Capacitor question...probably a very basic one

[alank2]

I am used to what regular aluminum electrolytic capacitors look like with the stripe going down one side with the negative marking in them.

I am seeing a second type that looks very similar, but the marking is a gold/copper color instead.  Does that mean it is a different type of cap or still just an alum?

[mariush]

All electrolytic and polymer capacitors should have the strip representing NEGATIVE side.

Some polymer capacitors in surface mount form (look like larger ceramic capacitors or resistors) have the strip representing POSITIVE side (but there's also a + sign on the bar)



The yellow capacitors are tantalum, the black ones are polymer or some polymer variety of capacitors

[alank2]

This looks JUST LIKE an axial aluminum capacitor, just colored differently...

[uncle_bob]

Hi

Simple answer:

The cap guys make this stuff up as they go along. You should *always* check the polarity markings against the data sheet unless it is very obviously marked + or -.

Bob

[alank2]

The picture is terrible, but are the two caps on the left a different type of cap than the ones on the right/bottom?

[uncle_bob]

The picture is terrible, but are the two caps on the left a different type of cap than the ones on the right/bottom?

Hi

They are all aluminum electrolytic caps. You would *think* that gives you a clue to how they are marked .... dig up the data sheet and see what the factory decided to do ...

Bob

[mariush]

There's 5 electrolytic capacitors in that picture, all of them are with the negative side towards the bottom of the picture.  Regardless of color, the bar shows the negative, you can even see the -- signs inside the bar.

The circuit board (motherboard or whatever) also fills the negative side with color (white) but DO NOT ASSUME it's always the case. A long time ago, some manufacturers used the filled section for positive side of capacitors, nowadays almost everyone uses the filled side of the circle for negative side but it's not a rule. 

In IT , Asus and Asrock are two big manufacturers that love to use this uncommon convention on motherboards and other devices they make, here's a motherboard example where polymer capacitors (surface mount and radial, like electrolytic capacitors) are used, and the pcb uses the filled half of circle or filled section of rectangle for positive instead of the normal way to do things :

[alank2]

So they are all just electrolytic caps then?  Why the different color?  Different manufacturer?  The gold ones have a top that is not flat and looks like pressure may have pushed on it - do you think they are bad?  This is from an old netgear router...

[mariush]

Electrolytic capacitors have a liquid (or semi-liquid) electrolyte in them. Each time the capacitor is subjected to voltage above its rating, or too high current, or too high temperature, the electrolyte inside it can degrade a bit and release gasses which would be stuck inside the capacitor case. When too much gas is formed inside, the pressure inside would be too much and the capacitor would pop / explode violently.

In normal operation, the capacitor's electrolyte shouldn't release gases but just to be extra safe, manufacturers weaken the tops of capacitors a bit my making a pattern, which can be a +, a K  or some other shape.  If too much gas is formed, the gas inside pushes against the top and those grooves act as the weak point where the metal can break safely, the aluminum in those grooves will break and the gas will eject like a puff of smoke instead of capacitor blowing up.

Depending on how the grooves are made, it's possible for the tops to look a bit swollen from the factory but if one of those capacitors is substantially different than others, maybe it's a bit bad  and you should consider replacing it - capacitors don't go bad in an instant, their parameters simply degrade so circuits may still work for some time even with a dying capacitor.

Polymer capacitors are using a solid electrolyte, which can't really form any gas, so there's no longer a need to make those grooves on top of capacitors.  That's why you don't see any patterns/grooves/cuts in the capacitors in the picture above.

[Psi]

Solid polymer caps can have the top marking signifying + or -. Usually its -

Tantalums are almost always line = +

Normal electrolytic are always line = -   (some have no line and are bi-polar)

Best approach is to check the circuit/cap datasheet

[KD0CAC John]

Yes just different manufactures , when they went into production they just tried to find the price for the values needs , many products will have more than one manufacture on the same board , for all kinds of reasons .
If there is a bulged cap , it probably is a bad cap .   

[helius]

Caps with gold markings are sometimes EDLC supercaps. They have the negative pin marked.

[Psi]

Then you get the cheap caps from aliexpress.
Where the factory worker accidentally let the machine make 10000 caps with the plastic wrap around the wrong way and hence the polarity is labeled wrong. 

