RLC and ESR meter, or a device for measuring capacitors, inductors, and low-resistance resistors.

Lately, failing electrolytic capacitors have become one of the main causes of radio equipment breakdowns. But for proper troubleshooting, a capacitance meter alone is not always enough, so today we'll talk about another parameter: ESR.
I'll try to explain what it is, what it affects, and how it's measured in this review.

First, I should say that this review will be radically different from the previous one, even though both are about measuring instruments for electronics hobbyists.
1. This time it's not a kit, but more of a "semi-finished product"
2. I won't be doing any soldering in this review.
3. There won't be a schematic in this review either. I think it'll be clear by the end why.
4. This instrument has a very specific purpose, unlike the previous "jack-of-all-trades."
5. Lots of people knew about the previous instrument, but almost nobody has heard of this one.
6. This will be a short review

First, as always, the packaging.


No complaints about the packaging: simple and compact.


The package contents are very basic: just the instrument itself and a manual. Test leads and a battery are not included.


The manual isn't exactly packed with information either—just general statements and pictures.


The instrument's specifications, as listed in the manual.


And now, in simpler terms.
Resistance
Range — 0.01–20 Ω
Accuracy — 1% + 2 digits.

Equivalent series resistance (ESR)
Range — 0.01–20 Ω; works with capacitors from 0.1 µF
Accuracy — 2% + 2 digits

Capacitance
Range — 0.1 µF–1000 µF (3–1000 µF measured at 3 kHz; 0.1–3 µF at 72 kHz)
Accuracy — depends on the measurement frequency, but is about 2% ± 10 digits

Inductance
Range — 0–60 µH at 72 kHz and 0–1200 µH at 3 kHz.
Accuracy — 2% + 2 digits.

First, I'll explain what ESR is.
Many people have heard the word "capacitor" quite often, and some have even seen one :)
If you haven't, the photo below shows the types most commonly found in electronic equipment.


A capacitor usually looks like a little component with two leads, but in reality all components are more complex than they seem at first glance.
To start with, no component is ideal. In addition to its main parameter, it has a whole bunch of “parasitic” ones.
Since we're talking about capacitors, let's take a closer look at one as an example.

In real life, a capacitor's equivalent circuit looks roughly like the one shown below.
The diagram shows:
C — equivalent capacitance, r — leakage resistance, R — equivalent series resistance, L — equivalent inductance.

Put simply:
Equivalent capacitance — the capacitor in its “pure” form, i.e. without any imperfections.
Leakage resistance — the resistance that discharges the capacitor independently of the external circuits. To use a water-barrel analogy, this is natural evaporation. It may be greater or smaller, but it is always there.
Equivalent inductance — you could think of it as an inductor connected in series with the capacitor. For example, it comes from the capacitor plates being rolled up. This parameter affects the capacitor at high frequencies, and the higher the frequency, the greater the effect.
Equivalent series resistance, ESR — this is the parameter we're looking at.
You can think of it as a resistor connected in series with an ideal capacitor.
It comes from the leads, plates, physical limitations, and so on.
The cheapest capacitors usually have higher resistance, while more expensive LowESR ones have lower resistance. And then there are Ultra LowESR capacitors.
To put it simply (and very roughly), it's like filling a barrel through a short, thick hose versus a long, thin one. The barrel will fill either way, but the thinner the hose, the longer it takes and the greater the losses over time.


Because of this resistance, a capacitor can't be discharged or charged instantly. Also, when operating at high frequencies, this resistance is what heats the capacitor.
But the worst part is that a regular capacitance meter doesn't measure it.
I've often had cases where a meter showed a bad capacitor had normal capacitance (or even higher), but the device still didn't work. Measuring it with an ESR meter immediately showed that its internal resistance was very high, so it couldn't work properly (at least not where it had been installed).
Some of you have probably seen bulging capacitors. If we set aside cases where capacitors bulged just sitting on a shelf, the rest are caused by an increase in internal resistance. A capacitor's internal resistance gradually increases during operation, either because it's being used outside its proper operating conditions or because it overheats.
The higher the internal resistance, the more the capacitor heats up from the inside. The more it heats up internally, the more its resistance increases. Eventually, the electrolyte starts to “boil,” and the resulting increase in internal pressure makes the capacitor bulge.

