Reversing DC motor controll

wayneh

Joined Sep 9, 2010
16,479
The logic to accomplish this is always so much harder than you'd expect! But you're well on your way. Just find a reference that shows how to reverse a motor with a relay ("relay as H-bridge") and you'll save yourself a lot of head scratching.

I have just one wrench to throw in the works: Remember Murphy's Law. What do you want to happen if/when both momentary switches are pressed. Blowing a fuse might be OK. It's an event that shouldn't happen often, but ML tells us that it WILL indeed happen.

https://www.instructables.com/Two-Relay-DC-Motor-Control-Simple-H-bridge
 
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Tonyr1084

Joined Sep 24, 2015
5,481
Welcome to AAC.

Off to a decent start, but we're going to need some clarification. Do you want to "Push the UP button" and have it go all the way to the UP LIMIT? Or do you want it to go UP only while you're pushing the UP button? There's a difference.

If your goal is to send something to full up position then stop with just a single command then a push button isn't the best way to go. Let me be a little clearer on this: Suppose you are moving a sled from ground level to the second floor. You push the button once and let go while the sled moves all the way up. OR you want to move the sled HALF way up. You push the button and hold it as the sled rises. When it's at the level you want you release the push button? Same would apply to the down command as well.

I understand the desire for the "ON" "OFF" switch, that makes sense. But there are other things to consider as well. Power source is important. If you want to move a heavy load you need a power supply with sufficient power to do the work. So tell us about the motor and the power supply. How many amps does the motor draw at a dead stall and what's the peak amperage at the rated voltage of the supply? Also important is the amperage going through the switches. A small motor shouldn't be a problem for a small push button, but a big motor will burn the switch out.

Are you opposed to doing this with relays? If the switches are small and the load is big then you can use the switches to activate relays that will control the heavy load.
 

sghioto

Joined Dec 31, 2017
1,795
This will work if you want to keep with what you have originally proposed.
Again this assumes that the UP switch can handle the motor current.
EEE Motor Reverse with switches.png
 

Tonyr1084

Joined Sep 24, 2015
5,481
Using two relays and small PB Switches, this works up to 2 amps motor draw. You can raise or lower (something) to whatever level you like without exceeding the limits. 2 amps because that's how big I drew the PS. In the event you push both UP and DOWN at the same time the motor does nothing. And when the relays are both off (or both on) they can act like a dynamic brake for the motor.
1609606352296.png
 
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Tonyr1084

Joined Sep 24, 2015
5,481
I agree with MaxHeadRoom. But the TS said he has the buttons he wants to use. To utilize them we "Probably" need relays. He hasn't answered whether he wants full control or full limit for each condition. For full limit - I agree, a toggle DPDT is all that's needed with limit switches and steering diodes.
 

djsfantasi

Joined Apr 11, 2010
7,187
Hello,

Perhaps the TS wants to control a hoist.
Then momentairy buttons can be usefull.

Bertus
Perhaps.

But he didn’t say that. Perhaps he wants to lift a TV up for viewing; hide it when he’s done. That’s as good a guess as yours. Then momentary buttons could be useful.

He DID say he wanted limit-to-limit control.
 

Tonyr1084

Joined Sep 24, 2015
5,481
Since Captain Bret hasn't responded since his initial post, I can only say this for myself, but I'm not sure what he wants. His description isn't as crystal clear as it should be. That's why in post #3 I asked for clarification whether he wants to go fully to the stop limit regardless of whether he holds the button or not. If you want full limit travel each time then a toggle switch such as MaxHeadRoom suggests then a toggle switch with limit switches would be all that's needed. Since the TS has posted pictures of push button switches it wouldn't make sense that he wants to push And Hold the button till it reaches full limit. Sure, limit switches prevent the possibility of jamming gears or burning motors, but why hold a button for several minutes (exaggerated on purpose) just to slew something to full up or full down? Use of a push button suggests the TS wants to be able to stop mid way up or down. Just like an overhead crane. You don't raise the load to full limit height; you raise it enough to move it onto or over something else. PB's makes sense for controlling height of lift. That's why I asked for clarification.

Someone posted while I was composing.
 

djsfantasi

Joined Apr 11, 2010
7,187
Did anyone else look at his attachment? He clearly (to me) states that he wants limit-to-limit operation.

