:?: Hi All!
Hope you can help me. I am building a project in which I require a low speed dc motor (12v) to have its polarity reversed everytime the power is turned off, then on again...
on(clockwise) - off-on(counterclockwise)-off-on(clockwise) etc. the transmission of power will be handled by a digital timer (intermatic dt17)

thanks in advance!

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kugiman

 

Here is an idea: you need two 12V relays. The first one has double pole double throw contacts (DPDT). So, you have two commons, two normally open (N/O) and two normallt closed (N/C) contacts. Your 12V supply power (from your timer) goes to the common contacts. Then you bridge one of the N/O contacts to the other N/C contact, do that to both sets of the N/O and N/C contacts. Each wire to the the motor connects to one set of contacts. The relay contacts reverse the polarity, eg. relay on, motor runs in one direction, relay off, motor runs in reverse.

Now you need to control the relay so that it is alternately on or off. You do that with a second relay which must be a 'latching relay'. If you don't know these, its a relay that (magnetically) remembers the last state it was in. Each alternate power pulse to its coil changes the contacts. It only needs one set of contacts that can handle the current of the motor reversing relay coil. Wire the latching relay coil to the motor power from your timer. It will then alternately turn the reversing relay on or off as the power comes on.
Hope that makes sense, draw it out before you ask more question, it may then become clearer.
Klaus

 

You can also use H-bridge. Serach this forum for "H-bridge" you'll find links and schematics of the same.

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