reverse direction of dc motor with a switch or timer

[tpk]

Hi there,
i have a 12v dc motor that i am using to spin a string from a fixed point (for a larger application). essentially, i need a switch or controller that allows me to change the direction of the motor after a certain amount of time, right before the tension of the string becomes too much and the motor fails. i don't know much about electronics and i'm wondering what is the simplest way to achieve this, and what products are there that can aid in doing this?
thanks for any help!

[pebe]

What length of time are you considering, and is the motor reversed continuously back and forth, or is a one-time reversal?

[tpk]

hi, sorry for posting so many times! I'm new to this.

it would need to be a continual reversal. I am working to figure out the period, I believe it will be about 30 minutes each direction.

[pebe]

OK. Give me a few days and I'll sort something out for you.

[pebe]

The simplest possible way would be to use one of those mechanical mains timers where 15minute segments can be turned on or off. You could set these to give successive periods of 30min on and 30min off. The output from the timer would energise a double pole changeover relay, that I could give you connections for.

Alternatively, you could use a counter IC to feed the relay. I have a suitable circuit, if you want it.

[PradeepKumar]

Pebe I agree with your suggestions. It seems to support the entire project for a DC motor with a timer or a switch control.

[awright]

You have not described clearly what the mechanical aspects of your winding up string device is, but presumably if the string can wind up to the extent of stalling the motor it is also either pulling tension on the string or torquing the far end of the string. If feasible in your application, can you rig up a set of contacts to sense the tension or torque and activate a relay or circuit to reverse the motor? Sensing torque would be best, since that could activate contacts specific to the direction of motor rotation.

Ideally you would use microswitches activated by the torque or tension to achieve positive transitions rather than simple contacts pushed together that can have noisy, tentative contact.

The simplest approach would be to have the switches activate a "latching relay" with DPDT contacts to reverse polarity of the power applied to the motor. You can purchase latching relays that rely on permanent magnets or mechanical latches in the relay or you can create your own by using a plain relay with a third contact to hold the relay closed. Circuit details are simple but would vary depending upon the type of relay and configuration of actuation contacts you employ.

[KMoffett]

awright,

That thread was last replied to almost two years ago. You are creating a zombie.

Ken