The 280 pound capacitor

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
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/128859641@N02/35050368241/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??

Re: The 280 pound capacitor
Cursitor Doom wrote...
Quoted text here. Click to load it

 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.


--  
 Thanks,
    - Win

Re: The 280 pound capacitor
On 06/08/2017 01:39 PM, Winfield Hill wrote:
Quoted text here. Click to load it

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


Re: The 280 pound capacitor
wrote:

Quoted text here. Click to load it

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.


Re: The 280 pound capacitor
On Friday, June 9, 2017 at 9:06:01 AM UTC-4, snipped-for-privacy@tubes.com wrote:

Quoted text here. Click to load it


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.


Re: The 280 pound capacitor
bitrex wrote:
Quoted text here. Click to load it

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

Re: The 280 pound capacitor
Quoted text here. Click to load it

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
We've slightly trimmed the long signature. Click to see the full one.
Re: The 280 pound capacitor
Quoted text here. Click to load it

66 uF, 276 kV, 3000 A  
but that was an aggregation of multiple cans.  


Re: The 280 pound capacitor
Ralph Barone wrote...
Quoted text here. Click to load it

 Did the series caps have voltage-equalizing mediation?


--  
 Thanks,
    - Win

Re: The 280 pound capacitor
Quoted text here. Click to load it

This was an AC application (partially cancel the series inductance of a 500
kV power line), so voltage equalization wasn't a huge concern. The
individual cans did have bleed resistors inside, but those were to meet the
requirement that a can would have a safe voltage on it 15 minutes after
deenergization.  The cans were also arranged in an H configuration with a
CT to measure the unbalance current between the four sections. If the
unbalance exceeded a critical value, the bank would be tripped out.  


Re: The 280 pound capacitor
Bert Hickman wrote...
Quoted text here. Click to load it

 Whoa, you have 11 of them!  My caps look like those.


--  
 Thanks,
    - Win

Re: The 280 pound capacitor
On a sunny day (Fri, 9 Jun 2017 08:05:20 -0400) it happened bitrex

Quoted text here. Click to load it

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/high-voltage-shunt-capacitor/
Dangerous place...


Re: The 280 pound capacitor



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/128859641@N02/35050368241/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??




*************************************************************



I've come across these type of 5 terminal capacitor before.  3 pins are just  
for mounting and are not used in circuit.
(Are they not stamped with an "x"?)



Gareth.  


Re: The 280 pound capacitor
On a sunny day (Thu, 8 Jun 2017 17:28:02 -0000 (UTC)) it happened Cursitor

Quoted text here. Click to load it

Nothing, it is a crappy old Philips, the contacts to the pins go wrong too.
Just replace with some caps with right capacitance / voltage and sintered wires,
not that crap.


Quoted text here. Click to load it


Re: The 280 pound capacitor

Quoted text here. Click to load it

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).

Quoted text here. Click to load it

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.

Quoted text here. Click to load it

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.





Re: The 280 pound capacitor
says...
Quoted text here. Click to load it
Sounds like the $ 100,000 diode for the military that could have been  
replaced by a diode that cost less than one dollar except for the  
military spec.  Seems the military supply depot did not have any.  The  
company that made them did not have any,so they had to make one.  Could  
not make just one, had to do it in a large batch.  Probably made 10 to  
20 thousand of them.  

Re: The 280 pound capacitor
On Thursday, 8 June 2017 19:56:29 UTC+1, Dave Platt  wrote:
Quoted text here. Click to load it

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

Re: The 280 pound capacitor
On Thu, 8 Jun 2017 17:28:02 -0000 (UTC), Cursitor Doom

Quoted text here. Click to load it

Insane ripoff. Good reason to never buy Marconi.

Looks like you ripped out the hole plating on one pin. With luck, it
will be one of the passive mounting pins.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

We've slightly trimmed the long signature. Click to see the full one.
Re: The 280 pound capacitor
On Thu, 08 Jun 2017 12:19:54 -0700, John Larkin wrote:
  
Quoted text here. Click to load it

Fortunately it is. :-)

Re: The 280 pound capacitor
On Thursday, June 8, 2017 at 1:31:39 PM UTC-4, Cursitor Doom wrote:

Quoted text here. Click to load it
  
Quoted text here. Click to load it

Many years ago, my Tek 7603 failed to start.  I pulled the power supply out
 and was driven nuts by a simple DC voltage regulator problem in the power  
supply.  A bypass electrolytic capacitor would have been the obvious soluti
on, except this scope used at least a half dozen extra large Mallory built  
capacitors in parallel, and there's no way they all died together.  Adding  
a bit of external capacitance though brought the voltage right back and the
 scope to life.  Turns out those big caps were dropping out one by one over
 the years and gave no indication of anything going wrong as they did, unti
l the very last one opened when the supply went out.

Why did I mention all of this?  Because I just removed those big Mallorys a
nd stuck in some standard electrolytics of maybe half the total value and t
aking up about a tenth of the physical area of the originals, and the scope
 still runs daily with a perfectly clean and stable trace.

In other words, I doubt you'll see any difference by doing what you instinc
t tells you.  That cap may be very low ESR, have special impedance specs or
 ripple current specs, but I'd be stunned if it makes any real world differ
ence with off the shelf caps.  If it were mine, I'd use Panasonic FR series
 caps.

Site Timeline