Driving 3V Solenoid with 6V  - Page 1
Forum section: electronics / beginners

author: elefurtronik
author_rank: Regular Contributor
timestamp: January 11, 2023, 03:55:03 pm
content: 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.

author: Sherlock Holmes
author_rank: Frequent Contributor
timestamp: January 11, 2023, 04:03:48 pm
content: Quote from: elefurtronik on January 11, 2023, 03:55:03 pmIf 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 usingsomeof 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.

author: pcprogrammer
author_rank: Super Contributor
timestamp: January 11, 2023, 04:22:12 pm
content: It will work, but you need a 1W resistor at minimum to keep it whole. 3V * 270mA = 0.81WYou 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.

author: elefurtronik
author_rank: Regular Contributor
timestamp: January 11, 2023, 04:28:37 pm
content: Quote from: pcprogrammer on January 11, 2023, 04:22:12 pmI 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.

author: Terry Bites
author_rank: Super Contributor
timestamp: January 11, 2023, 04:43:53 pm
content: 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

author: BillyO
author_rank: Super Contributor
timestamp: January 11, 2023, 05:04:47 pm
content: Quote from: elefurtronik on January 11, 2023, 04:28:37 pmYou 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.

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 11, 2023, 06:30:05 pm
content: Quote from: pcprogrammer on January 11, 2023, 04:22:12 pmPower increases by 4 as voltage doubles, should be 25%!3v/270mA = 11ohms , 0.82W6v²/11 = 3.3W50% of 3.3W: 1.63W25%: 0.82W

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2023, 07:42:42 pm
content: Quote from: DavidAlfa on January 11, 2023, 06:30:05 pmThat'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.

author: elefurtronik
author_rank: Regular Contributor
timestamp: January 11, 2023, 07:50:31 pm
content: 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.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 11, 2023, 07:51:40 pm
content: Use a 3 volt Zener.Put it in series with the solenoid.It will hold back the other 3 voltsMake sure the zener can handle the current,

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 11, 2023, 08:15:47 pm
content: 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.

author: Sherlock Holmes
author_rank: Frequent Contributor
timestamp: January 11, 2023, 08:48:34 pm
content: 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 simplebuck converteris the next best thing if a resistor really is not viable.

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 11, 2023, 09:06:03 pm
content: 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)

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: January 11, 2023, 09:16:37 pm
content: Quote from: Wallace Gasiewicz on January 11, 2023, 07:51:40 pmYes, 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.

author: james_s
author_rank: Super Contributor
timestamp: January 11, 2023, 09:23:36 pm
content: Quote from: elefurtronik on January 11, 2023, 07:50:31 pmWhy 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.

author: elefurtronik
author_rank: Regular Contributor
timestamp: January 11, 2023, 10:27:31 pm
content: Quote from: james_s on January 11, 2023, 09:23:36 pmI 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?Quote from: basinstreetdesign on January 11, 2023, 09:16:37 pmCan I find 1W SMD Zener that you know?

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2023, 10:30:04 pm
content: Quote from: elefurtronik on January 11, 2023, 07:50:31 pmDo you know the inductance of the coil? Please post the data sheet.Quote from: elefurtronik on January 11, 2023, 10:27:31 pmPWM 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.

author: elefurtronik
author_rank: Regular Contributor
timestamp: January 11, 2023, 10:40:20 pm
content: Quote from: Zero999 on January 11, 2023, 10:30:04 pmUnfortunately, 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 :/

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2023, 11:10:29 pm
content: Quote from: elefurtronik on January 11, 2023, 10:40:20 pmNo, 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.

author: james_s
author_rank: Super Contributor
timestamp: January 12, 2023, 03:59:01 am
content: Quote from: elefurtronik on January 11, 2023, 10:27:31 pmA 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.

author: pcprogrammer
author_rank: Super Contributor
timestamp: January 12, 2023, 07:01:04 am
content: Quote from: DavidAlfa on January 11, 2023, 09:06:03 pmForgot 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 converterA 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.

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 12, 2023, 09:39:35 am
content: 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.

author: Terry Bites
author_rank: Super Contributor
timestamp: January 12, 2023, 03:48:59 pm
content: If you use any linear soltion, it will have to boil off the I*Vdrop watts.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 14, 2023, 01:08:27 pm
content: 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_oW2YQBut 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.

