Basic electronics, go! The linked capacitor from Elna ( http://www.elna.co.jp/en/capacitor/double_layer/catalog/pdf/dk_e.pdf) has an internal resistance of 30 ohms.
Intel rate their 32GB X25-E at 2.4W active (we aren't interested in idle power usage, if its idle, we don't need the capacitor in the first place) on the +5V rail, thats 0.48A. (P=VI) V=IR, supply is 5V, current through load is 480mA, hence R=10.4 ohms. The resistance of the X25-E under load is 10.4 ohms. Now if you have a capacitor discharge circuit with the charged Elna DK-6R3D105T - the largest and most suitable from that datasheet - you have 40.4 ohms around the loop (cap and load). +5V over 40.4 ohms. The maximum current you can pull from that is I=V/R = 124mA. Around a quarter what the X25-E wants in order to write. The setup won't work. I'd suggest something more along the lines of: http://www.cap-xx.com/products/products.htm Which have an ESR around 3 orders of magnitude lower. t On 22 May 2010 18:58, Ragnar Sundblad <ra...@csc.kth.se> wrote: > > On 22 maj 2010, at 07.40, Don wrote: > > >> The SATA power connector supplies 3.3, 5 and 12v. A "complete" > >> solution will have all three. Most drives use just the 5v, so you can > >> probably ignore 3.3v and 12v. > > I'm not interested in building something that's going to work for every > possible drive config- just my config :) Both the Intel X25-e and the OCZ > only uses the 5V rail. > > > >> You'll need to use a step up DC-DC converter and be able to supply ~ > >> 100mA at 5v. > >> It's actually easier/cheaper to use a LiPoly battery & charger and get a > >> few minutes of power than to use an ultracap for a few seconds of > >> power. Most ultracaps are ~ 2.5v and LiPoly is 3.7v, so you'll need a > >> step up converter in either case. > > Ultracapacitors are available in voltage ratings beyond 12volts so there > is no reason to use a boost converter with them. That eliminates high > frequency switching transients right next to our SSD which is always > helpful. > > > > In this case- we have lots of room. We have a 3.5" x 1" drive bay, but a > 2.5" x 1/4" hard drive. There is ample room for several of the 6.3V ELNA 1F > capacitors (and our SATA power rail is a 5V regulated rail so they should > suffice)- either in series or parallel (Depending on voltage or runtime > requirements). > > http://www.elna.co.jp/en/capacitor/double_layer/catalog/pdf/dk_e.pdf > > > > You could 2 caps in series for better voltage tolerance or in parallel > for longer runtimes. Either way you probably don't need a charge controller, > a boost or buck converter, or in fact any IC's at all. It's just a small > board with some caps on it. > > I know they have a certain internal resistance, but I am not familiar > with the characteristics; is it high enough so you don't need to > limit the inrush current, and is it low enough so that you don't need > a voltage booster for output? > > >> Cost for a 5v only system should be $30 - $35 in one-off > >> prototype-ready components with a 1100mAH battery (using prices from > >> Sparkfun.com), > > You could literally split a sata cable and add in some capacitors for > just the cost of the caps themselves. The issue there is whether the caps > would present too large a current drain on initial charge up- If they do > then you need to add in charge controllers and you've got the same problems > as with a LiPo battery- although without the shorter service life. > > > > At the end of the day the real problem is whether we believe the drives > themselves will actually use the quiet period on the now dead bus to write > out their caches. This is something we should ask the manufacturers, and > test for ourselves. > > Indeed! > > /ragge > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss >
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