# Powering a Solenoid Valve with batteries

#### TXDJ

Joined Jul 11, 2020
5
Hi everyone,
Is it possible to power a solenoid valve with AA, AAA or 9v batteries for an extended period of time?
I can make it work with 8 AA batteries, but after a couple of hours they run out of power and the valve stops working.
Worth mentioning that my project requires the solenoid valve to get energized at random intervals, for 1 or 2 seconds each time.
I would like to maximize how long the batteries will last and minimize the number of batteries needed.
The solenoid valve I am considering is https://www.bc-robotics.com/shop/plastic-water-solenoid-valve-12v-12-nominal/ but am happy to use a different valve if recommended.

Joined Feb 20, 2016
3,591
One way you can extend the battery life is to operate the valve at full battery volts, then reduce the power by using PWM to a lower current. The valve will hold in at less current that it takes to operate.
Make sure you have a reverse diode across the coil.
Some experimenting will be needed to set the PWM holding current. Reduce the PWM until it drops out then operate it again and make sure you have the holding current a bit higher than the dropout.

#### GetDeviceInfo

Joined Jun 7, 2009
1,733
I would look at a motorized valve. Power to open, power to close. Throttling might be a bonus, for both flow and power.

#### ronsimpson

Joined Oct 7, 2019
816
The motorized valve saves power if you want it left on for long times. It will not save power if the valve is off most of the time. I have seen them used with batteries.

#### MrChips

Joined Oct 2, 2009
21,650
Do the simple calculations.
Find out how much current (in mA or A) the solenoid takes when ON.
Determine how many hours the solenoid will be ON over a day/week/month/year.
mA x number of hours = mAh
or
A x number of hours = Ah

Match this with the mAh (or Ah) rating of the battery and this will tell you how many days/weeks/moths/years the battery will last.

#### DNA Robotics

Joined Jun 13, 2014
571
Another version of what Dendad said. The resistor charges the capacitor to 12 volts. When you turn the switch on, the cap dumps its charge thru the solenoid, operating it. The resistor is sized to keep the solenoid engaged, then it recharges the cap when the switch is opened.

#### GetDeviceInfo

Joined Jun 7, 2009
1,733

#### crutschow

Joined Mar 14, 2008
25,256
One way you can extend the battery life is to operate the valve at full battery volts, then reduce the power by using PWM to a lower current. The valve will hold in at less current that it takes to operate.
Below is the LTspice simulation of a circuit to perform that operation using a 555 timer.

The power to the circuit is controlled by M3 and Q1, so that the circuit doesn't draw any current when off.
(If you already have a switch to control the power than you can eliminate M3 and Q1.)
At the start (Vin goes high, red trace ), M2 inhibits the 555 to initially apply full power to the solenoid and pull it in.
After that, the 555 starts generating PWM pulses (yellow trace) to efficiently lower the solenoid current to its holding value (blue trace).

The time for the solenoid pull in with no PWM is determined by the time-constant value of R2C3, and these values can be adjusted to give the minimum time required to pull in the solenoid.

The hold current is determined by the PWM duty-cycle, which can be adjusted by pot U2 to slightly above the minimum to keep the solenoid held in.

This circuit should significantly reduce the power requirements for the solenoid operation.

This circuit effectively does what DNA Robotics' circuit does, but doesn't waste power in the series resistor.
Basically the PWM acts as a lossless resistor to limit the current. so the battery current is less than the solenoid current when the PWM is active, proportional to the PWM duty-cycle.
This can be seen by the difference in the solenoid hold current (blue trace) compared to the power supply current (green trace).

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#### TXDJ

Joined Jul 11, 2020
5

[B]GetDeviceInfo[/B]: if I don't get my current setup to work I will look into the motorized valves and the generator.

[B]crutschow[/B], thank you for the schematics, Ill purchase the components and try it out.
I'm new at this and making this circuit will be a big project for me, but I feel quite comfortable with everything except "The time for the solenoid pull in with no PWM is determined by the time-constant value of R2C3, and these values can be adjusted to give the minimum time required to pull in the solenoid"
Does this mean I should get different values of R2 and C3 to work out the minimum time required to pull in the solenoid? If this is the case, can you please list the combination of R2 and C3 I should try? (hope my question makes sense)

As a next step, and once I get this circuit working, I would like to work out how long the batteries will last with this setup "in the real world". Ultimately the circuit (and the solenoid valve) will be activated manually with a push button, so to simulate how long the batteries will last, I am thinking of a circuit to energize the solenoid valve (lets say) once every minute for 2 seconds and a counter to register how many times the valve actually opens, and let it run until the batteries die.
Any suggestions on how I can do this circuit? If there is a smarter way to work this out, please let me know.

Cheers!

#### crutschow

Joined Mar 14, 2008
25,256
Does this mean I should get different values of R2 and C3 to work out the minimum time required to pull in the solenoid?
Only if you need the absolute minimum to save power.
The value is rated for an operate (open) time of ≤ 0.15 sec and the simulations shows a time of about 0.16 sec, so it should be reasonably close as it.
If it's not opening properly, then you will need to increase the value of R2.
Any suggestions on how I can do this circuit? If there is a smarter way to work this out, please let me know.
Sound like a lot of work just to determine battery life.
Easier just to measure the battery current after adjusting the PWM duty-cycle for the minimum hold current, and use that to calculate the battery life based on the battery's AH rating.

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