Capacitor wrap cutting brief tutorial - diyAudio
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Old 4th September 2014, 03:43 AM   #1
SonyFan is offline SonyFan  United States
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Default Capacitor wrap cutting brief tutorial

I have noticed on many vintage amps and on many high-end consumer products the top portion of the heat shrink on capacitors is often removed. My guess is for looks or to remove the phenolic disk found on top of some caps to better expose the vents, though they should function with this disk in place. I don't know why in particular, maybe someone will mention it, but I like the look of it. Cutting something round is a perfectly simple task. In this case, it requires few tools and produces a stunning result for a few minutes and possibly no money invested.

You will need a razor blade of some sort (the ones that go into retractable razors are best since they are completely flat) and a clamp. Also needed is a strong shim, but this can be anything.

First: pick a shim of your desired thickness. Determine this by placing the razor blade on the shim and allowing it to protrude slighltly. Stand your capacitor on its top and push it up to the blade. Adjust the shim until the blade falls where you want your cut.

Next, lay the blade on your shim flush with its edge. Clamp the blade in this position, allowing only a small portion of the blade to protrude over the shim. This will set your cut depth, the shrink wrap on most capacitors is only slightly thicker than paper.

Last, push the capacitor firmly against the blade, then slowly rock it with ample force to cut. You may hear the wrap crackly slightly as it becomes free. If any excess remains after one rotation, carefully remove what you can before another rotation. Excess material hanging on after one rotation is rare and indicates that you are not using enough pressure or the blade is too dull.

One warning: don't try to spin the capacitor. Just rock it against the blade like you are rolling it down the blade.
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Old 4th September 2014, 03:44 AM   #2
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Old 4th September 2014, 03:51 AM   #3
SonyFan is offline SonyFan  United States
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Of course they are doing this in my love, Sony...

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Old 4th September 2014, 09:09 AM   #4
DF96 is offline DF96  England
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Personally I think they look better in their original state, and inside an amp who cares anyway?

Minor snags with doing this:
- you destroy any warranty
- you may reduce the ripple current rating - bare aluminium is a poor heat emitter
- you may increase the risk of mechanical resonance
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Old 4th September 2014, 12:11 PM   #5
SonyFan is offline SonyFan  United States
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Quote:
Originally Posted by DF96 View Post
Personally I think they look better in their original state, and inside an amp who cares anyway?

Minor snags with doing this:
- you destroy any warranty
- you may reduce the ripple current rating - bare aluminium is a poor heat emitter
- you may increase the risk of mechanical resonance
It's a cosmetic mod and whether or not it looks good is a matter of opinion. Inside an amp or not, obviously I care. You might want to do your research before trying to bring my idea down for no reason. The bold statement is just plain foolish. Not to mention, so is sending back a $7 (in my case) part for warranty when the shipping would be more than it cost. Plus you can't warranty anything that has been soldered (to most vendors) so once you're sure your parts work it doesn't matter- cut away.

I shouldn't have to justify a cosmetic mod, why are you even posting if you don't like it? I have an easy solution for you: don't do it.
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Old 4th September 2014, 12:50 PM   #6
AndrewT is offline AndrewT  Scotland
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The can emits heat better when the wrapper is still attached.

The can is not completely isolated from the electrodes.
An exposed can could become a short for electric signals.
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Old 4th September 2014, 01:28 PM   #7
kevinkr is offline kevinkr  United States
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I've always thought it was a cost saving measure. Outfits like Sony buy caps in very large quantities and perhaps the fraction of a penny saved by leaving out the disk over the top and shortening the wrap is worthwhile in very large volumes.

Plastic is a good insulator so I can't imagine that this is thermally worse that having the wrap and disk in place unless you believe the only relevant cooling mechanism is radiation.

From a safety standpoint this might be an issue at higher voltages, here I don't think there is a big issue.

In terms of resonances I doubt it makes a difference, the innards may sing at high frequencies, but I doubt the wrap does much to help attenuate that based on my experience.

If you like the way it looks I suspect what you done is not going to create an issue.
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Old 4th September 2014, 01:53 PM   #8
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Many experiments have been carried out to prove that cans wrapped in a dark plastic coating emit heat better than nude cans.

I'm with the school that would leave them in their jackets as they were designed and made to be used.
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Old 4th September 2014, 02:00 PM   #9
kevinkr is offline kevinkr  United States
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Can you provide a link to an experiment demonstrating this is the case. Thanks..
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Old 4th September 2014, 02:58 PM   #10
DF96 is offline DF96  England
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Quote:
Originally Posted by SonyFan
It's a cosmetic mod and whether or not it looks good is a matter of opinion.
Which is exactly why I said
Quote:
Originally Posted by DF96
Personally I think they look better in their original state,
Quote:
The bold statement is just plain foolish.
The statement you highlighted just happens to be a fact. The only question is whether a black plastic covering has sufficient thermal resistance to negate the advantage of a black thermal emitter. My understanding is that tests have shown that leaving the covering in place results in cooler running for the cap, and hence better ripple current rating. I doubt if the manufacturers would do it otherwise, as plastic costs money and so does the machine to do the wrapping. They could just stick, print or etch a label on the bare can - which is what happened in the old days 50 years ago.

Quote:
I shouldn't have to justify a cosmetic mod, why are you even posting if you don't like it?
I am not asking you to justify it. You have already given your reason for doing it: cosmetics. We have agreed that this is a matter of opinion. My posting was to alert people that there are downsides to this change.

That is the way this forum works: one person posts something, other people reply. Maybe other forums are different?
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