Electric components to toggle DC motor polarity

[dcwatson84]

I think this has already been defined, but the thread has taken many turns. So for clarity...

The required inputs are simply a timer momentarily turning on a power source via a latching-relay. (The timer cannot hold a relay open, so it needs to be a latching-relay).
The response is that a motor should run until it triggers a switch, then the system should shut off. When the timer activates again, the motor should run in the *reverse* direction until it hits another switch. So this implies the switches might need to perform two functions 1) stopping the system, and 2) flipping a switch/h-bridge to reverse the motor.

The timer and the motor are constraints that cannot be changed.

 

[Tony Stewart]

My wiring cct #66 and alec_t's will accomplish this.
signal input is N.O. contact closure to V+ which closes with cap across contacts for wetting if mechanical.

ok?
your choice.
winch reversal switch that I selected is $21 but easy to connect wires

 

[dcwatson84]

I'm looking at that. You talk about the "reversal" switch. I dont understand what you mean by that or what type of component is. I need that reversal to be automated, and the timer cannot do it.

 

[alec_t]

Adding caps to my post #71 circuit, as suggested by Tony in post #77, proved trickier than I expected, since I found they slowed FET turn on/off and led to unacceptable shoot-through current. So, here's a hybrid circuit where the FET bridge has been replaced by two non-latching relays: one for direction control and the other for power switching to substantially eliminate standby current. Latching and direction alternation are controlled by the CD4013. D1/C1 should prevent IC supply droop when the relays/motor draw current.

 

[KeepItSimpleStupid]

Best shot at #2.

There is a circuit used all of the time for safety. You have a norm open switch for start and a norm closed switch for stop. Both are momentary. Cutting power also unlatches the latch.

It uses one of the relay poles to latch itself. The start switch goes across thta NO contact of the relay. The momentary NC switch goes directly in series with the relay coil.

 

[Les Jones]

I've been thinking about making a latching relay toggle when power is applied to the whole circuit. (I.E. Without power to any of the circuit between the timer on periods.) I cannot think of an easy way to do it. All the ways I have thouht of require generating a sequence of events which requres quite a few extra components. This results in a design that is more complex than using a microcontroller. As an alternative to a latching relay a small geared motor with two disks mounted on the shaft would solve the problem. One disk would have two notches spaced at 180 degrees. This would have a micro switch pressing agains it so that it's contacts were open when the lever dropped into the notch and closed when the lever was away from the notch. The contacts would be in series with the samll geared motor. Threre would be a relay and capacitor that generated a pulse when power was applied. The normally open contact on this relay would be on papallel with the micro switch contacts. The pulse would be long enough to drive the motor away from the notch then the motor would continue to run until the microswitc lever dropped into the next notch. So each time power was applied the motor would rotate 180 degrees. The second disk would have only one notch in it. This disk would opperate two single pole changeover microswitches (Or One DPDT micro switch if such a device exists.) These two microswitches would form a reversing switch for the main motor. This would result in the main motor alternatly driving up and down when power was applied. This would meet your wishes not to use limit switches (Or over current sensing.) which I think is a bad design idea. It would not require much effort to to use magnets and reed switches mounted on the door to act as limit switches. Security alarm contacts would be the easiest way to obtain these. These could not be used directly in series with the main motor as they work the wrong way round but could be used with a relay or transistor.

Les.

 

[Tony Stewart]

1. 
2. Does battery have a trickle charger?
3. What is the max current you can tolerate in order to make this reliable, 20mA ?
4. IS there a concern with motor pulley jam and gravity?
5. Is there a concern with door jam interference and chicken?
6. Are there any other concerns not in your list of requirements, which need to be summarized to start the design details.

 

[Tony Stewart]

Adding caps to my post #71 circuit, as suggested by Tony in post #77, proved trickier than I expected,

Indeed with mixed MOSFETs and RElays.
Fortunately I just remembered releasing DC motor current on OPEN has the same effect as discharging a Cap on CLOSE depending if current limits are similar and both can serve to wet contacts within range without welding contacts. So it does not need to be applied to all contacts, just ones with TTL or CMOS levels of current on contacts rated >2A.
So C5,6 not req'd.

 

[spec]

Another circuit for what it is worth. This time relative with a single timer input.
It is just an outline and I haven't bothered to draw in the integrated circuit power lines or analyze it in any detail.

​

 

[Tony Stewart]

Ah, good point - I guess what Im saying is that the limit switch is being used to apply current, not to cut it. This current is then being used to alter the state of other latches in the system. Maybe that completely defeats the purpose of limit switches, since they are designed to act quickly when a limit is reached?

I guess I should redesign my system with that in mind? I understand how I could use that switch to kill the motor, but I also need to use that switch to alter the state of the system at the same time, because it's acting as the reversal signal.

Should I scrap the "limit" switch, and use a "momentary" switch? Which I think can be used like a normal switch, to apply current when the door pressed against it?

1. A latch in electronic systems is also a memory cell, such as an SR FF or D FF or RAM cell.
2. In passive relays, a latching relay requires no power to preserve its "state"
3. In the example of a non-latching reversing driver with dual coil, it is made into a latch by the end stop switches. (see power driver below)
4. Thus the switches when open at the end of travel become the memory cell when open.
5. Both cannot be open at the same time. When both closed, direction is controlled by the input direction controlled switch, by any means.
6. The limit switch both apply and cut current as it becomes a logic state or memory state to indicate position when open.

a non-latching polarity reversal power switch.
perhaps overkill here.

