Increase the capacitance of smoothing capacitor after rectifier

[supersabre]

I have a vcr that keeps blowing up the capacitor after about 2 years.
The cap is SAM YOUNG KXL 16v 1000uf. The cap is identical to chemicon, same vent, same "v" marking on the bottom between the leads.

My friend has the same vcr but with 10v 1000uf. And the cap keeps blowing up after few years. After replacing the diode and cap with chemicon KY , the capacitor is still running very hot.

I talked to my repair guy at the service center. He said he saw the same thing for this model.

The capacitor is responsible for smoothing 5.8v.(see the picture)

I 'm just wonder if the capacitance is increased from 1000uf to 2200uf.

Does it help to prevent the overheating of the cap?
Will it damage the power supply?

[linuxguru]

Re: Increase the capacitance of smoothing capacitor after rectifier

The topology is most probably a flyback/buck converter - you cannot avoid high ripple currents on the secondary side with this design. Your best bet is to use an ultra-low ESR cap at that location, or better still to parallel two low-ESR caps if you can make it fit.

[999999999]

Re: Increase the capacitance of smoothing capacitor after rectifier

If there is enough space to use a larger diameter cap and/or taller do so. You can probably go up to 2200uF ok if it fits, but I would not go much over that instead increasing the voltage rating of the cap to get it larger (which will reduce ESR in a desirable way as well as choosing a cap make & model that is very low ESR to start with as linuxguru mentioned). Make sure it's still at least 105C rated but practically any really low ESR cap is at least this high.

You might also consider upgrading the other 470uF/10V cap after the inductor (per schematic, might be C35 but it's number is fuzzy to read).

[gonzo0815]

Re: Increase the capacitance of smoothing capacitor after rectifier

The problem is, that the caps is before the coil, which means that it has to take the most ripple current.

The question is, where does the heat come from?
If it is generated within the cap itself, then you should use one of the low or very low ESR series like Panasonic FC or may be better FM.
If the unit is not getting hotter than may be 50 -60°c a very low esr series cap like Rubycon MBZ, MCZ or equivalent could be used.

If the heat is delivered from the outside, e.g. the fast switching diode or other hot elements, you should use one of the long endurance low esr series like YXF, may be Panasonic FC or an Panasonic FM with real big diameter, at least 10mm, better 12mm.

The bigger the cap, the more endurance, at least for the not ultra low esr series like FC, FM and similar.
Instead of increasing the capacitance, it should be safer to increase the voltage to archive this.

Make sure, that you used either a ultra fast recovery diode or a shotky diode as rectifier replacement, but i think this should be obvious.

[gonzo0815]

Re: Increase the capacitance of smoothing capacitor after rectifier

Comparing the data of the KY UCC series, i would suggest to use a Panasonic FM.
It has less then half of the ESR of KY series and similar endurance.
Furthermore, i think that Panansonic FM caps are probably from higher quality, at least there are more than one case of bulged UCC low esr caps in in hot environment and high ripple load.
If this does not help, try to ad an 10uF MLCC or even a smaller (about 1uF) MLCC X7 cap or try to find some solid polymer capacitor with the appropriate values (i would say Oscon SEPC series should fit).