Driving 3V Solenoid with 6V

[elefurtronik]

Hello,
I would like to drive a 3V Solenoid Valve with 6V battery. I use MOSFET to control the SV. Is it possible to drive how I have shown in the schematic.

3V Solenoid pulls 270mA current as written in the datasheet.

[Sherlock Holmes]

Hello,
I would like to drive a 3V Solenoid Valve with 6V battery. I use MOSFET to control the SV. Is it possible to drive how I have shown in the schematic.

3V Solenoid pulls 270mA current as written in the datasheet.

If your source can deliver 6v at 270mA then the resistor is fine, the 0.8W power dissipated by the resistor is wasted of course, but if that's not a concern then this works.

You could put an LED into the circuit too, that way you're using some of the power, a visual indicator that the solenoid is ON might be useful and the power used would have been wasted anyway. Obviously you'd need to recalculate the value if the resistor to achieve the desired forward voltage for the diode.

[pcprogrammer]

It will work, but you need a 1W resistor at minimum to keep it whole. 3V * 270mA = 0.81W

You might consider using pulse width modulation and not use the resitor. Drive the solenoid with 50% or less at 25KHz or so and see what it does. The pulse current will be higher then the 270mA, so your MOSFET needs to be up for it.

Don't forget the diode across the solenoid to avoid voltage spikes.

[elefurtronik]

It will work, but you need a 1W resistor at minimum to keep it whole. 3V * 270mA = 0.81W

You might consider using pulse width modulation and not use the resitor. Drive the solenoid with 50% or less at 25KHz or so and see what it does. The pulse current will be higher then the 270mA, so your MOSFET needs to be up for it.

Don't forget the diode across the solenoid to avoid voltage spikes.

I think 1W will be too big. I don't want to use through hole components. But SV will not work stable with PWm I think.

[Terry Bites]

I'd use a 2W 12 Ohm, they are esaier to find and cheaper as a rule.  Stand the reistor off the PCB (if you use one). Let it breathe.
If you value your mosfet, put an 1N914 in parallel with the coil.

A 1W resistor running continuously at 80% power will get hot. About 80'C hot!

Rule of thumb. Percentage of rating is roughly the same as the temperature it will reach.
You don't want to go above 70'C if you can avoid it

[BillyO]

I think 1W will be too big. I don't want to use through hole components. But SV will not work stable with PWm I think.

You could put four 1 amp diodes is series.

You could use four 47ohm 1/4 watt SMT resistors in parallel.

But PWM will work fine with a solenoid valve and is probably you best bet as there will be little or no loss of power.

[DavidAlfa]

Drive the solenoid with 50% or less at 25KHz or so and see what it does.

Power increases by 4 as voltage doubles, should be 25%!

3v/270mA =  11ohms , 0.82W
6v²/11 = 3.3W
50% of 3.3W: 1.63W
25%:  0.82W 

[Zero999]

Drive the solenoid with 50% or less at 25KHz or so and see what it does.

Power increases by 4 as voltage doubles, should be 25%!

3v/270mA =  11ohms , 0.82W
6v²/11 = 3.3W
50% of 3.3W: 1.63W
25%:  0.82W 

That's true of a resistive load, but don't forget the solenoid is partly inductive and only the resistive element dissipates power. If you apply 50% PWM at double the voltage, it won't dissipate double the power, because the inductive element will limit the current to a lower value. It of course depends on the frequency. Not much current will flow at 25kHz.

If PWM is an option, then turn it into a current sink, with a delay on the feedback, to make it oscillate.

[elefurtronik]

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

[Wallace Gasiewicz]

Use a 3 volt Zener.
Put it in series with the solenoid.
It will hold back the other 3 volts
Make sure the zener can handle the current,

[Doctorandus_P]

I'm all for PWM'ming. The solenoid is likely quite inductive and it may work well, but there is no guarantee. It may get hot because of induced eddy currents. Adding an extra inductor to keep the current more stable will probably help then.
--------------------------
Instead of a big 1W power resistor, you can also use a few smaller resistors in series.

