DPDT Momentary Switch and H bridge

Hi, everyone! I posted a topic a while ago that was similar to this. Basically, I have decided now to use a dpdt momentary switch for an h bridge that I am using, instead of 4 buttons. I posted the schematic for that h bridge down below. I would ensure that only sw 2 and 3 can be on at a time, and only sw 1 and 4 can be on at a time. Thus, I can control the motor both ways. Now, instead of having all the buttons, I want to just have a dpdt momentary switch like this: https://www.amazon.com/gp/product/B07ZX8M3XC/ref=crt_ewc_img_dp_2?ie=UTF8&psc=1&smid=A2RFXKS6GNXFWP

Here is the old schematic with the buttons: (Its called download.png)

Would this be an accurate schematic for wiring the new dpdt switch: (Its called dpdt.png)

Thanks for all your help!

EDIT: On the schematic I forgot to include vcc and gnd. Vcc is where the 2 diodes cathodes’ are connected to, and what sw 1 and 3 also connect to. Basically gnd is at the bottom of the circuit, and vcc is at the top, but under the motor. I will post the new schematic below.

download1.png

OPs images

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Yup. The new circuit is basically the old one, but just put in terms of a singular switch that takes place of the 4 buttons used.

Here is the updated schematic with proper labeling:

dpdt1.PNG

Paul, thanks for the reply. Would I need to add fly back diodes to that, or does that prevent the current from getting through?

Rapid80: Would I need to add fly back diodes to that, or does that prevent the current from getting through?

"Flyback" diodes are not commonly used with switches as the switches can generally handle small voltage surges without damage. If this is indeed at 5 V, this should be quite negligible.

And in fact motors - particularly permanent magnet field motors - do not generate switching "kickback" impulses of any significant degree though it is considered good practice to provide such protection when using semiconductors to control them. :grinning:

I am using some transistors and a mosfet for a logic gate that controls when to supply the 5 volts, but if you are absolutely sure kickback wont be a problem, then thanks for the circuit!

A motor control relay setup using STDT relays. The same can be done using two STDT switches/buttons if desired.

reversemotor.jpg

The switches you linked to are not rated for DC current and I have forgotten what your motor current is? There is a difference between switching AC or DC current even into a purely resistive load which a motor is not. Watch this video:

https://www.youtube.com/watch?v=Zez2r1RPpWY&feature=youtu.be

Toggle Switch 125V 20A Momentary Automatic Reset Switches 250V 15A DPDT ON -Off- ON 6 Terminal pin Rocker Switch with Metal Waterproof Cap (Pack of 2 pcs)

Nothing about the switch having a DC rating? Now again, what was the DC current load?

Ron

Paul__B:

Not the best way to wire the switch - if one pole gets a welded contact and sticks in place, the other pole switching shorts the power supply. Best to wire just like the two separate SPDT switches (like post #8)

Paul__B: "Flyback" diodes are not commonly used with switches as the switches can generally handle small voltage surges without damage. If this is indeed at 5 V, this should be quite negligible.

And in fact motors - particularly permanent magnet field motors - do not generate switching "kickback" impulses of any significant degree though it is considered good practice to provide such protection when using semiconductors to control them. :grinning:

Its not just good practice, its essential. Here's the voltage from a smallish motor (cordless screwdriver I think, about 2 inches long), with 12V from a (fairly flat) 10xAA NiMH pack brushed across the terminals. Note the vertical scale is 50V/div, and the 'scope has measured a 264V pulse. That's bad news, even though its very short. (For instance it can degrade insulation in the windings, and cause severe EMI to surrouding circuitry).

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Thanks for the replys. That is so interesting ron. Does that mean I cant use these switches? I decided to go with these instead because they are smaller: https://www.amazon.com/gp/product/B07XHQ8WB4/ref=crt_ewc_img_srh_1?ie=UTF8&psc=1&smid=A135XTKU400AZ0

They still say ac though…

The max current the motor can draw is 1.5 amps.

If I cant do these switches because of the different switching, could I know a little more on how to do the relay stuff? What would make the relays a better option? Thanks!

When I was posting this I saw Mark made a new reply. Thats crazy! I didnt think it would be that bad… Would that mean even if I did use a dpdt switch I would still need diodes?

Ya, I am leaning away from using dpdt switches. In that case, does anyone know a good h bridge circuit using 2 momentary push buttons that wont short circuit the power supply if they are both pushed?

"Ya, I am leaning away from using dpdt switches. In that case, does anyone know a good h bridge circuit using 2 momentary push buttons that wont short circuit the power supply if they are both pushed?"

Maybe wire them like the SPDT relays? I think that is the way most two button motor control switches work.

Ahh, yes. So how would that work? If I am using 5v do you know any good relays? I am unsure about how the circuit works. How does that control the motor both ways? Thanks for the suggestion!

Going back to the dpdt switches, I dont think using such low voltage and current would make an arc. Also, I heard a "snubber" can help, but I dont know much about that.

FYI

See D3 and F3:

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Rapid80:
Going back to the dpdt switches, I dont think using such low voltage and current would make an arc. Also, I heard a “snubber” can help, but I dont know much about that.

Then have at it. As to a “snubber”? You have flyback diodes in your design, you have no need for a snubber.

Ron

Dang that looks intimidating. What does that all mean? What does all that do?

Just saw Rons reply as I was typing this. When you say "Then have at it", are you saying that as like "Then find out itll go wrong" or... what...

Then as you say, fly back diodes should be enough. Thanks!