Hi. Here's an interesting question for you: Can you actually use your Lcr meter to measure capacitors in circuit? Because if you could, that'd be really handy, right? You can like all these uh, electrolytic caps and things. You can go in there, and you'd be able to test them in circuit troubleshooting a Pcb because everyone knows one of the major failure modes for products. If you've seen a lot of my repair videos, a lot of them, especially like you know, Tv repairs or something like that, it'll just be like a blown cap in the power supply, a blow and wet electrolytic, uh, capacitor.

and not all of them can be identified with. like, you know, it's burst out, it's leaking, or whatever leaking capacitors you have to actually test them. Is the capacitance good? Is the Esr or equivalent series resistance good? Well, can you actually measure them in circuit? And the answer is surprisingly yes. you can do a pretty decent job of it, But as always, there's traps for young players.

Let's take a look at it, right? So let's just try and measure a capacitor in circuit. I've got my Lcr meter here. It's just set to auto mode, so it'll determine whether it's capacitor, inductor, resistive, Whatever it is. Uh, measuring at uh, one Kilohertz, that's a fairly nominal, uh, test frequency.

And let's measure this big bad boy here, shall we? What do we get? Will it auto detect it? Oh oh. Resistance. Oh, it's one. That's one.

Ohm, it's one. Ohm. Oh, we've come a gutter. Well, let's actually force it into capacitance mode and try it again.

There we go. That's more like it. Look at that. a thousand mic and what is the value of this capacitor? Sure enough, it's a thousand mic.

We measured that in circuit. no worries whatsoever. It's practically bang on and we can measure the equivalent series resistance of that capacitor as well, because that's very important for high frequency ripple applications. You can come a gutter that way.

So let's put in Esr mode here now. Uh, you measure that at a hundred kilohertz if your meter can do 100 kilohertz because that's the uh, general industry specification for Esr. There we go: Esr mode. So we have to short the leads together because these are like really long.

So I'm going to null that out there. and unfortunately, it looks like I can't null out in Esr mode on this agilent meter. Anyway, let's let's let's call that an Ohm. So so we'll now measure that in circuit.

There you go. One point, oh two. Ohms. Something like that.

So we're talking under 0.2 Ohms. Um, that sounds pretty good for a thousand mic. Uh, cap, Esr, we'll compare our whack up a data sheet here for a Rubycon, which is the brand of this one and that's probably going to be very close. Let's try another popular Lcr meter.

This is the De-5000 This is Iet one, but you can get these for about a hundred bucks. They're pretty darn good. bang per buck. Let's give this one a go.

Can it do it? Uh, nope. It's Kamagatsa, but if you put that on manual range there it is. Well, just uh yeah. pretty close to a thousand mike there.

Uh, 0.91 Ohms there. so that's not too far off the other meter. But we did have to manual range it. So one kilohertz there, we measure pretty much bang on to a thousand microfarads.

Let's change the frequency at 10 kilohertz, huh? Six, uh, 700 Nano farads? What? 100 kilohertz, 1600 nano farads. And at 100 Hertz, we're actually up to 1200 micro farads. What's going on? So what does this actually measure? If we desolder it from the circuit without any of the other components actually affecting it? Well, it's actually 855 microfarads at 100hz and 120 Hertz. It's not going to be much different because that's the same frequency one Kilohertz 820.

And at 10 Kilohertz, it's basically measuring. Well, that's not actually open. That's like basically short. That's what happens when you short circuit A on a capacitance meter.

It measures oil like that. Otherwise, it'd be measuring like picofarads if it was actually open. And at 100khz 1700 nanofarads, so it's all over the shop now. of course, this is a very large value cap a thousand microfarads.

So um, one of the things that you're supposed to know when you're using Lcr meters like this is that for large value capacitors like this, you're supposed to use the lower frequency like 100 hertz, 120 Hertz and that really gives us our capacitance value. So if you were to give me this cap and say measure it right, I'd put on the 100 the lowest frequency uh, mode 100 hertz and that will give us the greatest resolution. Um, and we'll talk about, uh, different range resistors in a minute. Um, but yeah, that's going to give us the best value And the Esr 1.3 ohms.

So basically our Esr was pretty much, uh, bang on to where we were before. Of course we have to subtract the one ohm of the leads here, so you know we did a fairly good job measuring the Esr of that capacitor in circuit and we'll repeat the same measurement on the other Lcr meter using the proper short lead measurement interface like this. So you know this is going to be this is going to be the real deal at 100 Hertz there, 848, 120 Hertz 843 Basically the same and at one kilohertz. as you can see, we've lost some resolution here.

Um, and so it's not as good. 761 Microfarads and at 10 kilohertz, it's going. Nope, that is too big a capacitor. I can't measure that, thank you very much.

and it's going to tell us the same at 100 kilohertz as well. Hi Brief whiteboard interlude. I actually, um, started shooting how an Lcr meter works and I ended up like shooting 20 minutes worth of footage. So yeah, that was just made this video too long.

