Polarity changer 9V DC

Using Arduino Project Guidance
1

Hi,

I am dealing with a 9V DC solenoid valve which has a shaft that moves one side if you apply current and to opposite side if you switch the polarity.

But the current shall be timely limited (ca. 500 ms). If the current is always on the valve is getting very hot quickly (drags almost 2 amps).

For my need I have a smart home actuator on 230V AC that can trigger a relay to give a signal.

Q: How to build the arduino to switch polarity, load solonid is 2 amps 9 V (18W)
I probably need some transistors to handle the load.

Thankful for all help.

Sketch:

image
image690×575 105 KB

2

Use a H-bridge.

3

Use two relays, one to swap the poles +/- and the second to switch the power on/off.

The Arduino simply needs to identify the input state, set the polarity, and pulse the power relay for xxxmS.

You could use an H- bridge if you want to skip the relays, they’ll need a transistor each anyway - to handle the relay voltage & current.

4

I would use an H-bridge motor driver to reverse polarity, but you only have 1 input. How does the MCU know which polarity to output?
https://www.pololu.com/product/2997

5

Umm, no! :astonished:

That involves using a DPDT relay which is less durable for the same size and actually complicates matters quite unnecessarily.

Two SPDT relays are much more practical, arguably safer - one for forward and the other for reverse. :+1:

6

Hi

This is so nice, answer in short time, thanks for help.

My next question is to help a newbie to make the wire layout (like my sketch) .
Witch pins:
From ESP8266 goes to the "two SPDT's"
and
Which pins goes to my solenoid.

Maybe there must be some resistors in the circuit also..

Thanks up front!

M

7

Don't forget, with 2 SPDTs, you will need 4 kickback suppression diodes to protect the relay contacts and minimize EMI. They are included on a motor driver.

2017-07-31_19-22-56
2017-07-31_19-22-561023×536 67.9 KB

8

A bridge is most convenient. :sunglasses:

Only comment on that diagram is that it is recommended that the Normally Closed relay contacts be those connecting to the negative or "ground" of the supply. :grin:

9

Solenoids aren't 'constant duty' devices typically.

10

Agreed * 2 (I didn't make that diagram).

11

Even less so if AC solenoids which do not fully pull in and close the magnetic circuit, so overheating and making a bad smell.

Memories of my washing machine. :astonished:

12

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