Why would a cap in a router run very hot

sam_sam_sam

I found a pop up cap in the router a few month ago and today I found the same cap very very warm almost
to hot to touch but the router still works the supply voltage is 12,40 when the router is hook up the supply voltage is 11.90 replacement switching power supply


I found one in the switching power supply today pop up and one transistor fryed in it output voltage was rated at 12 volts @ 1 amp out voltage was 8.7 volts no load the router still working but real flake

Dr_Acula

A warm cap is probably about to die soon. Is it an electrolytic? If so, it probably is heating up and losing its electrolyte and as that happens, the capacitance probably falls which makes it even hotter.

What is the voltage rating on the cap? Sometimes they run the cap right at the limit to save on costs. Then you throw away the unit and buy another one. Perfect inbuilt obsolescence!

Hopefully you have got to this in time and can replace the component before it gets so fried that you can't read the writing on the side.

RDL2004

Whenever I replace electrolytic caps, I always use 2x the power supply voltage for the WVDC rating and use 105° C rated parts if at all possible. I would replace those bad caps as soon as you can.

kwinn

Dr_Acula and RDL2004 are correct. Switching power supplies run at high frequencies and have very high peak currents which can cause heating of capacitors. They require low ESR (Equivalent Series Resistance) capacitors which are more expensive. Most inexpensive switching supplies use less expensive capacitors.

Peter KG6LSE

I agree too .
its not the Voltage . Its the current.. the charge discharge cycteing at 40+ KHz for a SMPS is appoching RF and casues Local heating from a wound cap like most electrolitics are ..
I have the same issue with the rail that powers the HV inverters in LCD desktop screens // 90% of the time its the 12V rail caps .

One time I mesured allmost 20A peak on the cap charge cycles . ( shunt and a O scope ) on one Viewsonic set

Peter

Kevin Wood

What router are you using? It might be worth seeing if there was a recall or extended warranty.

Ron Czapala

The capacitor could just be defective. Many Samsung LCD TVs had bad capacitors in the power supply section. I replaced the bad caps in my Samsung and it work great now..

http://forums.parallax.com/showthread.php?126804-Bad-capacitors-Samsung-LCD-TVs&highlight=samsung

Unknown

Sounds like it could be a scheme of using cheaper products so that it would burn out quicker so you will be forced to buy a new one.

I've seen this before but can't tell if it is connected.

Peter KG6LSE

this whole Filter cap on SMPS's going bad thing is not just one brand . I have seen Every imaginable device have issues that are pratclry the same failure mode .'

Smart cookies use a few smaller caps in parallal and use a few diff valuies .

1µF for fast transients 10 for slower stuff and a few 100s or so for the bulk of the filtering.

as we know a 1µF carmic cap has a Very fast Dv/Dt response rate On the whole in comparison to normal electrolytics . so use them for the fast stuff . If you have voltage potential from DV/DT then there is current flow .. and that along with Mr Ohm = heat . so if we can lower the Ω then we can have less heal loss . and volla our problem is solved .


I have seen the insides of Really good SMPS lab supplys and what not and they all use the stepped cap design .

Peter

sam_sam_sam

Thank to all that have reply

I am going to replace this again with two caps instead of one and hope this will help

I also found three chips in this router that run very very warm also most to warm to touch

This router has always run very warm from the first day that I bought this