On Aug 22, 9:24 am, Austin Shackles
 wrote:
> On or around Thu, 21 Aug 2008 22:59:03 퍝, 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!

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 ?

On Sun, 31 Aug 2008 14:57:50 -0700 (PDT), BobKellock
 wrote:

>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

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=08365&f=motor_reverse933.jpg

http://xs.to/xs.php?h=xs231&d=08365&f=three_phase_contactor931.jpg


                                         
                               jim

On or around Fri, 05 Sep 2008 19:39:12 +0100, pentagrid@yahoo.com
enlightened us thusly:

>
>       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.

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

On Sat, 06 Sep 2008 10:22:56 +0100, Austin Shackles
 wrote:

>On or around Fri, 05 Sep 2008 19:39:12 +0100, pentagrid@yahoo.com
>enlightened us thusly:
>
>>
>>       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.
>
>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.

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!

On 6 Sep, 10:22, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol-
las.net> wrote:
>
> 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.  

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.

On Sat, 06 Sep 2008 10:22:56 +0100, Austin Shackles
 wrote:

>On or around Fri, 05 Sep 2008 19:39:12 +0100, pentagrid@yahoo.com
>enlightened us thusly:
>
>>
>>       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.
>
>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.



  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