Printing a capacitor

for all subjects/topics not covered by the other forum categories
Post Reply
User avatar
roland
Posts: 3437
Joined: Thu Aug 29, 2013 8:29 pm
Location: Born (NL)
Contact:

Printing a capacitor

Post by roland » Sat Aug 18, 2018 3:46 pm

As some of you might know, I also repair old radios. Currently I'm working on a Philips 208U-45 (march 1946) and it has some bad capacitors - just like many beebs from that era ;) Now I want to replace these bad capacitors with new ones, but they are so yellow.... There are many ways to reconstruct the old capacitors so that the new ones look like the originals. An example is at https://www.nfor.nl/radioforumservice/i ... kel-teer-c (in Dutch, but the pictures will give an idea of the process.

But in these modern times it should also be possible to print the new "housing" of the capacitor. They are symmetric so when I design a half capacitor and print it twice, then I can place the new capacitor in this half housing and glue the other half on it. Then paint it black and I have a new old capacitor. The problem is, I don't know how to make such a design. Can anybody here help me? The shape is quite simple: a cylinder with a conical top. The diameter of the cylinder is about 1.5 cm (or 0,5 inch) and the height of the top is about 0,5 cm (or 0,2 inch). The total length of the cylinder is 2.5 cm (1 inch) so the printed cylinder has to be only 1.25 cm (0.5 inch).
eronieuw.jpg
This capacitor should become ....
eronieuw.jpg (6.48 KiB) Viewed 1136 times
teercondensator.jpg
... like this model.
256K + 6502 Inside
MAN WOMAN :shock:

scruss
Posts: 149
Joined: Sun Jul 01, 2018 3:12 pm
Location: Toronto
Contact:

Re: Printing a capacitor

Post by scruss » Sat Aug 18, 2018 8:01 pm

I just put this together in OpenSCAD: Retro Radio Repair Axial Capacitor Cover
1d952e4f0f905d7fa35fcdb587a4f335_preview_featured.jpg
3d model of capacitor cover
I can't comment on the advisability/safety of doing this. These caps may get hot and expand, and a 3D printed shell would make a great heat insulator. Burning PLA smells great initially … then likely becomes a great conductor as it chars.

Here's the code. I took the sizes of the source capacitor from the Vishay datasheet.

Code: Select all

// https://stardot.org.uk/forums/viewtopic.php?f=11&t=15532 ...
// scruss - 2018 - OpenSCAD
$fn=16;     // no of segments in circle - best left as is

module vishay() {
    /*
    model axial capacitor as two cylinders
    
    Vishay Roederstein
    400 V 0.1 uF axial
    https://www.vishay.com/docs/26013/mkt1813.pdf
    diameter	7.0
    length		19.0
    lead diameter	0.7 mm
    */
    union() {
        cylinder(d=7,   h=19 / 2);     // capacitor body
        cylinder(d=0.7, h=40 / 2);     // capacitor leads
        /* though the Vishay cap doesn't have conical ends,
            add one to help with print overhang
            NB: walls get quite thin
        */
        translate([0, 0, (19 / 2) - 1e-6])cylinder(d1=7, d2=0,  h=5 * (7 / 15) - 1);
    }
}

module halfcase() {
    /*
    half capacitor size, from roland's description
    cylindrical body with a short cone on top
    */
    union() {
        cylinder(d=15, h=15 / 2);   
        translate([0, 0, (15 / 2) - 1e-6])cylinder(d1=15, d2=0, h=5);
    }
}

difference() {
    /* output difference between case and capacitor models */
    halfcase();
    minkowski() {
        /* add a small allover tolerance so capacitor fits */
        vishay();
        sphere(d=0.5);
    }
}
The wall at the end of the cap is mighty thin and may not print well.

Hope this helps and doesn't burn anything down.

User avatar
roland
Posts: 3437
Joined: Thu Aug 29, 2013 8:29 pm
Location: Born (NL)
Contact:

Re: Printing a capacitor

Post by roland » Sun Aug 19, 2018 10:20 am

Thanks for your efforts. I think the heat won't be a big problem because other attempts to make new old capacitors are working with the same principle: make a new housing either by wood, pvc (electricity pipes) or even with clay.

