motor starting and reversing.

I bet this appears twice now. it seems to be in limbo, so reposting...
got cheap on ebay a box with forward reverse stop buttons, but that's all it is, the box and contactors under the buttons. The start buttons have push-to-make switches and the stop one has push-to-break.
So... can I make it drive the single-phase motor on the lathe, forward and reverse, and if so what else does it need. I already have stop-start-overload switch thing, but that only goes one way. It's also not no-volt release, which is not ideal.
currently, reversing is done with a pair of SPDT switches, which is far from ideal, especially as they're only just big enough current rating.    

Austin Shackles wrote:
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Dis you see my reply Austin?
Bob

On or around Mon, 18 Aug 2008 18:04:46 +0100, Bob Minchin
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nope. whole thread seems to be AWOL. unless it was by email, in which case, you need to fix the address, or it goes into a rarely-checked spambin.

Austin Shackles wrote:
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I replied usenet thus:
"Use your existing stop start overload as the NVR and starter and wire the new box as a latching forward/reverse switch. Bob "

On or around Mon, 18 Aug 2008 21:46:10 +0100, Bob Minchin
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ah, right. Hmmm.
the swtiches in the new box are not latching though. They're just push-to-make. I get the impression it's intended to control something else.
Also, the current switch is not NVR (although that too was cheap), and I'd prefer it if it was.
I may have to hunt a proper one...

On Tue, 19 Aug 2008 08:22:34 +0100, Austin Shackles
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Get thee to your nearest electrical wholesaler, plumbing shop or larger DIY shed and get a DPST or DPDT relay with base, if needed. Use the start button to energise the coil. One pair of NO contacts to also energise the coil, giving the latching function and the stop switch in series with those contacts. The other contacts are now latching on, no-volt release. Total cost about £5-£8. Use a contactor with auxiliary contacts if the current demands it.
Mark Rand RTFM

Austin Shackles wrote:
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Hi Austin,
Sorry I had made too many assumptions 1 that your existing switch was NVR 2 that the new box had some contactors in behind the buttons
Mark is pointing you in the right direction for the NVR bit but you will need a second relay wired to latch the reversing AND most importantly, to lockout any change of direction when the motor is running. Single phase motors MUST be configured as forward or reverse before starting them. Once started, trying to change direction will have no effect. You might want to consider two start buttons, one for each direction and a common stop button. Just make sure you can't operate both start buttons at the same time.
HTH
Bob

On or around Tue, 19 Aug 2008 17:31:17 +0100, Bob Minchin
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It might be that I'm not being as precise as I could, either.
The new box has 3 buttons, 2 green and a red in the middle, and it's designed to be a controller for forward-stop-reverse. Each button has a non-latching switch beneath it. The 2 greens have NO (push-to-make) and the red in the middle has NC (push-to-break).
If I follow Mark's post right, I can use a DPST relay, with 1 pair of contacts supplying the motor and self-feeding the coil through the stop button, while the other terminals switch the motor neutral.
Energise the coil using start button 1, once energised it will stay energised until the stop is hit, breaking the coil circuit and motor circuit both. Lack of supply volts will also release the relay which won't re-energise by itself until power is supplied by the start button.
All that's good for one direction.
The same circuit wired differently would make the motor go the opposite way - so either 2 DPST relays or one DPDT provided it has 2 coils, and an "off" state with nothing connected by default.
The motor could be run from a single giant DPDT switch, provided it was on-off-on, but this would lack overload and NVR.
Hmmm. The existing switch can do the overload bit, and has no NVR. Might feed the relays alluded to above from that.
Does that sound right? nothing so far prevents pressing the "start reverse" button while the motor's running forward. Unless a DPDT relay can only have 1 coil energised at a time?

On or around Tue, 19 Aug 2008 19:09:43 +0100, Austin Shackles
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[snip stuff]
this is more or less what I have:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R308521
although naturally at a fraction of the price.
Is what I'm looking for called a "contactor"? I see plenty of such things, although I've yet to find a DPDT. However, I can, AFAICT, do the job with 2 single-way ones.

