Fwd: Cost comparison of Geeks to Maxs was Re: Maxwell VS. MMC capacitors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>


>X-Envelope-From: alwynj48-at-earthlink-dot-net  Sun Feb 29 11:29:52 2004
>Reply-To: "Robert Jones" <alwynj-at-earthlink-dot-net>
>From: "Robert Jones" <alwynj48-at-earthlink-dot-net>
>To: "Tesla list" <tesla-at-pupman-dot-com>
>Subject: Cost comparison of Geeks to Maxs was Re: Maxwell VS. MMC capacitors
>Date: Sun, 29 Feb 2004 10:26:31 -0800
>X-Mailer: Microsoft Outlook Express 6.00.2720.3000
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>
>Hi Dave and all,
>
>Sorry Dave I thought you were comparing  Geek caps to used eBay Maxs
>
>I also forgot to square the voltage ratio for the size comparison i.e. J
>capacity.
>
>Here is a better comparison:
>
>EBay: Used Max 37667 0.03uf -at-35kV
>2.25" x 4.25" x 6"
>"Buy now" price $125 say $140 with shipping
>
>The equivalent J capacity Geek cap is 61.25 caps say 62 caps,
>which would cost say $200 with shipping.
>
>Initial conclusion yes you can get more bang for your buck with a Max
>because the equivalent Geek MMC costs 42% more.
>But the Max is used so you don't know how long it will last.
>
>A better conclusion: A volume comparison of the Max and Geek caps indicated
>a Max could contain 24 Geek caps say 31 if they were rectangular. So the
>energy density at rated voltage of the max is about twice that of the Geek
>caps.  That may mean they have a better cap or they are pushing it. (see
>more comments below) Also because the Maxs are used I would want to operate
>them at say half rated voltage to make certain I get some life out of them.
>That makes the 35kV Max a 17.5kV Max with an equivalent Geek MMC of just 17
>caps,  cost say $60 with shipping.  Now the Max costs 130% more than the
>Geek MMC.
>
>My overall conclusion unless you get a very good price deal on your Maxs
>they are more expensive per J for reasonable life.
>
>Yes you could push your luck on the voltage of the Max but apparently you
>can do the same on the Geeks. Say operate at 3000V to more than double there
>J capacity. I think that gives about the same volume energy density.  My
>understanding is the Geek caps are state of the art so if the Maxs have a
>higher energy density they get it with a reduction in life expectancy. Some
>one has already commented that Maxs are just potted MMCs.
>
>Has any one dissected a dead one. Are they extended foil or what? Can any
>one comment on the higher energy density of Maxs compared to Geeks.
>
>If I think I can a get Max 37667 0.03uf -at-35kV for well under $60 I will bid
>on it other wise its Geek caps for me. I will only operate it often at half
>rated voltage,  2/3 occasionally and  if I feel very very lucky that day at
>the rated voltage.
>
>A side issue. From memory I had big cap 27uF rated at 5kV at 70C and 7kV at
>50C my conclusion was I could run it at 10kV at 25C. Anybody know the
>temperature to voltage rating  law for Geek caps.
>
> >  >I had assumed the CD caps where cheaper than even used Maxwells. I need
>to
> >  >check out ebay again.
> >  >Even at twice the price you could say you know what your getting with
>the
> >  >MMC. If its bang for your buck it may be worth the risk of a eBay Max
> >
> >
> > Build it, test it, let us know what happened, that's what I did :-)
>
>I agree the gold standard is experiment.
>But you can go along way with analysis. Its cheaper, quicker, insightful and
>some time exhaustive (meaning I don't need to build and test every perpetual
>motion machine to know none of them will work)
>The trick is knowing the limits of  theory and when to perform an
>experiment.
>
>Bob
>
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Saturday, February 28, 2004 5:47 PM
>Subject: Re: Maxwell VS. MMC capacitors
>
>
> > Original poster: dgoodfellow-at-highstream-dot-net
> >
> >
> >