High current PSU
Freitsu, Fri Oct 22 2010, 08:18AMI was visiting the local fleamarket and what a good thing I did! :D
What I found there was some BIG transformer (35€) 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 (10€) 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. :)
Re: High current PSU
Proud Mary, Fri Oct 22 2010, 09:17AM
Online it is common for the Greek μ 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 μμF.
Millifarads are never used on capacitor markings to avoid the very confusion you have happened upon.
What directory? Where are your X-ray setup pics?
Proud Mary, Fri Oct 22 2010, 09:17AM
Freitsu wrote ...
21500MFD (is that Milli farad???)
It is microfarads, Freitsu, also written μF, the Greek letter μ - mu - being the SI prefix indicating micro, the one millionth part, or 10E−6.21500MFD (is that Milli farad???)
Online it is common for the Greek μ 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 μμF.
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. :)
Look in the pics/ directory for some pictures of my x-ray setup. :)
What directory? Where are your X-ray setup pics?
Re: High current PSU
Freitsu, Fri Oct 22 2010, 09:32AM
Alright, I learn something new every day. I haven't come upon MFD as uF or μF before and I don't remember being teached that in school 10+ years ago eigther... :)
The x-ray pics are here:
Freitsu, Fri Oct 22 2010, 09:32AM
Alright, I learn something new every day. I haven't come upon MFD as uF or μF before and I don't remember being teached that in school 10+ years ago eigther... :)
The x-ray pics are here:
Re: High current PSU
Proud Mary, Fri Oct 22 2010, 02:43PM
In informal spoken English, people will sometimes say "muff" for μF, and "puff" for pF.
Proud Mary, Fri Oct 22 2010, 02:43PM
In informal spoken English, people will sometimes say "muff" for μF, and "puff" for pF.
Re: High current PSU
Arcstarter, Sat Oct 23 2010, 05:06AM
Arcstarter, Sat Oct 23 2010, 05:06AM
Proud Mary wrote ...
In informal spoken English, people will sometimes say "muff" for μF, 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 In informal spoken English, people will sometimes say "muff" for μF, and "puff" for pF.
Re: High current PSU
Steve Conner, Sat Oct 23 2010, 07:12PM
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.
Steve Conner, Sat Oct 23 2010, 07:12PM
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.
Re: High current PSU
Proud Mary, Sat Oct 23 2010, 08:02PM
The Wikipedia entry under Farad mentions the puff techno-jargon case here:
Proud Mary, Sat Oct 23 2010, 08:02PM
The Wikipedia entry under Farad mentions the puff techno-jargon case here:
Re: High current PSU
Arcstarter, Sat Oct 23 2010, 09:10PM
.
I also never knew there where commercially available capacitors down to 100femtofarads.
Arcstarter, Sat Oct 23 2010, 09:10PM
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 The Wikipedia entry under Farad mentions the puff techno-jargon case here:
.I also never knew there where commercially available capacitors down to 100femtofarads.
Re: High current PSU
klugesmith, Sat Oct 23 2010, 10:55PM
klugesmith, Sat Oct 23 2010, 10:55PM
Freitsu wrote ...
Alright, I learn something new every day. I haven't come upon MFD as uF or μF 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!
Alright, I learn something new every day. I haven't come upon MFD as uF or μF 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!
Re: High current PSU
Freitsu, Sun Oct 24 2010, 08:03AM
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.
Freitsu, Sun Oct 24 2010, 08:03AM
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!
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.Re: High current PSU
Freitsu, Tue Nov 09 2010, 10:35AM
I decided to build a regulated PSU of the whole thing, including box!
My dad helped me some with the making of that aluminium box.
Here are the pics:
Note the thermostat that you can see bolted onto middle cooling-element, it turns the fan on at +70C and off at +40C. It's usually cold enough under 15A that no fan is needed.
Things to work on is:
- Get bigger smoothing cap! 47000uF 80V isn't enough, voltage REALLY sags while drawing 30A @ 30V.
Current control isn't so accurate but atleast LM723 regulator can keep those 2n3055 transistors from frying!
The schematic for my PSU is taken from this site: (not my drawings! I stacked more of power transistors)
Freitsu, Tue Nov 09 2010, 10:35AM
I decided to build a regulated PSU of the whole thing, including box!
My dad helped me some with the making of that aluminium box.
Here are the pics:
Note the thermostat that you can see bolted onto middle cooling-element, it turns the fan on at +70C and off at +40C. It's usually cold enough under 15A that no fan is needed.
Things to work on is:
- Get bigger smoothing cap! 47000uF 80V isn't enough, voltage REALLY sags while drawing 30A @ 30V.
Current control isn't so accurate but atleast LM723 regulator can keep those 2n3055 transistors from frying!
The schematic for my PSU is taken from this site:
(not my drawings! I stacked more of power transistors)Re: High current PSU
Adam Munich, Tue Nov 09 2010, 10:56AM
Looks pretty good! Check old stereo receivers for smoothing caps, they have huge ones. They're high quality too; can't have hum in your music!
