two circuits one battery/motor

Thread Starter

tkuhrich

Joined Feb 7, 2011
4
I have a project where I need to build a very simple two circuit system using one battery and one motor. The battery is a 'AA' and the motor is 1.5v low speed.

When the current is flowing in a positive direction, the motor needs to run until a limit switch is hit to stop the motor. When the current is flowing in a negative direction, the motor needs to run until a different limit switch is hit to stop the motor.

I can make one circuit work at a time, but as soon as I try to hook up the second circiut, I can never get the motor to stop regardless of the current flow.

Reversing the current flow is a manual process by design, it is accomplished by turning the 'AA' battery around in the mount.

Thanks in advance,
Kent
 

SgtWookie

Joined Jul 17, 2007
22,201
Not to step on Wookies toes here or anything, but it should also work like this

They sell DPDT switches with the X pre-made on the bottom.
I'm afraid that you didn't read our original posters' requirements.

They have TWO limit switches; one switch needs to shut off the motor when it's running in one direction, and the other switch turns off the motor when it's running in the opposite direction.

You can't wire the limit switches in series, as when one is open, reversing the polarity on the switch will not close the opened switch.

Our O.P. can't use one of those DPDT switches with the built-in crossover with the two separate limit switches.
 

Thread Starter

tkuhrich

Joined Feb 7, 2011
4
Hey guys, thanks for the two solutions however, the project will require the manual reversing of the polarity, not a switch. I have to use diodes to keep the current flowing in the right direction.

Thanks,
Kent
 

magnet18

Joined Dec 22, 2010
1,223
I'm afraid that you didn't read our original posters' requirements.

They have TWO limit switches; one switch needs to shut off the motor when it's running in one direction, and the other switch turns off the motor when it's running in the opposite direction.

You can't wire the limit switches in series, as when one is open, reversing the polarity on the switch will not close the opened switch.

Our O.P. can't use one of those DPDT switches with the built-in crossover with the two separate limit switches.
Whoops, I apologize :(

I agree they cant use one with a crossover, but this one should work... (I hope)



Granted, its not much simpler than your original.
 

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magnet18

Joined Dec 22, 2010
1,223
Hey guys, thanks for the two solutions however, the project will require the manual reversing of the polarity, not a switch. I have to use diodes to keep the current flowing in the right direction.

Thanks,
Kent
In that case, doing this-

Should allow you to do the exact same thing as reversing the battery manually.
(and you can use one with a built in crossover for this :))
 

Attachments

SgtWookie

Joined Jul 17, 2007
22,201
If you attempt to use diodes with such a low voltage, you will lose a good bit of power in the diodes alone. A standard silicon diode like a 1N4002 will drop around 0.7v across itself with only a 20mA current flow; that's nearly half of your available voltage supply. If more current is required to run the motor, the voltage drop across the diode will be worse.

You could possibly use Schottky diodes, but even a 1N5817 would drop around 0.34v across itself.
 

Thread Starter

tkuhrich

Joined Feb 7, 2011
4
I just wanted to say thanks to you guys for helping me. I have put the circuit together and it works great! The only thing left is put all the other pieces with it and see how well the whole project is received.

Thanks - Kent
 

SgtWookie

Joined Jul 17, 2007
22,201
Which circuit did you wind up using?
Simply indicating the post number will be adequate. For example, this is post #11, as indicated in the upper right corner.
 

Thread Starter

tkuhrich

Joined Feb 7, 2011
4
I ended up using post illustration #9. It was what was asked for in the project list and I could build it quickly with what I had on hand. I may remove the diodes and end up with a switch, but I'll have to wait and see.

Again, thank you for your input and advice!
Kent
 
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