How to maintain a dc Voltage(for two electrovalves command)

Thread Starter

badrove

Joined Mar 18, 2008
12
Hello,

i have two electrovalves placed in serie. the supply of each electrovalve is about 2VDC but to maintain this electrovalve opened 0.5 VDC is enough.

i don't now how to do this.
i Have 5Vdc to command each one separately
(the scheme has to be based on using transistors...)
Best regards,
 

Caveman

Joined Apr 15, 2008
471
badrove,
This is not quite enough info. I'm guessing that you mean electronic water valves?
You need to know current requirements as well as exactly what you are doing. Do you just want them always to be open? If not, what is the control. If so, just get a pipe.:)
 

beenthere

Joined Apr 20, 2004
15,808
We have to know more about the valves in order to answer your question. What is each valve's electrical rating - what voltage and current to pull in, what voltage to hold open, what voltage to drop out?
 

SgtWookie

Joined Jul 17, 2007
22,201
It is not necessary to send E-mail to forum members about this.

You will receive much more rapid response if you simply post on the forum.

As you did not include any additional information in the E-mail you sent to me other than what is already in your post, I can't really help you with it either.

More information from you is necessary in order to suggest a viable solution. Until then, any guesses we might make probably would not help you very much.
 

Thread Starter

badrove

Joined Mar 18, 2008
12
Excuse me sgtwookie to mail you , i 've got wet.
about my problem, i want to command the two electrovalves separately via a microcontroller. i suppose that this micocontroller generate a 5vdc but to command each valve i need just 2Vdc at the begining and a 0.5v to maintain each valve open.
 

SgtWookie

Joined Jul 17, 2007
22,201
I want to command the two electrovalves separately via a microcontroller. I suppose that this micocontroller generate a 5vdc but to command each valve i need just 2Vdc at the begining and a 0.5v to maintain each valve open.
You still have not told us what the current requirements of the valves are. What is their rating? It should be something like: 500mA at 5V, something like that. Or perhaps it is rated in Watts, or VoltAmps (VA)

What is the manufacturer and part number of these valves? Do you have a datasheet for them?

And how much current do you have available to control these valves?

The microcontroller does not generate a 5v output, but it can source or sink a small amount of current at (perhaps) 5V or ground.

What is the part number of the microcontroller that you are using?
 

Thread Starter

badrove

Joined Mar 18, 2008
12
hello,

all what i know about valves is :

Mark by ink:
- Part Number : 7401-6501
- Openin voltage < 1.4V dc (pressure: 60 mBar)
- holding voltage < 0.4V dc
- coil 40 ohm.
valve for natural gaz and LPG. Ref : AM-EB 62DP0066.

About the microcontroller i use a "R5F21264SNFP" LQFP32-7x7-0.8 Renesas.
 

Caveman

Joined Apr 15, 2008
471
So that means you need 1.4Vdc/40Ohms = 35mA to turn the device on. Probably not going to work with any standard micro output.

How about something like the included circuit.
Note that a diode should probably also be used around the coil.

This is not the most power efficient because you don't drop the voltage after switching, but it is simple.

There is a way to do that, but you need to know how long to hold it before dropping which depends on the valve.
 

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SgtWookie

Joined Jul 17, 2007
22,201
A variation on the theme... ;)

This circuit is more complex, but it initially provides a higher voltage to switch the valve quickly, and then a lower holding current.

The output from the microcontroller is high for the valve to be off, and low for the valve to be on. R3 ensures that the base of Q1 is pulled to 5V to keep the valve turned off if there is no input, or if the output of your uC is open collector. R4 limits the current through the base of Q1.

When Q1 is off, C1 charges to 5V via R1 and R2 (see the blue "A" trace on the simulated O-scope display)
When Q1 is turned on (by the yellow trace "B"), C1 discharges via R2 through Q1, resulting in a higher initial voltage (see the green trace "C"). R1 continues to supply current when C1 is discharged.

The transistor will drop about 0.6v across itself when conducting. The remaining 4.4v is dropped across R1 and the coil, L1. R99 does not actually exist; it merely represents the resistance of the coil. D1 is present to take care of the reverse EMF spike that will occur when the coil is de-energized.

Note that it will take around 200mS to put a reasonable charge on C1. Attempting to rapidly open and close the switch won't work.
 

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