So at insert at this point I would say go watch that previous video which I've already released on how Lcr meters work and it explains everything I'm going to be talking about later on in this video. So you definitely should watch this. Link it down below and up there. So if we actually go back to this board and measure uh, what's actually on the board after we remove the cap, we can see uh, well, at least the parameters of what uh, we had actually in circuit surrounding that capacitor And I don't know.

I haven't like traced this out or anything. I've got no idea uh, what it's doing, what it's a bulk for. Obviously, it's a bulk cap for you know, some sort of, uh, supply or something like that. But if we probe that, you can see, well, it's it.

Thought it was a one microfarad or something. Now it's 4.8 ohms at one kilohertz. So that's a You know, it's fairly low impedance around there. Now at 100 kilohertz, it thinks it's an inductor that is low impedance.

So that's why. Actually, uh, you know we had a little bit of trouble uh with different meters actually measuring such a large value cap and you could only do it at low frequencies. So let's measure this cap in circuit 470 Microfarads. it looks like it's the same type and everything.

So let's measure that at 100 hertz in fixed capacitance mode and 422 micro farad. so we can actually measure that in circuit. But one of the um, extra tricks of measuring uh in circuit is that not only uh to manually select the capacitance mode or the inductance mode if you're measuring inductors, but also swap the leads like that and aha well oh there we go. It still might have some residual charge in there, you might have to leave it.

but if you swap the polarity, you can get extra in circuit parameters that can actually change depending upon the polarity that you've got there. And you can see that's only 690 Nanofarads. And there we go. Let's put in that direction.

You saw that it was 690 Nanofarads before it was Nanofarad. So now we had to actually like clear that and do it again. Oh, I thought it was nano nano Nano? Nope, Nope. Nope.

Nope. 690 nano farads? What's going on right? It's playing silly buggers, It really doesn't like that at all. So we'll range this deliberately to microfarads like this so it's not going to get confused at all. 420 microfarads and we can measure it that way as well.

But you can see how if you let the meters auto range. well, you can really come a gutter. And it turns out for most large value capacitors, we can actually go around in circuit and actually measure them. Here's another 1000 Mic Jobby, There it is there.

1100 No wackers. There you go. 979. We can do 10 microfarads.

There, it is there. It's practically bang on. Here's 100 microfarads down here. See, we can actually get reasonably close and I've tried this on dozens of different boards and hundreds of different types of caps in various circuits.

I've got a whole bunch of them up there and it generally just works pretty fine. but then you do again. Eventually get ones that are so low impedance around them that well, you can't measure diddly squat because it's basically a short circuit. measure resistance like that.

There we go. like 33 Ohms. It's just like way too low impedance. Whatever is around that uh cap there.

It's like on the output of this uh, little transformer thing here. Like who knows what's going on there. But you know there are some that you can't measure, but a good lot of caps in circuit. You can actually measure not too badly at all and measure the Esr as well.

But of course capacitors in circuit actually have active components usually around them. They could be voltage regulators. They can be, uh, like I mentioned before, a this could be like the reset pin of a micro or something. You might have some like Rc um, you know, startup thing.

You know something like this or something like that. You want to measure that cap in circuit to see if it's still any good or gone bust and stuff like that, and inside the chip, you can have Esd protection diodes like this and you can have active parts so effectively you've got like a diode and the power supply can act as a short circuit at a frequency like really low impedance. So effectively you can have like one or two diodes in parallel with the capacitor that you're trying to measure. and well, if you've got too high a test voltage that's going to clip it, let's go to the scope.

so you should actually test this for your Lcr meter. You should really get to know the output signal levels of your Lcr meter here. So let's just do the Agilent jobby here. I've got my Uh capacitance substitution box here and across it.

I've actually got two parallel diodes like that to simulate, um, some active circuitry that you might get on a Pcb. So I've got it disconnected here and you can see that we're getting like a selected 100 Hertz there and we're getting 2 volts peak to peak. And of course, um, that is more than enough to uh, clamp on these two silicon back-to-back diodes. And at the moment it thinks it's 15 nanofarads because I've got it going into the scope and everything.

But don't worry about that. Okay, let's plug it in and you can see that our signal levels dropped. You can see though it has not clipped, it's still a sine wave so it's actually dropped to uh, about 220 millivolts peak-to-peak Which is not enough to clip. Uh, these.

I've got a hundred mic sorry, a 10 microfarad capacitor in there. So with the 10 microfarad capacitor at 100 hertz, uh, with the particular range resistor that, uh, the Lcr meter has chosen, the signal level is not enough to actually turn on any active devices in circuit. So if we're actually trying to measure a 10 microfarad cap in circuit, we're not going to be switching on at least any active elements. And that helps a lot with in circuit measurements.

and you'll notice that this is the same 150 220 mic, I can go up the highest one. I've got Two thousand. Mike There you go. We're down in the noise.

