Finding out "Ripple Current" rating

[x32]

Hello,

I have CM-7000 converter box that I want to re-cap.

I've read FAQ's so I do have a good idea what I need to do. But one thing I'm not sure about is what "Ripple Current" rating I need to get.

For example, four of the cap on the board are labeled: Chang / 470uf / 10v / 105c / -40+

From that info, how do I find out the ripple current rating?

Thanks,

[x32]

Re: Finding out "Ripple Current" rating

I'm asking because I noticed when looking for caps on Digikey, that they have a ripple current rating in the specifications, and I don't know if I should be worried about what rating I'm getting.

The caps I'm replacing are the aluminum electrolytic type's.

[mariushm]

Re: Finding out "Ripple Current" rating

Generally the higher the ripple value, the better.

Chang is apparently a brand of Huawei, see the website there: http://www.huaweiec.cn/index_en.asp

If you can determine the series, then here you should be able to find the datasheet for them : http://www.huaweiec.cn/product04_e.asp

My guess would be that Panasonic FR, FM series are good alternatives. Nichicon is also good (PM series I believe), Rubycon is also known but I couldn't recommend you a series.

If the selection for 10v is small, you could also try searching for 16v capacitors or even higher voltage rating, but make sure the capacitors would fit in the space you have on the board.

ps. bookmark this website in the future: http://capacitor.web.fc2.com/

[PCBONEZ]

Re: Finding out "Ripple Current" rating

Can't really tell you anything more than a quess without the name of the series.
That's like saying you need an engine for a Ford.
Well, a Ford - what?

I've seen Chang used in places that suggest some of them have decent specs.
http://www.huaweiec.cn/product_list_e.asp
.

[x32]

Re: Finding out "Ripple Current" rating

Thanks for the links, I'll go ahead and bookmark them.

I re-checked the caps for a series number but oddly there isn't one. Only the caps on the logic board has a number but those are made by a different brand.

Since all the Chang caps are in the power supply, should I aim for replacements with the lowest ESR?

[PCBONEZ]

Re: Finding out "Ripple Current" rating

If there is a CDxxx type number on it that is shown in the data sheet list.

[x32]

Re: Finding out "Ripple Current" rating

Nope, no series indication on any of the Chang caps.

[PCBONEZ]

Re: Finding out "Ripple Current" rating

With the 1000uF 10v and that temp range these are the only possible series.
I listed the 1000uF 10v can sizes in those series.

LF . 10x20mm
GF . 8x20mm & 10x16mm
GD . 8x16mm & 10x12.5mm
RS . 8x20mm & 10x16mm
FM . 12.5x20mm
KM . 8x11.5mm
RM . 10x16mm & 10x20mm

So measure the cap to narrow it down.
Then of what is left use the one with the best specs to be conservative.
.
Then do the same thing with the other cap sizes.
.
In the future, it helps A LOT if you give the dimensions of the cap you are looking for along with the other specs when you first ask.
Usually just diameter is enough.
Sometimes [like this time] the length is also needed.
.

[x32]

Re: Finding out "Ripple Current" rating

All the Chang power supply caps are KM series, I now have the ripple rating's but I could not find the ESR in the chart. Do I just match the tangent instead?



Sorry for posting this question so late, I got sidetracked by something else...

[PCBONEZ]

Re: Finding out "Ripple Current" rating

Those are GP caps [General Purpose]. Not even low ESR.
It's still a good idea to use low ESR caps simply because they have higher quality standards and they don't usually cost more.

As common with GP caps the Ripple in the data sheet is stated at 120Hz and you need to know Ripple at 100kHz.

There is a Frequency Coefficient chart in the data sheet.
Use that to convert Ripple from 120Hz to >10kHz.

For example for 6.3v-25v caps multiply the Ripple@120Hz by 1.20 to get Ripple@100kHz [or rather "10kHz or greater"].

Once you have the Ripple @100kHz find some entry level low ESR caps [Panasonic FC, Nichicon PW, Chemicon LXZ or KY, there are probably dozens of series that will work] and choose the replacements based on the Ripple.
You want the same or more for Ripple.
- No need to got nuts looking for high numbers though.
It doesn't make the circuit work differently at all.
The rating is only a current -limit- for Ripple. [Like an amps rating on wire.]
Once you have enough - you have enough - and more won't matter.
The concern is ensuring you have at least as much as the old caps.
.

[x32]

Re: Finding out "Ripple Current" rating

DAMN! I should have asked this question much earlier...

I finished converting the ripple rates, I'm now going to go ahead and order the caps. Thanks a lot PCBONEZ for your help.