Austin Shackles wrote:
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http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R308521
Unless the motor is a big bugger then relays ought to do the job and these are readily available as change over types. You will need two poles to do the main switching and at least one extra pole on each to do the 'logic' of the latching and interlock.
Bob

wrote:
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In addition to that, if you wire an NC contact pair of the forward relay in series with the coil of the reverse relay and vice-versa, then you will avoid the possibility of both being on at once, with resultant loss of magic smoke.
With a bit of thought and a lot of sketching, it should be possible to do this with the double pole(or auxiliary pole on contactors) relays, without needing the rarity of triple pole devices.
Contactors are basically relays with more robust contacts, usually with a bar that joins two separate contacts. a bit better for breaking higher currents, but not necessarily needed for manually operated switching of a domestic lathe.
Mark Rand RTFM

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Actually, I should never have attempted to describe the wiring so late at night. Mia Culpa. There's an error.
You need to connect the NO1/NC2 junction to the junction of the Start relay contact and Motor Run winding. NOT directly to Main L. That way, the Start winding is not energised continuously, but only when the Start relay is operated.
In addition. You can use 2off DPDT relays for the reversing function with the coils connected in parallel. That gives you 4off Change-over contacts. Wire the remaing NO contacts across the Start Switch and you then have single button operation. Viz. Press Start (now renamed Forward) - Motor runs forward. Press Reverse - Motor Runs Reverse.
Mark. Wrote "In addition to that, if you wire an NC contact pair of the forward relay in series with the coil of the reverse relay and vice-versa, then you will avoid the possibility of both being on at once, with resultant loss of magic smoke."
Not only does that need additional contact sets, but it doesn't matter if you push the Reverse button as well as the Start. No smoke will appear. The circuit is safe. In addition, the reverse relay, as I describe it (modified connexions as above), would de-actuate the start relay if one of its NC contacts was in series with the start relay coil, so the motor wouldn't run.
I have the circuitry for using contactors, but you still need additional relays to do the interlocking - it's still necessary to swap the conexion of the two ends of the Start Winding wrt the Run Winding and you can't do that with two DPST contactors. BTW, the Interlocking relays also provides the safety operation from covers and guards micro-switches.
Regards Andy

On or around Wed, 20 Aug 2008 01:56:23 -0700 (PDT), houstonceng
[mucho snippage, will study it all later]
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It's too bloody invovled. Why doesn't someone just sell a box with forward-stop-reverse buttons and switchgear in it? It's a piece of piss to get stop-start boxes...
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. But finding them, in sufficient current range, is far from trivial.
I did find 30A relays somewhere for a good sounding price, so that will be the way to go. I'll have a think about the circuit.

On Aug 20, 5:11 pm, Austin Shackles
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I suppose that the reason for the scarcity of Fwd-Rev-Stop control gear for single-phase motors is that, in general, industry uses 3- phase motors and control-gear and manufacturers/suppliers must, ecconomically, serve the bigger market.
I'm a little worried by your statement, "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." If this is a single-phase (induction) motor - as you appear to say in your first posting - reversing requires the "Start Winding" to be reversed relative to the "Run Winding" - not the whole motor connexion reversed wrt Mains. This is a single-phase induction motor we're talking about and not some other type ?
If it's a brushed - so called universal - motor, it would still not reverse if the live and neutral were swapped.

On or around Wed, 20 Aug 2008 13:19:19 -0700 (PDT), houstonceng
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sorry, too little info again. The motor has a 4-terminal block and 2 links - live and neutral to opposite corners, and then it's "links vertical" makes it go one way and "links horizontal" the other. I presume that does indeed alter the direction of the start winding.
However, it's possible to arrange a DPDT switch to do the same job as the aforementioned links. At the moment, it's got 2 SPDT switches which have to be switched in unison, 'cos I failed to find a fat enough DPDT. The ones on it are only just high enough rating. Hence wanting a better solution. I reckon though that I can replace that pair of SPDT switches with 30A relays; the existing stop-start switch can stay to supply the reversing part and provide overload trip. The existing switch doesn't have NVR, but I can arrange that in the relays for forward reverse. In normal operation, the main switch will stay on and the stop start buttons and relays will do the starting and stopping, and NVR.
I just need to get me head around the circuit.
Just thought. the relays need to default to "disconnect", and only contact one way or the other when energised. I don't know if you can get such things.