Proud Mary I've never heard that before. A lot of people just say UF though.
Adam Munich, Tue Nov 09 2010, 10:56AM
Looks pretty good! Check old stereo receivers for smoothing caps, they have huge ones. They're high quality too; can't have hum in your music!
Proud Mary I've never heard that before. A lot of people just say UF though.
Re: High current PSU
Nicko, Tue Nov 09 2010, 11:02AM
FWIW, when doing my internship at ITT (actually STL Harlow) I remember using "puff" for pF but always "micro" and "milli" for u & m. "muff" was something completely different...
Cheers
Nicko, Tue Nov 09 2010, 11:02AM
Steve McConner wrote ...
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.
I've always liked the way that sensible s/w packages, like LTspice, convert "u" to "µ" in the right places, i.e. for component values.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.
FWIW, when doing my internship at ITT (actually STL Harlow) I remember using "puff" for pF but always "micro" and "milli" for u & m. "muff" was something completely different...
Cheers
Re: High current PSU
Freitsu, Tue Nov 09 2010, 11:17AM
Thanks Grenadier!
It looks pretty robust, almost like USSR. ;)
Freitsu, Tue Nov 09 2010, 11:17AM
Thanks Grenadier!
It looks pretty robust, almost like USSR. ;)
Re: High current PSU
Proud Mary, Tue Nov 09 2010, 11:20AM
Good work, Freitsu!
It may not suit all users, in all circumstances, and applications, but it is often convenient to use industrial or automotive lead-acid accumulators to meet occasional or intermittent heavy current demands. When not in use, the batteries can be kept float charged, so they are always ready for use.
I also find lead acid cells, such as the Enersys Cyclon* I've pictured below, very convenient as floating X-ray heater supplies in grounded anode configurations, and which you might find useful in your own X-ray work:
* RoHS exempt
Proud Mary, Tue Nov 09 2010, 11:20AM
Good work, Freitsu!
Freitsu wrote ...
voltage REALLY sags while drawing 30A @ 30V.
voltage REALLY sags while drawing 30A @ 30V.
It may not suit all users, in all circumstances, and applications, but it is often convenient to use industrial or automotive lead-acid accumulators to meet occasional or intermittent heavy current demands. When not in use, the batteries can be kept float charged, so they are always ready for use.
I also find lead acid cells, such as the Enersys Cyclon* I've pictured below, very convenient as floating X-ray heater supplies in grounded anode configurations, and which you might find useful in your own X-ray work:
* RoHS exempt
Re: High current PSU
Freitsu, Tue Nov 09 2010, 11:39AM
I think I will go the capasitor way, but using sealed lead-acid batteries is not a bad idea eighter!
Freitsu, Tue Nov 09 2010, 11:39AM
I think I will go the capasitor way, but using sealed lead-acid batteries is not a bad idea eighter!
Re: High current PSU
Tesla Fan, Mon Nov 15 2010, 02:23PM
Hi Freitsu, nice work with the power supply!
I will show you two 24V transormers i have, maybe you can compare the size to find out about the VA rating of yours. The smaller is 700VA and the bigger 1600VA (input is 220V, i assume you have the same in Finland).The small uses 2.5mm wire and the big somewhere about 4.5mm.
As for the voltage sag, it seems kind of normal to me. 30V x 30A = 900VA which is not a small amount of power. I am pretty sure that it is normal to have a little voltage drop when you get near the max current capability of the transformer. I know for sure that when a 24V transformer (AC circuit) is under heavy load (more than its normal rating), voltage can go down to even 17V.
For example, if you connect a 0.1Ohm resistor to your transformers output, it will "try" to draw 240Amps! Since your transformer is not rated at 6KW, he cannot supply that current and the voltage with sag (big time, since this is practically a shortcircuit for the transformer).
I could be wrong, but be sure of your theory before spending money on bigger caps.
-- WARNING - "REDNECK's", UNSAFE WAY TO GET AN ESTIMATE OF A TRANSFORMERS VA RATING -- 
It just occurred to me, you can use that as a (crude, unsafe, vicious) way to get a rough estimate of your transformer rating: If you have a multimeter, monitor the primary current draw (eg connect it is series with one of 220V input cables) and for only a second shortcircuit the secondary. Then you can meause the exact main voltage and multiply the two numbers to get the VA rating (4,5A at 220V = ~1000VA). Actually you will get a bigger number, as all transformers can be over-loaded to some extent, and ONLY for a very very short period. I know, i know it is cruel, and i assume you have the skills to do that without blowing up you multimeter or killing yourself (mains 220V are involved).
-- USE AT YOUR OWN RISK as a last resort method only -- 
Tesla Fan, Mon Nov 15 2010, 02:23PM
Hi Freitsu, nice work with the power supply!
