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Replacement capacitors [message #244612] Mon, 17 February 2014 16:23 Go to next message
Keith Jamison is currently offline  Keith Jamison
Messages: 41
Registered: May 2013
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Member
I have worked with electronics since 1984 and I always understood that the voltage rating of a capacitor is important to preserve the specific function of the capacitor within an RC circuit - by that I mean, the Rise Time of the capacitor (63.2% x Vsupply).


I've been fortunate to track down almost all of my capacitors of their original values for recapping Classic Macs. Two caps were not available and I chose the recommended replacement (C1 on the Plus A/B) and the second capacitor was replaced with one that was 10% out of voltage tolerance (a 200V instead of the 180V original).

Would someone explain why some suggestions are given to replace 16V caps with 35V or 50V, please? I would like to understand this better. It would certainly make ordering capacitors much easier.


I'll admit, my area of knowledge is more towards discrete integrated circuits and not power supplies.

By the way, for any members in the United Kingdom, RS (rswww.com), Farnell (uk.farnell.com) and Rapid Electronics (www.rapidonline.com) have been able to supply over 99% of my capacitors. I used eBay just once to purchase 0.1uF 50V capacitors. I have been able to purchase Panasonic, Nichicon and Elna brands.

Many thanks,

Keith
- - - - -
Mac Plus - Classic - Classic II - LC - 7250/120 - PB165 - PB1400 - PB3400 - PBG3(3x) - iMac G3 Rev B - G3 (Blue White) - iMac DV (2x) - iMac Slot(x4) - eMac (x4) - iBook G3 - iBook G4 (12") - iBook G4 (14") - MacBook (1.8GHz) - MacBook (2.0GHz) - iPhone - iPad G3 - some PC stuff. Wow, that's like a lot. I need to get out more!

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Re: Replacement capacitors [message #244613 is a reply to message #244612] Mon, 17 February 2014 17:11 Go to previous messageGo to next message
js@cimmeri.com is currently offline  js@cimmeri.com
Messages: 39
Registered: January 2013
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Member











Keith Jamison wrote:


I have worked with electronics since 1984 and I always
understood that the voltage rating of a capacitor is important to
preserve the specific function of the capacitor within an RC circuit -
by that I mean, the Rise Time of the capacitor (63.2% x Vsupply).




It's not.  The capacitance value is.








I've
been fortunate to track down almost all of my capacitors of their
original values for recapping Classic Macs. Two caps were not available
and I chose the recommended replacement (C1 on the Plus A/B) and the
second capacitor was replaced with one that was 10% out of voltage
tolerance (a 200V instead of the 180V original).


It's best to get close to the original design spec.  Exceeding by a
little is ok.     But sometimes, parts are not spec'd properly coming
from the manufacturer for any number of reasons -- parts availability,
price, error, etc.



Remember, many of the caps we're dealing with already have a wide +-
spec... maybe +20% -%10 or whatever.








Would
someone explain why some suggestions are given to replace 16V caps with
35V or 50V, please? I would like to understand this better. It would
certainly make ordering capacitors much easier.




Because they're being lazy and don't mind spending the tiny extra for
the added "strength" of the cap -- the added strength of which in this
case all goes to waste.   It's really an economic decision.    Think if
you're a manufacturer -- every cent saved adds up to a lot in high
volume, so you don't want to have extra expense or waste in your parts
selection.   A cap should be spec'd to the part of the circuit where it
resides.  Going way over that spec is just a waste of materials and
money.  



- JS.









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Re: Replacement capacitors [message #244614 is a reply to message #244613] Mon, 17 February 2014 17:40 Go to previous messageGo to next message
Keith Jamison is currently offline  Keith Jamison
Messages: 41
Registered: May 2013
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Thanks for your reply, JS.

I wish I had paid more attention at Uni when they were going over all of this.

Cheers!

Keith





On Monday, 17 February 2014, 22:11, "js@cimmeri.com" <js@cimmeri.com> wrote:



Keith Jamison wrote:
I have worked with electronics since 1984 and I always
understood that the voltage rating of a capacitor is important to
preserve the specific function of the capacitor within an RC circuit -
by that I mean, the Rise Time of the capacitor (63.2% x Vsupply).
>
It's not.  The capacitance value is.



>
> I've
been fortunate to track down almost all of my capacitors of their
original values for recapping Classic Macs. Two caps were not available
and I chose the recommended replacement (C1 on the Plus A/B) and the
second capacitor was replaced with one that was 10% out of voltage
tolerance (a 200V instead of the 180V original).
It's best to get close to the original design spec.  Exceeding by a
little is ok.     But sometimes, parts are not spec'd properly coming
from the manufacturer for any number of reasons -- parts availability,
price, error, etc.

