3 Solenoid valves

Hi,

it it OK to connect 3 12V solenoid valves to a single power supply? The power supply is rated 1 amp.
Normally the solenoids are producing water drops in sequence and are active for 50-100ms only.
I will want to have then all open at the same time later though.

The diagram for a single solenoid is from http://bildr.org/2011/03/high-power-control-with-arduino-and-tip120/

Without stating the coil current requirements for the solenoid type it's hard to answer your question definitively, but assuming the sum of all coil currents doesn't exceed the supply current rating, all should be OK.

The solenoids are rated at 250mA. So should be OK with 1 A supply.

Thanks for the confirmation.

Power supply seems ok. Just add at least 1000 mfd cap which will take care of inrush current of solenoids.

Solenoids do not have inruschcurrent, when you connect them they do not draw current at all. Then the current start raising, it is an induktor. Motors have start/inrush current.

Pelle

@ Pelle,

Your knowledge about solenoid seems awesome ! :frowning: From where did you get this wonderful information ? - "Solenoids do not have inruschcurrent, when you connect them they do not draw current at all." !
May I request you to google for "Solenoid" ?

Solenoids are indeed inductive, so the current builds up in them slowly. However, "slowly" is a relative term. If the power supply is distant from the rest of the system, then adding a 1000uF capacitor connected between the TIP121 emitters and the solenoid +ve terminals (as suggested by Pelle iknowvator) is a good idea.

One problem you may have is that the current in the solenoids decays too slowly because of the flyback diodes, and they take too long to release. You can speed up the current decay by connecting resistors in series with the flyback diodes. If using 12V 250mA solenoids with TIP121s, do not exceed 220 ohms series resistance.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indtra.html

And when the plunger moves you have the the electro motoric force, ehhh don't know whats in english.

Pelle

dc42:
Solenoids are indeed inductive, so the current builds up in them slowly. However, "slowly" is a relative term. If the power supply is distant from the rest of the system, then adding a 1000uF capacitor connected between the TIP121 emitters and the solenoid +ve terminals (as suggested by Pelle) is a good idea.

One problem you may have is that the current in the solenoids decays too slowly because of the flyback diodes, and they take too long to release. You can speed up the current decay by connecting resistors in series with the flyback diodes. If using 12V 250mA solenoids with TIP121s, do not exceed 220 ohms series resistance.

You can also use an VDR resistor for even faster reelese.

Pelle

" then adding a 1000uF capacitor connected between the TIP121 emitters and the solenoid +ve terminals (as suggested by Pelle ??? ) is a good idea."

iknowvator:
" then adding a 1000uF capacitor connected between the TIP121 emitters and the solenoid +ve terminals (as suggested by Pelle ??? ) is a good idea."

I have NOT suggested an 1000 uF capacitor, look in post #3 it is iknowvator who have suggested that.

I think it's idiotic, gives high inrush current for the power supply.
I suggest an small capacitor 0.1 to 10 µF for bypassing.

Pelle

iknowvator:
" then adding a 1000uF capacitor connected between the TIP121 emitters and the solenoid +ve terminals (as suggested by Pelle ??? ) is a good idea."

My mistake - I've corrected that post now.

What are corrected?

Pelle

Pelleplutt:
What are corrected?

Pelle

My reply #6, in which I incorrectly attributed the suggestion to add a 1000uF capacitor to you.

thanks for the replies.

So, add a small capacitor 0.1 to 10 µF connected between the TIP121 emitters and the solenoid +ve for bypassing (not 1000uF ) and add a resistor (max 220 ohms) in series with the diode (preferable a vdr if release speed is important).

Is this correct?

thanks

VDR = Voltage Dependent Resistor

Yes start so, It is also important to make the wiring in right way too.
It's not so easy to write how to do, take a picture and we say good or poor

Pelle

Pelleplutt:
VDR = Voltage Dependent Resistor

Yes start so, It is also important to make the wiring in right way too.
It's not so easy to write how to do, take a picture and we say good or poor

Pelle

Is it 3 capacitors, one for each TIP121, or 1 capacitor shared by all three?

Assuming the components (with the possible exception of the solenoids and the Arduino) are all quite close together, one capacitor will do.

PS - you've labelled the resistors as 220K, but 220 ohms is the maximum value to use.

If you want fast operating of solenoids, using 1000 mfd is very useful as it will provide you backup for inrush current and prevent the noise. Well this you will understand only when you make a practical circuit. Using small cap will not be able to provide instant current requirement and this will create noise while making it On or OFF. Try it to better understand the behavior of operating solenoids.

Perhaps you have inrush current in india, but rest of the world don't.
Solenoid are induktive.

Electrical motors have Inrush current or as we say, starting current.
transformers, especially toroidal transformers have inrush current when operating on AC.
Solenoid operated with AC have higher current until the anchor is drawn but no inrush current. For example contactors.

Pelle