Need a simple circuit analyzed for its troublesome behavior

LesJones

Joined Jan 8, 2017
3,296
I agree with MisterBill that is is not wired anything like the circuit in your first post. The pictures are not very helpful as there is no one picture with all the components together so we can follow the wires. The picture of the switch shows it is fully cross connected so there is no way the limit switches can each stop the rotation in only one direction. The resistance tests 1 and 2 show that there is no direct connection between the supply negative and the common terminals on the limit switches as shown on your circuit diagram. (Also I asked for you to have both limit switches activated. For example using sticky tape or an elastic band. ) I suggest that you re wire it from scratch ticking off each wire on the diagram as you connect that wire.

Les.
 
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MisterBill2

Joined Jan 23, 2018
9,034
At one time, at one job, I wound up adding a note to the release drawings that stated " Machine will not function as intended unless wired according to the print", because one panel wiring person kept making wrong connections. It did get my point across.
 

Thread Starter

jkbrand

Joined May 8, 2021
29
When I look at the wiring t does not seem like it matches the circuit shown. What it looks like is that terminals 4 and 4 are tied, as are terminals 1 and 6, which are supposed to be tied. If that is the case, then somehow the two switches are in series, and that would cause exactly the problem as described. The black wires from 3 and 4 go to a junction block but they should go each to a limit switch only. And there is another wire leaving the connections to 1 and 6, while in the circuit that is not the case. So it is not wired like the diagram shows.
The construction has way too many connectors to be easily traced.
I now understand the black wires from 3 and 4 should each go to a limit switch. (I was naively thinking that if the black wires are common, they could be ganged together. My mistake.) OK, dumb question, but now that 3 and 4 are going to their respective COM terminals on the limit switches, where does the source negative connect? Sorry for my ignorance, guys, but I'm encouraged as we ARE getting closer. Finally, when the wiring ultimately *does* match the schematic, will there still be a need for diodes?
 
I'm going to say this:

I don't think it;s possible to do this with just SPDT limit switches. There is two funtions to perform:
1. Turn off the motor
2. Allow current to pass in the reverse direction.

You can do it with two SPDT relays and two SPDT limit switches and you can do it with 2 diodes and two limit switches.
The diode method has it's limitations like max current and no dynamic braking (stopping instantaneously). The diode has to handle the surge motor current only for the duration of getting the motor off the limit.

It would work for a PSC timing motor because there is a common and a CW and CCW wire, so the limit switches would go in each one.

My $.02
 

MisterBill2

Joined Jan 23, 2018
9,034
I'm going to say this:

I don't think it;s possible to do this with just SPDT limit switches. There is two funtions to perform:
1. Turn off the motor
2. Allow current to pass in the reverse direction.

You can do it with two SPDT relays and two SPDT limit switches and you can do it with 2 diodes and two limit switches.
The diode method has it's limitations like max current and no dynamic braking (stopping instantaneously). The diode has to handle the surge motor current only for the duration of getting the motor off the limit.

It would work for a PSC timing motor because there is a common and a CW and CCW wire, so the limit switches would go in each one.

My $.02
Certainly it is both possible and simple to have a circuit that stops the motor at each end of travel using just the two limit switches and the directional control switch, as shown in the diagram of post #1. THAT circuit will work very well, within the current limits of the switch. Several of us have agreed that the circuit will functin as claimed. The only problem is that whatever circuit has been wired is not the one shown.
 

LesJones

Joined Jan 8, 2017
3,296
Re post #63. I have no idea which terminals you are talking about using numbers as there are no numbers on your diagram to tie up with these numbers.

Les.
 
@jkbrand You wanted a wiring diagram, I found one here for what I am proposing. https://electronics.stackexchange.com/questions/293726/limit-switch-on-reversing-motor

Your DPDT switch has the Usual X wiring. Take the motor from the middle terminals and power from either end.

The schematic goes in series with your motor as drawn. Polarities vs motor directions are not shown.

Hopefully, you can clearly see the operation. If the motor is between limits, the diodes are bypassed, so the motor cn travel in either direction.

Only one limot switch should open at a time and current can only flow in the direction of the diode cross that limit switch. it only needs to use the diode path until the limit switch closes.
 
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MisterBill2

Joined Jan 23, 2018
9,034
Re post #63. I have no idea which terminals you are talking about using numbers as there are no numbers on your diagram to tie up with these numbers.

Les.
Post #20 has the same circuit, but with terminal numbers on the DPDT switch so that it could be discussed more easily. The DPDT switch is only supposed to have half of the cross, with the 2 limit switches feeding the other side, one switch for each direction. And really, the drawing is fairly good and the circuit is about as simple as a circuit could be. The only improvement would be to use a switch symbol instead of the switch drawing. It must be confusing a lot of folks.
 
I think, I see it if it works this way. Assume the center poles going to the motor. The common poles.

Center being off, you cross one set of terminals.

Now with the middle/ the center pole going to the other terminal of the motor supply either nothing or the opposite polarity to say the top terminal. e.g. the top right terminal gets supplied +V or nothing through a limit switch and the bottom right gets supplied -V or nothing from the limit switch.

if you wire it wrong, you end up connecting +V to both sides of the motor or -V to both sides of the motor.

