Axial Inductors

• Axial inductors (color ring inductors) are underrated components that can be super handy in low-power applications.
• Understanding their limitations, like lower saturation current and power handling, is key to using them effectively.
• These inductors are perfect for beginners and budget projects while still offering decent performance for signal filtering and small power supplies.

If you’ve ever ignored axial inductors (commonly called color ring inductors) because they just look like resistors with color bands, you’re not alone. I did the same for years. But after some testing and experiments, I realized these inexpensive little components are actually pretty useful—especially for low-power projects.

I found them simple to identify (thanks to those colorful rings), cheap, and surprisingly flexible when used in the right context. Now, I want to share what I’ve learned—the good, the bad, and what these inductors are really capable of.

What Exactly Is an Axial Inductor?

An axial inductor is essentially a coil of thin copper wire wrapped around a ferrite core, shaped kind of like a dumbbell. The coil is enclosed in a small molded body and marked with color bands that indicate its inductance value, similar to resistors. Because of this, they’re often mistaken for resistors at a glance.

These inductors operate on the same basic principle as any coil:

• When current fluctuates through the coil, it generates a magnetic field.
• This magnetic field opposes changes in current, providing "inductance."
• The value of inductance is represented by those colored rings, making it easier to identify without expensive testing gear.

While surface-mount device (SMD) inductors exist and sometimes have printed values on them, axial inductors remain popular for their low cost and straightforward identification—which makes them a great choice for hobbyists and quick prototyping.

Why I Ignored These Components for So Long

For years, I collected kits of these color ring inductors but never got around to really testing them. The problem? Datasheets are almost nonexistent for these cheap components. Unlike many power inductors where you get detailed specs (like saturation current, DCR, power rating, etc.), these kits usually only mention basic inductance values and some vague “1 watt power rating”—which doesn’t tell you the full story.

Without datasheets, you don’t know:

• Maximum current before saturation
• Exact power dissipation
• Equivalent series resistance (ESR)
• Frequency response details

That lack of specs scared me off from trusting them in anything serious. But that’s actually standard with many budget inductors—you have to test and figure out their limits yourself.

Practical Testing: How Do Axial Inductors Perform?

I wanted to put these axial inductors to the test, so I set up a simple boost converter circuit. A boost converter steps up voltage from a lower DC input to a higher output voltage, and it relies heavily on the inductor’s ability to store and release energy efficiently.

Here’s what I found:

• The original boost converter coil handled about 1 amp output current smoothly.
• The axial inductor with the same nominal inductance (22µH) could only manage about 0.5 amps before voltage instability and noise spiked.
• Beyond 0.5 amps, the power output became unreliable, and the circuit got noisy.

This suggests that while inductance values might be similar, the axial inductor’s saturation current and power handling are roughly half that of a dedicated power inductor designed for converters.

What Limits the Axial Inductor?

The secret lies in the saturation current of the inductor’s core. Saturation current is the point where the magnetic core stops behaving like an inductor and starts acting more like a simple resistor — at which point performance quickly degrades.

I ran a test with an oscilloscope and PWM pulses to figure out when saturation kicks in:

• The original boost converter inductor saturated at about 4 amps.
• The axial inductor saturated at around 1.6 amps — a big difference.

Once the inductor saturates, it can overheat, lose inductance, and risk damage. This is why axial inductors can’t handle the same power as beefier coils—temperature and material quality play a huge role.

So, When Should You Use Axial Inductors?

Given their limitations, axial inductors are ideal for:

• Filtering applications: cleaning up noise in signals or power lines at low current.
• Signal processing: oscillators, RF circuits where currents are very low.
• Beginner electronics projects: experimenting without risking expensive gear.
• Low power converters or boost converters where current draw stays low (<1A).

Avoid axial inductors in:

• High current switching power supplies
• Applications demanding tight inductance tolerances
• Circuits where heat dissipation is critical

Why They Still Matter

Sure, axial inductors aren’t perfect. They are no superstar in heavy-duty power electronics. But they fill an important niche. Because these components are so cheap and readily available, they become perfect for experimenting, prototyping, and learning.

Their color-coded labeling is intuitive and saves time. For beginners or budget builders, they offer an affordable way to understand inductance without breaking the bank.

Summary in Bullet Form:

• Identifiable by color rings just like resistors.
• Affordable and great for low-power filtering and signal use.
• Limited by lower saturation currents and less documented specs.
• Not suited for heavy power supplies but perfect for experiments and beginner projects.

FAQ Section

Q: What is the difference between an axial inductor and a power inductor?
A: Axial inductors usually have a simple ferrite core with thin wire and lower saturation currents, making them suitable for low-power uses. Power inductors are designed to handle higher currents and come with more detailed specifications like saturation current and resistance.

Q: Can axial inductors be used in boost converters?
A: Yes, but only in low current boost converters. For currents over about 0.5 to 1 amp, they may saturate and cause problems.

Q: How do I read the value from a color ring inductor?
A: The colors correspond to numbers, similarly to resistors. You match the ring colors to an inductor color code chart to find the inductance in microhenries (µH).

Q: Are data sheets available for color ring inductors?
A: Often, no. Most budget axial inductors only list inductance and a vague power rating. More detailed specs are rare, so practical testing is often necessary.

Q: Where can I buy axial inductors?
A: They are widely available online (sites like AliExpress or electronic component suppliers). Usually, they come in assorted kits at very low cost.

If you want to learn more about how inductors work or try them yourself, check out resources on electronics fundamentals or try the kit linked in the video description above. Understanding the capabilities of these modest components opens up new possibilities for your projects!