Quick capacitor questions for the 8RDA+

[Jeff7]

I'm recapping my 8RDA+ board - replacing all capacitors rated 1000uF or higher. The voltage regulator capacitors were rated 10V, 2200uF. I've got some 6.3V 2200uF caps here - are they ok? I'd assume so, as the CPU doesn't need more than 2V max. And if those caps had to process more than 6V, I'd figure that the manufacturer of the board would use 16V capacitors to be safe.
So anyway, are 6.3V caps ok instead of 10V caps in the voltage regulation circuity?

Edit: Just checked the voltage on the caps with a voltmeter - 5.16V. So it's under 6.3V, but, well, 10V is about twice the voltage, which is what I usually see used.
Is there any real danger to using these 6.3V capacitors though?

 

[farscape]

They are rated 10 volts for a reason.

You might only be reading 5.16v, but you are not taking into account the "floating AC" or ripple that may be riding on that DC signal. You could have (in case of a faulty signal) a 2v peak to peak ripple on top of your 5 volts - you meter will only read the average and only see 5 volts - not the fluctuation going from 3 to 7 volts. In that case you are exceeding the breakdown capacity of the cap (6.3v)and you get a short and a blown cap. If you set your meter for AC you will read zero volts because the signal never crosses the "zero volts" or changes polarity. You can only see this ripple/float on a scope.

If you set your meter on DC and stick it in your outlet, it will read ZERO volts - the average of the signal that is there - about 370V peak to peak. I wouldn't want to stick my fingers in that outlet because my meter was reading 0 volts DC.

 

[DayLaPaul]

I have the same board. Why are you replacing the capacitors for? Just wondering.

 

[Jeff7]

Originally posted by: DayLaPaul
I have the same board. Why are you replacing the capacitors for? Just wondering.

Bulging/bursting capacitors prevented the thing from POSTing.


Edit: Great, I guess I need to e-mail the folks at Badcaps.net, who sent me the capacitors.
Either that, or - do I absolutely need low-ESR capacitors? I've got some regular capacitors here, at least I think they're normal ones, though they seem more compact that most I've seen. They're rated 16V 2200uF. Would they work, or is their power not clean enough for a CPU?

 

[Mark R]

The filter capacitors on high-performance switching regulators are one of the most critical parts in the circuit. Typically, a manufacturer will design the circuit for one specific model of capacitor from one manufacturer.

This is because of the critical importance of ESR for these capacitors. Higher-voltage rated electrolytic capacitors have a lower ESR for the same capacitance (at the expense of larger physical size, and higher cost) - however, it may be cheaper to use 3 10V capacitors than 5 or 6 6.3V capacitors in order to get a satisfactory ESR.

The capacitors used in the CPU voltage regulator circuit absolutely must be 'High-ripple current', 'Low ESR' rated. If the ESR is too high it could cause poor power quality - if the caps are particularly bad, the regulator may not even be able to start up, or may produce a randomly widely varying voltage. If the ripple current rating on the caps aren't high enough, then they are likely to overheat and fail within a short period of time.

 

[Jeff7]

- NEED 10V caps, not 6.3V
- NEED low-ESR caps

Darn it. Why can't you all just tell me what I want to hear? Geez.



Ok, guess I'll e-mail the people (person?) at Badcaps.net and get the capacitors I need. I sent for 10V 2200uF, but got 6.3V caps. Hopefully they'll be good about resolving this.