On or around Thu, 21 Aug 2008 10:08:39 +0100, Austin Shackles
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'k, a quick search reveals no such thing. However, I reckon this:
http://www.roman-road.co.uk/temp/PICT0373.JPG
should do it using either 2 DPNO or 2 DPDT (as shown) relays. Wire the relays as discussed upthread for NVR effect.
Now, someone tell me why it won't work. The only thing it doesn't do is prevent you pressing the reverse button while it's running forwards, but that's not something I'd be inclined to do anyway, I don't think the machine is designed for instant-reverse.
Actually, (albeit crudely) it does do that: energising both relays simultaneously will connect a live direct to a neutral, and that will take out a breaker somewhere, provided the relays are fat enough that the breaker opens before the relays burn out...
The supply is via an overload switch (set to about 11A ISTR) and the whole workshop is on a 40A breaker on the distribution board... also there's a 13A fuse in the supply to the lathe, 'cos it's plugged into a socket.

On Aug 21, 12:01 pm, Austin Shackles
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If you have DPDT relays as shown, why not just use one for reversing. If you wire relay B contacts (reading from top) to the motor tags 3,2,2,3 in that order, the motor would run Fwd when the relay wasn't energised and reverse when it was (as per my description of the wiring in an earlier posting) You could then use the other relay for the NVR Start function. The problem you would have with only two DPDT relays is that you wouldn't get a latching (remaining on) when the Reverse button was released. You'd need an extra DPDT relay on the reverse to do that.
Using a single DPDT relay to swap the motor Start winding means you can't connect Mains L to Mains N in any way. Even if you press Start and Rev simultaneously.
If I had a simple way of posting a circuit diagram, all would be clear and a lot easier than it sounds.

On or around Thu, 21 Aug 2008 09:09:24 -0700 (PDT), houstonceng
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yeah, that would be a possibility, now you mention it. As I said, it only takes 1 DPDT to do the reversing bit.
If I could find a relay which was the equivalent of an on-off-on switch then it'd only need one. In fact, the DPDTs in my circuit could be DPNOs, since only 1 contact pair on each is being used, although that doesn't have any gain in safety.
Hmmm. could interlock it, it just needs an extra pole in the relays so that the forward relay, once energised, breaks the circuit for the reverse button and vice versa. In fact, might be able to run it through the live terminals in the DPDT. I shall study it some more.

On or around Thu, 21 Aug 2008 22:59:03 +0100, Austin Shackles
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A bit more thought and several more bits of paper and I reckon this circuit does it.
http://www.roman-road.co.uk/temp/DSC00200.JPG
shown in the off state. The forward start button is fed from the reverse relay and the reverse start is fed from the forward relay, so that either will work from rest.
Once it's running forwards, it self-excites through the stop button, so it latches, and the supply to the reverse start button is interrupted. Pressing the forward button again has no effect, just connects live to live. The only thing this one doesn't do is prevent pressing forward and reverse at *exactly* the same instant. However, you'd need to be clever as the relay operating speed is pretty fast.
Just one fly in the ointment now: the box as supplied only has one set of terminals in the stop button, and my circuit requires 2. However, there's scope to add another set if I can get hold of the right one. Considering the price, if the bloke has more of them, I could just buy another box and rob the switch from it.

On Aug 22, 9:24 am, Austin Shackles
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Yes. That circuit would work. I'm just a bit worried by the fact that applying mains to the motor terminals 1&4 when the circuit, as you posted it last, is in the "at rest" (ie Off state). By this means you could cook the motor as it will not rotate until either the FWD or REV button is pushed. Similarly, you'll have to be quick to hit the main switch as pushing the STOP button will have no effect if the motor is running.
Not, IMHO, a very safe way of controlling the motor.
BTW. What wattage/hp is this motor ?