inductor gauge and polarity switching efficiency

[Njguy]

I was wondering if inductors with thin gauge wire with many turns compared to thicker gauge wire with fewer turns are any less efficient when it comes to high speed polarity switching? Hard to put this in words for the Google wizard so I figured Id ask my wizards here. Thanks guys.

 

[crutschow]

It depends upon the current through the inductor. It's the IR loss in the wire resistance that determines efficiency.

What's "polarity switching"?

 

[Njguy]

It depends upon the current through the inductor. It's the IR loss in the wire resistance that determines efficiency.

What's "polarity switching"?

*frequency... do you have a proper term?

 

[crutschow]

*frequency... do you have a proper term?

"Frequency" refers to an alternating current or signal (AC), such as a sinewave. Is that what you are referring to?

 

[Njguy]

yes which switches the polarity is what I meant. So you are saying that the efficiency depends on the wire not necessarily the amount of loops and gauge?

 

[crutschow]

yes which switches the polarity is what I meant. So you are saying that the efficiency depends on the wire not necessarily the amount of loops and gauge?

No. The number of loops (wire length) and wire gauge is what determines the resistance of the wire, which is what determines the power lose (efficiency).

 

[dr pepper]

The length and diameter of the wire in a coil affect its dc resistance, this is one of the main factors for losses.
A coil with few turns of thicker copper would be much less inductance than a coil of many more turns of thin copper, so isnt a good comparison.
That said usually the more copper the less resistive losses there will be, other issues come into play such as coupling, its not as easy to get thicker turns right up close to the core, so other losses start to appear.
All depends what you need.

 

[Njguy]

This may be a stupid question but the higher the resistance in the wire means that the inductor will be drawing less amps, so less power? So thin gauge wire with many loops is more efficient than thicker gauge wire with fewer loops.

 

[crutschow]

This may be a stupid question but the higher the resistance in the wire means that the inductor will be drawing less amps, so less power? So thin gauge wire with many loops is more efficient than thicker gauge wire with fewer loops.

Normally you design an inductor to carry a specific current. In that case the lower the resistance, the lower the power loss.

 

[dr pepper]

To go a bit further than cruts, resistance in an inductor is parasitic (allthough sometimes is used as a design parameter) and dissipates power the same as well a resistor would.
A perfect inductance would have zero resistance.
Its this resistance that is partially responsible for inductors heating up under power.

 

[Njguy]

To go a bit further than cruts, resistance in an inductor is parasitic (allthough sometimes is used as a design parameter) and dissipates power the same as well a resistor would.
A perfect inductance would have zero resistance.
Its this resistance that is partially responsible for inductors heating up under power.

It seems like a strange dichotomy because if an inductor has more resistance due to more loops (longer wire) then the amount of current goes down and the inductor doesn't heat up as much.

 

[dr pepper]

Nope not really, more turns increases the resistance, but only very slightly, not enough of an increase to decrease current noticeably.
The dichotemy is often one of the designers, how much to trade off effeciency and how hot you dare run the core, the les copper the smaller and cheaper, but worse parasitics.

 

[crutschow]

It seems like a strange dichotomy because if an inductor has more resistance due to more loops (longer wire) then the amount of current goes down and the inductor doesn't heat up as much.

Normally the inductor is designed so that the resistance is only a small part of the inductive reactance, thus the resistance does not have a significant effect on the current. Remember that the coil inductance goes up by the square of the number of turns, whereas the resistance goes up directly proportional to the number of turns, so you gain inductance faster than resistance.

 

[ChrisP58]

It seems like a strange dichotomy because if an inductor has more resistance due to more loops (longer wire) then the amount of current goes down and the inductor doesn't heat up as much.

That would be true if the inductor was the end load of whatever your circuit is. But inductors are usually series elements between the power source and the load. Assuming that your end load needs a certain amount of power, both voltage and current, any resistance in the inductor means some of the your input power is dissipated in places other than the load, and therefor reduces the system efficiency.