author: elefurtronik
author_rank: Regular Contributor
timestamp: January 14, 2023, 01:29:00 pm
content: 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.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 14, 2023, 01:34:31 pm
content: Put the Zener in SERIES with the coil. Not to Ground. Neg on zener to 6 V supply and other end to coil.Another suggestion:https://www.mouser.com/c/power/power-management-ics/ldo-voltage-regulators/?output%20voltage=3.3%20VOr big one:https://www.sparkfun.com/products/526More one watt Zener this time 3 Volthttps://www.ebay.com/itm/254955329925?hash=item3b5c859985:g:NqMAAOSw2R9ghRw0&amdata=enc%3AAQAHAAAAoHPHQMNDQ6093PeLHLPd0EJBpJhNLxHGbWZDfaSoM%2BnvOZgyzFbzix1eIOo2lpCRtsZ%2F8eIHccijPWWqAvovjqlYcNosxseedPwH0o4KD8OIR4v%2F2UiQs%2BuXQIjkRwnDt2eaIl6LmAZtJdFVAwkFsVLPQoSuhVzLGqpLa3VwgzrAuwACVwCB8gtlMVjMUSKBs8YEWz5zSMpd6ypf%2BP4LoSk%3D%7Ctkp%3ABk9SR6anuoi2YQ

author: Zero999
author_rank: Super Contributor
timestamp: January 14, 2023, 06:36:53 pm
content: Quote from: Wallace Gasiewicz on January 14, 2023, 01:08:27 pmExcept it won't be able to dissipate 1W, without putting it on a huge copper plane to act as a heat sink and even then it's optimistic.https://www.mouser.co.uk/datasheet/2/427/zm4728a-1767906.pdfQuote from: elefurtronik on January 14, 2023, 01:29:00 pmThat won't work, because the heat won't be able to escape, causing it to get too hot.It doesn't matter whether a resistor, or zener diode, it will still have to dissipate the same amount of heat.

author: elefurtronik
author_rank: Regular Contributor
timestamp: January 14, 2023, 08:36:17 pm
content: I am now thinking to put a small linear voltage regulator to the source of my p-channel MOSFET to attenuate the Vdd voltage. This might work. My system will work maximum 1500ms and I don't think it is going to get too hot.

author: Zero999
author_rank: Super Contributor
timestamp: January 14, 2023, 11:05:02 pm
content: Quote from: elefurtronik on January 14, 2023, 08:36:17 pmIt doesn't matter. It will still have to dissipate the same amount of power as a resistor or zener diode. The fact you're only running this for 1.5 seconds (you should have mentioned that as the start of the thread) which will limit the heating. How often is it going to be operated? Just use a chunky 1W ceramic power resistor, which will be much more reliable than an active circuit such as a linear regulator.

author: james_s
author_rank: Super Contributor
timestamp: January 15, 2023, 12:21:22 am
content: Oh yeah, if it's only 1.5 seconds then a resistor is the way to go IMO, at least if the duty cycle is low. I was assuming much longer periods.

author: elefurtronik
author_rank: Regular Contributor
timestamp: January 15, 2023, 01:00:12 am
content: Quote from: Zero999 on January 14, 2023, 11:05:02 pmI don't have space in my box for the chunky resistor. :/ It will operate 20 times a day.Quote from: james_s on January 15, 2023, 12:21:22 amIf I can control SV with PWM then it can be as much as lower. However, it is digital on/off for moment.

author: james_s
author_rank: Super Contributor
timestamp: January 15, 2023, 01:11:58 am
content: "Chunky" is relative. You can get a small surface mount resistor that is perfectly capable of dissipating a watt for 1.5 seconds at such a low duty cycle. You can typically overload a resistor quite severely if the duty cycle is low.The key thing to remember is that absolutely any kind of linear dropper is going to dissipate the same amount of heat. Doesn't matter if you use a resistor, a zener, a transistor based regulator, a linear regulator IC, anything, the amount of heat is the same.

author: Zero999
author_rank: Super Contributor
timestamp: January 15, 2023, 09:10:31 am
content: Quote from: elefurtronik on January 15, 2023, 01:00:12 amThen use a smaller resistor and it will get hotter. It doesn't matter what device is used to dissipate the power, it will still produce the same amount of heat. You have a choice between a higher temperature and smaller component, or lower temperature and a larger component. It's just physics. P = V×I and the more power, the more heat. If you put 1W of heat into a tiny space, it will get much hotter, than 1W into a much larger volume.1.5 seconds 20 times per day is a low duty cycle, which will limit the heating to some extent.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 15, 2023, 09:17:17 am
content: PWM is the correct answer. You need the freewheeling diode and proper layout anyway, even if you switch once a year. So why not switch 10000 times per second?With PWM, current varies in triangular waveform. Use high enough frequency, and force ripple becomes low enough not to matter (make dI = 10% of DC current or so. dI = difference between maximum and minimum current. Mechanical force is relative to current). With high enough frequency, the thing operates in CCM, meaning current is never zero (which is what you want to avoid force ripple, of course). Then the formula for duty cycle is easy: D = Vout/Vin. So in this case, simply 50%.Efficiency is good, too. For even better, you might want to consider synchronous rectification because even with a schottky diode with say Vf=0.4V, efficiency will be diode-limited to (3-0.4)/3 = 87%. But that's not bad compared to the resistor idea.In general, high-efficiency strategies help with miniaturization because you don't need the space for heat sinking / dissipation. Also eases the design. In this case, it's a total no-brainer as you need all the components there anyway. I'm assuming you are using microcontroller or similar which can easily produce the square wave.