Need a circuit/configuration to operate 2-wire 12v linear actuator with limit switches (fully open/fully close)

Thread Starter

AmirB

Joined Feb 25, 2020
10
Hi and thanks in advance.
Need a circuit/configuration to operate 2-wire 12v linear actuator with two build in limit switches (fully open/fully close). I need a pushbutton operated control circuit to initiate a single full cycle (extract-contract). Mechanically savvy but have only basic theoretical and practical knowledge in electronics. Basic idea was to use the fully open micro switch to trigger relay to reverse polarity, tried several configurations but no luck. Appreciate help with a working design. Andrew Hagin
 

LesJones

Joined Jan 8, 2017
2,522
Do you have access to the limit switches or is the only way you know it has reached a limit switch is when the current drops to zero ? I imagine the two limit switches are in series with the motor and that there is a diode in parallel with each limit switch. Is this a correct assumption ? Do the limit switches have change over contacts (A common plus an NC and an NO contact.) ? Show us the configurations that you have tried that did not work.

Les.
 

AlbertHall

Joined Jun 4, 2014
9,331
Would it be acceptable for there to be a short delay after the first motion stops and second motion beginning?
If this is the case then a simple timer would the job. The button triggers the timer which controls a relay. This applies voltage to the actuator. The time is set so that the motion will be completed before the timer resets and re;eases the relay which now applies the reverse voltage to the actuator.
 

Thread Starter

AmirB

Joined Feb 25, 2020
10
Would it be acceptable for there to be a short delay after the first motion stops and second motion beginning?
If this is the case then a simple timer would the job. The button triggers the timer which controls a relay. This applies voltage to the actuator. The time is set so that the motion will be completed before the timer resets and re;eases the relay which now applies the reverse voltage to the actuator.
thanks, will try. it will do the job as an interim solution. still looking for a step generated action.
 

Bernard

Joined Aug 7, 2008
5,399
This does work, Dr tried it out on me. Object is to turn on power, SW1 then push momentary Start,
SW2; Actuator starts withdrawel of 60 ml of blood which is radiated with UV; when end of travel
is reached, SW4, NC, motor reverses, blood is re injected . When SW5 opens, the motor stops.
This was from about 1997. Suggested from book " Into the Light by Dr. William Campbell Douglass.
Scan.jpg
 
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crutschow

Joined Mar 14, 2008
24,403
Can the limit switches carry the motor current?
If so the circuit below should work (assuming the limit switches open when the limit is reached, the connections are available).
The PB operates the relay, which then latches through the Open Limit Sw, and powers the motor to the Open position.
When the Open Limit Sw opens, the relay is released, which reverses the voltage to the actuator until the Closed Limit Sw opens.
D1 momentarily carries the motor Open current at the start until the Closed Limit Sw closes.

If the limit switch can't carry the motor current, then you could add another relay in place of the Closed Limit Sw, operated by the Closed Limit Sw.

1582658227194.png
 
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Thread Starter

AmirB

Joined Feb 25, 2020
10
Do you have access to the limit switches or is the only way you know it has reached a limit switch is when the current drops to zero ? I imagine the two limit switches are in series with the motor and that there is a diode in parallel with each limit switch. Is this a correct assumption ? Do the limit switches have change over contacts (A common plus an NC and an NO contact.) ? Show us the configurations that you have tried that did not work.

Les.
will check, also will send diagram of
Can the limit switches carry the motor current?
If so the circuit below should work (assuming the limit switches open when the limit is reached, the connections are available).
The PB operates the relay, which then latches through the Open Limit Sw, and powers the motor to the Open position.
When the Open Limit Sw opens, the relay is released, which reverses the voltage to the actuator until the Closed Limit Sw opens.
D1 momentarily carries the motor Open current at the start until the Closed Limit Sw closes.

If the limit switch can't carry the motor current, then you could add another relay in place of the Closed Limit Sw, operated by the Closed Limit Sw.

View attachment 199970
Thanks, will try ASAP. On site at clients all week. Will be back at the workshop Monday.
 

