recapping with used caps from older boards

[nico-e]

Hi,

i have several older K7 mainboards with bad caps and i have some older P2 to P3 slot1 boards from 1996 to 1998 with good caps with the same specs(I think i have read that the cap problems started before 1998).

Now my question is can i use caps from the old, slow but still working Boards for the "newer" boards?

another question is should i recap only the broken caps (or only the broken ones type for example all of 1000µf 6.5v) or all caps wich I have on the boards?

Thanks
nico-e

[Topcat]

Re: recapping with used caps from older boards

Cannibalizing caps from old boards = bad idea. Just buy new ones, its not like they're all that expensive. As a rule, replace all the caps 1000uF and up.

If you're just recapping these old boards for practice, and not intending on using them for anything except tinkering, then yes, scavenge the caps from the junk boards.....but if the boards being recapped are going to actually be used for something, just buy new caps.

[PCBONEZ]

Re: recapping with used caps from older boards

If the board is just a toy to learn on then that's okay.

If it's for anything important, then no. - Don't do it.

Several reasons for saying that. Here's two:

1- Electrolytic caps are called that because they basically have an electrolysis chemical reaction going on inside them. They have a life span because the chemicals in the electrolyte does eventually wear out. They also [usually] eventually dry out.

2- The voltage on the side doesn't mean anything on used caps. A caps voltage rating is based on how thick the oxide layer on the aluminum foil is. Caps will 'reform' the layer to the actual applied voltage in just a few hours. [Unless the applied voltage is too high for the thickness of the layer in which case they will short internally.]
Ripple current strips the oxide layer off the aluminum foil. The applied DC voltage puts the oxide layer back by way of electrolysis. It's like electroplating only it's the oxide that is plating out. [They used to call this characteristic 'self healing'.] The DC voltage is only going to put it back as thick as the applied voltage.
- So. Someone takes a 16v cap and puts it on 3.3v. Two hours later it's a 3.3v cap even though it says it's a 16v cap on the side. Much later you pull this cap and put in on a 12v circuit -> SHORT CIRCUIT!

.

[nico-e]

Re: recapping with used caps from older boards

1- Electrolytic caps are called that because they basically have an electrolysis chemical reaction going on inside them. They have a life span because the chemicals in the electrolyte does eventually wear out. They also [usually] eventually dry out.

how long should or could caps live wich are not affected by the Electrolytic problem wich the cheaper ones have after 1998?

2- The voltage on the side doesn't mean anything on used caps. A caps voltage rating is based on how thick the oxide layer on the aluminum foil is. Caps will 'reform' the layer to the actual applied voltage in just a few hours. [Unless the applied voltage is too high for the thickness of the layer in which case they will short internally.]
Ripple current strips the oxide layer off the aluminum foil. The applied DC voltage puts the oxide layer back by way of electrolysis. It's like electroplating only it's the oxide that is plating out. [They used to call this characteristic 'self healing'.] The DC voltage is only going to put it back as thick as the applied voltage.
- So. Someone takes a 16v cap and puts it on 3.3v. Two hours later it's a 3.3v cap even though it says it's a 16v cap on the side. Much later you pull this cap and put in on a 12v circuit -> SHORT CIRCUIT!
.

as i understand I can use higher voltages caps? is there a "replacing rule" could this example work?
I need to replace 1000uF 6,3V can i use 1000uF 16V or higher? maybe this is cheaper :-D

[c_hegge]

Re: recapping with used caps from older boards

You can sometimes get away with using 2nd hand caps on motherboards if:
1. You know the voltage that was previously applied to it and
2. The salvaged cap is a good brand like panny or rubycon

I have successfully used 2nd hand caps under those circumstances, but I would still encourage new caps.

[PCBONEZ]

Re: recapping with used caps from older boards

how long should or could caps live wich are not affected by the Electrolytic problem wich the cheaper ones have after 1998?

That's a bit to open to answer.
The conditions the caps are used in affects that BIG TIME.
Each 10C reduction in operating temperature doubles a caps lifetime.
Each 10C increase cuts it in half.
It's logarithmic.

You seem to be thinking there is was one problem with caps, the famous 'capacitor plague' one.
That isn't true.
There are actually more like 7 or 8 'capacitor plagues'. Some have come and gone. Some have been around as long as caps have and continue today.
-
ALL caps made with Chinese or Taiwan sourced Aluminum [no matter when made, including 50 years ago and yesterday] have nearly the same problem as the *famous* capacitor plague caps, it's just slower. Root cause is different, the failure is the same. This happens because naturally occurring impurities in the CH & TW Aluminum leach into the Electrolyte and break it down. How much of those impurities are in the Aluminum varies from batch to batch which is why sometines 'cheap' caps last for years and other times they fail in 6 months.
- Japanese, US, and European made caps don't have that problem because their Aluminum doesn't have those impurities and they actually have QA programs that work.
-
The Nichicon HN and HM problems are NOT related AT ALL to the 'stolen electrolyte formula' of the CH & TW Aluminum problem.
No Japanese brands were affected by the bad formula.
Japanese cap manufacturers don't use CH & TW sources for Aluminum.

as i understand I can use higher voltages caps? is there a "replacing rule" could this example work?
I need to replace 1000uF 6,3V can i use 1000uF 16V or higher? maybe this is cheaper :-D

The voltage marked on the side of a cap is it's MAX voltage.
[Assuming it's a new cap.]

.

[MXM]

Re: recapping with used caps from older boards

^ yo PC nice posts, thanks.

i agree canibalizing caps should be an emergency procedure and should be avoided unless u definetly dont have another choice. or for learning, or devices that will do unimportant jobs...

jm2c

peace.