Remember, many of the caps we're dealing with already have a wide +-
spec... maybe +20% -%10 or whatever.



>
> Would
someone explain why some suggestions are given to replace 16V caps with
35V or 50V, please? I would like to understand this better. It would
certainly make ordering capacitors much easier.
>
Because they're being lazy and don't mind spending the tiny extra for
the added "strength" of the cap -- the added strength of which in this
case all goes to waste.   It's really an economic decision.    Think if
you're a manufacturer -- every cent saved adds up to a lot in high
volume, so you don't want to have extra expense or waste in your parts
selection.   A cap should be spec'd to the part of the circuit where it
resides.  Going way over that spec is just a waste of materials and
money.  

- JS.

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Re: Replacement capacitors [message #244622 is a reply to message #244614] Tue, 18 February 2014 07:39 Go to previous messageGo to next message
The One True Stickman is currently offline  The One True Stickman
Messages: 85
Registered: April 2013
Karma: 0
Member
(Apologies if the list already received a half-baked reply, hit send too
early...)

Actually, you're not remembering all wrong there Keith, though JS is
correct for this application. In this case the actual value is not nearly
so critical for power filtering as it would be for a timing circuit (R/C or
otherwise), and electrolytic caps generally are not as affected by supply
voltage as ceramics or tantalums. The actual value for those types of caps
can be affected significantly by supply voltage and temperature - see this
article for a discussion of that pitfall, if you're really interested:

http://www.maximintegrated.com/app-notes/index.mvp/id/5527

But, again, we're doing basic filtering so it's not quite so critical -
unless you are recapping with tantalums, in which case you definitely want
50V caps for safety margin. :)

Also, to add to JS' answer to your question why to suggest replacing a 16V
cap with a higher voltage rating - that is also mostly economics, but on
our end instead of saving pennies at volume we're looking at what we can
get that's decent and available in small quantities right now where we are.

Stickman


On Mon, Feb 17, 2014 at 5:40 PM, Keith Jamison
<keithjamison_uk@yahoo.co.uk>wrote:

> Thanks for your reply, JS.
>
> I wish I had paid more attention at Uni when they were going over all of
> this.
>
> Cheers!
>
> Keith
>
>
>
> On Monday, 17 February 2014, 22:11, "js@cimmeri.com" <js@cimmeri.com>
> wrote:
>
>
> Keith Jamison wrote:
>
> I have worked with electronics since 1984 and I always understood that
> the voltage rating of a capacitor is important to preserve the specific
> function of the capacitor within an RC circuit - by that I mean, the Rise
> Time of the capacitor (63.2% x Vsupply).
>
> It's not. The capacitance value is.
>
>
> I've been fortunate to track down almost all of my capacitors of their
> original values for recapping Classic Macs. Two caps were not available and
> I chose the recommended replacement (C1 on the Plus A/B) and the second
> capacitor was replaced with one that was 10% out of voltage tolerance (a
> 200V instead of the 180V original).
>
> It's best to get close to the original design spec. Exceeding by a little
> is ok. But sometimes, parts are not spec'd properly coming from the
> manufacturer for any number of reasons -- parts availability, price, error,
> etc.
>
> Remember, many of the caps we're dealing with already have a wide +-
> spec... maybe +20% -%10 or whatever.
>
>
>
> Would someone explain why some suggestions are given to replace 16V caps
> with 35V or 50V, please? I would like to understand this better. It would
> certainly make ordering capacitors much easier.
>
> Because they're being lazy and don't mind spending the tiny extra for
> the added "strength" of the cap -- the added strength of which in this case
> all goes to waste. It's really an economic decision. Think if you're a
> manufacturer -- every cent saved adds up to a lot in high volume, so you
> don't want to have extra expense or waste in your parts selection. A cap
> should be spec'd to the part of the circuit where it resides. Going way
> over that spec is just a waste of materials and money.
>
> - JS.
> --
> --
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> You received this message because you are a member of the Vintage Macs
> group.
> The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our
> netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml
> To post to this group, send email to vintage-macs@googlegroups.com
> To leave this group, send email to
> vintage-macs+unsubscribe@googlegroups.com
> For more options, visit this group at
> http://groups.google.com/group/vintage-macs
>
> Support for older Macs: http://lowendmac.com/services/
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> "Vintage Macs" group.
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> email to vintage-macs+unsubscribe@googlegroups.com.
> For more options, visit https://groups.google.com/groups/opt_out
> .
>
>
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Re: Replacement capacitors [message #244624 is a reply to message #244622] Tue, 18 February 2014 15:15 Go to previous message
Keith Jamison is currently offline  Keith Jamison
Messages: 41
Registered: May 2013
Karma: 0
Member
Thanks, Stickman.