[Sherlock Holmes]

I don't know if PWM is really overkill here. This is a simple DC device and needs just a simple solution, there are no "timing" requirements mentioned. The solenoid is an inductor but also might be under a physical load which will influence its DC and transient characteristics so a PWM seems like over engineering.

A simple buck converter is the next best thing if a resistor really is not viable.

[DavidAlfa]

I wouldn't drive it with 25KHz neither, mainly for the said edd currents, they're usually solid iron (not ferrite), won't be happy at KHz range, but anyways it would be overkill.
100-200Hz should be good enough, most cars drive their solenoids at similar frequencies.
The back-EMF diode will also make it turn off slower (The current keeps circulating for a small time)

[basinstreetdesign]

Use a 3 volt Zener.
Put it in series with the solenoid.
It will hold back the other 3 volts
Make sure the zener can handle the current,

Yes, I vote for this.  This will have more consistent and predictable voltage drop than an LED or several diodes in series.  And certainly not 3 x 1N4148 in series.  They can't handle the 270 mA.  The zener should be rated for 1 Watt or more (preferably more) to keep it cool.

[james_s]

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

Why do you feel like it won't work? Have you tried it? Does the datasheet for the solenoid say it can't be driven with PWM?

You could include a buck regulator on the board to supply 3V for the solenoid, they can be quite small and highly efficient.

[elefurtronik]

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

Why do you feel like it won't work? Have you tried it? Does the datasheet for the solenoid say it can't be driven with PWM?

You could include a buck regulator on the board to supply 3V for the solenoid, they can be quite small and highly efficient.

I tried before with my 6V solenoid valve and it didn't work with PWM. Now I am going to use the same solenoid's 3V one. I will check that small buck regulator. When I use a buck regulator, what are the losses?

Use a 3 volt Zener.
Put it in series with the solenoid.
It will hold back the other 3 volts
Make sure the zener can handle the current,

Yes, I vote for this.  This will have more consistent and predictable voltage drop than an LED or several diodes in series.  And certainly not 3 x 1N4148 in series.  They can't handle the 270 mA.  The zener should be rated for 1 Watt or more (preferably more) to keep it cool.

Can I find 1W SMD Zener that you know?

[Zero999]

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

Do you know the inductance of the coil? Please post the data sheet.

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

Why do you feel like it won't work? Have you tried it? Does the datasheet for the solenoid say it can't be driven with PWM?

You could include a buck regulator on the board to supply 3V for the solenoid, they can be quite small and highly efficient.

I tried before with my 6V solenoid valve and it didn't work with PWM. Now I am going to use the same solenoid's 3V one. I will check that small buck regulator. When I use a buck regulator, what are the losses?

PWM should work. If it didn't, it was most likely because you used the wrong frequency, or no fly-back diode.

The losses depend on the buck regulator itself.

[elefurtronik]

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

Do you know the inductance of the coil? Please post the data sheet.

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

Why do you feel like it won't work? Have you tried it? Does the datasheet for the solenoid say it can't be driven with PWM?

You could include a buck regulator on the board to supply 3V for the solenoid, they can be quite small and highly efficient.

I tried before with my 6V solenoid valve and it didn't work with PWM. Now I am going to use the same solenoid's 3V one. I will check that small buck regulator. When I use a buck regulator, what are the losses?

PWM should work. If it didn't, it was most likely because you used the wrong frequency or no fly-back diode.

The losses depend on the buck regulator itself.

Unfortunately, the datasheet doesn't mention the inductance of the coil but I requested it from the supplier. I hope they answer.

I didn't use a flyback diode but isn't the flyback diode for protection of the MOSFET basically? I mean the inductor should discharge and if there is not a flyback diode, we can see very high voltage spikes. I didn't understand why it doesn't work when there is no flyback diode. I used 980Hz :/

[Zero999]

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

Do you know the inductance of the coil? Please post the data sheet.

