• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

How to drive a a 6V solenoid lock

Kian

Member
Hi all,

I got a 6V solenoid lock (https://www.alibaba.com/product-detail/5V-6V-12V-and-24V-Electric_62042294641.html) and I would need to control it using a microcontroller. I am powering my microcontroller with a 3.7 V lipo battery.

The solenoid lock is rated 6V and requires a current of about 0.8A. I know I need to using a MOSFET as a switch to drive it, just like driving a motor. I can only use one 3.7V lipo in my design. So I presume I would need a boost converter to boost the voltage to 6V. However, I can't seem to find a boost converter that can give a high current output.

Can anyone advise how I can drive the solenoid? Thanks in advance!
 

Pommie

Well-Known Member
Most Helpful Member
Try it and see. Your application may work at the slightly lower voltage.

Mike,
 

Kian

Member
Hi,

Thanks for the replies so far.

Mike, I believe its more of a current issue. Somehow I am choosing the wrong boost converters in my previous designs. I was using a ISL9111AEH50Z-T7A but somehow it didn't work.

AK, I am designing my own PCB and I have a size and shape constrain with the PCB.

narkeleptk, I will try the boost converters you suggested. Thanks!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
AK, I am designing my own PCB and I have a size and shape constrain with the PCB.
It's quite easy to fit a Chinese module on your own PCB (which is what I do), as you can buy the modules from China for less than the local cost of the IC or the inductor.

These are the ones I've just reordered:


However, if you're really hampered by the physical shape required, you might be forced to go for the more expensive route.
 

Dr_Doggy

Well-Known Member
i find it is easier to find a 6v power supply, then use BUCK converter to step down to the low power microcontroller, or a more common 12 supply and buck to 6
 

ronsimpson

Well-Known Member
Most Helpful Member
From my experience, if 6V @ 800mA pulls the lock back, then probably it will hold back at 3V @ 400mA. (must be tested)
I was using a ISL9111AEH50Z-T7A but somehow it didn't work.
The ISL9111 has a max output voltage of 5.25V. and you can not get more than 300mA out of it.

Here is a idea. Use a higher voltage boost up power supply (low current is OK maybe only 100mA). It can charge up a large capacitor to 7 or 8 volts. When you want the lock open connect the 8 volt supply to the lock. The 8V will drop down to the supply voltage of 3V in a short time. By then the lock will have opened and probably will hold at the lower voltage. It might take 1 second for the boost supply to charge up the capacitor again depending on output current.
 

Beau Schwabe

Active Member
I would just try the 6V solenoid with 3.7V and see what the results are.

At my previous job we had an issue with 12V water solenoids burning out with a 15V supply so we switched to 24V solenoids and they were just fine with the 15V supply. I used a bench top power supply to reduce the voltage to see where the 12V and the 24V solenoid started to fail and in both cases it was near 30% of the rated voltage.

3.7V is 62% of the rated 6V so I would think the solenoid would be fine, but you will need to test this for yourself.
 

ronsimpson

Well-Known Member
Most Helpful Member
3.7V is 62% of the rated 6V so I would think the solenoid would be fine
Next year when the lock is dirty there will be trouble. (at any voltage but the problem will be worst at 3.7V)
Making one for your use, this lower voltage is OK but this is not something for production. Some parts will work at 60% but not all. Next year some Chinese engineer will think about saving 1 meters of wire by reducing the turns a little. Who will ever know that happened. The lock still works when testes at 6V. Why not save some money?
 

Beau Schwabe

Active Member
Next year when the lock is dirty there will be trouble. (at any voltage but the problem will be worst at 3.7V)
Perhaps.

The OP could always try a "Dickson Charge Pump" to deliver more current.

Here is a YouTube video I made several years ago of a Dickson Charge Pump in action ... Sorry for the mispronunciation. I didn't catch myself until the very end of the video - ahh well.
 

Kian

Member
Hi all, I went with a boost converter MT3608 and step up the voltage from the Lipo (3.7V) to about 6.5V.

However, seems like I am having problems now with the transistor drive circuit. I think I am most likely using the wrong transistor and resistor. Can someone advise how to choose the correct transistor to use?

Currently I am using the MMBT222A with the base connected to the microcontroller pin with a 1k resistor in between. The microcontroller when high, gives 3.3V. The emitter is connected to ground. The collector is connected to the negative terminal of the solenoid and the positive is connected to 6.5V (from the boost converter). I have a diode connected across the solenoid.

120213
 

Nigel Goodwin

Super Moderator
Most Helpful Member
The specs on that look pretty poor, low gain and high voltage loss collector to emitter, assuming someone can suggest a suitable small power FET that's 3.3V logic compatible that could well be a better choice. However, for now, you could try getting more base current - lower the value of the 1K - what is the max current out of your I/O pin?. 100 ohm should provide about 26mA drive, which will at least give the transistor more chance of turning ON a bit.
 

ronsimpson

Well-Known Member
Most Helpful Member
Here is why the transistor will not work/gets hot/ and how you can see why.
Your poor little transistor needs to switch 800mA. Top graph shows collector current verses gain and the graph does not go to 800mA. The gain will be about 10. (gain is input current and output current)
Go to the second graph and look at the 500mA line. You wan the transistor to close to the 0.3 or 0.2V mark. To do that you need 20-50mA in the base. Your computer probably can not deliver that much current if the resistor was zero ohms.
120215
 

Kian

Member
Thanks for the reply. I googled and found many are using MOSFETS instead. I think maybe that is my problem since I was using a BJT. Here is an example schematic I found online:

120217

Do I need actually need a GATE resistor? And what value to use? I am always confuse with how to choose the right BJT/MOSFET and also choosing the resistors needed.
 

ronsimpson

Well-Known Member
Most Helpful Member
Logic level MOSFET:
I picked a part that 20V 3A and has a good gate.
MOSFETs are turned on by voltage not current. Left graph shows what happens with 1.4V from Gate to Source. The D-S stays closed below 1/2A and tears open above 1/2A. At 1.8V G-S the part can stay closed up to 4A.
120216
You might also look at:

Most MOSFETs need more than 3V to turn on well!!!
I would use a 22 ohm resistor or some value from 10 to 100 ohms. It will work with out a resistor.
 

Kian

Member
Hi all,

I am still having problems with the circuit. I have changed to BJT to a MOSFET with a 100ohm resistor at the gate. And this is controlled by an Arduino pin.

Also, I am using this boost converter module (MT3608):

https://www.aliexpress.com/item/32952119052.html

I have adjusted the boost converter output voltage to about 6.5V and the input is powered by a Lipo battery with 3.7V. I also have a flyback diode across the solenoid lock. The solenoid lock is rated 6V and requires a current of about 0.8A.

This is what is happening now. If I connect the lock first then connect the lipo battery to power up everything, nothing happens and the boost convert output drops to 1V and stays there. Then I disconnected the lipo battery and disconnect the lock. Connect the lipo battery first and use a voltmeter to measure the output of the boost converter. It reads 6.5V. Next I connect the lock, and the arduino give a logic high to drive the gate and the lock switches very quickly on and off then stops forever. (The Arduino is programmed to lock and unlock the switch every 5 seconds). I measure the boost converter output and it reads 1V again and it stays at 1V.

Its seems like now its the boost converter that is giving problem?
 

Latest threads

EE World Online Articles

Loading

 
Top