why are electrolytic caps so much worse than in 1981?

You can get them at 100C, the ESR anyway, but the 2nH ESL, only in hybrids. Cheers, Harry

Reply to
Harry Dellamano
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Got links in freezer, bring some beer and I will cook them up. Mosfets will hit 1.0m Ohms before any caps do. If this was in 1981 he was off by at least two orders of magnitude. Maybe his Wheatstone Bridge got wet. Terry, keep submitting, you've got some good stuff. Regards, Harry

Reply to
Harry Dellamano

was

I've got a couple of 1.6 ?? milliohm electros at work - 47000 uF 16V, I think they are. Got them from Farnell at AU $50 each when we needed to test our milliohm meter at low values. They are not particularly big.

Roger

Reply to
Roger Lascelles

Hi All,

my copy of Eugene Hnateks "design of solid-state power supplies, 2nd ed" arrived last week. Its a great book, there is a wealth of information on self-oscillating dc-dc converters (Graham, you would probably be quite interested in it). On p. 280 he states:

"The lowest ESR in aluminium [capacitor] construction is what is known as the 'stacked foil' type; with all other styles it is typically an order of magnitude higher. Representative values would be 0.5 milliOhms for a stacked foil device and 5 to 20 milliOhms for other styles"

and on p.585 he states:

"Stacked foil exhibits inductance values as low as 2nH and provides superior ripple-curent ratings"

Wow, 2mOhms ESR, 2nH ESL - thats one hell of an electrolytic capacitor. He repeats the < 1mOhm remark in several places throughout the book, so its probably not a typo. Where can I get these puppies :)

Cheers Terry

Reply to
Terry Given

Hi Harry,

I suspected as much. All his work seemed to be done for NASA, so $$ was probably not much of a concern. I havent seen an ESR that low though, and I have looked at a lot of big caps over the last decade or so. Got any links?

Cheers Terry

Reply to
Terry Given

?! now I'm confused. Still, if I'd have said I have a few maggot-packs in the freezer you would no doubt be confused too. Aint dialects fun :)

LOL. the bit that surprised me was it was repeated several times.

I have worked with some 150uF 900Vdc 1.2nH (not a typo) film caps though. They were a special, designed by our resident albanian/serbian croat (interesting fella), and were fantastic. Based on RBs idea, I thought up a way of reducing the inductance on a big electrolytic - down to the 2-3nH region. Hard to convince a cap manufacturer to make them though.

I really enjoy this NG, I have learned an awful lot of really useful stuff, and "met" some wicked smart people. If any of you are ever in NZ, look me up.

Cheers Terry

Reply to
Terry Given

Hello Terry,

Since Google doesn't have an English - English translation mode: I believe you guys in NZ speak more of a UK style and then "links" might be "bangers". There is a subtle difference though. Our links are usually a bit more meaty and harder.

Regards, Joerg

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Reply to
Joerg

The problem isn't the bits you recognize/recognise, but the ones that are invisible, such as "table the discussion" having different meanings or the use of "E-Z" which can be spoken as "ee-zee (easy) or as "ee-zed (eased)".

BTW, I do not agree that electrolytic caps are worse than they were in 1981. Perhaps the cheap ones are, but the mil-spec ones have not changed for the worse.

Reply to
Guy Macon

Hnatek is not talking about electrolytic parts here.

Aluminium is used as an electrode material in polycarbonate, polyester and polystyrene film capacitors as well. It can be a deposited film or simple foil.

Stacked film refers to polycarbonate film caps first marketed by Siemens and TRW. These are identifiable by their markedly sharp-edged box-shaped bodies, as they are cut from larger continuous 'rods' of laminated stock, after schoopage is applied. They differ from conventional construction, which is involves individual part rolling (and flattening, in many cases to reduce real estate use).

Leads are stitch welded to the schoopage, or they can be reflowed.

A protective coating of epoxy is sometimes applied to reduce delamination.

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Some interesting work has been done identifying apparent standing-wave behavior in this type of construction - dependant on physical size, mounting terminal method and orientation - at frequencies where most other film caps are just stray inductance.

RL

Reply to
legg

Hi Joerg,

now owuldnt an english-english translator be a cute bit of software, eh wot? We dont use the term bangers, but most would recognise it. sossys, snags, snarlers..... most of which are really just sausage-shaped bread in a casing. I had 10kg of incredibly spicy Boerwoerst (sp?) made a month or so ago, by a butcher up near Kopu. Absolutely delicious, he uses his own meat (ooh er, sounds a bit rude) - the butchery is on his farm. Damn they are good, and cheaper than the crap the stupormarket sells.

Cheers Terry

Reply to
Terry Given

Indeed.

my question was really "are these numbers crap?" in the hope someone can show me where to by 0.0005Ohm ESR 2nH ESL electrolytics.

Cheers Terry

Reply to
Terry Given

Ah, that explains it nicely. I have looked at using Capsticks before, but avoided them on the grounds of cost.

Perusing the siemens data, none seem to get much better than 10mOhms at resonance. The capsticks go down to about 2.5mOhms.

So Hnateks numbers are still wildly optimistic, but being out by an order of magnitude is a lot better than being out by two orders of magnitude (he says, stating the blindingly obvious. Still, I need the typing practice :)

Cheers Terry

Reply to
Terry Given

Paktron data also documents an apparent frequency-dependance of ESR, that makes me hold my nose. ESR is unlikely to behave in this manner, so just what ARE they measuring for their published specs?

RL

Reply to
legg

I read in sci.electronics.design that legg wrote (in ) about 'why are electrolytic caps so much worse than in 1981?', on Sun, 6 Mar 2005:

They are probably using a model that is somewhat too simple, maybe just C R and L in series. To get an ESR that is independent of frequency, the model needs at least a resistor in parallel with the C to model dielectric loss.

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Reply to
John Woodgate

Not quite, but kinda:

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Reply to
JeffM

I would expect some frequency dependance (ie skin/proximity effect), but thats the opposite of what the curves show. Paktron are not the only ones to display such plots of ESR with frequency, I have analagous Hitachi AIC cap plots, and seem to recall seeing others too.

perhaps its a frequency-dependant loss mechanism, and a parallel-to-series conversion to get to "ESR"

Cheers Terry

Reply to
Terry Given

I think this must be it (see my last post). Ripple current ratings for electrolytics are generally higher at HF than LF, often by around 30% or so. Thus the losses must be higher at LF, which would lead to the observed "ESR" curve using the P-S approach.

Whether or not the same is true for film caps, beats me.

Cheers Terry

Reply to
Terry Given

A Paktron article includes a graph of ESR vs frequency for a number of types. Supposedly this data is collected and interpreted using the same methods and equipment.

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I think the effect in film types at lowering frequencies is related somehow to dielectric absorption, which can have effects at very low frequencies that are a bit spooky.

Some dielectrics have very low absoption, though, without altering the ESR vs frequency plots published, so it's a mystery to me. A parallel R in a film cap model would likely have too large an order of magnitude to affect it.

RL

Reply to
legg

Cyril Bateman's articles in Electronics World mention and explain ESR versus frequency.

EW April 1995, page 287. "Power dissipation in capacitors".

EW December 1997, page 998. "Understanding capacitors".

--
Tony Williams.
Reply to
Tony Williams

Hi Tony,

can you please scan & post it to ABSE? or provide a summary?

Cheers Terry

Reply to
Terry Given

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