Solenoid getting too hot

[varunme]

i have a hand made solenoid which is getting too hot while operation, the core i used is the rod from printer and the copper wire is the one used for making transformers, it is powered from PC smps, 5V 25A rail, the heat is such that i made a cellophane tape for making rigid, the heat dissolved the tape

what can be the reason, how can it be solved?

 

[Audioguru]

Electrical heating of a wire is caused by the voltage times the current. To reduce the heat then reduce the voltage, reduce the current or reduce both.
A transformer does not get hot when it has no load because it operates from AC, not DC. But your solenoid is simply a piece of wire with DC in it so its inductance does not reduce the current like in an unloaded transformer.

 

[varunme]

A commercial solenoid on the same supply doesn't heat up

 

[jiripolivka]

Bad design of your solenoid.

 

[varunme]

in what ways i went wrong?

 

[Audioguru]

A commercial solenoid on the same supply doesn't heat up

Are the solenoids powered from DC?
The commercial solenoid does not heat up because the wire is thinner and longer so it has a much higher resistance. If the resistance is half then the heating is doubled. Maybe its resistance is 10 times the resistance of yours. Then the temperature difference is 10 times.

 

[varunme]

yes, both were used in same DC from the PC smps. ok I will try thinner wires.

 

[Electro nS]

Electrical heating of a wire is caused by the voltage times the current. To reduce the heat then reduce the voltage, reduce the current or reduce both.

i think u got this wrong , the heat is caused by current not voltage , because Power loss is i2R , so usually to increase power we increase voltage and decrease current .

 

[chuckey]

5V at up to 25 A is a huge amount of power to push into a solenoid. Does it perform its function? It would be better to put a magnetic short circuit along the outside of the coil, it will greatly increase the magnetic field through the centre of it, so you can operate at a lower power level.
Frank

 

[Audioguru]

i think u got this wrong , the heat is caused by current not voltage , because Power loss is i2R , so usually to increase power we increase voltage and decrease current .

Power (causing heat) is I squared R, or is V squared divided by R, or is V times I.
The heating is reduced if you reduce the voltage, or reduce the current, or increase the resistance.

Since the resistance is fixed then the heating power is increased when the voltage is increased due to Ohm's Law (I= V/R, then when V is increased I is also increased).

 

[varunme]

@chuckey yes, it performs the function, it is a very powerful magnet. I cant use magnetic short circuit since i want cylindrical structure and small size.

 

[varunme]

can we reduce the current with series resistor?

 

[Audioguru]

If you reduce the current with a series resistor then the total power (heating) is less but the resistor will get very warm. If the resistance of the resistor equals the resistance of the solenoid then the total resistance is doubled so the total power (heating) is half of what it was without the resistor. Then the resistor and the solenoid share the reduced power and each dissipates 1/4 of the power without the resistor.
Of course the solenoid pulling power will be weaker.

It would be much more efficient to reduce the voltage that feeds the solenoid which will also reduce its current and power.

 

[chuckey]

If you halve the cross section of the wire, you double the resistance for the same number of turns, but you can get twice as many turns on the former. So to fill the former would result in four times the resistance, or a quarter of the current. but the magnetic field varies as n^2, so you have four times the inductance , times one quarter of the current gets you back to square one, BUT the power dissipation is now V X I/4 = P/4 .
The other thing to investigate is to see if you core has gone into saturation, once all the magnetic domains are aligned increasing the current does not increase the magnetic field.
Frank

 

[varunme]

I have halved the cross section, but heat produced is some what reduced, former i used 50, now used 30. can it be due to the property of the wire to produce more heat?

 

[Audioguru]

Heat is produced by the voltage times the current. The current is decreased when the resistance is increased. Thinner or longer wire has increased resistance.

 

[varunme]

i am asking wheather this is not suitable for dc since, it is used for ac?

 

[Audioguru]

A solenoid operating on AC draws less current due to its inductance. The inductance is increased when its number of turns of wire is increased and if it has a ferrous core maybe made with insulated laminations like used in a power transformer.
A solenoid will have a higher current, higher heating and be more powerful when powered from DC.

 

[chuckey]

" i used 50, now used 30. " 50 or 30 what?, turns, gauge of wire?. . .
Frank

 

[Audioguru]

To reduce the heat you need a proper magnetic core, or more turns of wire, or thinner wire that has a higher resistance, or less voltage or all of these.