But capacitors don't always bulge. Sometimes they look perfectly normal and have the right capacitance, yet still don't work properly.
Connect one to an ESR meter, and instead of the usual 20-30 mΩ, you'll get 1-2 Ω.
I use a homemade ESR meter that I built many years ago from a circuit posted on the ProRadio forum. The design is by Go.
This ESR meter comes up in my reviews quite often, and people often ask me about it. When I saw a ready-made unit among the store's new arrivals, I decided to order one and give it a try.
I was also intrigued because I couldn't find any information about this meter anywhere. That made it all the more interesting :)

The meter looks like a “semi-finished product,” i.e. an assembled unit without an enclosure.
To make it easier to use, though, the manufacturer mounted the whole assembly on these little plastic “feet.” Even the nuts are plastic :)


The terminals for connecting the component under test are located on the right end of the device.
Unfortunately, it uses a two-wire connection, which means that the longer the test leads (if you use them), the greater the measurement error.
Better designs use a four-wire connection: one pair charges and discharges the capacitor, while the other measures the voltage across it. With this arrangement, the leads can be a meter long without making any significant difference to the readings.
There are also two circuit board contacts next to the terminals. They are used to calibrate the device (I only figured that out later).


There is a compartment on the bottom for a 6F22 9 V battery (PP3).


The device can also be powered by an external power supply connected via the MicroUSB port. When power is connected to this port, the battery is automatically disconnected. If you use it frequently, I recommend powering the device from USB, since the battery drains quite noticeably.
The photo also shows that the battery strap is reusable. Its buckle has a tab that you press to release it.


Assembled, it looks something like this.


The device is switched on and controlled with a single button.
Power on — press and hold for more than 1 second.
In operating mode, pressing the button switches between L and C-ESR measurements.
Power off — press and hold the button for more than 2 seconds.


When switched on, the device first displays its name and firmware version, followed by a warning that capacitors must be discharged before testing.
If you hold the button for more than two seconds, the display shows “Powering off”; the device switches off when you release the button.


As I mentioned above, the device has two operating modes.
1. Inductance measurement
2. Capacitance and resistance (or ESR) measurement.
In both modes, the display shows the device's supply voltage.


Naturally, let's take a look at what's inside this device.
It looks noticeably more complex than the previous transistor tester, which indirectly suggests either a poorly thought-out design or better performance. I think the latter is more likely in this case.


There's not much to say about the display; it's the classic 1602 type. The only thing that surprised me was the black PCB.


I took two overall shots of the circuit board, one with flash and one without. The device really didn't want to be photographed and did everything it could to make things difficult, so I apologize in advance for the image quality.
Just a reminder: all the photos in my reviews are clickable.




The device's “heart” is a 12le5a08s2 microcontroller. I couldn't find any information on this specific controller, but the datasheet for another version mentioned that it's based on the 8051 core.


The measurement section contains quite a few components. The processor is also said to have a 12-bit ADC used for measurements. That's a pretty good resolution; the interesting question is how accurate it really is.
At first I thought about drawing up a schematic of this whole “mess,” but then realized there wasn't much point, since the device's measurement ranges aren't particularly impressive. Still, if anyone's interested, I can try to trace it out.


The measurement circuit also uses an op-amp, which seems pretty good to me. I used one like it in the current-shunt signal amplifier for my electronic load.


This appears to be the circuit that switches the power source between the battery and the USB connector.


There's almost nothing interesting on the underside of the board; apart from the button, there are no components at all :(


But I found something interesting even on the bare circuit board :)))
The thing is, when I got the device and was playing around with it, I simply couldn't get it to display the capacitance of a capacitor above 680 µF. It stubbornly showed OL, and that was it.
While inspecting the board, I couldn't help noticing three pairs of contacts for connecting buttons (judging by the labels).
First I shorted key2, and the screen showed “zero calibration” (rough translation) — OK.
Ha, I thought, now we've got you.
But no. Calibration took me ages because this device is so rare that there's no information about it at all. The only mention of calibration I could find was here.


Shorting the other pairs of contacts brings up what appear to be constant values on the screen.
There were other options too, with different letters, and sometimes shorting key3 would briefly display “Saved OK” (in English, of course).


