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Freitsu

Fri Oct 22 2010, 08:18AM

Registered Member #3147 Joined: Sun Aug 29 2010, 10:53AM
Location: Finland
Posts: 56

I was visiting the local fleamarket and what a good thing I did! :D

What I found there was some BIG transformer (35â‚¬) marked 24V output but no VA rating on it. :(
And also in a junkbox hidden in a corner I found a bunch of capasitors, I bought the one with biggest voltage rating of 40V (10â‚¬) and 21500MFD (is that Milli farad???)
That huge capasitor sure came in handy when building a DC supply of the whole thing today!

Only thing I couldn't find second hand was a bridge rectifier but I happen to have a 35A, 800V one laying around.

Here are links to pictures of PSU:

The secondary winding wire diameter is 3.8mm, how much amperage might I expect to pull from this puppy?

PS.
Only thing that I found to get warm was the bridge rectifier (I even put a heatsink on it as you can see in pictures) but it doesn't even reach body temperature while drawing about 9 amps from it... Oh yeah, the beast weighs about 8 kg!

PPS.
Look in the pics/ directory for some pictures of my x-ray setup. :)

Proud Mary

Fri Oct 22 2010, 09:17AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Freitsu wrote ...

21500MFD (is that Milli farad???)

It is microfarads, Freitsu, also written Î¼F, the Greek letter Î¼ - mu - being the SI prefix indicating micro, the one millionth part, or 10Eâˆ’6.

Online it is common for the Greek Î¼ to be substituted by the Roman u, so you will often see microfarad written as uF too.

In very old electronics writing and part labels, you will sometimes see pF written as micromicrofarad, or Î¼Î¼F.

Millifarads are never used on capacitor markings to avoid the very confusion you have happened upon.

Freitsu wrote ...

Look in the pics/ directory for some pictures of my x-ray setup. :)

What directory? Where are your X-ray setup pics?

Freitsu

Fri Oct 22 2010, 09:32AM

Registered Member #3147 Joined: Sun Aug 29 2010, 10:53AM
Location: Finland
Posts: 56

Alright, I learn something new every day. I haven't come upon MFD as uF or Î¼F before and I don't remember being teached that in school 10+ years ago eigther... :)

The x-ray pics are here:

Proud Mary

Fri Oct 22 2010, 02:43PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

In informal spoken English, people will sometimes say "muff" for Î¼F, and "puff" for pF.

Arcstarter

Sat Oct 23 2010, 05:06AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Proud Mary wrote ...

In informal spoken English, people will sometimes say "muff" for Î¼F, and "puff" for pF.

Haha, i have not once heard them called that. If someone insisted on saying it that way i would just slowly walk away

Steve Conner

Sat Oct 23 2010, 07:12PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

We always say "microfarads" and "picofarads" around the lab.

Some older American schematics used MFD to mean microfarads. And some other older American schematics used MFD to mean millifarads. You should never use either of these nowadays to avoid confusion, especially if you live in a country that uses the SI system of units.

You can always spot a German on electronics forums because they don't write "uF", they use the actual mu symbol. The reason is simply that German keyboards have mu on a key, but everyone else has to remember Alt+016-whatever, so they just type u instead.

Proud Mary

Sat Oct 23 2010, 08:02PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The Wikipedia entry under Farad mentions the puff techno-jargon case here:

Arcstarter

Sat Oct 23 2010, 09:10PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Proud Mary wrote ...

The Wikipedia entry under Farad mentions the puff techno-jargon case here:

That is something, even though i did not doubt you when you said it at first

.

I also never knew there where commercially available capacitors down to 100femtofarads.

klugesmith

Sat Oct 23 2010, 10:55PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Freitsu wrote ...
Alright, I learn something new every day. I haven't come upon MFD as uF or Î¼F before and I don't remember being teached that in school 10+ years ago eigther... :)

The x-ray pics are here:

Nice pictures. I hope you will tell us some stories about them (in a new thread).
My favorite is the beer can, a subject I've never seen before in amateur radiography.
Does the "box" picture show a plastic tub lined with sheet lead?
Where does the camera go?
Have you measured the x-ray exposure in the beam, or the leakage exposure??

-Rich

p.s. I have frequently heard and said puff for pF, but almost never muff for uF.
While we're on the subject of SI symbols, I'll make the usual reminder about type case.
When a unit is derived from someone's name, the symbol is capitalized.
But the unit name is all lowercase, except where any noun would be capitalized (e.g. at the beginning of a sentence, or perhaps in German). The symbols F and MHz stand for farad and megahertz, not Farad or Megahertz or MegaHertz!

Freitsu

Sun Oct 24 2010, 08:03AM

Registered Member #3147 Joined: Sun Aug 29 2010, 10:53AM
Location: Finland
Posts: 56

Klugesmith wrote ...

Nice pictures. I hope you will tell us some stories about them (in a new thread).
My favorite is the beer can, a subject I've never seen before in amateur radiography.
Does the "box" picture show a plastic tub lined with sheet lead?
Where does the camera go?
Have you measured the x-ray exposure in the beam, or the leakage exposure??

-Rich

p.s. I have frequently heard and said puff for pF, but almost never muff for uF.
While we're on the subject of SI symbols, I'll make the usual reminder about type case.
When a unit is derived from someone's name, the symbol is capitalized.
But the unit name is all lowercase, except where any noun would be capitalized (e.g. at the beginning of a sentence, or perhaps in German). The symbols F and MHz stand for farad and megahertz, not Farad or Megahertz or MegaHertz!

Thanks for the nice feedback!

That beercan radiograph is actually taken with a 6VS-1 HV shunt stabiliser vacuum tube! (I got a bunch of them if anyone is interested, but that doesn't belong in this thread) But rest is taken with that dental x-ray tube that there are pics of.

Nice observation, Rich! It's indeed a plastic tub (well, more like box) that's lined with lead!

I have actually done some heavy redesigning on the leadlined box now, before I just had the digicam sitting behind the flouroscopy screen but it got heavy interference from the rays so I decided to angle a mirror behind the screen and having camera hanging on top of the mirror. Some pictures of new setup might say more than I can say in 1000 words so here goes:

<- Sealed box with the geiger counter I use to check for leaks (I don't know how accurate method this is so please feel free to critisize my way. :)

<- Box with lid removed, notice the filament transformer on right. I just have a 6.8 ohm ballast resistor connected in series and it works like a charm!

<- I decided to move the flyback closer to x-ray tube to minimize corona between HV cables and lead shield, now that problem is gone.

<- Everything in place.

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