On or around Wed, 20 Aug 2008 01:56:23 -0700 (PDT), houstonceng
 enlightened us thusly:

[mucho snippage, will study it all later]

>
>Regards
>Andy


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.

-- 
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 Wed, 20 Aug 2008 13:19:19 -0700 (PDT), houstonceng
 enlightened us thusly:

>On Aug 20, 5:11 pm, Austin Shackles
> wrote:
>> On or around Wed, 20 Aug 2008 01:56:23 -0700 (PDT), houstonceng
>>  enlightened us thusly:
>>
>> [mucho snippage, will study it all later]
>>
>>
>>
>> >Regards
>> >Andy
>>
>> 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.
>>
>> --
>> 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!
>
>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.

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.
-- 
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 Thu, 21 Aug 2008 10:08:39 +0100, 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!

On or around Thu, 21 Aug 2008 09:09:24 -0700 (PDT), houstonceng
 enlightened us thusly:

>On Aug 21, 12:01 pm, Austin Shackles
> wrote:
>> On or around Thu, 21 Aug 2008 10:08:39 +0100, 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.

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.

-- 
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 Thu, 21 Aug 2008 22:59:03 +0100, Austin Shackles
 enlightened us thusly:

>
>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.

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.
-- 
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:

>On Aug 20, 5:11 pm, Austin Shackles
> wrote:
>> On or around Wed, 20 Aug 2008 01:56:23 -0700 (PDT), houstonceng
>>  enlightened us thusly:
>>
>> [mucho snippage, will study it all later]
>>
>>
>>
>> >Regards
>> >Andy
>>
>> 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.
>>
>> --
>> 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!
>
>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 ?
>

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. 

>If it's a brushed - so called universal - motor, it would still not
>reverse if the live and neutral were swapped.

Regards,

David P.

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

>On Aug 22, 9:24 am, Austin Shackles
> wrote:
>
>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.

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.  

>Not, IMHO, a very safe way of controlling the motor.

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

>BTW.  What wattage/hp is this motor ?

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

On Fri, 22 Aug 2008 22:35:44 +0100, Austin Shackles
 wrote:

>On or around Fri, 22 Aug 2008 05:44:44 -0700 (PDT), houstonceng
> enlightened us thusly:
>
>>On Aug 22, 9:24 am, Austin Shackles
>> wrote:
>>
>>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.
>
>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.  
>
>>Not, IMHO, a very safe way of controlling the motor.
>
>yeah, needs more work... It'd be a damned sight easier if I could just buy
>the necessary box.  
>
>>BTW.  What wattage/hp is this motor ?
>
>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...
>------------------------------------------------\   
>   >>  http://www.schlockmercenary.com/  <<      \  ...and Kill them.
>a webcartoon by Howard Tayler; I like it, maybe you will too!
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

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.

On Aug 22, 11:35 am, e...@whidbey.com wrote:
> > 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- Hide quoted text -
>
> - Show quoted text -

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

On or around Sun, 24 Aug 2008 02:47:21 -0700 (PDT), BobKellock
 enlightened us thusly:

>On 22 Aug, 09:24, Austin Shackles
> wrote:
>> On or around Thu, 21 Aug 2008 22:59:03 +0100, Austin Shackles
>>  enlightened us thusly:
>> ...............
>>
>> 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
>> .............
>
>That circuit will probably work but, in the interval between pressing
>the FWD or REV button and the relevant relay making contact (about
>10ms), current flows through both the other relay coils connected in
>series. Typically, the specified minimum coil operating voltage of a
>relay is 75% of its nominal voltage but some will work at a much lower
>voltage so you could have a race condition.
>
>During that same interval the button is carrying all the current to
>the start winding of the motor. Typically start/stop buttons are rated
>at 3A. If you happen to press the button near the peak of the AC cycle
>the current through the button will probably be considerably more than
>its rating which could result in shortened contact life or, even,
>contact welding.

There's a new one now, 201.JPG instead of 200.JPG - that circuit, as was
pointed out, won't stop again and has the motor permanent live, which I
didn't really intend.

The buttons don't supply motor current though, start or run.  they only feed
the relay coils.  Well, I suppose they supply current while the relay is
switching.  That's about 15ms if I recall the spec sheet right.  If it
causes issues, then it could have a current-limiting resistor in series with
the buttons, or something.
-- 
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!

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.

Bob