Re: Can someone help me put this together?


"John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> schreef in bericht
news:m2psl199jiptjc7cok53b5kbcidv0h6m6g@xxxxxxxxxx
> On Mon, 24 Oct 2005 13:46:22 GMT, Fred Bloggs <nospam@xxxxxxxxxx>
> wrote:
>
>>
>>
>>John Fields wrote:
>>> On 23 Oct 2005 08:49:55 -0700, paul.demay@xxxxxxxxxxxxxxxxxx wrote:
>>>
>>>
>>>>This is in theory right now, but here is what I am thinking:
>>>>
>>>>I have a circuit that gets power by a triggerable event - the power
>>>>lasts for 60 seconds then cuts off.
>>>>
>>>>When power is supplied, it activates a motor.
>>>>
>>>>When the motor completes 1 revolution, it hits a switch (SW1).
>>>>
>>>>SW1, when closed (hit my the motor) flips a relay (R1) which takes away
>>>>the power to the motor and remains in that position until the power is
>>>>cut to the circuit.
>>>>
>>>>When the power to the circuit is cut, R1 flips back.
>>>>
>>>>This way, I can shut the motor off after completing one revolution
>>>>regardless of how long the power to the circuit is applied. Once the
>>>>power to the circuit is cut, R1 flips back.
>>>>
>>>>This seems to me like it should work, but I cannot for the life of me
>>>>figure a schematic to wire it up.
>>>>
>>>>Any ideas?
>>>
>>>
>>>
>>>
>>> SWITCHED POWER IN>---+------O
>>> | |K1
>>> [COIL]- -|<---O
>>> | |
>>> O | |
>>> S1 |<- - -[MOTOR]
>>> O | |
>>> | |
>>> RETURN>--------------+-----------+
>>>
>>> Switched power comes in, goes through the normally closed contacts
>>> of the relay and into the motor, which starts turning. After one
>>> revolution, the motor closes S1, which allows current to flow
>>> through the relay's coil, opening the contacts, stopping the motor.
>>> As long as the motor doesn't override the switch, current will
>>> continue to flow through the relay's coil, keeping the motor off.
>>>
>>> If the switched power is cut, there will be no more current into the
>>> relay coil, so the contacts will close allowing current to flow into
>>> the motor the next time the power is switched on. Unfortunately, S1
>>> will still be made because the motor stopped when its contacts
>>> closed, so when power comes back on, current will flow through the
>>> relay coil, opening the relay's contacts and keeping the motor from
>>> turning.
>>>
>>> So it seems like what you need is a way to make the relay work
>>> quickly when the switch closes, but which will will keep it from
>>> turning on for a while when power is switched on, in order to let it
>>> ride over the switch at the start of the cycle.
>>>
>>> Since this seems to be essentially the same application you asked
>>> for on seb under "Probably a simple question, but...", I've posted a
>>> solution for you on abse under "Probably a simple question, but...
>>> (from seb)".
>>>
>>> In the future, if you'd crosspost it would make it a lot easier for
>>> everyone concerned to keep track of what's going on. :-)
>>>
>>
>>Well- he said the motor "hits" the switch, and there are all sorts of
>>mechanisms that will do that, so it's safe to assume the switch is
>>pulsed ON momentarily regardless of further motor travel. Then the only
>>requirement is that the switch close time exceeds R1 worst case
>>activation time, and R1 is self-latching with power applied.
>
> ---
> The way I see it is that if the motor comes to rest with S1 in the
> closed position there's no way for the motor ever to be started
> again unless the motor can outrun the relay.
>
> --
> John Fields
> Professional Circuit Designer

John,

As too often it all depends. This time the properties of SW1 stipulate the
possibilities you have for a solution. In the simple ones, timing will be
critical. For instance, when you assume SW1 to be a momentary switch, you
must be sure the motor cannot stop while SW1 is closed. So the relay you use
should be fast enough to be activated by SWI but SW1 (or the motor) should
be fast enough to have SW1 released before the motor actually stops. Another
SW1 requires another approach and you may need an extra relay or other
electronics to make it work the way you want. Worsed case you cannot be sure
whether or not SW1 is closed which requires some memory in a reliable
circuit. I'm sure you are able to make a working circuit but I don't like to
draw more schematics without more information from the side of the OP.

petrus bitbyter


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