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Science Groups Forum Index » Techniques - Microscopy » LED Illuminator for Flash Use
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| Joe |
 Posted: Wed Jul 08, 2009 4:05 pm |
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| helio |
| Posted: Thu Jul 09, 2009 3:58 am |
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"Joe" <see_real_one@sig.lin> wrote in message
news:2a29555fo0udfjtk95cnkeuq2dbds983ck@4ax.com...
Thanks for the news :)
I'm interested in driving a power LED (destined to microscopy purposes) by
an external 'supercapacitor', and I'm currently engaged in finding the best
type of capacitor.
Best regards |
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| UKoncology |
| Posted: Tue Jul 14, 2009 5:53 pm |
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On 9 July, 00:58, "helio" <forbid...@planet.it> wrote:
Quote: "Joe" <see_real_...@sig.lin> wrote in message
news:2a29555fo0udfjtk95cnkeuq2dbds983ck@4ax.com...
I still prefer a Xenon flash for photomicrography, but in light of the
recent discussions about using an LED for flash, I thought I'd post
this link to an article I saw this morning. It is about a 10A
supercapacitor-based LED flash driver. Maybe some of you can use this
information.
http://www2.electronicproducts.com/10-A_supercapacitor-based_LED_flas...
Thanks for the news :)
I'm interested in driving a power LED (destined to microscopy purposes) by
an external 'supercapacitor', and I'm currently engaged in finding the best
type of capacitor.
Best regards
This looks like just the thing! If anyone finds a source which will
sell one or two, rather than a thousand, please let the group know -
I'm sure several of us would be interested.
Unfortunately, it may be some time before they arrive in the
miserable, overtaxed, overpriced technological desert that is the
UK......
HJ |
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| helio |
| Posted: Wed Jul 15, 2009 6:24 pm |
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"UKoncology" <UKOncology@aol.com> wrote in message
news:110ddc30-01b9-4198-af21-577e8082575c@f16g2000vbf.googlegroups.com...
On 9 July, 00:58, "helio" <forbid...@planet.it> wrote:
Quote: I'm interested in driving a power LED (destined to microscopy purposes)
by
an external 'supercapacitor', and I'm currently engaged in finding the
best
type of capacitor.
This looks like just the thing! If anyone finds a source which will
sell one or two, rather than a thousand, please let the group know -
I'm sure several of us would be interested.
The first thing one thinks when he hears of 'supercapacitors' (like me,
reading Joe's message), probably, is 'capacitors with super powers'. Yet
Wikipedia indicates that supercapacitors (Electrolytic double-layer
capacitors-EDLC) are not so special: as an example, they have a very high
Power Density, but the Energy Density of Lithium Ion Capacitors, of similar
Power Density, is much higher. Supercapacitors are often used to temporarily
provide power to equipment during battery replacement', so one can deduct
that they excel as 'big current stores'
http://en.wikipedia.org/wiki/Types_of_capacitors
Now, the quantity of energy stored can't be the main concern of a
microscopist having to manage a 20 Watt LED. I think the first
characteristic has to be the discharge speed, as needed in the flash use and
in
frequency-modulated LEDs (I wonder what can appear by experimenting with
this). So, by reading the table showed on Wikipedia, it seems that the
Energy Storage Capacitors are the best. They are designed 'specifically for
intermittent duty, high current discharge applications' and their typical
uses include pulsed lasers'. Unfortunately, stored energy levels of these
devices can be lethal, so often they are shipped with a shorting installed.
This, I think, applies when the voltage exceeds 100-150 V, however, when
using
high discharge capacitors, you can't be too careful. Let me show what can
appear when using Flashlamp Rated Capacitors: "I can't over-emphasize the
risk of instant and total electrocution with even small flashlamp
capacitors. Where you have acquired some really large ones - say 12" x 18" x
8" weighing 60 pounds each - you may be better off selling them - you'll get
a lot of nice cash - and building a power supply with something just
slightly less lethal! Each one of those caps will kill dead a few dozen or
more people after sitting with the power off for a week! Seriously, they are
deadly and should be treated with the same respect as an equivalent size
block of sticks of dynamite (or C4 if you prefer) wired to detonators
sitting out in a thunderstorm.  "
http://www.repairfaq.org/sam/lasersps.htm#spscch
"For long duration pulses -Sam continues-ordinary high quality electrolytics
capacitors may work without self destructing and/or dissipating too much
energy inside the capacitor. However, for high-joule flashlamps operating
with short pulse duration, you won't get away with this for either or both
reasons. No, wiring 10,000, .01 uF, 1 kV disk capacitors in parallel
probably isn't a very viable solution! ".
Now, 10000 * .01 = 100, so I think that a 100 uF electrolytic capacitor (to
avoid the
risks of Energy Storage Capacitors) can be a good starting point. Lot of
them on ebay. About
electrolytics, Sam says "Sprague (a division of Vishay) 36DX and probably
the similar Durocap/Mallory CG, CGH, etc., work fairly well for discharges
that take a few hundred microseconds or more, and work well for discharges
that take at least a millisecond. With a 1 millisecond discharge, maybe a
couple to a few percent of the energy is dissipated in the internal
resistance of the capacitor. (Note: Duracap International, Inc. is the
actual manufacturer of the Mallory product line now.) For shorter flashes,
the Sprague TVA series (axial lead) is a little better than electrolytics
that have both leads on the same end. But for flashes under about 100
microseconds, I know that the usual electrolytics may not be the way to go."
Incidentally, I found on ebay a 'snubber' capacitor that seems good and
cheap to me:
http://cgi.ebay.com/630V-4-7uF-Pulse-High-Frenquency-Snubber-Capacitor_W0QQitemZ150298919395QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item22fe8381e3&_trksid=p3286.c0.m14&_trkparms=65:12|66:2|39:1|72:1205|293:1|294:50#ht_1714wt
One needs to wire in parallel 10 of these to get a 50 uF superfast capacitor
(total cost 30 $).
Quote: Unfortunately, it may be some time before they arrive in the
miserable, overtaxed, overpriced technological desert that is the
UK......
Now, imagine what happens in the technological heaven that Italy is. I
disperately needed layers of electrolytic grade copper, so I've been
searching all day long on google.it. Eventually, I ordered items in U.S.:
cost $30 , shipment fees $83.
Tito |
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