RE: [CAD_CAM_EDM_DRO] capacitor voltage rating ?

Only reason to go higher would be lifetime.

Most electrolytics have about a 5000 hour MTBF lifetime, some of the good
ones are 10,000 hours.

If you use a higher voltage rateing its MTBF increases quite considerably,
it's value at lower working voltage is also slightly higher, on some brands
much higher.

I design certain kit for a 20 year life continuous 24 hours a day operation,
we normally at least double the voltage rating to achiever this based on the
cap manufacturers data.

For a DIY machine though 5000 hours of a few hours a day will last for many
years.

Unless you want really long life with an 80 volt system, a good branded cap
at 100V will probably be OK, if it's a cheapy might be best to go to 125V.
150V you may find are more common.

In my machine I have a 150V ish DC supply, I have 250V caps not for the
lifetime, but because they were easy to get hold of.

It's also worth other rembering if they buy an old broken CNC machine to
retrofit, the caps are probably starting to struggle and would be worth
changing, also if there are any signs of pressure from within the cap like a
bulged end, change it.



Regs Mark



_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Jon Elson
Sent: 06 January 2007 22:09
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] capacitor voltage rating ?



Anders Wallin wrote:

>What voltage rating should I choose for caps to a psu with a 60 VAC
>secondary?
>That will produce about sqrt(2)*60 = 84 VDC (probably a bit more under
>no-load conditions)
>
>The webshop I am looking at has 100 V caps, would that be enough?
>
>
>

100 V should be fine. 125 if you are worried about the safety margin.
Definitely
no reason to go above that.

Jon





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