On Aug 21, 12:01 pm, Austin Shackles
 wrote:
> On or around Thu, 21 Aug 2008 10:08:39 퍝, Austin Shackles
>  enlightened us thusly:
>
>
>
> >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.
>
> '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.
>
> --
> Austin Shackles.  www.ddol-las.net my opinions are just that
> Travel The Galaxy!  Meet Fascinating Life Forms...
> ------------------------------------------------\  
>    >>  http://www.schlockmercenary.com/ <<      \  ...and Kill them.
> a webcartoon by Howard Tayler; I like it, maybe you will too!

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 Fri, 22 Aug 2008 17:05:03 -0700 (PDT), houstonceng
 enlightened us thusly:

>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.
>

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...
------------------------------------------------\   
   >>  http://www.schlockmercenary.com/  <<      \  ...and Kill them.
a webcartoon by Howard Tayler; I like it, maybe you will too!

On or around Sun, 24 Aug 2008 06:35:02 -0700 (PDT), BobKellock
 enlightened us thusly:

>My previous posting was incorrect when I referred to DSC00200.JPG. It
>was, in fact, regarding DSC00201.
>
>I've also spotted another "feature". If the fwd or rev button is held
>down at the same time as stop then the motor will run in the relevant
>direction. To an optimist this is the jog function but, to a
>pessimist, it's a no-no as stop should always override go.
>
>You shouldn't discount possible damage to the switches because of the
>short duration; it's the act of making or breaking contact that does
>the damage.  The holding current of most switches is normally many
>times greater than their switching capacity.

There's another circuit I may use instead, supplied by yon Houstonceng
chappie.  I shall study it.

I don't know the details of the button contacts, but they look quite solid. 

As for saftey features, it's got to be better than the current setup which
has no NVR and dodgy reverse switching.
-- 
Austin Shackles.  www.ddol-las.net  my opinions are just that
Travel The Galaxy!  Meet Fascinating Life Forms...
------------------------------------------------\   
   >>  http://www.schlockmercenary.com/  <<      \  ...and Kill them.
a webcartoon by Howard Tayler; I like it, maybe you will too!

In article
,  
 houstonceng   in uk.rec.models.engineering
wrote:

>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.  

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.   

 
>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.

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

>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.
>

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

>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.
>

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.)
 
>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.
>

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.