I downloaded your design and tried to print it. Unfortunately my 3D printer seems broken. The software says "Please link printer" and it does not show up on the USB device list. I have another project to start :cry:
256K + 6502 Inside
MAN WOMAN :shock:

User avatar
1024MAK
Posts: 9294
Joined: Mon Apr 18, 2011 4:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: Printing a capacitor

Post by 1024MAK » Sun Aug 19, 2018 11:07 am

An ideal capacitor should never get hot.

Real capacitors in low power signal paths don't get even slightly warm, let alone hot. By low power, I mean low current.

Electrolytic capacitors that experience high ripple currents (smoothing in power supply sections), some output stage coupling capacitors in power amplifier circuits, and similar applications may get slightly warm. But should not get hot. The main concern here, is if enclosed, the elevated temperature will reduce the lifespan of the capacitor.

Paper or plastic dielectric capacitors used as mains droppers, or filtering should not get warm in normal operation.

With all capacitor types, there should be a vent in any extra casing, just as a precaution in the event of a failure causing a pressure built-up.

Mark

scruss
Posts: 149
Joined: Sun Jul 01, 2018 3:12 pm
Location: Toronto
Contact:

Re: Printing a capacitor

Post by scruss » Sun Aug 19, 2018 12:08 pm

roland wrote:
Sun Aug 19, 2018 10:20 am
Unfortunately my 3D printer seems broken.
That's pretty much natural state for most 3D printers. I work with them for my day job, and keeping them running is endless hassle. Probably a system update knocked out your serial driver.
1024MAK wrote:
Sun Aug 19, 2018 11:07 am
An ideal capacitor should never get hot.
Yeah, ideally. But I've worked with utility-scale power inverters and reactive power conversion, and those things can get a smidge toasty. Admittedly, most of the heat in an inverter comes from the IGBTs - the circuit bears a vague resemblance to a power amp, after all - but those soup cans are something to watch for hot spots and sudden tinsel-bomb style failures. I just provided a warning as 3D printing gets used in all sorts of situations where it shouldn't.

The end caps of the design I uploaded are something like ½ mm of PLA. They won't hold any meaningful pressure in.

User avatar
roland
Posts: 3437
Joined: Thu Aug 29, 2013 8:29 pm
Location: Born (NL)
Contact:

Re: Printing a capacitor

Post by roland » Mon Aug 20, 2018 6:58 pm

I got my printer up and running but the printed result is not quite what I expected.....

IMG_3173.jpg
256K + 6502 Inside
MAN WOMAN :shock:

scruss
Posts: 149
Joined: Sun Jul 01, 2018 3:12 pm
Location: Toronto
Contact:

Re: Printing a capacitor

Post by scruss » Mon Aug 20, 2018 7:55 pm

Looks like your printer gave up ¾ of the way in. Either that, or your hotend sliced the top off the cone: is there anything stuck to the printhead?

I just made one:
halfcap.jpg
half capacitor cover
Apologies for the purpleness, it's what was loaded in the printer. PLA, 0.2 mm layers, nothing special.

I did have to chase the central hole out a lot, though. Small holes in sloped structures tend to close up, so I'd make that lead hole way bigger next time: maybe even a couple of millimetres.

User avatar
roland
Posts: 3437
Joined: Thu Aug 29, 2013 8:29 pm
Location: Born (NL)
Contact:

Re: Printing a capacitor

Post by roland » Mon Aug 20, 2018 8:03 pm

I will have to take a closer look at the printer. Now I''m printing a minion for a test but that one also fails. After printing the bottom grid there are no more layers although the printer is still busy printing nothing. Maybe the PLA feed gets stuck so it can't print any more.
256K + 6502 Inside
MAN WOMAN :shock:

scruss
Posts: 149
Joined: Sun Jul 01, 2018 3:12 pm
Location: Toronto
Contact:

Re: Printing a capacitor

Post by scruss » Mon Aug 20, 2018 11:13 pm

Looks like it's jamming or not feeding somehow.

