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Topic: Controlling Energise to Release Electromagnets: Not drawing enough current? (Read 400 times) previous topic - next topic

ruzbeh

Hello all,

This is my first post in this forum. I am a newbie with arduino, and currently working on a project.

The problem I am having is the part where I control an energise to release electromagnet with arduino.

I am using a similar circuit layout, which controls a 12V solenoid. It seems that the 12V magnet is not drawing enough current (~0.35 amp, whereas rated is 0.5A). Therefore, I am assuming this is the reason why it is not demagnetized fully. I have attached the circuit and the link of the magnet for reference. I have tried few other same magnets as well, so the magnets are working.

Any suggestions would help. Thanks in advance.

https://www.aliexpress.com/store/product/20-23D-Current-Degauss-Magnet-Voltage-Not-Magnetic-Electric-Magnet-Solenoid-Sucker-Electromagnet-DC-12V-24V/2342168_32819078236.html?spm=2114.10010108.1000023.3.236f675cvZRPnU

Robin2

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...R
Two or three hours spent thinking and reading documentation solves most programming problems.

outsider

I would guess your transistor is dropping too much voltage, can you measure the voltage from collector to emitter with the circuit enabled? If more than 0.2 volts you probably need a logic level MOSFET with an rds less than 0.05 Ohms like RFP30N06LE:
https://www.sparkfun.com/datasheets/Components/General/RFP30N06LE.pdf

ruzbeh

Thanks for the reply. I have just measured the voltage from collector to emitter: 11.98/11.99 V when on and 0.15 V when enabled.

Wawa

0.15volt C/E saturation when 'on' is good.
Not much improvement when you replace that TIP31 for a mosfet.
If supply voltage (12volt) doesn't drop when the solenoid is 'on', then the solenoid might not be 500mA.
Or you measured the current wrong.

Try to measure the resistance of the 12volt/0.5A solenoid. It should be 24ohm.
Leo..

ruzbeh

Thanks for the reply.

The measured resistance is 29.4 ohm. It looks like the rated current is not correct. This should be 0.41A.

However, still the maximum current drawn by the magnet is lower than that. I am using a DC regulated power supply from ISO-TECH, where I can monitor the current drawn.

Just connected the magnet directly to the power regulator, and the current it draws when switched on is 0.4A. Also, it is fully demagnetized.

Wawa

Things from China are rarely what they say they are.

Transistors have volt drop, wires have resistance.
That all lowers the voltage available for the solenoid.
If you want exactly 12volt on that solenoid, then you might have to increase the supply a bit.
Don't see why though.

Did you check your DMM agains the current readout of the supply.
Leo..

Paul_KD7HB

Things from China are rarely what they say they are.

Transistors have volt drop, wires have resistance.
That all lowers the voltage available for the solenoid.
If you want exactly 12volt on that solenoid, then you might have to increase the supply a bit.
Don't see why though.

Did you check your DMM agains the current readout of the supply.
Leo..
I think you are right about the Chinese in this case. It is identified as a "Degauss Electric Magnet". As I recall such things were run on AC to remove residual magnetism from tape recording heads.

I wonder where the seller found these and what they were REALLY designed for. I don't think the OP will ever be able to run enough current through the coil to balance out the core magnet. And if that was ever done, the core would probably have no magnetism left.

Paul

ruzbeh

Thank you for the suggestions.

I have increased the voltage to 13.5V, and it is drawing around 380mA. Which is serving the purpose of the application, though not fully demagnetized. I hope using 13.5V does not damage the magnet in the long run.

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