I will show you two 24V transormers i have, maybe you can compare the size to find out about the VA rating of yours. The smaller is 700VA and the bigger 1600VA (input is 220V, i assume you have the same in Finland).The small uses 2.5mm wire and the big somewhere about 4.5mm.
As for the voltage sag, it seems kind of normal to me. 30V x 30A = 900VA which is not a small amount of power. I am pretty sure that it is normal to have a little voltage drop when you get near the max current capability of the transformer. I know for sure that when a 24V transformer (AC circuit) is under heavy load (more than its normal rating), voltage can go down to even 17V.
For example, if you connect a 0.1Ohm resistor to your transformers output, it will "try" to draw 240Amps! Since your transformer is not rated at 6KW, he cannot supply that current and the voltage with sag (big time, since this is practically a shortcircuit for the transformer).
I could be wrong, but be sure of your theory before spending money on bigger caps.
-- WARNING - "REDNECK's", UNSAFE WAY TO GET AN ESTIMATE OF A TRANSFORMERS VA RATING -- It just occurred to me, you can use that as a (crude, unsafe, vicious) way to get a rough estimate of your transformer rating: If you have a multimeter, monitor the primary current draw (eg connect it is series with one of 220V input cables) and for only a second shortcircuit the secondary. Then you can meause the exact main voltage and multiply the two numbers to get the VA rating (4,5A at 220V = ~1000VA). Actually you will get a bigger number, as all transformers can be over-loaded to some extent, and ONLY for a very very short period. I know, i know it is cruel, and i assume you have the skills to do that without blowing up you multimeter or killing yourself (mains 220V are involved).
-- USE AT YOUR OWN RISK as a last resort method only -- Re: High current PSU
Steve Conner, Mon Nov 15 2010, 03:14PM
The short circuit method will give you an answer about 10 times bigger than the real VA rating. I just go with 100VA per kg weight.
Steve Conner, Mon Nov 15 2010, 03:14PM
The short circuit method will give you an answer about 10 times bigger than the real VA rating. I just go with 100VA per kg weight.
Re: High current PSU
Tesla Fan, Mon Nov 15 2010, 03:54PM
Thanks for the correction Mr. McConner , i guess it is a useless method after all... 
Tesla Fan, Mon Nov 15 2010, 03:54PM
Thanks for the correction Mr. McConner
, i guess it is a useless method after all... Re: High current PSU
pauleddy, Tue Nov 16 2010, 02:19AM
you need one of these caps
140000UF 50vdc
pauleddy, Tue Nov 16 2010, 02:19AM
you need one of these caps
140000UF 50vdc
Re: High current PSU
HazzWold 1993, Tue Nov 16 2010, 09:02AM
Not to hijack the thread but is there a limit of when there is too much capacitance in a smoothing cap? or is there better results to be had in using only the calculated amount?
HazzWold 1993, Tue Nov 16 2010, 09:02AM
Not to hijack the thread but is there a limit of when there is too much capacitance in a smoothing cap? or is there better results to be had in using only the calculated amount?
Re: High current PSU
Tesla Fan, Tue Nov 16 2010, 07:53PM
wow, 140.000μF , that could be handy
Tesla Fan, Tue Nov 16 2010, 07:53PM
pauleddy wrote ...
you need one of these caps
140000UF 50vdc
you need one of these caps
140000UF 50vdc
wow, 140.000μF , that could be handy
Re: High current PSU
Freitsu, Thu Nov 18 2010, 01:08PM
Could you please send that one to me?
Freitsu, Thu Nov 18 2010, 01:08PM
pauleddy wrote ...
you need one of these caps
140000UF 50vdc
you need one of these caps
140000UF 50vdc
Could you please send that one to me?
Steve McConner wrote ...
The short circuit method will give you an answer about 10 times bigger than the real VA rating. I just go with 100VA per kg weight.
I kind of thought the same thing. So almost 1kVA in my case, so far the PSU haven't let me down...The short circuit method will give you an answer about 10 times bigger than the real VA rating. I just go with 100VA per kg weight.
Re: High current PSU
pauleddy, Sun Nov 21 2010, 04:23AM
Unfortently this is my only one it it is has plans for my own super supply, enless you can give me a great offer or trade. :)
pauleddy, Sun Nov 21 2010, 04:23AM
Unfortently this is my only one it it is has plans for my own super supply, enless you can give me a great offer or trade. :)
Re: High current PSU
Proud Mary, Sun Nov 21 2010, 10:02AM
There is a very interesting discussion of this very topic in Linear Power Supply Design here:
Proud Mary, Sun Nov 21 2010, 10:02AM
HazzWold Labs wrote ...
Not to hijack the thread but is there a limit of when there is too much capacitance in a smoothing cap? or is there better results to be had in using only the calculated amount?
Not to hijack the thread but is there a limit of when there is too much capacitance in a smoothing cap? or is there better results to be had in using only the calculated amount?
There is a very interesting discussion of this very topic in Linear Power Supply Design here:
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