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Re: Solenoids remaining on.


Hi Jasen, Jonno and those interested,

Sorry not to reply sooner. I was hoping to think of a way to do it
like you suggest but have been struggling to do so. What do you
suggest to stop the motor at approximately the right time?

One way I thought of would be to have two electro magnets with one on
each side of the motor. A magnetic switch could be placed on the
rotating shaft. When the sensor came on it would switch on one of the
electro magnets and switch the other one off. When the sensor went off
the electro magnet that is on would go off and the one that is off
would come on. The electro magnet would be placed near the motor shaft
so that the magnetic reed switch on the rotating shaft moves close to
it. Each electro magnet would be made so that it keeps the reed switch
on for a 180 degree turn of the motor. If this method is used we would
have to be careful to avoid cable twisting.

If you have any other ideas or a simpler way, please let me know. Are
you sure that using crank would be simpler than the other way of
reversing a motor, bearing in mind setting up a crank would not be
needed for the other way?

Also, I am currently winding up a single strand of thin enamel copper
wire and would like to test it as a solenoid as well. The wire is
about 0.2 mm thick. I am winding it around a bit of pipe about 12mm
outside diameter. At what point do you think it would produce the
strongest magnetic force for a solenoid that is running of 12 volts
and 24 volts? How many meters would I wind on before I test it? I do
not want it to get too hot.

Your help is appreciated
Regards Richard



Re: Solenoids remaining on.


Quoted text here. Click to load it

I'd use microswitches  if you locate them out of the weather they last
for millions of cycles, in an application like this: basically forever.

arrange them so that each switch interrupts the current to the motor
(ie opens) just as it comes th the point where you want it to stop,
wether it stays open for 15 or 150 degrees after it opens isn't really
wery critical.

then you supply power via one of the switches to open the louvers and
the motor moves until that switch opens (and then everything stops)
anw when you want then close supply current via the other switch
and the motor runs until that one opens (by which time the first
switch has closed again)


   open        T
   ----------o | o-----+
             ~~~~~     |
   shut        T       |
   ----------o | o-----+----[(M)]----- 0V
             ~~~~~                    
                                  
the open/shut inputs could be provided by a SPDT relay or the
polarity could be reversed and a pair of common-emitter wired power
transistors could be used...

for testing I'd use a spdt switch.

Quoted text here. Click to load it

I'm guessing:  wind until the winding is as thick as the pipe is
(this comes fro observing the dimensions of commercial solenoids)

that wire may be too thin for 12V operation..


--

Bye.
   Jasen

Re: Solenoids remaining on.


Hi Jasen, and those interested,

Thanks for the info.

So do you think that this method would be much easier and less time
consuming than the other way of reversing a motor?

Sorry I am not to savvy on electronics. What do the symbols that look
like the letters M and T and l mean on the diagram?

How many micro switches would be needed?

I assume that you mean a common micro switch would be all right.

I thought that one switch would have to remain on while the motor
rotates through 180 degrees because I thought the motor would have to
turn 180 degrees before it stops. I am not sure about some of the
other things that you said. However, hopefully I will find someone who
can do it.

Do you know of anything made up that can do similar things to what you
explain?

What thickness of wire would be best to make a solenoid that is very
strong and does not overheat?


Your help is appreciated
Regards Richard


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