Voltage indicator RN-11 by Novatek-Electro

Today, a very brief look at a voltmeter that’s fairly ordinary, except that it can be mounted on a DIN rail—that’s really its main distinguishing feature.
As usual, I’ll take a look at it, run some tests, take it apart, and explain why I needed it.


I’ll start by explaining why you might need a meter like this in the first place.
Most of the time, a multimeter is all you need to measure voltage: probe the panel, check the voltage, and that’s it. But sometimes that’s inconvenient, or even impossible, and you still want to monitor the voltage without having to press any buttons, connect anything, and so on—for example, in the same electrical panel. That’s what determines the device’s design.

I needed to be able to check the voltage just by looking at the display, whenever I wanted.
I’ve already reviewed several devices from Novatek, and this one came in exactly the same little box as the others, except for the label.


The package contents are unchanged too: the device and the manual.


The manual contains all the necessary information: specifications, dimensions, usage notes, and so on. If you want the full version, you can download it from this link.



Specifications. One notable feature is the measurement range, from 100 to 450 V. No, I don’t need that much at home; I’m talking more about how the voltage relay from the same Novatek measures over a more modest range for some reason—up to just 350 V (actually 390–400 V)—while this one goes up to 450 V.


The second oddity is another mismatch between the warranty period stated on the website (10 years) and in the manual (5 years).


It looks very much like the devices from my previous reviews: the same gray color and the same two-module width.


1, 2. There’s a four-terminal block at both the top and bottom, but in practice only the two outer terminals on the top one are used. The others are just there for show. We’ll see why later.
3. The front panel has a display and that’s it—no buttons, knobs, or extra LEDs.
4. A spring-loaded latch on the bottom.


Now for why I bought it.
I have an electrical panel at home with a DigiCop voltage relay installed. I’ve had it since 2009, and it’s never let me down. It’s made by my former business partner, who’s also just a good guy :)
Not long ago, I posted reviews of the RN-263t voltage relay and the EM-129 energy meter with protection. I really liked the latter and wanted to install it in my panel, but, as always, there was one “catch”: the EM-129 has no input voltage display. Sure, you can connect to it with a smartphone, but “that’s not how we do things”—especially since doing that when the power’s out isn’t very convenient.

So here’s how it worked out: the old relay took up 3.5 modules, and the panel has 12, of which 8 are taken up by circuit breakers, leaving 4 free. The new relay is 2 modules wide, but I also wanted to be able to quickly check what was happening at the input if the relay cut the power. So I decided to get a voltmeter, giving me the functionality I needed while taking up all 4 available spaces in the panel. The only downside is that the old relay had a larger display.


Before testing it, I took the voltmeter apart. The case opens very easily: there are clips on the sides, and no seals.


The construction turned out to be interesting in its own way. Two side panels fit into the base and hold both the top and bottom boards in place. The panels are also secured with clips—a very solid, well-thought-out design.


Inside are two boards connected by a four-wire ribbon cable. The cable solder joints are secured with hot glue.


The top board has the display and an Atmega48 microcontroller. It’s clear that the board has a lot of components missing, and it’s marked RN-111N. I couldn’t find this particular voltage relay model, but I did find the RN-111M—here’s a link—which also has two four-terminal blocks.


The bottom board confirms my guess that this was originally a voltage relay. Interestingly, the four-terminal block on the bottom is there for a reason: it holds a standard, non-latching relay, and its changeover contacts are used. In other words, the relay can close the contacts when the voltage is out of range.


Some components are missing here too, which makes perfect sense. There are protective slots between the terminal block contacts.


The power supply section uses a capacitive dropper, followed by three Zener diodes, with the voltage then fed to an LM317 regulator. A classic solution for devices like this, but we'll come back to it later.


Let's put it back together and move on to testing.
When power is applied, the display briefly shows STA, as on the РН-263t, and literally 0.5-1 sec later the voltmeter switches to displaying the measured voltage.
The display isn't very large, but it's high-contrast and easy to read.