I will pot the circuit. I think 1W or 2W resistors will be big and also heat issue will occur. Solenoid‘s max working voltage is 4V. Maybe I can also adjust to 4 volt. I am still not sure how to control SV with PWM. I feel it wont work with PWM.

Why do you feel like it won't work? Have you tried it? Does the datasheet for the solenoid say it can't be driven with PWM?

You could include a buck regulator on the board to supply 3V for the solenoid, they can be quite small and highly efficient.

I tried before with my 6V solenoid valve and it didn't work with PWM. Now I am going to use the same solenoid's 3V one. I will check that small buck regulator. When I use a buck regulator, what are the losses?

PWM should work. If it didn't, it was most likely because you used the wrong frequency or no fly-back diode.

The losses depend on the buck regulator itself.

Unfortunately, the datasheet doesn't mention the inductance of the coil but I requested it from the supplier. I hope they answer.

I didn't use a flyback diode but isn't the flyback diode for protection of the MOSFET basically? I mean the inductor should discharge and if there is not a flyback diode, we can see very high voltage spikes. I didn't understand why it doesn't work when there is no flyback diode. I used 980Hz :/

No, the flyback keeps the current flowing through the solenoid during the off time. A PWM circuit will not work without a flyback, or perhaps freewheeling diode, is a more appropriate term.

I had a play with LTSpice. It's just a current regulator, with an RC network in the feedback to ensure oscillation. I may require a bit of tweaking, but it should work.

[james_s]

I tried before with my 6V solenoid valve and it didn't work with PWM. Now I am going to use the same solenoid's 3V one. I will check that small buck regulator. When I use a buck regulator, what are the losses?

A buck regulator is typically anywhere from 70-90% efficient. Even the worst case will be more than the 50% efficiency you're going to get with any linear method of dropping the voltage.

[pcprogrammer]

I wouldn't drive it with 25KHz neither, mainly for the said edd currents, they're usually solid iron (not ferrite), won't be happy at KHz range, but anyways it would be overkill.
100-200Hz should be good enough, most cars drive their solenoids at similar frequencies.
The back-EMF diode will also make it turn off slower (The current keeps circulating for a small time)

Forgot about those eddy currents and was mainly thinking about sound. On low frequencies you can most likely hear it beeping.

But add a filter to the PWM output and you basically have a buck converter 

A buck converter Is indeed a good solution, and look for a buck converter IC with an enable pin to turn the solenoid on and off. Some even provide soft start to reduce the currents at start up.

[DavidAlfa]

The protection diode itself will do this, at least for some time when it goes off, so the current won't be a noisy square signal, but triangular.

[Terry Bites]

If you use any linear soltion, it will have to boil off the I*Vdrop watts.

[Wallace Gasiewicz]

Here is a one watt 3.3 V  SMD Zener:

https://www.ebay.com/itm/284996435482?hash=item425b1c7e1a:g:4bAAAOSwTcdiBt01&amdata=enc%3AAQAHAAAAoNHFyGuZc6wusIvQpSTlTa1MIa8lB6iRMlN0hJtXW8UlURJdyKYdbnY4hvIWRtbTeqK38iKPCBsuDePKr0kuETV7T3ej6oG8vme33ldcSwQM1N%2BKnX62ZumvZMcWsn%2FkQldDYtzkXfpheK7XIavb1U7fbnGbU6%2FYbFJsKUmvlMlX913QeTja%2Br9Vfrtxob2IbPsqJ4osrkjUJSDunMtrvVI%3D%7Ctkp%3ABk9SR_yY_oW2YQ

But I do not know where your solenoid is., maybe it would be easy to put a regular thu hole axial zener in the wire feeding it and cover the zener with shrink tube.

[elefurtronik]

I think I can also put it directly onto the SV with a shrink tube. Then I will just connect the Zener diode's anode to GND and the cathode to the other lead of the SV.
But I think this Zener diode increases my power consumption compared without using it.