I need help with reversing a 12v dc motor with limit switches, non-stop.

Thread Starter

trouter2251

Joined Sep 19, 2020
6
In the photo, I have a dc motor with (2) limit switches. Basically the motor turns and activates a limit switch reversing the polarity. Direction of motor automatically changes direction until it activates the other limit switch. I have (2) dpdt(non-latching) relays and (2) limits switches. I had it wired to the attached diagram but smoked a few wires. Any help with wiring or right direction would be appreciated.
 

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Yaakov

Joined Jan 27, 2019
3,187
I am having a very hard time reading the provided schematic. Could you explain what you are actually try to do, that is, what is the motor doing and why? That might help.

A more traditional schematic that shows the really coils clearly might help as well.
 

Alec_t

Joined Sep 17, 2013
12,091
If the motor is a reasonably powerful one, the current and voltage transients which would occur by reversing it suddenly without allowing it to come to a halt first would be huge and likely to damage the switching device (relay or whatever).
 

Thread Starter

trouter2251

Joined Sep 19, 2020
6
In the photo, I have a dc motor with (2) limit switches. Basically the motor turns and activates a limit switch reversing the polarity. Direction of motor automatically changes direction until it activates the other limit switch. I have (2) dpdt(non-latching) relays and (2) limits switches. I had it wired to the attached diagram but smoked a few wires. Any help with wiring or right direction would be appreciated.
Duty cycle: I would like it to be 100%
Motor Specifications:
Rated Voltage: DC 12V
Reduction Ratio: 1:94.85
No-Load Speed: 50RPM
Rated Torque: 7.2Kg.cm
Rated Current: 0.92Amp
 

vu2nan

Joined Sep 11, 2014
169
It's difficult to decipher your schematic.

The following may be what you intended and it should work.

1.JPG

Smoking wires may be the result of a short circuit / inadequate wire size. Please check your wiring.

Here's another circuit using a single magnetic latch relay.

1.JPG

Nandu.
 
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Thread Starter

trouter2251

Joined Sep 19, 2020
6
What’s your duty cycle? This looks like solid state stuff.

When I turn power on to the dc motor it will rotate the blue lever in one direction until it triggers a limit switch reversing the polarity until the blue lever triggers a second limit switch which changes the polarity again and continues this motion back and forth until you turn off the power.
 

Yaakov

Joined Jan 27, 2019
3,187
When I turn power on to the dc motor it will rotate the blue lever in one direction until it triggers a limit switch reversing the polarity until the blue lever triggers a second limit switch which changes the polarity again and continues this motion back and forth until you turn off the power.
Could you explain what you are trying to accomplish once this works? What is the application?
 

crutschow

Joined Mar 14, 2008
27,243
Here's a circuit using a single DPDT relay with two SPDT limit-switches:
It includes the free-wheeling diodes needed to protect the relay contacts.

1615131027429.png
 

MisterBill2

Joined Jan 23, 2018
8,806
get rid of the diodes around the motor, they are not needed. And then make sure that the relay contacts both move at the same time, and have adequate clearance. AND this circuit is rather abusive of the motor and relay.
 

ApacheKid

Joined Jan 12, 2015
388
So this motor never completes even one revolution, it rotates at most 350 odd degrees, then rotates in the opposite direction some 350 odd degrees and repeats. I've never heard of this kind of device before, what's it used for? a gate opener?
 

crutschow

Joined Mar 14, 2008
27,243
get rid of the diodes around the motor, they are not needed. And then make sure that the relay contacts both move at the same time, and have adequate clearance. AND this circuit is rather abusive of the motor and relay.
Motors don't generate inductive spikes?
 

MisterBill2

Joined Jan 23, 2018
8,806
It almost seems like the function is for a headlamp wiper, or similar. Those use a simple crank and the motor runs in one direction, except that it reverses to park the wiper off the headlamp. 1970's technology in a different country across the ocean.
 

MisterBill2

Joined Jan 23, 2018
8,806
Why 3-pole?
Using a 3-pole relay will completely separate the motor circuit from the latch/unlatch function, and that does matter in a plug-reversing setup such as this one. The current spike as the motor decelerates to zero and then starts in the opposite direction is considerable. And I am wondering about the cycle rate, since motor heating may be a problem. And I am still wondering about the application, since a crank arrangement can provide the reversals with no motor reversing.
 

Yaakov

Joined Jan 27, 2019
3,187
And I am still wondering about the application, since a crank arrangement can provide the reversals with no motor reversing.
Gotta love those mystery applications! A mechanical solution seems obviously better here even if there is a need to stop at one or the other limit. I can’t see how beating a motor to death in this way is going to be justified by whatever it is being used for.
 

MisterBill2

Joined Jan 23, 2018
8,806
Gotta love those mystery applications! A mechanical solution seems obviously better here even if there is a need to stop at one or the other limit. I can’t see how beating a motor to death in this way is going to be justified by whatever it is being used for.
Imagine the motor driving a leadscrew for some reciprocating function. That is what I am thinking that it is for. Using a crank would provide a sine-wave velocity profile instead of a constant speed, and it might be that a constant velocity is required. The motor that can stand that sort of use would be a stepper motor with an electronic driver. But that would cost a bit more, and be a lot more complex electrically. This may be a low-budget project. And the application may indeed be "top secret." I can imagine some of those applications.
 
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