1
\$\begingroup\$

MY 1000 Watt True Sine Power Inverter blew a 25V 47uf capacitor. The shell was rattling around inside, and the ribbons were exposed. Yay, I found the problem! Sooooo, how can I tell the mounting polarity in order to replace the blown cap?

ALSO, would it be a silly idea to replace that cap with FIVE 60V 10uf caps in parallel (I have these available) essentially making a single 60V 50uf cap? ... or should I just buy a direct replacement?

Wondering what effect the slight variation in capacitance might have.

I'm kind of a novice, but the smoke is already out...what can I lose :P

Thanks in advance :)

\$\endgroup\$
4
  • 1
    \$\begingroup\$ I would seek for the cause of the fault rather than replacing the capacitor. Are you confident that it will not repeat? \$\endgroup\$
    – Rohat Kılıç
    Mar 13, 2020 at 15:22
  • \$\begingroup\$ I also found a spider inside...maybe he did it :P -- The unit went on a warm day, and has seen several years of use...so maybe it was just time? There are some other larger caps inside that seem to have bulging or domed tops, but i can't say if that's a result of build, or just wear and tear. I'll look around more closely to see if anything else obvious jumps out. Thank you. \$\endgroup\$
    – Bench Falco
    Mar 13, 2020 at 15:36
  • 1
    \$\begingroup\$ There is usually some marking on the circuit board to indicate the capacitor polarity. If there wasn't, then the people assembling it in the factory wouldn't know. \$\endgroup\$
    – Simon B
    Mar 13, 2020 at 15:51
  • \$\begingroup\$ Could it be so obvious? I feel an overwhelming sense of shame and embarrassment....thank you??? :P \$\endgroup\$
    – Bench Falco
    Mar 13, 2020 at 17:56

3 Answers 3

Reset to default
0
\$\begingroup\$

Wondering what effect the slight variation in capacitance might have

Almost certainly none. It's 6% Most large-ish capacitors have very wide tolerances in the first place, and circuits which use them are very rarely sensitive.

Good background at Wikipedia, which says:

Electrolytic capacitors, which are often used for filtering and bypassing, do not have the need for narrow tolerances because they are mostly not used for accurate frequency applications like in oscillators

\$\endgroup\$
1
  • \$\begingroup\$ Thank you, this helps a lot. \$\endgroup\$
    – Bench Falco
    Mar 15, 2020 at 17:03
2
\$\begingroup\$

Polarity? Use an ohm-meter to find what else is connected the cap traces. You may find the polarity on one of those. Ground/Power pours may be recognizable. See if it is connected to any. Check polarity on other devices connected to the pour. -ve side of caps, GND pins of IC's, etc.

The major difference with 5 caps in parallel to make 50uF may not be the capacitance, but the series resistance. A lower series resistance may do good things (like better ripple), bad things (like instability), or nothing. Depends on the circuit.

Like you say, the smoke is out so it doesn't hurt to try. Except that it sent the cap cover flying last time. So'd I'd close the enclosure or wear eye protection before applying power here.

The cap may not be the only thing that died. It may just be the most obvious. But try away - with caution.

\$\endgroup\$
2
  • \$\begingroup\$ Thank you. I will look around for more possible faults. I haven't even yet looked at what the particular circuit does... \$\endgroup\$
    – Bench Falco
    Mar 13, 2020 at 15:38
  • \$\begingroup\$ I should add that I learned a new term. Series Resistance....like I said, I'm a bit of a novice. Thanks again. \$\endgroup\$
    – Bench Falco
    Mar 13, 2020 at 20:16
0
\$\begingroup\$

You will find the negative pole where there is a white band with sparrows on the side of the capacitor. I don't think there will be a problem using 5 x 10uF... but one 47uF cap is not that expensive neither and may be easier to mount.

\$\endgroup\$
1
  • \$\begingroup\$ Yep, plenty of other caps on the board mounted like you say. Thanks \$\endgroup\$
    – Bench Falco
    Mar 15, 2020 at 17:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.