Solenoid Valve. Fluid Control Application.

[JeeShen Lee]

Hi Everyone, I'm new to the forum.  :)

I need help on Solenoid Valve.

I'm having a solenoid valve rating at 12Vdc, 3W but I couldn't find any spec from the datasheet on the turn on voltage (Von) and minimum turn on current (Ion). What value of resistor I should use in this case to limit my turn on current?

Please advice. Thanks in advance.

Regards,
JeeShen Lee

[KMoffett]

Do you have a make/model and link to the datasheet?  Are you thinking of trying to use an On/Off solenoid valve in a proportioning mode?

Ken

[JeeShen Lee]

Hello Ken,

Thanks for replying, I was waiting for someone who is willing to help in the past few days.

Here is the link to the datasheet.
http://malaysia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0342023

The part I received have 3W engrave on it (instead of the stated "Power consumption: 4W" on the page).

Sorry, I don't understand exactly what you meant by operating it at "proportioning mode". Do you mean Pulse Modulation Mode (PWM)? FYI, I plan to use it to control the flow of water (on/off the water tap), I'm not interested at the flow rate at the moment.

Btw, I'm planning to switch the solenoid using relay, do you have any other suggestions (like driving it using high amp optoisolator)?

Thanks in advance.

Regards,
JeeShen Lee

[KMoffett]

The linked data sheet said the power draw is 6VA (6 watts).  But, I would go with what is marked on the the valve, 3watts.

Yes, by proportioning I meant PWM driven to achieve a variable flow.  Some people want to do this with ordinary valves...and it doesn't work.

The coil current on your valve will be 3w/12V = 0.25A.  Almost any small relay with contacts rated at 1A DC should work.  I don't think that "optoisolators" are usually rated for that high a current.  I think you would be looking for "DC solid state relays".

To back up a bit...what are you trying to do in this project?  What are you using to control the relay that controls the valve?.  Do you need isolation between the valve and the controlling device? ???? :)

Ken

[JeeShen Lee]

Hello Ken,

Thanks for illustrating the method to obtain the nominal operating current. I found a document which supports your calculation. You may find the document below (provided by the manufacturer, HydraElectric).
http://www.hydralectric.com/docs/solenoid_valves_003.pdf
Note: Green, 12Vdc Servo Assisted 2/2 Way Solenoid Valve.

FYI, I'm trying to control my house's water tap with microcontroller (Microchip PIC, 5Vdc). I haven't started my drawing yet, but I will most likely go for either one of these implementations:
1. Microcontroller>Darlington Array>Relay>Valve  or
2. Microcontroller>Optoisolator>Relay>Valve
3. Microcontroller>BJT>Valve
4. Microcontroller>Darlington>Valve [suggested by Ken. Edited on 02.Aug]
5. Microcontroller>MOSFET>Valve [suggested by Ken. Edited on 02.Aug]


I will go for the cheapest option.  ;D

Thanks for your help, I appreciate it.

Regards,
JeeShen Lee
IM: [email protected]
 

[KMoffett]

Or:
4. Microcontroller>Darlington>Valve
5. Microcontroller>MOSFET>Valve

If you don't need to isolate the valve's power supply's ground form the microcontroller's power supply ground, then #3, #4. or #5 will be the cheapest and easiest. #3 and #4 will require a base resistor, #5 won't.

Ken

[JeeShen Lee]

Hello Ken,

Speaking of isolating the ground plane, what are the guidelines/reasonings for choosing one implementation (Isolate the ground plane) over another (Join the ground plane)?

As far as I understand, isolating the ground plane will help isolating the noise in high voltage side (normally, the load side) from the low voltage side (normally, the logic side). Any other idea?  ;)

Thanks.

Regards,
JeeShen Lee

[KMoffett]

Isolating the the digital power ground from the load power ground, is as you say, to keep the large load currents from traveling through digital ground traces. These currents can cause voltage drops along traces that the digital circuits misinterpret as signals.  If you arr not using isolation interfaces, opto-isolators or relays, you want to connect the load ground to the control ground a one, and only one, point.

Also when interfacing low voltage DC control circuits with AC line devices isolation helps protect the control circuit from the high voltages and voltage differences between control grounds and AC Neutral ground.

Ken