I’m looking to build a circuit to control a 3V latching solenoid valve. This type of valve will open when a 30ms pulse passes through the solenoid and will remain open without consuming any energy until an oppositely charged 30ms pulse passes through the solenoid.

To further explain how it operates, the solenoid has two wires, red and black. Connecting the positive pole of 2 AA batteries to the red wire and the negative to the black wire will open the valve. On the other hand, connecting the negative to the red wire and positive to the black wire will close the valve.

I want to control the valve using a push button. As long as I keep the button pressed, the solenoid will remain open. When I let go of the button, the solenoid will close.

Also need the circuit to consume the least amount of energy as it will only operate with 2 AA batteries.

This could be activated with either: 1) a 2 pin push button (normally open) or 2) a 3 pin push button (1 NO + 1 NC)… whichever makes it easier to accomplish what is needed.

Thanks for your help!

 

Depending on the quality and construction of the switch, its contact bounce period might exceed 30 ms, meaning that the switch is still generating signal edges after the first pulse has ended. Can the latch and release pulses be longer than 30 ms? 100 ms might make things easier. We'll get to that later.

To recap, let's call the latch pulse "positive" and the release pulse "negative".

1. Before the first button press: 0 V across the coil.

2. Pressing the button produces one 30 ms positive pulse across the coil.

3. Holding the button in the pressed state puts 0 V across the coil.

4. Releasing the button produces one 30 ms negative pulse across the coil.

5. Leaving the button released is condition #1.

Yes / No - ?

ak

 

I’m looking to build a circuit to control a 3V latching solenoid valve. This type of valve will open when a 30ms pulse passes through the solenoid and will remain open without consuming any energy until an oppositely charged 30ms pulse passes through the solenoid.

To further explain how it operates, the solenoid has two wires, red and black. Connecting the positive pole of 2 AA batteries to the red wire and the negative to the black wire will open the valve. On the other hand, connecting the negative to the red wire and positive to the black wire will close the valve.

I want to control the valve using a push button. As long as I keep the button pressed, the solenoid will remain open. When I let go of the button, the solenoid will close.

Also need the circuit to consume the least amount of energy as it will only operate with 2 AA batteries.

This could be activated with either: 1) a 2 pin push button (normally open) or 2) a 3 pin push button (1 NO + 1 NC)… whichever makes it easier to accomplish what is needed.

Thanks for your help!

Provide a part number for the solenoid so we can determine operating requirements.

 

You can achieve this function with a button wired to deliver either positive or negative, and a series capacitor so that only a pulse is sent.
No need for part numbers or other details.
Using a cap to send just a short burst can do it, but you may need to experiment with the capacitance. But the button may be hard to get.

 

It can likely be done with w SPDT (3-pin) push button and a large capacitor, as MB2 suggested (example circuit below):
We would need to know the resistance and inductance of the solenoid to determine the capacitor proper value, or you can determine it experimentally.

Can you measure the resistance of the coil?

 

Depending on the quality and construction of the switch, its contact bounce period might exceed 30 ms, meaning that the switch is still generating signal edges after the first pulse has ended. Can the latch and release pulses be longer than 30 ms? 100 ms might make things easier. We'll get to that later.

To recap, let's call the latch pulse "positive" and the release pulse "negative".

1. Before the first button press: 0 V across the coil.

2. Pressing the button produces one 30 ms positive pulse across the coil.

3. Holding the button in the pressed state puts 0 V across the coil.

4. Releasing the button produces one 30 ms negative pulse across the coil.

5. Leaving the button released is condition #1.

Yes / No - ?

ak

Hi Analogkid, thanks for your quick reply. Your understanding is spot on.
Regarding the latch and release pulse being longer than 30ms will work. I presume that a longer pulse also means more energy being consumed?

 

Provide a part number for the solenoid so we can determine operating requirements.

Hi eetech00, the solenoid valve I have on hand is https://www.aliexpress.com/item/4001183280553.html
But if you recommend another valve, am willing to purchase a new one.

 

You can achieve this function with a button wired to deliver either positive or negative, and a series capacitor so that only a pulse is sent.
No need for part numbers or other details.
Using a cap to send just a short burst can do it, but you may need to experiment with the capacitance. But the button may be hard to get.

Thanks MisterBill2, Ill look for such a switch. If you know where i could buy one online, let me know!

 

It can likely be done with w SPDT (3-pin) push button and a large capacitor, as MB2 suggested (example circuit below):
We would need to know the resistance and inductance of the solenoid to determine the capacitor proper value, or you can determine it experimentally.

View attachment 261701

MisterBill2 and crutschow beat me to it.

 

I presume that a longer pulse also means more energy being consumed?

Yes. Now that we have data, that is a hungry little puppy.

Quick math suggests that a 4,700 uF to 10,000 uF electrolytic capacitor will work in the simple switch circuits above. Good news - simple circuit, simple wiring. Bad news - cap size probably is larger than you expected. Still, an easy approach to test.

ak

 

Can you measure the resistance of the coil?

The resistance of the coil is 6.8Ω

 

Yes. Now that we have data, that is a hungry little puppy.

Quick math suggests that a 4,700 uF to 10,000 uF electrolytic capacitor will work in the simple switch circuits above. Good news - simple circuit, simple wiring. Bad news - cap size probably is larger than you expected. Still, an easy approach to test.

ak

Thanks everyone!
Tomorrow I´ll get the capacitors suggested by AnalogKid and try them with the circuit proposed by crutschow and report back.
Best!

 

The resistance of the coil is 6.8Ω

Yes, I missed that in the spec.

Using 3V requires a very large capacitor as AK noted.
If you can add batteries to provide 4.5V or 6V, the capacitor size can be significantly reduced.
The battery life will still be long, since the pulse will be short.

 

Hi everyone, I built the circuit suggested with the 4,700 uF capacitor and it works perfectly! Thanks everyone!

A variation to my initial idea is to control two identical solenoid valves with the same push button. When the button is pushed, both valves close and when the button is released both open. I dont have space constraints, so no issue with having 2 capacitors.
Help with how to modify the circuit are appreciated!

Thanks!

 

If the valves can work in series then you will only need a higher battery voltage. At east it seems that would be all it will take.

 

That is the question. Are you stuck with a max source of 3 V, or can you go up to 6 V?

ak

 

Not my ideal, but can go with 6 V.

 

Not my ideal, but can go with 6 V.

It is a trade-off, capacitor size and wiring complexity vs. battery size.

Batteries recover a bit after a period of high-current discharge. Based on a battery's amp-hour rating, if you expect to get x hours of continuous operation at a certain high output current, you might get a total of 1.25x or 1.5x total hours of operation if the same output current is produced in short pulses far apart in time.

1. Do you have the A-h or mA-h rating for the battery you are using?

2. About how many times per day will the solenoid be actuated?

ak