Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Question about electrolytic capacitor

Status
Not open for further replies.

VictorPS

Member
One silly question about electrolytic capacitor , for example, 4700uF, rated temperature 85degC working at an environment of 95degC, the capacitor is expected to fail after some time.

What will be the failure symptom of the cap? The cap become high resistance, short circuit or open circuit or ..? :roll:

Thank you, :)
 
The leakage current and equivalent series resistance may gradually increase too.
 
By far the most common cause of failure in modern electrolytics is high ESR, I would expect over heating to tend to cause that (capacitors near heatsinks or high wattage resistors fail high ESR).
 
What is ESR stand for? :?:
Is it ok to let the failure cap in parallel with a 12V battery? Will it have any bad or no effect to the battery?

Another question, an E.cap which rate its life as 5000 hours, so it may fail after 209days? But under normal working condition, a cap can continue working for many years (>10 year), am I right? :lol:

Thank you, :D
 
VictorPS said:
What is ESR stand for? :?:
Is it ok to let the failure cap in parallel with a 12V battery? Will it have any bad or no effect to the battery?

ESR is 'Effective Series Resistance', for a decent size electrolytic (100uF upwards) it should be well under an ohm. As the ESR gets higher, the capacitor no longer works as an HT decoupler - as it effectively has too large a resistor in series with it.

Another question, an E.cap which rate its life as 5000 hours, so it may fail after 209days? But under normal working condition, a cap can continue working for many years (>10 year), am I right? :lol:

Electrolytics, by their very nature, tend to have a fairly short life, as their electrolyte drys out they rapidly fail.

Modern electrolytics, made cheaply in the far east, are of absolutely pathetic quality - if the capacitor is driven fairly hard, as in a PSU, their life tends to be drastically reduced.

I only stock 105 degree electrolytics for replacement purposes, these seem to have a slightly longer life than 85 degree ones, but still nothing wonderful!.
 
I agree that Aluminum electrolytics are subject to failure, but take this in mind: what are your alternatives?

Tantalum's are VERY fragile, and should not be run over 50% of rated voltage. Also, they are quite expensive.

Films are large and expensive.

MLCC's are prone to cracking (smt).


There is a reason Aluminums are the prevalent choice where there is room.

Just look inside any electronic asembly.

NOTE: Far East manufacturers lead the world in this technology and by and far are the only choice in this market. The alternatives are pitiful.

Sean
 
VictorPS said:
What is ESR stand for? :?:
Is it ok to let the failure cap in parallel with a 12V battery? Will it have any bad or no effect to the battery?

Another question, an E.cap which rate its life as 5000 hours, so it may fail after 209days? But under normal working condition, a cap can continue working for many years (>10 year), am I right? :lol:

If the cap's leakage increases, it could slowly drain the battery.
A cap rated at 5000 hrs COULD fail in 1 hr. It's just supposed to be unlikely. I don't know their exact formula for arriving at a rating.

You need to consult the specifications on your capacitor for the temp rating. You might be able to find categorical information on how temp derates the lifetime of that class of capacitor.

One of the things I recall seeing was that elevated temps have a strong effect on the voltage rating. If you just increase the safety factor- i.e. use a 50V cap on a 12V system- you should be able to get greater resistance to the problems you forsee.

I'm pretty sure ceramics take heat well. And these days they make much higher capacitance, lower ESR ceramics. How much capacitance do you actually NEED? If you can get by with 1uF or less, you might be able to find a ceramic.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top