I clicked the link, read the post and PDF'd it for future reference.

I've read about replacing some caps with tantalum equivalents but I'm still essentially old school and I seem to be quite good at replacing the SMT caps on the logic boards as well as the through-holes. Currently I'm 5 for 5 on the Plus, SE/30, Classic, Classic II and LC logic boards.

Still, good information is handy to have at hand and I am still new to ideas of retrobrite, data sheets, dishwashers, recapping and refurbishment. I may know some stuff but I want to understand more about this so I can give something back as well.

Cheers,

Keith





On Tuesday, 18 February 2014, 12:39, "theonetruestickman@gmail.com" <theonetruestickman@gmail.com> wrote:

(Apologies if the list already received a half-baked reply, hit send too early...)


Actually, you're not remembering all wrong there Keith, though JS is correct for this application. In this case the actual value is not nearly so critical for power filtering as it would be for a timing circuit (R/C or otherwise), and electrolytic caps generally are not as affected by supply voltage as ceramics or tantalums. The actual value for those types of caps can be affected significantly by supply voltage and temperature - see this article for a discussion of that pitfall, if you're really interested:

http://www.maximintegrated.com/app-notes/index.mvp/id/5527

But, again, we're doing basic filtering so it's not quite so critical - unless you are recapping with tantalums, in which case you definitely want 50V caps for safety margin. :)

Also, to add to JS' answer to your question why to suggest replacing a 16V cap with a higher voltage rating - that is also mostly economics, but on our end instead of saving pennies at volume we're looking at what we can get that's decent and available in small quantities right now where we are.



Stickman



On Mon, Feb 17, 2014 at 5:40 PM, Keith Jamison <keithjamison_uk@yahoo.co.uk> wrote:

Thanks for your reply, JS.
>
> I wish I had paid more attention at Uni when they were going over all of this.
>
> Cheers!
>
> Keith
>
>
>
>
>
> On Monday, 17 February 2014, 22:11, "js@cimmeri.com" <js@cimmeri.com> wrote:
>
>
>
> Keith Jamison wrote:
> I have worked with electronics since 1984 and I always
understood that the voltage rating of a capacitor is important to
preserve the specific function of the capacitor within an RC circuit -
by that I mean, the Rise Time of the capacitor (63.2% x Vsupply).
>>
It's not.  The capacitance value is.
>
>
>
>>
>> I've
been fortunate to track down almost all of my capacitors of their
original values for recapping Classic Macs. Two caps were not available
and I chose the recommended replacement (C1 on the Plus A/B) and the
second capacitor was replaced with one that was 10% out of voltage
tolerance (a 200V instead of the 180V original).
It's best to get close to the original design spec.  Exceeding by a
little is ok.     But sometimes, parts are not spec'd properly coming
from the manufacturer for any number of reasons -- parts availability,
price, error, etc.
>
> Remember, many of the caps we're dealing with already have a wide +-
spec... maybe +20% -%10 or whatever.
>
>
>
>
>>
>> Would
someone explain why some suggestions are given to replace 16V caps with
35V or 50V, please? I would like to understand this better. It would
certainly make ordering capacitors much easier.
>>
Because they're being lazy and don't mind spending the tiny extra for
the added "strength" of the cap -- the added strength of which in this
case all goes to waste.   It's really an economic decision.    Think if
you're a manufacturer -- every cent saved adds up to a lot in high
volume, so you don't want to have extra expense or waste in your parts
selection.   A cap should be spec'd to the part of the circuit where it
resides.  Going way over that spec is just a waste of materials and
money.  
>
> - JS.
>
> --
> --
> -----
> You received this message because you are a member of the Vintage Macs group.
> The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml
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> To leave this group, send email to vintage-macs+unsubscribe@googlegroups.com
> For more options, visit this group at http://groups.google.com/group/vintage-macs
>  
> Support for older Macs: http://lowendmac.com/services/
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> To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscribe@googlegroups.com.
> For more options, visit https://groups.google.com/groups/opt_out
> .
>
>
>
> --
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>  
> Support for older Macs: http://lowendmac.com/services/
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