Polyester Cap Size: Red Vs Green

[Ginsly]

This is one of those times where I realize I still have a lot to learn. I'm sorting through some caps and realized I have what look to be red metallized polyester capacitors as well as mylar greenies. I'm a bit confused why the red ones would be so much smaller than the green ones at the same voltage (100v). Below is a pic of a 220nf greenie, 390nf red, 470nf greenie, and a 680nf red. As far as I know, these are both very similar types of poly caps - why are the red ones so much smaller?


Also- I'm not certain exactly what time of capacitors these are (below). Can't definitively say if the blue ones are ceramic, mlcc, or polyester - I figured the slightly taller one is ceramic and the shorter one is an mlcc...? No clue about the orange one!

 

[Ginsly]

I'd love an assist! I realize this is rudimentary stuff, but I'm baffled by the difference in size between the greenies and reds - and again, same voltage.

As far as the other examples, I'm just not used to those form factors. The shorter blue one is 100nf and REALLY small, so it almost has to be an MLCC. I'm just used to the round-ish mustard-colored ones.

 

[Harry Klippton]

I've never used that kind of cap and I'm not sure why you'd want to

 

[Ginsly]

I've never used that kind of cap and I'm not sure why you'd want to

Which one? Greenies or reds? The blue ones? I posted several different caps, just trying to clear up some confusion.

I hear ya, though - I generally use c0g mlcc for pf, box film for nf, and electros for uf. I just have a bunch of these polyester caps and am trying to figure out what's what. The red ones aren't very big even for higher-nf values, so I'd considering using them in certain situations - I'm just curious what the difference is between the reds and greens. The green mylar 470nf is giant, but the higher-value red polyester 680nf cap is less than half the size - why?

 

[spi]

Wait until you see smd caps. It's not the size that matters, it's the ... wait what's the topic again?

 

[Ginsly]

Wait until you see smd caps. It's not the size that matters, it's the ... wait what's the topic again?

Ah it was only a matter of time!

Okay, ya made "the joke", now help me sort this out!

 

[Brett]

All caps shown (aside from the orange cap) are film. Size differences can be (but aren’t necessarily limited to) material, tolerance, manufacturing differences.

Generally, the box film, greenies, and the red ones pictured are regarded to as performing similarly in low voltage applications. That isn’t conclusive, but a general consensus. Most of the time, box film caps are used in layouts because they are compact for more densely populated boards.

The two blue caps are almost certainly both ceramic. MLCC is ceramic, just a different construction technique and can be made with higher quality materials, see X7R, C0G, for more in-depth understanding.

The orange cap looks like a dual electro cap, but it’s difficult to tell from the pic.

I’m not sure why any of this matters all that much, but I know you’re often very inquisitive, and I hope this helps.

 

[Ginsly]

Generally, the box film, greenies, and the red ones pictured are regarded to as performing similarly in low voltage applications. That isn’t conclusive, but a general consensus. Most of the time, box film caps are used in layouts because they are compact for more densely populated boards.

Got it! Yep, it seems like I could pick box, red, or green and have it perform the same way in nearly any pedal. In almost 100% of situations it makes sense to pick the smallest, most reliable part possible - which is a box cap. I suppose MLCCs are even smaller, but seem to have some possible drawbacks in certain positions/circuits - I'm still a little unclear on that. I just happen to have some reds and greens and would like to get some use out of them (when space allows).

The two blue caps are almost certainly both ceramic. MLCC is ceramic, just a different construction technique and can be made with higher quality materials, see X7R, C0G, for more in-depth understanding.

I figured they were both ceramic, but I was wondering if there is some sort of visual indicator that would indicate an MLCC. I know a bit about XR7 vs C0G, and that's why it would be nice to know whether what I have is an MLCC or not. That being said, I won't necessarily know what dielectric they contain even if I CAN determine that it's an MLCC!

I’m not sure why any of this matters all that much, but I know you’re often very inquisitive, and I hope this helps.

Part selection can be pretty critical or pretty flexible depending on the component or circuit, and I'm still working out what all of the little differences are. And yes indeed, you've often been very helpful in that regard!

 

[Brett]

I just happen to have some reds and greens and would like to get some use out of them (when space allows).

I have a decent amount of the red ones and you know what those big bulky caps are good for? Breadboarding. It keeps your assembled PCBs uniform and properly spaced (since most boards are designed for box films caps now).

that's why it would be nice to know whether what I have is an MLCC or not

I won't necessarily know what dielectric they contain even if I CAN determine that it's an MLCC

Then treat them as you would any other standard ceramic. Organize by value and just use them in the same spot as the other wackadoo caps, the breadboard. When a circuit calls for a specific grade of ceramic, you'll know it's not one of those. Hopefully, you'll have a grab bag of caps you've purchased specifically for that purpose.

Part selection can be pretty critical or pretty flexible depending on the component or circuit

You usually see this with JFETs and Germanium BJTs, but at the low voltages we see in guitar effects, capacitors are typically pretty forgiving as long as the capacitance is right and your electro's aren't too leaky.

 

[Ginsly]

I have a decent amount of the red ones and you know what those big bulky caps are good for? Breadboarding. It keeps your assembled PCBs uniform and properly spaced (since most boards are designed for box films caps now).

Absolutely! I do indeed use them for breadboarding, and some of the smaller red ones will likely be good for certain vero/perf projects.

You usually see this with JFETs and Germanium BJTs, but at the low voltages we see in guitar effects, capacitors are typically pretty forgiving as long as the capacitance is right and your electro's aren't too leaky.

Gotcha. I'm not sure how ESR readings might affect performance in a given circuit, but from what I gathered here it wouldn't make a huge difference. I need to look into that, as it would be good to know definitively. Thanks Brett!

 

[darwin999]

Several factors go into determining the size.

A capacitor's capacitance is proportional to (1) the dielectric constant (a measure of the electrical polarizability) of the insulator, as well as (2) the area of the metal plates on each side of the insulator; and (3) it is inversely proportional to the thickness of the insulator. So these factors, as well as the different materials used in different types of capacitors, determine the ultimate size, geometry and volume of the capacitor.

MLCC capacitors use materials with a high dielectric constant - hence their area can be smaller, and thus their size tends to be smaller than capacitors that use plastic as the insulator, which have a smaller dielectric constant.

As the voltage rating goes up, the thickness of the insulator increases so that the insulator doesn't experience dielectric breakdown - i.e., when the electric field gets so large that destructive ion motion occurs (an arc down, which leads to shorts or other damage). Hence higher voltage rating generally leads to larger volume for a given style of capacitor.

But they are all capacitors. There are some detailed differences in behavior - e.g., electrolytics tend to deviate from ideal behavior at high frequencies (hence you often see a smaller non-electrolytic in parallel to deal with high freqs); the capacitance of MLCC's can decrease at high voltages as the dielectric constant of their insulating materials is voltage-dependent; etc.

Hope this helps.

 

[phantom]

Well, I learned something here. Does that mean I get to go home now ?