."
See my confusion with your explanation ? "The Contactor" instead of "Contactors" and the implication (incorrectly inferred) that a contactor and DPDT switch were all that is needed.
Since you also said :- "Same basic idea, consider the two starting coils to be a single, centre tapped coil. Or feed a single start winding from one side of a 240/240-0-240 transformer. We can choose to reverse either the start or the run windings. I'd choose the one with the lower current demand every time. (Unless it's a DC motor.)"
I think you should re-read what I said about 220v, 3 wire, 1-phase motors in USA on Jet and Griss lathes. 220v is supplied (via two poles of a contactor) across the centre-tapped (110v - 0v - 110v) RUN winding and the motor direction is dictated by connecting the free end of the (110v) START winding to one end of the RUN winding - using the 3rd pole of the contactor (the other end is connected to the centre- rap of the RUN winding. The reversing circuit uses a second 3-pole contactor to connect the RUN winding to 220v as before and the free end of the START winding to the other end of the RUN winding. To ensure that the two contactors are not operated simultaneously, to provide NVR and guard interlocking, additional relays are used to provide the logic and hold functions.
In any case, suggesting that "ye olde forward/stop/reverse gear lever is ok", isn't a solution to Austin's request for a "how-to" using his Push-buttons, that Bob, Mark and I are trying to provide.
Andy
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Austin, Andy (houstonceng) and I have been pooling our thoughts, off- group, on a the design for a 3 button reversing starter which has been finalised (until somebody reports an error).
Circuits and notes can be seen at: http://chainganger.co.uk/Page1/PDF/Reverser.pdf
Comments are welcomed.
Bob
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 31 Aug 2008 14:57:50 -0700 (PDT), BobKellock

A bit late but may still be of interest
The circuits all look OK but you've chosen to to switch BOTH the live and the neutral lines of the single phase input (in the off position neutral is no longer connected to the motor or the relay sequence).
In single phase systems it's only necessary to isolate the live line - the neutral line can always remain connected .
Using live line switching and permanently connected neutral the control complement can be simplified and reduced to two, three phase motor control relays fitted with 240V coils.
These are fitted with three heavy duty MAKE contacts and two light duty contacts. One light duty contact is normally OFF the second is normally ON. The construction guarantees "BREAK before MAKE"
One relay is used to switch the motor to forward, the second relay is used for reverse. The light duty contacts are interconneced to provide no volt release and to interlock the forward and reverse functions.
When forward or reverse is selected the other button is disabled. If both are accidentally pressed "simultaneously" whichever button actually makes contact first takes over and disables the other.
The snag is that I don't know of a retail supplier of the necessary relays - my own are all rescued from scrap machinery!. These are fairly easy to find but may not have the right combination of light duty MAKE and BREAK (twin MAKE is common). However,in the ones I have played with, MAKE or BREAK operation is determined by the way the contacts are assembled into the bakelite housing. It's pretty easy to open the housing and reassemble with the contacts moved to the desired locations.
Alternatively, any pair of three phase contactors can be augmented with a separate pair of light duty relays. The light duty MAKE and BREAK function must be on the same relay and the contact arrangement should be of BREAK before MAKE design (most small relays fitted with a pair of changeover contacts work this way) .
The system will still function correctly if the incorrect MAKE before BREAK relay type are used but the both button pressed protection is lost. If Forward and Reverse are are pressed simultaneously there is a small chance (dependent on relative time delays) of a catastrophic supply short circuit.
However it's still an OK system if the Forward and Reverse buttons are arranged so that it is physically impossible to press both at once.
I've posted the circuit and also JPG of a typical three phase contactor in the xs.to image hosting site :-
http://xs.to/xs.php?h=xs231&d 365&f=motor_reverse933.jpg
http://xs.to/xs.php?h=xs231&d 365&f=three_phase_contactor931.jpg
jim
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On or around Fri, 05 Sep 2008 19:39:12 +0100, snipped-for-privacy@yahoo.com enlightened us thusly:

provided, of course, that the relay action times allow this. Relays are quick but not instant, ditto contactors.
OK, not likely, but we are trying to deal with sod's law as well, to an extent, and sod's law dictates that if someone's daft enough to press both fwd and rev at the same time, the contacts will make sufficiently close together as to cause a problem if the possibility exists.
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 06 Sep 2008 10:22:56 +0100, Austin Shackles

Then I suggest that you use a mechanical interlock between contactors. I would not use relays in such an application.
--
Richard

Email address is valid but remove burrs before sending!
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6 Sep, 10:22, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol- las.net> wrote:

So cross wire the fwd / rev buttons thru the aux contacts on the opposite relay. Whilst fwd is running there is no feed to the rev button. Then put a big stop button between the two so you need two hands.
Failing that have a two position switch to select fwd / rev and a start stop button. The advantages of this on single phase is that you can switch from fwd to rev whilst running ready to hit stop then start like at the end of a thread.
John S. I had this system on my Myford for years with just one mains relay swapping wires.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On or around Sat, 6 Sep 2008 03:49:14 -0700 (PDT), John S

that (the cross-wiring) is what the circuit we ended up with does.