 

[dcwatson84]

1. A latch in electronic systems is also a memory cell, such as an SR FF or D FF or RAM cell.
2. In passive relays, a latching relay requires no power to preserve its "state"
3. In the example of a non-latching reversing driver with dual coil, it is made into a latch by the end stop switches. (see power driver below)
4. Thus the switches when open at the end of travel become the memory cell when open.
5. Both cannot be open at the same time. When both closed, direction is controlled by the input direction controlled switch, by any means.
6. The limit switch both apply and cut current as it becomes a logic state or memory state to indicate position when open.

a non-latching polarity reversal power switch.
perhaps overkill here.

#1 & #2 - That's exactly why I wanted to use latching relays - because they easily act as memory.
#4 - The problem with that is that I do not want the system to consume *any* power when it is offline. The switch should perform some state altering action, and then cut its own power. Right now that action is to flip an H-bridge which controls motor direction. Then I need the entire system to power down, since it has been set in the reverse state.
#5 - In my design both switches are open when the door is in travel. When one switch closes it swaps the motor direction and then cuts power.
#6 - I also dont need a limit switch - as the directional switch acts in the exact same way, it cuts power after flipping the H-bridge.

a non-latching polarity reversal power switch.
That's sort of what I need - except I'm still not seeing it without at least one latching relay. I dont want the system to consume any power when not in motion. The battery has a trickle charger but I cant risk a week of cloudly days causing a dead battery.

 

[Tony Stewart]

**broken link removed**
DPDT latching relay , K1 $5.54 stock

Try this to drive the motors with limit switches
You still need to convert input SPST up/down to SPDT to choose coils. This must be active in one direction always but can be very low <1mA easily powered by PV.

your design ref#5,6? where

 

[dcwatson84]

I've been thinking about making a latching relay toggle when power is applied to the whole circuit. (I.E. Without power to any of the circuit between the timer on periods.) I cannot think of an easy way to do it. All the ways I have thouht of require generating a sequence of events which requres quite a few extra components. This results in a design that is more complex than using a microcontroller. As an alternative to a latching relay a small geared motor with two disks mounted on the shaft would solve the problem. One disk would have two notches spaced at 180 degrees. This would have a micro switch pressing agains it so that it's contacts were open when the lever dropped into the notch and closed when the lever was away from the notch. The contacts would be in series with the samll geared motor. Threre would be a relay and capacitor that generated a pulse when power was applied. The normally open contact on this relay would be on papallel with the micro switch contacts. The pulse would be long enough to drive the motor away from the notch then the motor would continue to run until the microswitc lever dropped into the next notch. So each time power was applied the motor would rotate 180 degrees. The second disk would have only one notch in it. This disk would opperate two single pole changeover microswitches (Or One DPDT micro switch if such a device exists.) These two microswitches would form a reversing switch for the main motor. This would result in the main motor alternatly driving up and down when power was applied. This would meet your wishes not to use limit switches (Or over current sensing.) which I think is a bad design idea. It would not require much effort to to use magnets and reed switches mounted on the door to act as limit switches. Security alarm contacts would be the easiest way to obtain these. These could not be used directly in series with the main motor as they work the wrong way round but could be used with a relay or transistor.

Les.

I understand not having all the bells and whistles may seem like a bad idea..... but again - this is a chicken coop door.

The design youre describing is much like the original motor apparatus. It used mechanical gears to operate a physical switch. It simply wasn't reliable. It fell out of calibration far too often. Which is why im taking everyones advice in using switches triggered by the door. These will *act* as limit switches, because they will cut the power, but they wont actually be limit switch components.

 

[dcwatson84]

**broken link removed**
DPDT latching relay , K1 $5.54 stock

Try this to drive the motors with limit switches
You still need to convert input SPST up/down to SPDT to choose coils. This must be active in one direction always but can be very low <1mA easily powered by PV.

your design ref#5,6? where

Thanks for the link. I'm checking it out. I assume it's best to use a "power" relay for the motor amperage? Even though the signal relays seem to be able to handle 2A?

 

[alec_t]

#5 - In my design both switches are open when the door is in travel. When one switch closes it swaps the motor direction and then cuts power.

Can you post this design? Having cut the power, how do you restore it so that a subsequent pulse from the timer will allow the motor to run in the reverse direction?

 

[Tony Stewart]

Thanks for the link. I'm checking it out. I assume it's best to use a "power" relay for the motor amperage? Even though the signal relays seem to be able to handle 2A?

7.5A Inrush, Sealed-Fully

this problem is not hard yet taking too long

 

[KeepItSimpleStupid]

Here **broken link removed** is an IMPULSE relay. Yep, expensive.

The two automotive relays and two limit switches won't consume power unless the motor is running. The limit switches cause the UP/DOWN relays to drop out.

The impulse relay will accept a pulse from your timer. Done!

 

[Tony Stewart]

ok now generate (edit) 0.5A pulses >75ms from your timer.

then ensure closed state remains synchronized. as this is a toggle solenoid, not set / reset or fwd/rev

 

[KeepItSimpleStupid]

The impulse relay https://www.nteinc.com/relay_web/pdf/RLY76_77.pdf (Datasheet) does not require a bi-polar pulse,

 

[ccurtis]

Watson: You might be interested in the idea at post #41: https://www.electro-tech-online.com...-use-a-little-help.140677/page-3#post-1176137