But back to calibration.
The device fought me every step of the way.
First, I tried shorting the terminals with tweezers and calibrating it that way, but afterward the device showed the correct capacitance and a negative resistance for capacitors.
Then I shorted the two test pads on the board. The device started showing resistance correctly, but the capacitance measurement range narrowed to 220–330 µF.
After a long search online, I came across this phrase (the link is just above): “Use 3cm thick copper wire for short circuit to clear”
That meant “use copper wire 3 cm thick.” I thought 3 cm thick was a bit extreme, and they probably meant 3 cm long.
I cut off a piece of wire about 3 cm long and shorted the pads on the board. It worked much better, but still not quite right.
I took a wire about twice as long and repeated the process. After that, the device worked reasonably well, and I did the rest of the tests after this calibration.

First, I gathered various components to test how the device works.
In the photo, they're arranged in the order I'll test them, except the inductors are facing the other way.
All components were tested from the lowest value to the highest.


Before testing, I checked with an oscilloscope what the device was outputting at its measurement terminals.
Judging by the oscilloscope readings, the frequency is set to about 72 kHz.


The inductance readings matched the values marked on the components quite well.
1. 22 µH inductance
2. 150 µH inductance
By the way, during calibration I noticed that none of the adjustments affected the accuracy of capacitance or inductance measurements; they only affected the accuracy of resistance measurements.


With a 150 µH inductor, the signal at the terminals looked like this


Small-capacitance capacitors also caused no problems.
1. 100 nF, 1%
2. 0.39025 µF, 1%


Waveform when measuring a 0.39025 µF capacitor


Next up were electrolytic capacitors.
1. 4.7 µF 63 V
2. 10 µF 450 V
3. 470 µF 100 V
4. 470 µF 25 V lowESR
A separate note about the 10 µF 450 V capacitor. The readings really surprised me, and this isn't a defect in a particular component, since the capacitors are new and I have two identical ones. Both gave the same readings, and other meters showed a capacitance of around 10 µF. What's more, this meter did show readings of around 10 µF a couple of times. I don't understand why.


1. 680 µF 25 V low-impedance
2. 680 µF 25 V lowESR.
3. 1000 µF 35 V standard Samwha.
4. 1000 µF 35 V Samwha RD series.


Waveform at the terminals while testing a standard 1000 µF 35 V Samwha capacitor.
In theory, when measuring high-capacitance electrolytics, the frequency should have dropped to 3 kHz, but the oscilloscope trace clearly shows that the frequency didn't change during any of the tests and stayed around 72 kHz.


The 1000 µF 35 V Samwha RD series capacitor sometimes gave this result too. It happened when there was poor contact between the leads and the measurement terminals.


After taking the group photo, measuring the parts, and putting them away, I remembered that I'd forgotten to measure the resistors.
For the measurements, I used a couple of resistors:
1. 0.1 Ω 1%
2. 0.47 Ω 1%
The second resistor's resistance is somewhat high and clearly outside the 1% tolerance, closer to 10%, in fact. But I think this is probably because the measurement uses AC, and the wirewound resistor's inductance affects the result. The small 2.4 Ω resistor, for example, measured 2.38 Ω.


While looking for information about the meter, I came across photos of it a couple of times showing simultaneous measurements at different frequencies, but my meter doesn't display that. Again, I have no idea why :(
Maybe it's a different version, or something else, but there is a difference. I got the impression that mine only measures at 72 kHz.
A high measurement frequency is good, but it's always handy to have an alternative.


Summary
Pros
The device showed fairly good accuracy in use (though only after calibration)
Leaving aside the fact that I had to calibrate it, you could say it’s ready to use right out of the box, though I may just have been lucky.
Dual power supply.

Cons
No information at all on how to calibrate the device
Narrow measurement range
My device only started working properly after calibration.

My take: Honestly, I have very mixed feelings about this device. On the one hand, I got some pretty good results; on the other, I ended up with more questions than answers.
For example, I still haven’t figured out exactly how to calibrate it properly. I also don’t understand why my 10 µF capacitor reads 2.3, or why measurements are only taken at 72 kHz.
I don’t even know whether to recommend it. If you really don’t want to solder, you could use this one or the transistor tester from my previous review. If you want better performance (mainly a wider range) and don’t need to measure inductance, you could build Go’s C-ESR meter.
The 1000 µF upper capacitance limit was a real disappointment. I could easily measure 2200 µF, but the device’s accuracy dropped and it clearly started reading capacitance too high.

That’s all for now. I’d be very grateful for any information about this device and would be happy to add it to the review. I suppose someone else may have one too, though that seems very unlikely, since I couldn’t find anything about it—even though many devices are copies of designs that are already well known.

The product was provided by the store for review.