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Head scratcher - can I make this circuit from relays, diodes and switches only?

rhd

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Good god, no one wants to wire up 47 relays to turn a motor, Sean. That's when you give up and switch to arduino.

Here's what I came up with. It's basically a low-tech H-bridge to switch polarity. One obvious weakness is that it shorts 12V if you press the power button while one of the limit switches is not engaged. A DC breaker would remedy that, though. I'm sure it could be improved, but like I said, first draft.

That is very sharp. It took me a couple minutes just to figure it out (I didn't catch on to the fact that those were NC end stops at first).

I do need to figure out a way to avoid the short, because it's possible that the circuit could be triggered when the mechanism has slacked somewhat and released from the end stop.
 

Alaskan

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For myself, I'd just use a three position DPDT switch wired to reverse the polarity when switched from side to side, but off when in the middle position.
 
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lasersbee

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The problem with a push ON-push OFF button is that you would
need to push the 1st button back OFF before you pressed the
2nd button ON after the limit switch stopped the 1st motor
direction. I could be wrong. Didn't see your complete circuit idea.

Jerry
 

Alaskan

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Yea, I saw the problem and edited my post while you were writing yours.
 

lasersbee

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N/P.....;)


For myself, I'd just use a three position DPDT switch wired to reverse the polarity when switched from side to side, but off when in the middle position.
That makes sense... Even if you only had a push button...
you would still need a human action to push it again...
So it's not a greater leap to push the 3 position switch to
the other side and you save 2 relays and diodes.

Jerry
 
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lasersbee

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Cyparagon

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I do need to figure out a way to avoid the short
I'm not seeing an idiot proof solution that doesn't require adding at least two more relays. Is two more relays too hairy?

Having a button for CW and a button for CCW would be ideal. Even then, some jackass could push both CW and CCW to short it.

A breaker is a common way to make circuits idiot-resistant. Why is a breaker not an option for you?
 

Alaskan

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Limit switches to break the power if they hold the switch down too long would work fine, simple to do. You can get spring loaded DPDT switches too, so they don't stay in one position or the other. See if some idiot can screw that up, not.
 

lasersbee

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I'm not seeing an idiot proof solution that doesn't require adding at least two more relays. Is two more relays too hairy?

Having a button for CW and a button for CCW would be ideal. Even then, some jackass could push both CW and CCW to short it.

A breaker is a common way to make circuits idiot-resistant. Why is a breaker not an option for you?
The two button approach problem of hitting both at
the same time could be solved using a DPST switch
instead.

Jerry
 

Illuminum3415

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I can't think of a way beyond a transistor circuit to clamp the motor though, you can cut power to it but the remaining magnetism generated by the stator would still cause the motor to move, possibly past their limits even with limit switches in place. Theres inertia to deal with too. How big [HP] is the motor by any chance?

I think it would be kind of neat to see a 50+ relay circuit in action.
Look up Zusie the relay computer
Zusie - My Relay Computer
 
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