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LC100-A : A precise LC meter for 3.75$

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edavid:
The problem with the AADE/LC100-A style LC meters is that they are only accurate for near-ideal components.  Parasitics will quickly degrade the measurement.  If you have the money for a DE-5000, it's a much better value, since it makes true (phase-sensitive) LCR measurements.

elecdonia:

--- Quote from: edavid on December 22, 2022, 01:51:55 am ---The problem with the AADE/LC100-A style LC meters is that they are only accurate for near-ideal components.  Parasitics will quickly degrade the measurement.  If you have the money for a DE-5000, it's a much better value, since it makes true (phase-sensitive) LCR measurements.

--- End quote ---
Pro” and “lab grade” LCR meters allow the user to select the test frequency. Fortunately capacitors tolerate wide variations in test frequency. However this isn’t the case when measuring inductors. Selection of appropriate test frequency is quite important when measuring inductors. The only control available to the LC100-A user is to select small L or large L. LC100-A test frequency for small L is 50-600kHz. Test frequency for large L is about 50kHz maximum. However this may still be too high for accurate measurement of some inductors.

Example: A 60Hz power transformer should be measured with a test frequency in the audio range, no higher than 1 or 2 kHz. Use of an appropriate oscillation frequency is critically important when measuring inductors with cores made of powdered iron or steel laminations. Another factor when measuring large inductors is that a winding with multiple layers of thin wire may possess considerable internal capacitance.

The test frequency used by the LC100-A in small L mode is considerably higher than when using large L mode.
Generally the small L mode is reasonably accurate for air-core and ferrite-core inductors.
However, small L mode is likely to be grossly inaccurate for inductors with powdered iron or laminated steel cores. In fact even the large L mode may be inaccurate for laminated steel cores.

Fortunately pressing the small button on the LC100-A displays the oscillation frequency of the measurement. If this frequency is well outside of the normal operational range of the inductor under test then the displayed test result for inductance is probably inaccurate.

bffargo:
Note that years on now, (almost?) all of these that are being sold on eBay and AliExpress now are the "B" (F?) grade clones that use both the wrong inductor to compare against, as well as other questionable components. See the various discussions linked from the other forums about how to address this when (not if) you get one that isn't close to accurate. Highly unlikely you will find the original run accurate ones from 7 years ago anywhere anymore.

elecdonia:

--- Quote from: JacquesBBB on June 11, 2016, 09:21:47 am ---…I measured some coils and  seem to have problems for low inductance values.
For the same  transformer coil I get 11.73 mH on the HiL scale and 754 uH on normal L scale.
Any hint ?

My guess is 11.73 mH is the right value as primary gives 4.47 H and this is a  240V/12V  transformer,
so I expect that the ratio of inductance will be roughly 400 (20^2).

--- End quote ---
Yes, 11.73mH is likely to be reasonably accurate.

If measurement result is lower for normal L mode compared to HiL mode, this indicates the inductor under test cannot function well at the (much higher) test frequencies employed by LC100-A normal L mode.

Inductors and transformers intended for mains frequency operation (50/60Hz) must be measured with test frequencies in the audio range, preferably no higher than 1 or 2kHz. As much as possible the test frequency should be similar to the frequencies the inductor under test will encounter during normal operation.

Low frequency inductors/transformers have cores made from a stack of many thin sheets of iron or steel. These thin sheets are known as laminations. Although some very expensive wide-band audio transformers made with laminated iron/steel cores are functional up to 50kHz or a bit higher, this isn’t the case for typical 50/60Hz power transformers. Their high frequency performance is limited by eddy current losses in the laminated iron core along with stray capacitance in the windings. These can only be measured by LC100-A HiL mode.

Another popular core material is known as powdered iron. These are often painted or wrapped with tape in bright yellow, red, green, or blue, especially when the core has a toroid shape. These are functional up to about 100kHz and are commonly used in switching power supplies. These should also be tested with LC100-A HiL mode.

Ferrite cores are usually grey in color. They have a much larger frequency range which can extend up to many MHz. For ferrite cores the LC100-A can test them in either range.

Coils with no core (air core) can handle extremely large frequency ranges. Either normal L or HiL mode may be used when measuring air core inductors with LC100-A.

LC100-A test frequency range for normal “ small L “ mode is between 50kHz and 500 or 600kHz.
Test frequency for “ HiL “ mode is much lower, from roughly 100Hz up to 50kHz maximum.

elecdonia:

--- Quote from: bffargo on December 23, 2022, 04:22:22 pm ---Note that years on now, (almost?) all of these that are being sold on eBay and AliExpress now are the "B" (F?) grade clones that use the wrong inductor to compare against, as well as other questionable components. See the various discussions linked from the other forums about how to address this when (not if) you get one that isn't close to accurate. Highly unlikely you will find the original run accurate ones from 7 years ago anywhere anymore.

--- End quote ---
I agree that most of the currently available LC100-A units come with an unacceptable inductor which has a powdered iron core.

Powdered iron cores are often painted bright yellow (or another bright primary color) and are usually in the toroid donut shape with 20-30 turns of wire wrapped in a single layer around the core. Unfortunately the internal losses of powdered iron cores prevent them from functioning well in the LC100-A oscillator circuit.

Therefore the first improvement for an inaccurate LC100-A is to replace the factory inductor with a proper ferrite core inductor. The replacement inductor may be anywhere from 50uH up to 100uH. The exact inductance value doesn’t matter. It is OK to use 56uH, 68uH, 82uH, or 100uH.

What does matter is the inductor must have a ferrite core, not a powdered iron core.

Ferrite cores are almost always a dull grey color. They aren’t brightly colored. Acceptable ferrite cores may be in the toroid donut shape or in a form known as “binocular” where there are two holes in the core with the wire wrapped through the two holes. I have also had success with “radial” inductors where the core is shaped like a dumbbell with the coil in the middle. Additionally, some of the tiny SMT “shielded” inductors where the coil is entirely inside the ferrite core also work very well. I will post photos of several inductors and provide a simple method to evaluate them for use in the LC100-A.

There are two other components in the LC100-A which determine its accuracy. These are the two reference capacitors. However, the capacitors used by the LC100-A manufacturers are generally “good enough” to use without replacing them. The main issue is the (poorly chosen) factory inductor.

So, improving LC100-A accuracy usually requires replacing only one part: the inductor.

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