Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old June 9th 17, 12:06 AM posted to sci.electronics.repair
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Default The 280 pound capacitor

On Thursday, 8 June 2017 19:56:29 UTC+1, Dave Platt wrote:
In article ,
Cursitor Doom wrote:

Questions: what makes this thing so special as to cost so much?


At a guess - exact replacement parts might no longer being made,
the equipment manufacturer has a small remaining stock, there
may be no other source. Some owners of the equipment (e.g. military
and some businesses) may have an "exact replacement only" policy
for spare parts, to avoid the need to send equipment through a
formal requalification process.

So, Marconi can charge that much for a cap, because there are people
willing to pay it (rather than scrap the whole piece of equipment).

Why have the designers used such a huge capacity cap in this low current
drain application?


Might be "because they could". Or, possibly, some of the downstream
circuitry might have poor power-supply rejection, and having a truly
huge filter cap might be the only way to get ripple-related noise
and sidebands down low enough to meet the device's specs. They might
also have figured that this part might be prone to degrade over the
years (as it apparently has done?) and they installed one of larger-
than-initially-required capacity to stave off the effect of this
aging and degradation.

If I can source a generic electrolytic of the same spec or better for
30 quid, why should I not use that instead of the bespoke replacement??


The extra hold-down terminals might be needed in order for the device
to meet its reliability specifications, when installed under
conditions of high vibration and possible acceleration shock (e.g. in
military installs, on boats or airplanes). Without the additional
pins soldered to the board, vibration could result in the cap
shaking back and forth, with all of the stress placed on the two
solder joints (and the PCB traces) resulting in stress cracking.

A standard modern cap of the same capacity and voltage rating, and
equal or better temperature and lifetime specs, is likely to be a good
deal lighter than the original. If you can find one which fits the
connection terminals, and don't mind the fact that it might break
loose if you use the equipment in a bomber that's flying through
intense flak explosions for months on end, I suspect it'd work out
just as well for you.


Marconi Instruments were hot on vibration tests since they're key to reliability in military use. Competitor equipment often failed their tests.

As well as what has been mentioned, a big cap would presumably help ride over an arcing mains connection, giving reliable service where a lesser device would cause malfunction.

As said if you're just using it on a bench you can put whatever cap you like there. It won't be a low ESR type on a 50Hz PSU. If you glue it down it will improve its shock/vibration resilience, but not to match the original marconi & mil specs.


NT

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Old June 9th 17, 01:00 PM posted to sci.electronics.design,sci.electronics.repair
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Default The 280 pound capacitor

On 06/08/2017 01:28 PM, Cursitor Doom wrote:

This is the only pic that came out for some reason, but it's got most of
the important info on it. You can't quite see, but it has 5 terminals for
some reason, but on the board only 2 of them are connected. It's gone
seriously low-res internally, BTW, so *does* need replacing.

Questions: what makes this thing so special as to cost so much?
Why have the designers used such a huge capacity cap in this low current
drain application?


Probably because they got a bunch of large value weird-ass caps cheap
and that's what they use in everything. Like a guy who asked me why they
used a 1N4002 in this one mass-produced rack effects box when a 1N4001
would've been fine from a ratings perspective and it's cuz "that's what
they use in everything"

If I can source a generic electrolytic of the same spec or better for
30 quid, why should I not use that instead of the bespoke replacement??


They're like 5 bucks:

http://www.mouser.com/ProductDetail/United-Chemi-Con/ESMH160VSN473MR50T/?qs=sGAEpiMZZMtZ1n0r9vR22dBjIkbB%252b54P4MErU9o8dM Q%3d
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Old June 9th 17, 01:02 PM posted to sci.electronics.design,sci.electronics.repair
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Default The 280 pound capacitor

On Fri, 9 Jun 2017 08:05:20 -0400, bitrex
wrote:

On 06/08/2017 01:39 PM, Winfield Hill wrote:
Cursitor Doom wrote...

I tore down a Marconi signal generator today. ...
faulty smoothing cap in the PSU .. GBP280.


I have a 280-pound capacitor, four of them in fact.
Well, they must weigh something in that vicinity.
They cost $500 each, including pallet shipping.


The physically largest capacitor I ever saw in person was a PIO type
rated IIRC for a couple of uF at several kV; it weighed about as much as
a bowling ball and was about the same size


At 280 lbs, it would take several big men to move the thing. (Or a
forklift). Not the kind of thing you can just replace on your work
bench, because the bench would probably collapse.

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Old June 9th 17, 01:05 PM posted to sci.electronics.design,sci.electronics.repair
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Default The 280 pound capacitor

On 06/08/2017 01:39 PM, Winfield Hill wrote:
Cursitor Doom wrote...

I tore down a Marconi signal generator today. ...
faulty smoothing cap in the PSU .. GBP280.


I have a 280-pound capacitor, four of them in fact.
Well, they must weigh something in that vicinity.
They cost $500 each, including pallet shipping.


The physically largest capacitor I ever saw in person was a PIO type
rated IIRC for a couple of uF at several kV; it weighed about as much as
a bowling ball and was about the same size

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Old June 9th 17, 01:46 PM posted to sci.electronics.design,sci.electronics.repair
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Default The 280 pound capacitor

bitrex wrote:
On 06/08/2017 01:39 PM, Winfield Hill wrote:
Cursitor Doom wrote...

I tore down a Marconi signal generator today. ...
faulty smoothing cap in the PSU .. GBP280.


