Power conversionBench electronicsTest and identify

Power inductor

Also called choke, toroid, VRM inductor, 1R0.

A coil used as energy storage in a switcher, or as a choke. Motherboard VRM inductors are easy to desolder and are often marked with the inductance (1R0 means 1.0 µH, R47 means 0.47 µH).

If you are new to this category

These parts change wall power into the lower voltage a device uses. A sealed supply with a label is the safer kind. An open board from a lamp can still be connected to the wall on the side that looks like low voltage. Isolated means the output is not electrically connected to the wall. If you are not sure, treat the output as live.

Read the label out loud: volts, amps, and the polarity symbol. Then measure. A number you remember from a similar brick is not a measurement.

A sealed supply versus an open board

Left: a brick. The label is your spec, and the plastic is the safety barrier. Right: a board taken out of a lamp or a charger. Unless you have checked that the output is isolated from the prongs, do not let it touch a project you will handle while it is plugged in.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Mark	Three-digit or R notation, in µH, when anyone bothered to mark them
Current	Not printed. A tiny bead is not a 10 A inductor. Size and the original rail are your only clues.
Saturation	Powdered-iron and ferrite behave differently. If you do not know the mix, do not design a high-current buck around it.

Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.

What people actually use it for

Repair of the same board
A choke you can measure
Learning, more often than a precision design

Leave this one when

Unmarked, and the new design depends on saturation current. Buy a catalog inductor.

Buying a new one is the better idea when

Any switching regulator you want to work on the first try.

How to tell if this one still works

Inductance meter if you have one. A meter on resistance should read very low and not open. Open means a cracked winding.

Tools you will want: Iron, Meter.

Where people actually find it

3 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.

Harvest at a glance
From	Call	How many	How often	Where it sits
Fluorescent fixture	Worth it	1	sometimes	Magnetic ballast.
Desktop PC	Bonus	several	usually	VRM next to the CPU socket.
Solar garden light	Bonus	1	usually	On the board.

Worth pullingFluorescent fixture1 · sometimes
In this particular machine
A large iron choke. Useful as a choke, not as a toy.
Where to look
Magnetic ballast.
How to get it out
Heavy.
The condition to expect
Humming ones may be failed.
Bonus, if you are already in thereDesktop PCseveral · usually
In this particular machine
Shielded inductors, often marked in µH.
Where to look
VRM next to the CPU socket.
How to get it out
Desolder only if you can read the mark.
The condition to expect
Fine electrically; the value is the question.
Bonus, if you are already in thereSolar garden light1 · usually
In this particular machine
The boost inductor.
Where to look
On the board.
How to get it out
Leave it on the board. The board is the circuit.
The condition to expect
Good.