The voltmeter tries to start up at 35 V, but the display just flickers because there's not enough voltage for it to work properly.
At 67 V, the meter started working and displayed Lo to indicate that the input voltage was too low. If you lower the input voltage, it starts rebooting in a loop again at 60 V.


The voltmeter starts displaying the input voltage at 100 V, just as stated in the description. It also said that the error could be up to 2 V in the 150-250 V range, and up to 4 V elsewhere.
I tested the entire range from 100 to 450 V in 25 V increments and found that the error was actually 3 V from 100 to 225 V, dropped to 2 V at 250 V, and then decreased to 1 V as the voltage increased up to 450 V. If you raise the voltage further, at 450 V the voltmeter displays Hi, indicating that the limit has been exceeded.

The voltmeter behaved normally even at the maximum input voltage; at least, I didn't notice any overheating.


Of course, someone might say this is just an ordinary voltmeter, but I think attentive readers will have noticed the modest TrueRMS label. Yes, this meter isn't just a voltmeter: it's also suitable for measuring voltages with waveforms other than a sine wave.


Of course, I tested this too. I used a regular Mustek UPS and powered it from an adjustable power supply.
1, 2. Output with no load, input voltage of 13 and 14 V. I actually tried four settings: 11, 12, 13, and 14 V, but the UPS switches the transformer windings, so the output at 11 and 12 V was the same as at 13 and 14 V.
3, 4. Same input voltage, but with a resistive load—a light bulb—connected to the output.

The photo shows that the readings match those of the TrueRMS multimeter (right) and differ significantly from the regular one (left). There's one small oddity, though: as far as I remember, a regular multimeter should read high with a square wave, but for some reason mine showed a lower voltage. Then again, I haven't used it to measure UPS output voltage in so long that I may have forgotten—maybe that's just its "quirk".


Overall, measuring a square wave seems to work beautifully, if it weren't for one significant "but". During the test, which lasted about 15 minutes, I noticed a strange smell, clearly something overheating. Since the voltmeter had behaved perfectly well at an input voltage of 450 V, it didn't even occur to me that it might be the source.
It turned out the smell was coming from the voltmeter itself, so I opened it without disconnecting it from the UPS and measured the component temperatures.
1. You can clearly see that the heat is concentrated around the input section, where the capacitor and Zener diodes are.
2. But it's the resistor connected in series with the capacitor that's heating up—and quite badly, reaching about 260-270 degrees.


Since the UPS was powered from an adjustable power supply, I also noticed a difference in its power consumption: it used 6.6 W with no load, but 15.1 W with the voltmeter connected. Of course, not all of the difference was due to the voltmeter heating up, but it was still quite noticeable.


And, of course, the conclusions.
Overall, the voltmeter suits my needs: it measures voltage, and together with the ЕМ-129 it takes up exactly four spaces in the electrical panel. The display is good, though I would have liked it to be a little larger.
But there are some drawbacks. The stated error is 2 V in the 150-250 V range, but I got closer to 3 V in practice; at higher voltages, the error became noticeably smaller. Unfortunately, the bigger problem is that changing the values of the input voltage divider won't help here, since the error is greater at lower voltages, not higher ones.

And then there's TrueRMS. It's certainly a good feature, and the voltmeter really does measure the square wave at the UPS output correctly, so no complaints there. The problem is the increased heating in this mode, which isn't exactly ideal. Sure, you could say the voltmeter isn't designed for this, and to be honest, I don't really need it either. But then again, what's the point of TrueRMS if you're only measuring sine waves? Of course, TrueRMS can improve measurement accuracy when there is a high level of interference or the waveform is not quite a sine wave (for example, when powered by a generator). However, the test showed that when measuring ordinary mains voltage, the voltmeter did not quite meet its stated accuracy.

In short: It is neatly made, works, and has a TrueRMS measurement function. I’m happy with it, but the accuracy could be better, and it could run cooler when powered by a square wave.

That’s all. I hope this was useful.