Suggestions required for operation of SET on a latching Relay

Thread Starter

FSDCan

Joined Feb 15, 2024
6
How to get the SET to work in the attached by-directional motor control circuit.
To SET;
Switch Position must be in UP position not the DWN position.
The magnetic reed switch RESETs the latching relay at the end of the UP movement of the motor drive.
Once this happens the latching relay will activate the motor to go DOWN but the UP will not work until the latching relay is SET.
This will enable the operation of both directions until the reed switch (RESET) is tripped again.
The SET mode can be done by momentarily touching the Green wire to negative 12 volts, but only momentarily.
This being a negative pulse to SET.
The latching relay will not SET if the UP/DWN switch is in the middle or neutral position.
 

Attachments

Thread Starter

FSDCan

Joined Feb 15, 2024
6
Well I got the circuit to work, but not the way I wanted to do it. Used two magnetic reed switches wired as per the diagram attached (below). Spacing them apart (2 inches) so there is no overlap. One would operate the RESET of the latching relay to stop the UP motion and the other to SET the latching relay when in the DOWN motion.Screenshot 2024-02-17 115612.png motion.
 

Thread Starter

FSDCan

Joined Feb 15, 2024
6
So, what was the question? The instructions seem clear enough, though its a pretty clunky way of doing it.
Thanks for your reply. I agree this is a clunky way of doing it.
I am very open to a better solution. the motor being controlled is a 12V 10amp automotive wiper style.
Basic use is to control the length / position of the end of a stainless steel cable. Up to over 200 feet.
Personally I would like to use a small MMI / PLC solution but the cost is prohibitive. The MMI solution would give lots of nice features. UP/DWN, auto stop at desired total length, auto stop at top and auto stop at a preset length.
 

Irving

Joined Jan 30, 2016
3,890
Assuming the cable doesn't stretch much, a simple pulse encoder and a pair of pinch wheels will be a cheap solution to determining how far the cable end is - that could be ultra-cheap depending on the resolution required 0.1mm, 1mm, 10mm, ??? A simple Arduino can count pulses and say how far the end is. You can still have reed switches to determine up and down limits though its not clear what operates the reed; how is the magnet attached to the cable?

What's your approx budget?
 

Irving

Joined Jan 30, 2016
3,890
Here's how I would do it.... 2 cheap automotive relays, two reed switches. Pulling /UP to -ground (battery-) turns on relay 1 and makes the motor drive up until reed switch 2 is activated (upper limit), turning off relay 1. Pulling /DOWN to ground turns on relay 2, making the motor drive down until reed switch 2 is activated (lower limit), turning off relay 2. /UP & /DOWN can be activated by 2 push buttons or a centre off toggle switch or a microcontroller, The second output of each reed switch can be used to tell the microcontroller that the limit has been reached.

1708194343782.png
 

Thread Starter

FSDCan

Joined Feb 15, 2024
6
Great solution. But the reed switches must be within a foot of the cable spool. Reed switches are activated by a cylinder shaped magnet 1/4 inch wide by 2 inches long in heat shrink tubing to the cable (mostly for magnetic field strength. The cable goes into water at different depths. Currently there is a small counter with a spring belt drive from the motor shaft as the length indicator. This was the original manufactures solution and it sorta kinda works OK. Accuracy wasn't a huge issue. Also the original UP stop was a micro switch activated by a plastic bead snapped to the cable and they have had issues with this and have stopped manufacturing that solution. So I decided to make my own solution. My best solution would be a Horner Electric 12DC powered MMI / PLC (all in one) with a 3 to 4 inch touch screen and a automotive 40amp relay. The whole solution can be then monitored by a proxy with a target on the cable spool. The only problem being the price is $1500+
 

Irving

Joined Jan 30, 2016
3,890
Is this a salt water environment (stainless steel cable suggests it is)? Marine operation has all sorts of issues!

OK on the reed switches. One easy option is magnetically polarised switches that depend on which way round the magnet is. This can be done with the existing switches by using smaller magnets alongside/near the switch that aren't strong enough to activate the switch without the other magnet...

If counting drum rotations is accurate enough then I'd suggest a magnetic encoder on the drum shaft, or if thats not possible, a belt drive to an auxilary shaft. You can get very accurate (16000 counts/rev) magnetic sensors that can be completely sealed in an IP67 enclosure and only needs a single external magnet concentric to the shaft.

Regarding the MMI/PLC, do you mean one of these?
s-l1600.jpg

Stupidly expensive and massive overkill. Correct me if I'm wrong, but all you need is a counter for length and a couple of push buttons for up & down. Of course if you want to program, say, a sequence of depths and then step through them a little more complexity is needed but thats still overkill.

You could easily build a custom unit fully sealed to IP67 for under $200
 

MisterBill2

Joined Jan 23, 2018
18,538
Interesting string of ideas, all without getting the actual purpose of the project. What I think I see is automating an anchor winch on a boat of some medium size. Pay the line out until either it is manually stopped, or reaches the end of the cable, or rewind it all the way unless it is manually halted. What is not totally obvious is what the center-off reversing switch that I saw in at least one circuit would ultimately be for..
What is often used in such an application is a three button scheme with three buttons, Raise, Lower< and STOP. Often a selector is also included for AUTO/MANUAL selection.
Certainly sensing the endpoints will be the challenge.
The relay scheme suggested by Irving will certainly be good for powering the motor,, it is an arrangement suggested and used quite a few times here and elsewhere. For a control PLC check the AUTOMATION DIRECT website, they have much better pricing and quite a spread of choices. AND free programming software.
For knowing the cable position a photo-reflective proximity switch looking at the end of the cable spool should be able to count revolutions very well, and interface with the PLC.
 
Last edited:
Top