motor polarity

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=115700
Printed Date: July 18, 2025 at 2:43 AM

Topic: motor polarity

Posted By: bper
Subject: motor polarity
Date Posted: August 17, 2009 at 2:48 PM

I have a small motor from a car window which uses reverse polarity to switch directions which I'm using for a project. If for some unexpected reason 12v+ pwr hits both sides of the leads as opposed to having one gnd and one 12v+, would this damage the motor? Would putting a fuse between the pwr source and motor wire leads alleviate this? Current draw from the motor is about 400ma.

Replies:

Posted By: KPierson
Date Posted: August 17, 2009 at 3:42 PM

No, it would not hurt the motor. The motor needs voltage potential to operate - if you put 12vdc on both sides of the motor there will be no potential, and therefore no current will flow.

You could possibly run in to an issue if you had 12vdc on one lead and say 5vdc on the other, as this would effectively put 7vdc to the motor which could damage it.

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Kevin Pierson

Posted By: bper
Date Posted: August 18, 2009 at 3:15 AM

Thanks! So I have a 20A (NO) relay going to each motor (2 motors, 2 relays total). Since the motors use about 400mA each, would I need to put at least a 800mA fuse (1A) before the relays after the 12v+ pwr source, or does it have to be 20A for the relays?

Are fuses even required to be placed after the 12v+ power source before the ckt? Or should they be within the ckt (like between the relay and motors) or would I be all right w/o any fuses?

Posted By: KPierson
Date Posted: August 18, 2009 at 5:04 AM

Fusing depends on your application (and power source). Ideally, you would place a ~5A fuse between the power source and the relay.

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Kevin Pierson

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