LC100-A : A precise LC meter for 3.75$

[JacquesBBB]

I was lacking a device to measure small caps and I came across this incredible deal  on ebay

http://www.ebay.fr/itm/111926481261?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I  took the chance, order it on  May 17, for 3.75$ including postage, and just got  it today. It is provided with a decent usb cable, alligator hooks, and seems to work just fine

Here are some examples of  measure  of 1% caps I have.

A                          B         (A-B)/A
nom.         prec.  meas.     
value
(pf)         

33        1%    32.65          0.011
3300     1%    3290           0.003
22000   1%    21950         0.002
10000   1%    9964           0.004

I  have also  some old caps of lower values

A                          B         
nom.               meas.     
value
(pf)         

12                      12.68
15                      15.35
18                      18.84
27                      27.54


I must say that I am perfectly happy with this device which is based on STM8S103.

[lukaq]

what the?? how is it that cheap? and most countries are excluded from sending to

[PedroDaGr8]

looks to be a typo. Already all sold out, seller now sells them for $14.

[JacquesBBB]

Yes you are right,  they probably made a mistake in the price when they put it at $3.75.
They were  fair to send it  anyway.

I  have 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 the normal scale. Any hint ?

My guess is that the 11.73 mH is the right value as the 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).

[elecdonia]

It’s time to either bump this old thread in a major way or start a new thread for the LC100-A inductance/capacitance meter.

The LC100-A is widely available from many vendors. Typical price is now $15-25 USD.  It is worth every penny!

While many LCR meters are offered by major test gear manufacturers, most are at least 5-10 times more costly than the LC-100A.

The LC100-A is a great companion to the $20 Transistor Tester devices which many of us already have on our workbenches. A C or L which is difficult to measure accurately with one of these devices might be measured more accurately by the other device. This is because the measurement technology is entirely different for Transistor Tester vs. LC100-A.

I have been using the LC100-A for several years. It is incredibly useful for projects containing inductors, such as switching power supplies and audio loudspeaker crossover networks. It is equally valuable for RF projects, especially when tuned circuits need to be measured. I first obtained an LC100-A to help me diagnose and restore vintage AM/FM broadcast band radios. This task frequently requires accurate measurement of very small C (1-500pF range) and also small L (5 to 500uH).

I will begin by posting links to several detailed discussions of the LC100-A:

The following thread from the Antique Radio Forum is a good starting place:
     antiqueradios.com LC100-A, LC200-A, and similar low-cost digital LC meters?

The LC100-A has also been discussed in these other EEVblog topics:
     EEVblog Other Equipment & Products board: china-lc200a-lc-meter-teardown
     EEVblog RF, Microwave, Ham Radio board: microwave-tl-coax-impedance

Other links to the LC100-A:
     VK4GHZ.com LC100-A LC meter mods
     ludens.cl Understanding, fixing, and improving the LC100-A
     Hackaday.io LC100A LC meter fix

This link describes a comprehensive redesign of the basic LC100-A circuitry which adds capability to measure Q of tuned circuits:
(in German but Google will translate)
     the-dg5mk-lcq-meter-v-2.3

Another home-brew version is described in the next link. It uses the Atmel ATmega8515 MCU. The ATmega328 could easily be substituted.
     http://uzzors2k.com/index.php?page=lcfmeter

[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]

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.

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]

…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).

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]

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.

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.