I want the motor to go up when the “UP” momentary switch is depressed and stop when it hits the “UP” limit switch.

I want the motor to go down when the “DOWN” momentary switch is depressed and stop when it hits the “DOWN” limit switch.
 

bertus

Joined Apr 5, 2008
21,022
Hello,

This is the text from the PDF:
I WANT TO CONTROL THE FORWARD AND REVERSE ON A 12 Vdc MOTOR.

I WANT THE MOTOR TO GO UP WHEN THE "UP" MOMENTARY SWITCH IS DEPRESSED AND STOP WHEN IT HITS THE "UP" LIMIT SWITCH.
I WANT THE MOTOR TO GO DOWN WHEN THE "DOWN" MOMENTARY SWITCH IS DEPRESSED AND STOP WHEN IT HITS THE "DOWN" LIMIT SWITCH.

ADDITIONALLY I WANT AN ON/OFF SWITCH FOR THE SYSTEM POWER.
BELOW ARE MY THOUGHTS BUT IT IS INCOMPLETE.

It looks like he wants to start the movement with momentairy buttons until the limit switches.

Bertus
 

djsfantasi

Joined Apr 11, 2010
7,187
Hello,

This is the text from the PDF:
I WANT TO CONTROL THE FORWARD AND REVERSE ON A 12 Vdc MOTOR.

I WANT THE MOTOR TO GO UP WHEN THE "UP" MOMENTARY SWITCH IS DEPRESSED AND STOP WHEN IT HITS THE "UP" LIMIT SWITCH.
I WANT THE MOTOR TO GO DOWN WHEN THE "DOWN" MOMENTARY SWITCH IS DEPRESSED AND STOP WHEN IT HITS THE "DOWN" LIMIT SWITCH.

ADDITIONALLY I WANT AN ON/OFF SWITCH FOR THE SYSTEM POWER.
BELOW ARE MY THOUGHTS BUT IT IS INCOMPLETE.

It looks like he wants to start the movement with momentairy buttons until the limit switches.

Bertus
Gee, that’s what I’ve been saying in several posts..
 

Tonyr1084

Joined Sep 24, 2015
5,481
I see only one momentary switch. He DID state that he's trying to START a drawing but doesn't clearly know all he needs. That's why he's asking for help. Again, push button suggests movement only during the pressing of the button. I'm in the process of planning a sled that will lift and lower wood products from the driveway up to the second floor over the garage. I'll need something I can operate a short distance or to full limit but not beyond limits. Toggle switches can get triggered by accident. Then my sled will move to limit. And if someone or something is in the way - - - . Hence, a push button commands human control over the process. And the design needs to be robust enough to not short or weld contacts together. The plan I drew this morning I have saved. It'll probably be something along these lines, however, with a much heavier motor, supply and relays. The switches can remain small. AND I can have the same set of switches upstairs and down stairs at the same time so I can control the sled from ground level or from the second floor.

So this is why I'm assuming the TS wants to be able to stop mid way. Boy it sure would be nice if the TS could just clarify that one detail. For now all WE can do is assume (and possibly argue intent) what the TS wants.
 

djsfantasi

Joined Apr 11, 2010
7,187
I see only one momentary switch. He DID state that he's trying to START a drawing but doesn't clearly know all he needs. That's why he's asking for help. Again, push button suggests movement only during the pressing of the button. I'm in the process of planning a sled that will lift and lower wood products from the driveway up to the second floor over the garage. I'll need something I can operate a short distance or to full limit but not beyond limits. Toggle switches can get triggered by accident. Then my sled will move to limit. And if someone or something is in the way - - - . Hence, a push button commands human control over the process. And the design needs to be robust enough to not short or weld contacts together. The plan I drew this morning I have saved. It'll probably be something along these lines, however, with a much heavier motor, supply and relays. The switches can remain small. AND I can have the same set of switches upstairs and down stairs at the same time so I can control the sled from ground level or from the second floor.

So this is why I'm assuming the TS wants to be able to stop mid way. Boy it sure would be nice if the TS could just clarify that one detail. For now all WE can do is assume (and possibly argue intent) what the TS wants.
You’re assuming push button causes movement only while it depressed, because of your experience. I see the push button “initiating” an action and the limit switch “stopping” the action. Again, that’s my personal experience. I’ve designed more circuits for that application.
 
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