We're getting some common mode noise on there because we're using a single um ended, uh scope here and let's see if we can get this to clamp right at. Well there we go. It's starting to distort a little bit. So at one volt, uh, peak to peak there you can see and that's at uh, 15 microfarads.

So if we go down to 10 you can see, it starts to get a little bit distorted. And now as we go down, I'm now one microfarad. We're trying to measure a one microfarad cap and you can see that it is clamped and I'm down to a hundred nanofarads there. Now we've got absolutely no chance of measuring In this particular case, a hundred nanofarad cap using this particular range resistor in circuit that has active diodes and other you know, elements, active silicon elements in them.

We've just got no chance of measuring that accurately. But large values of caps? Yeah, because it drops all the way down. but you can't just like increase the frequency to do this because it actually gets worse. As I said, because of the large capacitance value.

and you'll see our 120 Hertz. You might saw it drop a little bit at one kilohertz. Yep, look at our signal level. now.

it's tiny tot. It's absolutely tiny top. We're getting the common mode noise and everything right? Pretty horrible stuff. And at 10 kilohertz, forget it because what you're doing is trying to measure a large value of capacitance at a large frequency.

And you can't do that because it's your signal level is going to be too low. even for any range resistor you try and select in. There doesn't matter. But at 100 hertz, of course, um, we can measure that.

There's 220 microfarads. I'm measuring that, No problems whatsoever. 33 Microfarads. You know it's measuring 28 because this is these aren't exact values, right? But we're measuring that in circuit with those diodes across it.

It's only once we get to those low values or we can go down even lower. I'm now in the nanofarad range. That's 1.5 nanofarads, and you can see that. All of that, that's 10 picofarads, right? We just cannot measure that.

Okay, because the based on the frequency that we're using, the Uh low and the low value capacitance, the input, the reactants, that impedance is very high and doesn't matter what range resistor we use, we just can't do it. It's only those large value caps. So coincidentally, though, the caps you usually want to measure in circuit are like your large value electrolytics and you can actually do it. It works fairly well.

And I've repeated this with other Lcr meters. and yeah, pretty much, um, all the ones that I've tested, they were able to give you a low enough uh signal level that actually doesn't clip. and you can experiment with your own Lcr meter and some caps. And in this case, it starts clipping about.

Oh, 15 microfarads. Let's call it, 10 microfarads at 100 hertz. Even though it's clipping, it can can actually still measure them. I'm going 2.2 microfarads now.

It starts to get a bit off, right? It can't measure it anymore. One microfarad, right? And it's measuring 7.2 It just nah, nah, it just can't do it. And right down at 100 Nanofarads, it's showing 16 microfarads, right? It's completely off. But anything above 10 microfarads? Yeah, no worries, you can measure that in circuit with other active elements in there, but that doesn't mean you won't get other, you know, low impedance stuff.

Uh, like you know, transformers or other, um, things which act as uh, low impedances and then that can ruin your day. But yeah, it actually works pretty well. And for this particular, Um, Lcr meter, if I manually arrange it, there's really not many spots where it actually hits the sweet spot of being able to measure. There we go.

It can measure like this is 15 nanofarads here, measuring 15.8 there, but you can see that the waveform's a little bit distorted. Um, yeah, it's not. It's not good, and it's over ranged at that point where the actual signal level is low enough not to clip and you'll see that, uh, we've got a clip waveform here. 470 Picofarads.

It's way off. and if we actually arrange it there, you can see how it's different with the different ranges. And if we go down to the picofarad range, yeah, we can get values like, uh, 6.8 nanofarads that don't clip, but they're well over range that, um, it can't measure them on that range. But as I said, it works remarkably well for the high value caps.

In this particular case, over 10 microfarads. But every Lcr meter is going to be different depending on the range, resistors, and whatnot. So you've got to really test your own Lcr meter to see what its limits are. And this Iet meter, um, it goes down to like one microfarad before it starts to clip there.

But anything above that, it's going to be super duper accurate in circuit it. Just if the signal level is low enough for it not to clip, that's 150 mic. And there it is. even though our signal level is very small, so I have to gain that up.

But of course it, it does that internally. So if I actually remove the diode here, this is 100. uh, micro farads and you'll see it has no impact at all on the measurement. It's not doing anything because it's not really conducting.

But now let's actually put a resistor in parallel and see what that does. Actually, I have to use this resistance box because this one only does. uh, high values in fixed and variable. I won't know what I've got.

So anyway, so there it is. right. So there's there's a hundred microfarad capacitor. it's reading a bit low.