Power gets supplied to either the top two terminals or the bottom two terminals.

I can see that working. Thick head, I guess.
 

LesJones

Joined Jan 8, 2017
3,296
Mister Bill, Thanks for pointing out post #20. Now post #63 makes sense .

jkbrand, You are still not reading the diagram. 3 and 4 are shown connected to the NC connections on the limit switches. Again on the diagram it clearly shows the common on the limit switches connected to the negative output of the power supply.

When the switch is in the upper position. (Connecting 1 to 2 and 4 to 5) the negative feed to the motor is via LS1 then 4 to 5 on the switch. The positive feed to the motor is via 1 and 2 on the switch. So when LS1 opens the motor stops.

When the switch is in the lower position. (Connecting 2 to 3 and 5 to 6) the negative feed to the motor is via LS2 then 3 to 2 on the switch. The positive feed to the motor is via 5 and 6 on the switch. So when LS2 opens the motor stops.

(It would not matter if the NC and common connections on a limit switch were swapped over but I pointed out the error when you said " now that 3 and 4 are going to their respective COM terminals on the limit switches, " to get you to FOLLOW THE DIAGRAM.)
You should now be able to see why each limit switch only stops the motor in one direction.

Les.
 

Thread Starter

jkbrand

Joined May 8, 2021
29
Mister Bill, Thanks for pointing out post #20. Now post #63 makes sense .

jkbrand, You are still not reading the diagram. 3 and 4 are shown connected to the NC connections on the limit switches. Again on the diagram it clearly shows the common on the limit switches connected to the negative output of the power supply.

When the switch is in the upper position. (Connecting 1 to 2 and 4 to 5) the negative feed to the motor is via LS1 then 4 to 5 on the switch. The positive feed to the motor is via 1 and 2 on the switch. So when LS1 opens the motor stops.

When the switch is in the lower position. (Connecting 2 to 3 and 5 to 6) the negative feed to the motor is via LS2 then 3 to 2 on the switch. The positive feed to the motor is via 5 and 6 on the switch. So when LS2 opens the motor stops.

(It would not matter if the NC and common connections on a limit switch were swapped over but I pointed out the error when you said " now that 3 and 4 are going to their respective COM terminals on the limit switches, " to get you to FOLLOW THE DIAGRAM.)
You should now be able to see why each limit switch only stops the motor in one direction.

Les.
Les, you're right. I messed up not taking the laptop to the shop and instead relied on my memory. My wife (an RN) has pointed out that my dementia is getting worse, and with what I've been doing lately in other arenas, I can no longer disagree. I wish I were joking, but I'm not. OTOH, at my last two doctor's appointments my GP has encouraged me to keep my brain active, and I imagined this circuit issue would be a good way to do that. I can't count the number of times I've thought perhaps it's not. I appreciate everyone's thoughts and advice. Truly.
Mister Bill, Thanks for pointing out post #20. Now post #63 makes sense .

jkbrand, You are still not reading the diagram. 3 and 4 are shown connected to the NC connections on the limit switches. Again on the diagram it clearly shows the common on the limit switches connected to the negative output of the power supply.

When the switch is in the upper position. (Connecting 1 to 2 and 4 to 5) the negative feed to the motor is via LS1 then 4 to 5 on the switch. The positive feed to the motor is via 1 and 2 on the switch. So when LS1 opens the motor stops.

When the switch is in the lower position. (Connecting 2 to 3 and 5 to 6) the negative feed to the motor is via LS2 then 3 to 2 on the switch. The positive feed to the motor is via 5 and 6 on the switch. So when LS2 opens the motor stops.

(It would not matter if the NC and common connections on a limit switch were swapped over but I pointed out the error when you said " now that 3 and 4 are going to their respective COM terminals on the limit switches, " to get you to FOLLOW THE DIAGRAM.)
You should now be able to see why each limit switch only stops the motor in one direction.

Les.
SUCCESS!! Took apart all the wiring and one-by-one replaced each wire from the limit switches and the DPDT switch. My thanks to all who contributed to my finally getting it wired according to the schematic and despite my multiple bumblings. I tried to attach a video file showing the operation, but the system says my file extension (.mp4) is not allowed. The video shows my alternately pressing the DPDT rocker and reversing direction at each stop. No more "sticking." Hooray. Again, thanks everyone! Would love to share the video if someone has a suggestion, and as long as no wiring is involved, I can probably produce it....
 

Thread Starter

jkbrand

Joined May 8, 2021
29
Good idea. Someone responded I could try to change the file type to "txt", post it, and have folks download it, and rename it to .mp4. Let's see if that works. If not, I'll try to ZIP it and re-send. Apologies for the video quality, but I'm guessing the file might've been large enough to force it being resized to fit.
 

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MisterBill2

Joined Jan 23, 2018
9,034
It was clear to me and many others that the circuit shown would work as desired. So thanks for letting us know that it finally does work.
Yeats ago I had a stamp for shop release drawings that read "Machine will not work as intended unless wired as drawn." The forman did not think that it was at all funny. But several other folks got a big laugh out of it.
 
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