[uncle_bob]

Then you get the cheap caps from aliexpress.
Where the factory worker accidentally let the machine make 10000 caps with the plastic wrap around the wrong way and hence the polarity is labeled wrong. 

Hi

... and since they are cheap, we fiddle the production line to use them .... Lots of stinky smoke when somebody gets confused (or loud bangs if they are tantalum). It does make for a lot of lively conversation on the line.

Bob

[jitter]

So they are all just electrolytic caps then? 

Those in your picture, yes, they are.

Why the different color?  Different manufacturer? 

Whether or not they are from a different manufacturer, I can't tell from the photo. Given that the style of the negative electrode marking looks pretty much the same for all of them (apart from the colour), my guess would be that they're from the same manufacturer. You should be able to compare them, or post a photo taken from the other side?

If they are from the same manufacturer, the different colours may just mean that they're different types. There's more to the specs of a cap than just the capacity and voltage rating. There's also mounting style, size, ESR, lifespan, max. temperature etc. to be considered. As an example, just look at this overview of all the different series in the aluminium capacitors range of just Nippon Chemicon, one of the very reputable A-brands.

The gold ones have a top that is not flat and looks like pressure may have pushed on it - do you think they are bad?  This is from an old netgear router...

A bulged top is not a good sign. Even worse is when the crosses in the top (manufactured weak spots to prevent explosion) burst and start spewing electrolyte. Electrolyte may also be leaking out at the base (look for signs of fluid on the board). As an example I added an attachment of the cap inside a CFL that had failed, it had started buzzing and the light output started to drop sharply. The bulged cap was the cause.

If you intend to keep running the router, replace them with a suitable item. The type should be printed on it, often just a couple of letters and/or numbers; in my example it would be a Rubycon of the CFX-series, a quick google finds the datasheet.
If I were to replace this cap, but wasn't able to source the same Rubycon, I'd find another cap with similar or better ratings for e.g. ripple current and dissipation factor, because in this particular application, those will be important parameters.

If you can't find a datasheet, my personal rule of thumb is that gold printing usually indicates Low-ESR types (especially with Chinese/Taiwanese caps). You will want to replace them with Low-ESR caps as general purpose caps might have a bit too high an ESR for that circuit and they will heat up more and wear out faster.

When dealing with general purpose caps, then replacing them with whatever you have lying around of similar capacity and the same or higher voltage rating will normally do just fine.

[Tandy]

Often a manufacturer will use a gold colour to indicate the capacitor is a low ESR variant, but there is no guarantee, particularly cheap unknown brands who will use gold because they to try and make them look special.

Almost certainly a bulged capacitor in a netgear router is bad, in my experience netgear like many uses the cheapest components as they are built down to a price.

[jitter]

Often a manufacturer will use a gold colour to indicate the capacitor is a low ESR variant, but there is no guarantee, particularly cheap unknown brands who will use gold because they to try and make them look special.

Well... gold is also used by the big name manufacturers to indicate that they're "special", e.g. audiofoolery stuff...

[Mechatrommer]

the gold stripe is lower voltage rating 6.3V, the white stripe is 10V and above, from my experience at least striping out and reusing caps from motherboards.

[jitter]

the gold stripe is lower voltage rating 6.3V, the white stripe is 10V and above, from my experience at least striping out and reusing caps from motherboards.

We're talking about electrolytic caps here, they don't have any colour coding AFAIK. The used colours are at the mercy of the manufacturers.

[wraper]

the gold stripe is lower voltage rating 6.3V, the white stripe is 10V and above, from my experience at least striping out and reusing caps from motherboards.

You confuse voltage rating with series and manufacturers. 6.3V usually go for CPU power where ultra low ESR series are needed. So they usually are different series than rest of the board uses. Also gold colored LOW ESR capacitors are made only by a few A-brand manufactures while others usually don't use fancy colors (well maybe for some audiofool series, and some rare LOW ESR series).

[alank2]

Allright, new caps arrived today.  Put them in and router seems to work again.

Old removed bulged caps:

1000uF labeled = 160uF measured
470uf labeled = 151uF measured
2nd 470uf labeled = 116uF measured