HOw do you measure a capacitor?

[gnugear]

How can I measure a capacitor that has no markings on it? Can it be done with a multi meter?

[chloortablet]

Yeah but the multimeter must have an "option" to do that.

You can`t measure it with a normal multimeter, and if you want to do it right you really need a capacitor checker/device to do it.

[JD]

You can measure the capacitance with most decent DMMs (measured in Farads, F). You will not be able to tell whether or not it's any good under a high voltage load until installed.

[gnugear]

I just need a reading. I want to replace it and all I can find is a manufacturer's name but no number.

[gnugear]

You can measure the capacitance with most decent DMMs (measured in Farads, F). You will not be able to tell whether or not it's any good under a high voltage load until installed.

Do you know how to do it? I have a digital meter from Radio Shack. This is the model ...

http://www.radioshack.com/product/index ... age=search

[JD]

According to the manual in the link, this meter unfortunately does not appear to measure capacitance.

[RRJackson]

This thread has been dead for a while, but I wanted to bump it and mention something. I have a Fluke 79 that can test capacitors. It's kind of amazing how many aren't anywhere near spec. I bought 40 axial film 2 uF caps from an auction a while back and not a single one of them was over 1.68 uF. They were all still in the tape strips, so it wasn't like they'd been sorted and ditched.

Another recent buy of five 2 uF caps yielded ranges from 1.93 to 2.02.

The same thing happens a lot with resistors. I recently bought twenty Ohmite 1 ohm 1% wire-wound resistors and they all tested at 1.6 ohms, which really seems insane from something I paid a premium for to make sure they had a tight tolerance.

Testing and matching components is a big part of the job. It's not very sexy, but I feel like it's worth the effort. Although, even if you let someone A/B an amp with a 1.68 uF cathode bypass cap against an amp with a 2.02 uF cathode bypass cap I'm not sure most people would hear a difference. So maybe all the testing and matching is just busywork.

-Rob

[hired hand]

A lot of caps are 20%.
1 Ohm may be asking a lot from your meter.
Do you have a 1% 100 Ohm.? Measure that, if it is close then you know your meter has a tuff time with a near short of 1 Ohm. Put it in series with the 1 Ohm and see what your meter says.
best

[demonufo]

Fluke or no Fluke, you're not really going to be able to get any sort of accurate reading at 1ohms without a properly designed low-ohms meter. Especially an auto-ranging meter. Just because it says Fluke on the packet doesn't mean it's good at everything. Other than general fault-finding, I wouldn't go trusting an auto-ranging meter for anything really, no matter who made it.

I also wouldn't pay too much mind to how a multimeter measures capacitors. There are too many variables that come into play without proper equipment (the leads alone can have a MASSIVE effect), and a multimeter isn't best equipped to do this.

[Harold]

I wouldn't go trusting an auto-ranging meter for anything really, no matter who made it.

Interesting ... Care to explain this?

[demonufo]

The accuracy just isn't the same as dedicated bridges (well, on most autorangers anyway)... and my last calibration certificates (albeit now a year out of date since I no longer have an employer paying for it ) back that up.
I still prefer my AVO 9 over any of my other multimeters which are a few of flukes 112, 233 & 175 (which is particular all over the place) , a generic £100 Maplin White Gold (which is actually pretty good), a nice Metrix analog, Meterman, Megger...

[Reeltarded]

Amen.

[RRJackson]

You know, the resistance across the probes hadn't occurred to me. 1 ohm is probably not something I'm going to be able to measure accurately with my Fluke. Since all the 1 ohm Ohmite's were exactly 1.6 ohms it's probably a good guess that they're all to spec.

FWIW, I have some 1% tolerance 100k resistors that I picked up at an aerospace surplus place and they all read very close to dead-on.

BTW, in case it came off strange, I wasn't mentioning that I was using a Fluke in some sort of Mad Men-y, "Best of all, it's a Fluke!" kind of way. It's an older Fluke. A 79 Series II, which is at least two generations removed from the current lineup. I was just mentioning it to get as many of my variables out there as possible so if someone was like, "You know, Flukes never could accurately read lower impedances!" I'd be like, "Oh, well that explains a lot..."

-Rob

[demonufo]

No, it didn't come off as strange, it's just because of the reputation of Fluke, some users expect them to be able to do everything perfectly once they've shelled out hard-earned for it. Truth is, there's always a compromise with auto-rangers, and resistances below 20 ohms or so is a really big ask for anything other than a dedicated low-ohms meter.

[RRJackson]

No, it didn't come off as strange, it's just because of the reputation of Fluke, some users expect them to be able to do everything perfectly once they've shelled out hard-earned for it. Truth is, there's always a compromise with auto-rangers, and resistances below 20 ohms or so is a really big ask for anything other than a dedicated low-ohms meter.

Nah, all meters seem to have some shortcoming or another. An acquaintance of mine who works at a local defense contractor was telling me some specific reason why they aren't allowed to use Fluke 77 meters on certain kinds of projects, but I was drinking a lot that night and the details are hazy. Some kind of issue with microwave cavities or LNBs causing it to give false readings, if I remember right.

This is the first time I've run into an issue (that I'm aware of) with my 79, but my thing with tools is that I don't mind 'em not being perfect as long as I can figure out what it is they're actually OK at.

-Rob