I have a 280-pound capacitor, four of them in fact.
Well, they must weigh something in that vicinity.
They cost $500 each, including pallet shipping.


The physically largest capacitor I ever saw in person was a PIO type
rated IIRC for a couple of uF at several kV; it weighed about as much as
a bowling ball and was about the same size


Our 170 pound energy discharge capacitors, each 70 uF at 12 kVDC:
http://capturedlightning.com/photos/...ps/MAXCAP3.JPG


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Old June 9th 17, 02:14 PM posted to sci.electronics.design,sci.electronics.repair
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Default The 280 pound capacitor

On a sunny day (Fri, 9 Jun 2017 08:05:20 -0400) it happened bitrex
wrote in :

On 06/08/2017 01:39 PM, Winfield Hill wrote:
Cursitor Doom wrote...

I tore down a Marconi signal generator today. ...
faulty smoothing cap in the PSU .. GBP280.


I have a 280-pound capacitor, four of them in fact.
Well, they must weigh something in that vicinity.
They cost $500 each, including pallet shipping.


The physically largest capacitor I ever saw in person was a PIO type
rated IIRC for a couple of uF at several kV; it weighed about as much as
a bowling ball and was about the same size


In the sixties I worked in a company that made HV transformers and equipment
for power stations, railways, etc, now the caps I have seen in the HV test room
were alsmost as big as me.
Soem of the transformers required a ladder to climb on those.
The caps looked a bit like these:
http://www.hvbright.com/products/hig...unt-capacitor/
Dangerous place...

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Old June 9th 17, 02:44 PM posted to sci.electronics.repair
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Default The 280 pound capacitor

On Friday, June 9, 2017 at 9:06:01 AM UTC-4, wrote:


At 280 lbs, it would take several big men to move the thing. (Or a
forklift). Not the kind of thing you can just replace on your work
bench, because the bench would probably collapse.



You realize the OP was referring to cost (280 pound sterling), not weight. If you're making a joke, the second poster beat you to it.

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Old June 9th 17, 03:39 PM posted to sci.electronics.repair
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Default The 280 pound capacitor

On Thu, 8 Jun 2017 17:28:02 -0000 (UTC), Cursitor Doom
wrote:

Hi all,

I tore down a Marconi signal generator today. It's been awaiting my
attention for quite a while. Can't recall the model number off hand but
it does 10kHz to 5.4Ghz IIRC. I bought it from some chap who told me it
had a faulty smoothing cap in the PSU 'cos it was generating signals with
ripple on it. He told me he'd been quoted GBP280 ($387 in US dough as of
today's date) for a new replacement from Marconi and I bought it on that
understanding. Anyway, I tore it down today and located the said
capacitor. Here it is:

https://www.flickr.com/photos/128859...in/dateposted-
public/

This is the only pic that came out for some reason, but it's got most of
the important info on it. You can't quite see, but it has 5 terminals for
some reason, but on the board only 2 of them are connected. It's gone
seriously low-res internally, BTW, so *does* need replacing.

Questions: what makes this thing so special as to cost so much?
Why have the designers used such a huge capacity cap in this low current
drain application?
If I can source a generic electrolytic of the same spec or better for
30 quid, why should I not use that instead of the bespoke replacement??


It will be a limited production component that is no longer made and
the remaining stock has a very high price. Replace it with an
electrolytic of the same capacitance and voltage rating. The extra
terminals are probably connections to internal parallel capacitors. I
once worked on a power supply that had a 600 uF capacitor but when it
went I discovered it was made of 8 x 100 uF in parallel all in the
same encapsulation with two terminals. I assume the 600 mark on the
case was a misprint.

Steve

--
Neural Network Software for Windows http://www.npsnn.com

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Old June 9th 17, 05:16 PM posted to sci.electronics.design,sci.electronics.repair
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Default The 280 pound capacitor

On Thu, 8 Jun 2017 17:28:02 -0000 (UTC), Cursitor Doom
wrote:

https://www.flickr.com/photos/128859...posted-public/


47,000 uF 16v. You should be able to find that in a physically
smaller package.
http://www.ebay.com/sch/i.html?_nkw=47000+uf+16v

Carefully remove the base from the capacitor, preserving only the base
and the can. If you're really careful, you might be able to also save
the vinyl insulator. Tear out the guts and throw it away. Install
the replacement physically smaller capacitor inside the can,
connecting the capacitor leads to the base to match the original.
Solder it back onto the PCB and you're done.

If you don't care if it looks like the original, forget the
aforementioned process and just solder the replacement cap to the PCB
in place of the can in any manner that will fit.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old June 9th 17, 05:26 PM posted to sci.electronics.design,sci.electronics.repair
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Default The 280 pound capacitor

"Bert Hickman" wrote in message
...
I have a 280-pound capacitor, four of them in fact.
Well, they must weigh something in that vicinity.
They cost $500 each, including pallet shipping.


The physically largest capacitor I ever saw in person was a PIO type
rated IIRC for a couple of uF at several kV; it weighed about as much as
a bowling ball and was about the same size


Our 170 pound energy discharge capacitors, each 70 uF at 12 kVDC:
http://capturedlightning.com/photos/...ps/MAXCAP3.JPG


I've worked with capacitors bigger than that, although I think they were in
sections so maybe it's not technically true to say "bigger capacitor"
(singular). :^) Ratings were around 100s uF, 2000V, lots of amps.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com



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