User avatar
Richard Russell
Posts: 936
Joined: Sun Feb 27, 2011 10:35 am
Location: Downham Market, Norfolk
Contact:

Re: Printing a capacitor

Post by Richard Russell » Tue Aug 21, 2018 9:31 pm

I'd probably just mould black Sugru around it. Low tech, I know, but the colour and increased surface area might even improve the thermal properties.

User avatar
roland
Posts: 3437
Joined: Thu Aug 29, 2013 8:29 pm
Location: Born (NL)
Contact:

Re: Printing a capacitor

Post by roland » Wed Aug 22, 2018 8:55 pm

I've never heared about Sugru. I'm now building capacitors from wood. Other people had good results with that. I'll post some pictures when they are ready.
256K + 6502 Inside
MAN WOMAN :shock:

User avatar
Richard Russell
Posts: 936
Joined: Sun Feb 27, 2011 10:35 am
Location: Downham Market, Norfolk
Contact:

Re: Printing a capacitor

Post by Richard Russell » Wed Aug 22, 2018 9:04 pm

roland wrote:
Wed Aug 22, 2018 8:55 pm
I've never heared about Sugru.
https://sugru.com/

So many uses!

scruss
Posts: 149
Joined: Sun Jul 01, 2018 3:12 pm
Location: Toronto
Contact:

Re: Printing a capacitor

Post by scruss » Thu Aug 23, 2018 4:04 pm

expensive, though: 40 g of Sugru costs roughly what I pay for 1 kg of PLA filament

colonel32
Posts: 65
Joined: Wed Jan 18, 2017 7:59 pm
Location: USA
Contact:

Re: Printing a capacitor

Post by colonel32 » Thu Aug 23, 2018 4:10 pm

Sugru is great. It doesn't last very long though. I don't know what the shelf-life is these days, but I used some that had expired, and it had denatured and lost its strength after setting. My biggest problem is that I don't use enough of it to be able to keep some handy for off-the-cuff repairs.

User avatar
danielj
Posts: 7564
Joined: Thu Oct 02, 2008 4:51 pm
Location: Manchester
Contact:

Re: Printing a capacitor

Post by danielj » Thu Aug 23, 2018 4:21 pm

Keep it in the fridge? Seems to last well beyond use by when I've done that.

User avatar
Richard Russell
Posts: 936
Joined: Sun Feb 27, 2011 10:35 am
Location: Downham Market, Norfolk
Contact:

Re: Printing a capacitor

Post by Richard Russell » Thu Aug 23, 2018 6:55 pm

danielj wrote:
Thu Aug 23, 2018 4:21 pm
Keep it in the fridge? Seems to last well beyond use by when I've done that.
Yep, that's what I do (in the bottom drawer where it's coldest) but shelf life is certainly an issue. Just too useful to be without though.

colonel32
Posts: 65
Joined: Wed Jan 18, 2017 7:59 pm
Location: USA
Contact:

Re: Printing a capacitor

Post by colonel32 » Thu Aug 23, 2018 7:44 pm

danielj wrote:
Thu Aug 23, 2018 4:21 pm
Keep it in the fridge?
Cheers!
Richard Russell wrote:
Thu Aug 23, 2018 6:55 pm
(in the bottom drawer where it's coldest)
And where all the most putrid salad water collects!!

No?! Just me, then :D

User avatar
IanS
Posts: 1045
Joined: Mon Aug 31, 2009 6:02 pm
Contact:

Re: Printing a capacitor

Post by IanS » Thu Aug 23, 2018 7:51 pm

danielj wrote:
Thu Aug 23, 2018 4:21 pm
Keep it in the fridge? Seems to last well beyond use by when I've done that.
It's in the FAQ - https://sugru.com/faq
Store your unopened single-use packs in the fridge (or freezer) to multiply the number of months left to use them by up to 3 times (you’ll find the use-by date printed at the back of each single-use pack).

Post Reply