Not sure the motor would like that, more to the point, not all the machines will stand that sort of instant reversing. Some will, some won't. In particular, any lathe with a screwed-on chuck will undo it's chuck. Which could of course be handy :-)
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6 Sep, 17:29, Austin Shackles > wrote:

I was referring to the typical single phase motor with centrifugal start as fitted to the Myford. Until the motor stops and the switch is closed the changes can't take effect.

Will ?? you read too many horror stories, but if it worries you that much stuff a centre in the end of the work and it can't unscrew as it has nowhere to go.
Incidentally in the 24 odd years I owned two Myfords I only ever had the chuck come loose twice, note loose not unscrewed. both times I was pushing the machine more than it was capable of, in fact in retrospect that was for the whole of the 24 years. Yes in theory they can come unscrewed and someone always has heard of a brother / co-worker / maiden aunt / escaped prisoner [ delete as required ] who had this happen to them.
After mixing with people who uses machine tools seriously for a living none have ever had this happen to them.
John S.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On or around Sat, 6 Sep 2008 11:40:58 -0700 (PDT), John S

when does the switch close though? It stays in circuit during start up until the motor is up to speed, but does it actually come to a halt before the switch re-makes?
and do ALL such motors do so?
The one that the circuit is intended for is a 2HP capacitor start/capacitor run with 2 caps on it. Without studying it in detail, I'd prefer to play safe.
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Austin Shackles wrote:

But the centrifugal switch doesn't close until the motor slows down - and it doesn't do that until the power is off. The start/reverse switch changes the direction of the starting coil - the main switch still controls the power - so it'll be fine unless you try and start it in the other direction before it's stopped.
My previous lathe was wired like this. It's a good system and is much cheaper than Dewhurst type reversing switches.
Russell
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If you try and start it in the other direction before it's stopped nothing will happen as it has forward momentum and will carry on, like a bad motor you rope start. It needs the centrifugal switch to be closed before it can start in reverse and this happens at low speed anyway so if you are that quick with the start button as soon as you hear it click then it will instantly reverse but only from a few revs.
This won't harm the motor as there are many standard 3 phase motors in industry that are designed to plug reverse and do so all day long.
John S.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

So long as the centrifugal switch hasn't remade.

But it won't do the motor much good if you do this too often. Besides which, if it's a Capacitor Start & Run motor it may not have a centrifugal switch !

But three-phase motors start and run using an entirely different principle to single phase motors - so you're not comparing like-with- like.

Andy
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 7 Sep, 11:45, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol- las.net> wrote:

It doesn't come to a halt before closing but , normally, it's not far off. Just try running the motor without any load connected, switch it off and listen for the switch to close. I think that there's a very strong chance that, if you press the reverse direction button just at the point the switch has closed then the motor will reverse OK.

No. The secondary winding of Permanent Split Capacitor (PSC) and Cap start/Cap run (CSCR) motors is normally called the Auxiliary winding, instead of Start winding, because it is always energised at the same time as the main winding and uses a heavier gauge wire.
If you reverse the connection to the Aux winding (plus its series capacitor) it will probably try to decellerate it and eventually reverse it but a lot of heat is generated and there will be a large current spike, particularly if the reverse connection occurs at, or near, a peak of the AC cycle. Single phase motors and controllers are made using this principle to stop them (known as plugging) but I wouldn't want to do it with a bog-standard motor.
Just because a motor has a centrifugal switch doesn't mean that you can switch it into reverse without it having any effect when the motor is running. CSCR motors have a centrifugal switch (although some have a timer instead) but that simply switches out the start capacitor; it still leaves the aux winding and its capacitor energised when the main winding is.

As it's a CSCR I'm sure that that's the wise way to go,
Bob
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 06 Sep 2008 10:22:56 +0100, Austin Shackles

Fair comment but sod has to be particularly vindictive to to cause a problem.
This is of course a setup that I have used for many years without problem but,since I'm not addicted to simultaneously pressing Forward and Reverse buttons, this is not useful evidence.
There's no doubt that the Break before Make sequencing logic works fine if there's a significant time difference in the "simultaneous" pressing of the two buttons, What is less clear, as you have pointed out, is the behaviour if the relay closures are truly simultaneous.
To test this I disconnected the motor load (to avoid overheating from frequent stop starts) and proceeded to repeatedly press first Stop, then both Forward and Reverse buttons at the same time. Behaviour was as expected with correct closure by either of the two contactors in apparently random order. All went well for 50 successive attempts but at the 57th try the supply fuse blew!
This clearly justifies your comments but also gives some idea of the extent of the problem.
Accidental simultaneous pressing of both buttons is, in itself, a pretty rare event but even if it does happen there's something like a 50:1 on chance that the setup will still behave correctly. If it does fail, the supply fuses blows. This is the result of the short circuit across the motor terminals - there is no possibilty that this will damage the motor.
It's a simple and very convenient setup if you have have the right contactors and I will certainly continue to use mine. However it doesn't provide total protection against simultaneous selection of Forward and Reverse.
Jim
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.