Okay, no worries. And if we disconnect the oscilloscope, that actually doesn't make any difference. So that's really essentially no load on there, as you'd expect. Actually, let's change that frequency back to 100 hertz there.

Okay, so let's now put a 100k resistor in parallel. with that. You can see. It makes no difference whatsoever.

Let's go to 10k. Makes no difference whatsoever. Let's go down to 1k. Makes no difference whatsoever.

Let's go down to 100 Ohms. Okay, it's starting to make a little bit of a difference. Let's go down to 10 Ohms. Okay, and yeah.

10 Ohms. We start to have a problem in circuit that's 10 Ohms. There's like really low impedance stuff you saw and previously we measured like 30 ohms and stuff like that. Um, so it was obviously able to handle that.

So why does a parallel impedance if it's a pure resistor make? No really no difference unless it's so low that it actually kills the amplitude down like this. Okay, um, because which is a function of the it's going to be a function of with the range you're choosing the range resistor in there In combination with this, it's because it's a pure resistor. Just just like we talked about on the whiteboard in the other video, it's just effectively a parallel resistance across the capacitance. It doesn't really because it's a pure resistor.

It doesn't change the phase angle at all. and because, uh, there's not much else, uh, series resistance in there to actually get a voltage divider. um, type thing. The the source from the Lcr made is able to actually drive that capacitance.

it doesn't You can have, you know, look 100 ohms in parallel and still measuring exactly the same as 1k or anything else and you might think 100 ohms. No way it's going to measure that. But yep, whack it in parallel. And that's why you can effectively measure like high value capacitors at a low frequency like 100 hertz in in circuit relatively easily.

it actually works fairly well. So unless you've got like the waveform clipping or a really, uh, low impedance like you know, tens of ohms or something like that. Once again, every Lcr meter is going to be slightly different depending on what range resistor you've got in there, which is effectively the source impedance of your uh voltage, uh, source inside here, your Ac voltage source. But yeah, it's actually going to do a pretty decent job for large value caps.

So try it with your Lcr meter and see what it's like. I've tried several Lcr meters here, the ones that I've got and they all you know work in a similar sort of way for measuring high value caps. It's like it's rather surprising and I thought going into this video that I would actually find more of examples of in Circuit where it actually clips, but I just couldn't find them. And this is why some Lcr meters like this.

Global Specialties Lcr 58 Here they have different voltage test levels. There it is there. see: 0.5 volts Rms? Of course, that's Rms, so that is will actually turn on diodes. but we can actually switch that to a 0.1 volt Rms.

So 100 millivolt test signal. And the reason the specific reason that they have this functionality is so that diodes in circuit. Any active elements inside, chips, inside, regulators, or whatever. Any active elements at all bridge rectifiers, Whatever it is, Um, this won't turn them on.

But here's the funny thing. This video was originally not supposed to be a whiteboard tutorial on how Lcr meters work. It was supposed to show you this exact thing where you can get in-circuit things that screw up active elements that screw up your in-circuit capacitance measurements. and I thought I'd be able to find really good examples.

But I've tried hundreds of capacitors across like dozens of different boards and I can't actually find one example. Bloody Murphy's Law Could not find one example where the voltage actually made a difference. For large value capacitors, I can only get it to do it on the box if I use like, lower value caps, but all large value electrolytics that I measured in all sorts of different boards, I couldn't get it to do it. But anyway, Lcr meters.

Some do actually have a specific low voltage mode specifically to avoid, uh, active elements. So there you go. I hope you found that video interesting, even if it wasn't the video I originally intended uh to make and I did waffle on the whiteboard there. But hopefully you now get a good understanding of how Lcr meters work and some tips that you can use for measuring in circuit capacitors.

Make sure you manually set the function, the capacitance of the inductance that you want to do so that you don't confuse the auto ranging algorithm or the auto selection algorithm in there. And for large values of capacitors which is typically what you want to use in circuit, you measure them at the lowest frequency possible 100 hertz or Hertz and then also, um, don't forget to swap your probes around as well just to make sure that you're getting the same reading in both directions. and then you can, or at least similar reading in both directions, then you can be more confident that you're actually measuring an accurate capacitance value in circuit. And then, of course, if you're measuring the Esr measure it at 100 kilohertz.

You want to measure that at high frequency, and generally that works pretty well in circuit, but just compensate for your test lead resistance because these long, thin leads like this, they'll have like an Ohm or something like that. And yeah, you want to take that out if you're measuring uh Esr and then get to know your Lcr meter by measuring its signal level. And if you are measuring uh in circuit and your Uh Lcr meter does actually have the ability uh to set the voltage level, then you definitely want to set it on the lower level. even though I could not find a single silly example.

Um, I have this thing. If I do, I'll celebrate and whack the video on the second channel Anyway, I hope you enjoyed that. If you did and found it useful, please give it a big thumbs up. As always, discuss down below: catch you next time.