Reverse polarity in a push pull solenoid

Hi all,

I wonder if someone can help me with this issue:

I have a 24V push pull solenoid setup with the following schematics and the code I'm using in Arduino.

I put a spring to the solenoid but is getting very warm and the data sheet indicates to use reserve polarity instead (I understand -24V) of using a spring.
Any ideas to implement the circuit?

Thanks,

Toffe_Apple

Driving a solenoid with a transistor.jpg

solenoid_pump.ino (189 Bytes)

You need a circuit called a H-bridge. This allows you to reverse the polarity in a solenoid or motor.

You need a circuit called a H-bridge. This allows you to reverse the polarity in a solenoid or motor.

I doubt reversing the polarity will have any effect on your heating problem, nor will using an H-bridge help. You need to look at the specs on your solenoid and look at the "duty cycle". Many solenoids, you cannot hold on forever without heating.

A way around it: Connect the base of your transistor to an Arduino PWM pin. Turn on the output by using digital.Write(255). Then gradually decrease (255) until the solenoid drops out. You will need to write code that initially turns on the solenoid and after 1 second or so, reduce the PWM value to your dropout value. This will reduce your heating.

Note: The heating on a DC solenoid is a function ONLY of the wire resistance of the coil. If your solenoid resistance measures 240 ohms, it will draw 100mA and dissipate 2.4W at 24V. By PWM reducing the voltage, you will reduce the power. It's also a second order effect. If you cut the voltage in half, you will now dissipate 1/4 the power

Hi all,

Thanks for your answers.
After a little bit of work in the H-bridge you recommend me to do...
I've realized that at the moment I have a problem relating the heating in the PNP mosfet transistors.
I'm trying to run a push pull solenoid 24V 40W:

with 2 PNP (TIP32) and 2 NPN (TIP31) in a H-bridge configuration.
Why are the transistors getting so hot when they're driving the current both ways?
Attached in pictures the schematics and the numbers to calculate the value for NPN and PNP resistances. Arduino Mega 2560:

void setup()
{
pinMode (5, OUTPUT); // one direction
pinMode (6, OUTPUT); // other direction
digitalWrite (5, LOW);
digitalWrite (6, LOW);
}

void loop()
{
digitalWrite (5,HIGH);
digitalWrite (6, LOW);
delay(1000);
digitalWrite (5,LOW);
digitalWrite (6, HIGH);
delay(1000);
}

Hopefully someone can help me,

Many thanks,

Toffe_Apple.

NPN.numbers.jpg

PNP.numbers.jpg

schematics.jpg

Why are the transistors getting so hot when they're driving the current both ways?

Because that is a very poor design of a H-bridge and a TIP transistor has a Vsat of 1.2V each. So you are burning off 2.4V * I Watts of power where I is the current of the solenoid.

So if you have a current of 1.6A the the power the transistors are burning off is 3.84W. That will get hot.

Normally you use FETs for this sort of thing to prevent it from getting hot.

A normal solenoid will not reverse direction if you reverse the polarity.

They do not work by having north and south poles which attract or repel. That is a misconception.

When a solenoid coil has current applied to it, in either direction, it will pull the moveable iron component towards the centre of the coil. This is the point where the magnetic impedance of the magnetic field circuit is least. When the current ceases, a spring will move the iron component back to the original position.

Hi,

Thanks for your quick reply.
I've doing some work to do to run the same solenoid (24V 40W) with the schematics attached which drives 12V and 3A. Not success at all, the PNP transistors on top have exactly the same problem as before, they're very hot!

Has anybody a circuit to follow?

Regards,

Toffe_Apple

3AmpH-Bridge.gif