Thread Starter

AmirB

Joined Feb 25, 2020
10
Do you have access to the limit switches or is the only way you know it has reached a limit switch is when the current drops to zero ? I imagine the two limit switches are in series with the motor and that there is a diode in parallel with each limit switch. Is this a correct assumption ? Do the limit switches have change over contacts (A common plus an NC and an NO contact.) ? Show us the configurations that you have tried that did not work.

Les.
Thanks, will try ASAP. I do have access to the limit switches, already opened the cover. The two limit switches are in series with the motor. Need to check how they actually work.
On site at clients all week. Will be back at the workshop Monday.
 

Thread Starter

AmirB

Joined Feb 25, 2020
10
Do you have access to the limit switches or is the only way you know it has reached a limit switch is when the current drops to zero ? I imagine the two limit switches are in series with the motor and that there is a diode in parallel with each limit switch. Is this a correct assumption ? Do the limit switches have change over contacts (A common plus an NC and an NO contact.) ? Show us the configurations that you have tried that did not work.

Les.
Thanks, will try and let you know. I do have access to the limit switches, already opened the cover. The two limit switches are in series with the motor. Need to check how they actually work.
On site at clients all week. Will be back at the workshop Monday.
 

Thread Starter

AmirB

Joined Feb 25, 2020
10
Can the limit switches carry the motor current?
If so the circuit below should work (assuming the limit switches open when the limit is reached, the connections are available).
The PB operates the relay, which then latches through the Open Limit Sw, and powers the motor to the Open position.
When the Open Limit Sw opens, the relay is released, which reverses the voltage to the actuator until the Closed Limit Sw opens.
D1 momentarily carries the motor Open current at the start until the Closed Limit Sw closes.

If the limit switch can't carry the motor current, then you could add another relay in place of the Closed Limit Sw, operated by the Closed Limit Sw.

View attachment 199970
Thanks, will try and let you know. I do have access to the limit switches, already opened the cover. The two limit switches are in series with the motor. Need to check how they actually work. On site at clients all week. Will be back at the workshop Monday.
 

MaxHeadRoom

Joined Jul 18, 2013
20,057
Datasheet / vendor / part number of the actuator?

Are the limit switches SPST (2 pins) or SPDT3 pins)?
Typically like this.
You may have to fit some external logic with switches that operate just before the internal ones to do it with a single PB for automatic reverse.
Max.

1582667944358.png
 

Thread Starter

AmirB

Joined Feb 25, 2020
10
Can the limit switches carry the motor current?
If so the circuit below should work (assuming the limit switches open when the limit is reached, the connections are available).
The PB operates the relay, which then latches through the Open Limit Sw, and powers the motor to the Open position.
When the Open Limit Sw opens, the relay is released, which reverses the voltage to the actuator until the Closed Limit Sw opens.
D1 momentarily carries the motor Open current at the start until the Closed Limit Sw closes.

If the limit switch can't carry the motor current, then you could add another relay in place of the Closed Limit Sw, operated by the Closed Limit Sw.

View attachment 199970
Thanks MaxHeadRoom and crutschow

Will try ASAP. I do have access to the limit switches, already opened the cover. The two limit switches are in series with the motor. The switches are probably a parallel diode bridge but need to check how they actually work.

By client spec, the device need to operate by single pushbutton switch to initiate full cycle.

I am already committed to onsite service calls at clients all week. Will be back at the workshop Monday.
 

Thread Starter

AmirB

Joined Feb 25, 2020
10
Typically like this.
You may have to fit some external logic with switches that operate just before the internal ones to do it with a single PB for automatic reverse.
Max.

View attachment 199979
Thanks MaxHeadRoom and crutschow

Will try ASAP. I do have access to the limit switches, already opened the cover. The two limit switches are in series with the motor. The switches are probably a parallel diode bridge but need to check how they actually work.

By client spec, the device need to operate by single pushbutton switch to initiate full cycle.

I am already committed to onsite service calls at clients all week. Will be back at the workshop Monday.
 

MaxHeadRoom

Joined Jul 18, 2013
20,057
Hi and thanks in advance.
Basic idea was to use the fully open micro switch to trigger relay to reverse polarity, tried several configurations but no luck.
Do you want to operate a P.B. momentarily for the actuator to extend then automatically reverse.
Or press the P.B. for the whole for/rev cycle?
Do you have a model No. for the actuator?
Max.
 
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