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Lead screw limiters for motor - RF Cafe Forums

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 Post subject: Lead screw limiters for motor
Posted: Mon Feb 25, 2008 4:57 pm 
 
Captain
User avatar

Joined: Mon Feb 25, 2008 4:53 pm
Posts: 10
Hey guys

I'm using a car window motor to drive a lead screw with the standard automotive 12V system. Is there a simple way to put something inline so when the leadscrew reaches the end of the travel and hits a stop, it stops the current to the motor. the stock unit must have something built in but I need different limits. Im trying to avoid mechanical limit switches.

Troy :smt017


 
   
 
 Post subject:
Posted: Tue Feb 26, 2008 5:19 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 304
Location: London UK
Hi Troy
If you are against mechanical limit switches because of dust, then you might consider a ceramic magnet on the traverse driven by the lead screw , which operates a reed relay at the limiting points.


 
   
 
 Post subject:
Posted: Tue Feb 26, 2008 11:27 pm 
 
Captain
User avatar

Joined: Mon Feb 25, 2008 4:53 pm
Posts: 10
Thanks Mr. Nubbage

I am using this to open and close a vent in a shop so you're right that I am worried about dust and other crap in the air (including bugs). I need to open the unit and see where the existing limit switches connect into the circuit. So do you have a manufacturer to suggest for your kind of limit switch, or should I just do an Internet search for something? I'm guessing the current level that the switch needs to carry is pretty low so just about anything will work?

Thanks.


 
   
 
 Post subject:
Posted: Wed Feb 27, 2008 7:44 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 304
Location: London UK
Hi Troy
The beauty of the approach is that the components are readily available and very tolerant of environment.
Just google for "ceramic magnets" and "reed relays", and that should throw up a number of local sources in your area. When you have a handfull (and they are inexpensive) just fiddle around with different arrangements on a test fixture until you get reliable switching every time.
Reed relay contact ratings go up to several amps, and the sensing distance for the ceramic magnet is several millimetres, so tolerances are relaxed whilst still ensuring reliable operation. Ceramic magnets, as you might guess, are high-energy types and can operate up to quite high ambient temperatures without demagnetizing.
Give us some feedback how the project is going later.




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