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I request some knowledge regarding a circuit I am building.

Basic I have a circuit connected to a dc 12v motor and a dpdt switch to reverse the polarity of the motor and a variable potentiometer , I will need the motor to be stopped temporary via a microswitch, only in the reverse direction however the microswitch must have no affect in the forward. Is this possible using only 1 battery pack? And how would I have to wire the switch into the circuit for this to work? Thankyou in advance C.

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  • \$\begingroup\$ What type of microswitch are you using? Normally open (NO) or normally closed (NC)? With an NC this is trivial. \$\endgroup\$ – Polynomial Mar 11 '17 at 11:37
  • \$\begingroup\$ Thankyou for your reply, I'm using normally open, meaning the motor will run but when the switch is pressed will shut off motor. Regards \$\endgroup\$ – Mcccccc Mar 11 '17 at 11:55
  • \$\begingroup\$ You must assume we know what you know about this circuit. Like what kind of motor, make, model? Why you think a microswitch may affect forward. Why there is a potentiometer and how it is connected. Schematic? \$\endgroup\$ – Misunderstood Mar 11 '17 at 13:31
  • \$\begingroup\$ HI Thankyou for the reply, so the dpdt switch will allow the polarity of the motor to be reversed, currently the microswitch is just integrated within the wire from the dpdt motor terminal to the motor, meaning the motor can go forward and backward both being stored when the Normally open microswitch is off, the potentiometer allows me to limit the speed and also is in series, (from dpdt to motor) \$\endgroup\$ – Mcccccc Mar 11 '17 at 13:33
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    \$\begingroup\$ But perhaps a drawing of your schematic and mechanical idea would give us more of a clue... \$\endgroup\$ – Trevor_G Mar 11 '17 at 14:52
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What you want to do is quite easy.

However, the question of NC/NO needs to be addressed first. I assume that your microswitch is used as a mechanical limit switch. In this case, the "regular" or "normal" operation is with the switch closed, and it opens when the limit is reached. With this in mind this

schematic

simulate this circuit – Schematic created using CircuitLab

shows the way to wire the system without a limit switch. Note that the indicated position of the switch corresponds to forward travel. Activating the lower position produces reverse by reversing the polarity of the motor drive. This

schematic

simulate this circuit

uses the limit switch to interrupt current to the motor, but only in the reverse position. SW2, the limit switch, is shown in the NC position. When it opens, reverse drive will be interrupted.

There is one more condition, though. This assumes that the motor is a brushed DC motor. The circuit will not work on stepper motors or BLDCs (brushless DC motor) or AC motors.

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  • \$\begingroup\$ For the second circuit that you drew if switch 2 was to be 'normally open' as a closed circuit ( when pressed the vehicle will stop) would I have to wire them to the negative side of the battery? If that makes sence? \$\endgroup\$ – Mcccccc Mar 14 '17 at 21:06
  • \$\begingroup\$ @Mcccccc - The description makes sense, but the idea doesn't. You must use a normally closed limit switch. If you like, you can connect it to the negative battery lead, but then it must be connected to the 2nd from top lead on the DPDT switch. \$\endgroup\$ – WhatRoughBeast Mar 15 '17 at 0:19

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