Reusing old capacitors

[SenoritaCao]

I was opening an old computer that we used to use in our house about 10 years ago and I noticed it had Rubycon capacitors from top to bottom (Motherboard and power supply are just covered in them).

I hear that this particular brand of capacitor is excellent so I'm wondering if there are any dangers to reusing these ones since they're quite old. Also, if I do use these to recap a circuitboard, what should I do with regard to the capacitance and voltage labels? (Should I go for a higher or lower value)

Edit: I also found Taicon caps. I have never heard of this brand. Good or bad?

 

[Karadjgne]

If the caps were discharged, you should be fine, its mainly usage over time that hurts, so it's not so much how long they sat, but how much usage they saw before sitting.

If you recap a circuit board, use the exact same caps, as far as far ads and voltage goes. The only thing you can reliably get away with is changing tolerances, you can replace a +/- 10% with a +/-5% etc, but I'd not go the other way, you end up over volting other components that way.

Taicon caps are middling quality, not the worst, but far from good. Have to watch for temp ratings on any caps close to heat sources such as mosfets and heatsink transistors.

 

[adamjosiah]

This is an interesting topic, I can only speak with my experience as an avionics technician (which is a bit different than desktop computers). Replacing capacitors is not an issue, but you should be aware that all capacitors do have a life and it's hard to say how an old better quality capacitor would compare to a newer cheap one. Regardless, it is very important to make sure you replace capacitors with ones of the exact same capacitance. Circuits are designed with specific values of voltage, resistance and capacitance. You change one of those values on a circuit and you'll probably break something.

 

[SenoritaCao]

I read that capacitors discharge themselves over time. The largest capacitor by size (Which I'm currently assuming is a measure of its capacitance) is 200v 470uF. They haven't seen any power for 2 weeks and probably wont be used for a few more weeks. Probably enough time to fully discharge right?

 

[adamjosiah]

Capacitors are supposed to "discharge", charge and discharge is their function. What you may mean is they lose capacitance over time (their ability to hold a charge or the amount of charge they can hold). This is probably true to a point but probably not enough to really change its value. uF is a measurement of capacitance and usually corresponds to the size. Capacitors usually discharge over time but it depends on the circuit they're attached to. A better way to ensure a capacitor is fully discharged is to short them out using a resistor and then after mostly discharged, complete the short with a wire.

DISCLAIMER: Capacitors can cause bodily harm, mess with them entirely at your own risk