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Old 08-20-2010, 10:31 AM
janej janej is offline
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Default Using a DPDT to automatically reverse the polarity of motor

I am currently working on a project that requires a motor to run this way and then hit a switch that would enable it to reverse its polarity. However, I have to wait for a signal from an LDR and this signal is what would drive the motor the other way.

Is there an automatic DPDT switch that I could use?

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Old 08-20-2010, 11:32 AM
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marshallf3 marshallf3 is offline
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"All in one" I seriously doubt, easy to build with minimal components - yes.

Voltage & current requirements of the motor?
The very first course in engineering school should be how to use Google and Wikipedia
I very often misspell or miss things while making posts so come back and double check a few times.
I also have a full time job and often 10 projects going on at the same time so I'm not always online.
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Old 08-20-2010, 01:34 PM
mcgyvr mcgyvr is offline
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Start reading here... or Google "H-bridge switch" or "h-bridge relay"
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Old 08-20-2010, 01:54 PM
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SgtWookie SgtWookie is offline
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This is a circuit I whipped up awhile back for a fellow who used it in a model of a German WWII Tiger Tank:

It could probably be modified to suit your needs, but you'll need to give more specifics about your LDR and it's resistance when illuminated and dark.

The diagram shows two relays. The actual relay used was a dual form C H-bridge relay, NEC EP2 series. These are available from
You don't have to use an H-bridge relay though; a pair of SPDT relays could be used.
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File Type: png MotorReverseLimitSwitchLatching2.PNG (20.3 KB, 126 views)
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If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input.

Last edited by SgtWookie; 08-20-2010 at 02:17 PM.
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Old 08-21-2010, 11:06 PM
soda soda is offline
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I add a pic of how you can use a DPDT switch to reverse the motor direction. I use it all the time with no problems
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File Type: jpg reverse voltage.JPG (8.4 KB, 54 views)
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Old 08-22-2010, 10:26 AM
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williamj williamj is offline
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We need to know more about the motor, is it AC or DC, if AC... is it single phase or three phase. For a good circuit, accurate motor information is paramount.

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