Increase solenoid pull force

Hello everyone,

This is my first time posting here so please forgive me if I miss something. I am kind of new to the Arduino world and I am trying to troubleshoot this project I am working on.

Circuit: https://www.circuito.io/app?components=1331,9442,11021,842876There are some minor changes: I am not using the mosfet suggested in that website but I am using NTE Electronics Power Mosfet N-channel - Micro Center. Velleman Capacitive Touch Sensor Switch - Micro Center is the touch sensor I am using and Lock-style Solenoid - 12VDC : ID 1512 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits is the lock-solenoid I am using.

Code: Touch sensor - Google Docs am decent in basic C programming so this wasn’t difficult. Just took a while to refresh my memory. Before I get asked why I am using a FSR code for a touch sensor, TBH I am not sure either. I had issues trying to get the touch sensor to work behind a 2-3mm plastic but using FSR code and a touch sensor I am able to get it to work as I intend.

Current situation: Well as per the above code and just the circuit an its components themselves, this works perfect. I touch the sensor and the solenoid retracts and I take off my hand and the solenoid retracts.

Problem: In my application, there is a force (less than 50N) acting down on the flat side of the wedge. Something like this. Because of this force, the solenoid is unable to retract when I touch the sensor. When I remove this force, it works perfectly as stated above. My question is: Is there a way to increase the pulling force of the solenoid like, for example, passing more current? I would like to avoid buying a bigger solenoid due to space constraint.

If you need more info, please let me know and I will update the original post.

TL;DR: How to increase pulling force of a solenoid? Maybe pass more current?

Yes, more current.

Power the solenoid from a separate 12v supply capable of at least 1 amp.

cattledog:
Power the solenoid from a separate 12v supply capable of at least 1 amp.

I currently use one adapter which is 12V 1A output which is plugged into the arduino. Are you suggesting I use one more? If so how to go about it since the solenoid and the power adapter sockets don't match..

Reduce the friction by using a bit of Teflon. Use a roller or ball or something slick. Are you using steel on steel? Try brass instead of steel. Graphite lubrication can help.

Paul

Paul_KD7HB:
Reduce the friction by using a bit of Teflon. Use a roller or ball or something slick. Are you using steel on steel? Try brass instead of steel. Graphite lubrication can help.

Paul

Hello Paul, I tried to reduce friction but it didn't help. I don't think using a ball or roller since its the force causing the issue. I did reduce surface area of contact and used lubrication but it didn't help. :frowning:

That force will create friction not only on the wedge but on the inside of the solenoid. You can try to minimize the friction with PTFE or graphite. Or try different materials at the contact surface.

Regarding more power. I would do some tests with a bench power supply, measure voltage and current and increase the force slowly. That way you will get a feeling for how much more power you need to overcome the friction.
The Adafruit website states the solenoid is designed for 1-10 seconds activation times. That means there is likely not a lot of room for more power over the 12V x 650mA specified which is 7.8W. So, it probably gets a bit toasty warm inside. The wires are only coated with a thin layer for isolation. So, keep your measurements short and allow some time for cooling in between.

Klaus_K:
That force will create friction not only on the wedge but on the inside of the solenoid. You can try to minimize the friction with PTFE or graphite. Or try different materials at the contact surface.

Regarding more power. I would do some tests with a bench power supply, measure voltage and current and increase the force slowly. That way you will get a feeling for how much more power you need to overcome the friction.
The Adafruit website states the solenoid is designed for 1-10 seconds activation times. That means there is likely not a lot of room for more power over the 12V x 650mA specified which is 7.8W. So, it probably gets a bit toasty warm inside. The wires are only coated with a thin layer for isolation. So, keep your measurements short and allow some time for cooling in between.

Ohhh yes yes.. friction inside the solenoid! I didn't think about that. I will look into this. Many thanks!
Unfortunately, I do not have access to a bench power supply. I will ask my friends if I they have one.. Would I be able to reduce the resistance I am using on the board to increase the current to the solenoid? Website says to use a 1k or 2.2k ohm but I am using what looks like a 10k resistor since I am waiting for my package to arrive and didn't have anything less than that. Maybe I can use a multimeter to check the current flow to see if I can pass more current?

You can use a multimeter to measure the current trough the solenoid. You have a few seconds for the current to stabilize. But first make sure you have a flyback diode across your inductor. Otherwise the current when you switch off the solenoid may damage your meter. Its probably already in your circuit, but better save then sorry. :slight_smile:

I currently use one adapter which is 12V 1A output which is plugged into the arduino. Are you suggesting I use one more? If so how to go about it since the solenoid and the power adapter sockets don't match..

Taking the 12V from the Vin pin over to the Mosfet switching the solenoid is not going to give the full 12v at the solenoid. There is a 1 amp polarity protection diode on the Arduino which will drop .7 v. Then there is the issue of the resistance of the Arduino traces, the bread board, and connecting jumper wires plugged into headers.

Can you measure with a multimeter what voltage you exactly see a the solenoid?

Personally, I would prefer to power the UNO with 5V from the USB connector, and dedicate the 12v to the Mosfet/solenoid.

Would I be able to reduce the resistance I am using on the board to increase the current to the solenoid? Website says to use a 1k or 2.2k ohm but I am using what looks like a 10k resistor

What resistor? What is see in the circuit diagram is the resistor grounding the gate of the Mosfet. 10K should be good. I don't think the value will affect the current to the solenoid.
Typically there is also a 100-200 ohm series resistor between the Arduino pin and the gate.

All the suggestions about lubrication of the latch are good.

In the real world, your solenoid would have Teflon lining to grease the plunger. The power to the solenoid might be 48 volts or more to charge a rather large capacitor and the charge would be dumped into the solenoid to move the plunger. The excess current would only be there to start the move. Yes it is more complicated, but your design makes it that way. There are probably other ways to solve the problem, but I have only seen the two I mentioned.

Paul