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# Confused with dc car door lock motor

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#### NHN

##### New Member
I am seriously confused, I have a dc motor in a door lock that spins one way to lock & other way to unlock, it does this via reversing polarity which I guess is obvious, lol, but when I test the wires it has live on both when in use, can someone explain to me how this is possible please as I'm lost.

There are 2 motors, 1 is main lock 2nd is deadlock & they share a common wire, so 3 wires in total, I understand it switches in the control module from live to ground on the wires but how one motor runs on 2 lives has got me for sure.

If its obvious then excuse my thickness

How and where are you reading the voltage? How many volts are you reading at those points? Are you reading from frame ground to the motor terminals, and/or across the motor (i.e. swapping leads to check polarity)?

I'm not certain of how these motors are wired. It sounds like they are in parallel from a common wire. Are you reading the positive voltage on the common wire or on the other side of the motor? Or am I totally misunderstanding and they are in series? You say they have three wires, and one is common.

Is this what you mean ? :
wire---motor---"common wire"---motor---wire...if that is the case, they are in series and I would expect to see 6 volts dropped across each in a 12 volt system.

As I told you in another thread, it helps a great deal to have a schematic. Some people on the forum are automotive "gurus" and may be able to approach your question purely from specific experience (familairity with your exact circuit), but others like myself work from a more "fundamentals" approach and need either accurate descriptions with correct terminology and/or a schematic, photographs, or a sketch.

My gut feeling is that these two motors are 6 volt motors run in series and you are measuring 6 volts and 12 volts across one of the motors from frame ground but honestly I have no idea without a drawing.

Also, if you are really set on learning electronics, you really need to learn to use terminology that is accurate and descriptive.

For instance, you keep referring to the "live wire". While this is not an absolutely incorrect term, it is not very descriptive and can be inaccurate in some contexts. For instance, a ground wire is live when current is passing through it. A live wire is a wire with current passing through, and when a circuit is complete, ALL the wires are live. Don't believe me? Disconnect the ground wire of an automotive circuit and then switch it on...then read voltage from the ground wire to the frame. You will likely read 12 volts.

In order to find some information and "bone up" on your doorlock circuit, I did some Googling and looked at a lot of schematics on alarm installation websites.

I could not find schematics that included two motors or actuators for a single door lock mechanism. All I found as far as multi-motor configurations was driver and passenger side locks. All the motors appeared to be 12 volt DC and switched in parallel, with polarity reversal being the standard means of switching between locked and unlocked.

I could not find an example of a circuit which would have reason to have two positive polarities applied to the motor as might be the case with two 6 volt motors in series. I'm not ruling this out because you clearly indicate two motors are involved with one door lock. In that case, the voltage drops would look like this 0V---motor---+6v---motor---+12V. in this configuration one motor would read 6 volts on one connection and 12 volts on the other from ground. (two "live wires" as you put it)

The other scenario that I can conceive that might cause you confusion would be in the case of 12 volt motors with reverse polarity switching where a "brake" condition might occur during actuation. It is a method used in motor circuits to apply either two equal positive voltages to a motor or two equal ground voltages to a motor (either/or) in order to freeze it or brake it. Doing this quickly deteriorates the energy of the motor to stop it suddenly and hold it in place instead of allowing free spin (coasting)

So it wouldn't surprise me that when you actuate the door lock mechanism that the polarity changes across the motor from 0--12 when moving and then freezes at 12--12 volts when it is locked.

I hope you understand.

Ok been reading up, some misconceptions by myself, but slowly getting there which is actually fun aswell & as sad as sounds exciting lol.

Now I think I need to use a polarity conscious switching component inline with the motor feed wires so effectively in parallel with motors, as it obviously reverses polarity on the motor wires to make the motor change direction which is how the locks work (pic to follow possibly), so I could use the polarity sensing to trigger my 555 timer relay circuit, so surely a relay would suffice thats polarity conscious, not bipolar I think is the term.

The motors arent in series mate, the common wire isnt between them, it comes from further up line namely control module, then branches of to 1 leg of each motor.

Am I finally making sense fella?

Thanks for the info btw, it all helps trust me even if it one way flowing atm, no pun intended.

Also now I understand the braking you explain which actually does make sense & could apply to these, urrrm more knowledge gained.

Last edited:
I'm glad you learned a few things.

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