On 2013-09-17, Larry Jaques wrote:
On 17 Sep 2013 04:57:44 GMT, "DoN. Nichols"
wrote:
On 2013-09-15, Larry Jaques wrote:
[ ... ]
Yeah, current limiting seems like the way to go for safety. I don't
recall seeing that feature on any of the old supplies I ever worked
with, but it's been awhile. I could have forgotten.
My favorites were made by Power Designs, and I got them for good
prices at hamfests, because I knew them from having worked with them at
work. Two styles.
2005 0-20V 0-0.5 A adjustable in steps of 1 mV. Just dial
in the desired voltage from 0-10V, and a switch adds
another 10V if you need it. It has a nice current
limit. They even have the zener reference in a crystal
oven, so the voltage does not drift with room
temperature variations. Plug them in and the ovens
starts working, and once the front panel light for
the oven starts cycling, it will be stable.
3650 0-36V, 0-5A, with a variac built in so the difference
between the voltage out of the transformer and the
voltage desired out of the front panel terminals is not
too different, so you don't have to drop too much
voltage (and thus heat in the regulator.
I'll keep eyeballs peeled for those, Don. Thanks. Speaking of crystal
ovens, I have one from the '50s which I use as a fire safe. It's made
with that horrid OHMIGODWEREALLGONNADIE asbestos stuff.
Here is what my 2005s look like -- eBay auction #261287963296
including a back view showing the terminal strip where the
jumpers are -- or should be. :-) This is not the least expensive
in the auctions -- but the first with a good clear photo.
And *here*: (ebay auction #370875530364) is a newer version.
The other should be 3650-S (I went down and looked at it).
eBay auction #300756127978. To the left of center, down near
the bottom are a lamp and a knob. The knob sets the current
limit and the lamp turns on when the limit is actually limiting.
The switch to the right turns the meter from voltage to current.
The 2005 supplies have similar -- plus a button to short the
output so you can set the limit you want.
I got two of the 2005s in a rack-mount frame for practically
nothing. The seller said that he could not get them to work, and I
glanced at the rear panels, and found the jumper blocks where the
external sense could be wired had some wires coming from it going off to
nowhere. Just replace jumpers between the "+" and "+sense" terminals,
and likewise between the "-" and "-sense" terminals and they worked just
like they were supposed to. :-)
I love it when I find things like that. My neighbor gave his golf
cart to me when it wouldn't charge or run. I had to replace a $5
cable between batteries and sold the thing for $900. I gave him $100
for the thing after the fact, and told him "it cost under $50 to
repair." 
:-)
[ ... ]
Huh? How can an open harm a circuit? (Other than arcing, and its
resultant damage and chaos?)
The short which should be there is holding the voltage low. If
the open occurs, the voltage shoots up to whatever the supply is set to,
and this may be too much for something else connected to the same wires
-- or not too much, but the wrong polarity.
OK, I'll almost buy that. But what happened to those components
-after- the incident but -before- the short dropped the voltage, hmm?
Who knows -- but give them the best chance, at least. :-)
[ ... ]
The 9V batteries are probably no problem for most things in
older cars, but there may be things in the newer ones which don't like
even that much voltage. Just like an old analog multimeter which on the
Ohms range can provide enough voltage to zap a logic chip, while a
Digital one limits the maximum voltage to perhaps 1V or so.
Yeah, I keep forgetting that I stopped wrenching before most of the
cars went to digital systems. I haven't had to troubleshoot any of
the newer ones since I've owned only brand new trucks (2) since then.
Most of my work on cars was back when, too. Except for a few
things on the Mazda Navajo (really a Ford SUV with a badge change. :-)
The worst was changing the radius rods, which either required tools to
compress and take apart the front suspension (which I did not have), or
removing two big heavy rivets on each side on the rails below the front
seats. A combination of drilling and an air chisel to get those off.
:-) Replaced with bolts, of course. :-)
It's sure nice not having to get my fingernails dirty any more. I wish
I'd remembered to wear latex gloves during house painting this last
week, though. Oh, those new white 3mil nitrile gloves at HF are TITS,
guys. They're quite a bit like latex only they're 5 times tougher,
resistant to more solvents, and much easier to install/remove. I love
those things enough that I have a dozen in my BOB.
I've got some blue ones from MSC, and really like them.
[ ... ]
At a recent hamfest, I got a motor-generator -- 28 VDC input,
115 VAC three phase 400 Hz output. I could not run it from the total of
the power supplies on my bench, but I recently got a dainty little
transformer from a friend -- NOS. Dual primaries for either 120 VAC or
240 VAC input, and two center-tapped secondaries, each capable of 20 A
at 12V (or at 6V using the center taps). With the two secondaries in
series I get 24VAC at 20 Amps -- and that through a bridge rectifier
and with a big filter cap runs that motor-generator nicely.
Cool! Was your "dainty" above facetious?
A mere 16 lbs -- by the step on the bathroom scale holding it,
vs not holding it approach. :-) It is the larges which I have not built
into something, though the one in the Best Power Systems UPS is bigger.
And perhaps in a couple of smaller UPS as well.
The bridge rectifier is one of the metal housing ones, and I've
got it held in a small drill press vise as a temporary heat sink, and it
does get rather warm. :-)
20A usually isn't schmall.
Now that I own a ham radio (Baofeng UV-5R portable) I need to get my
tickee and go to those ham fests so I can find your treasures here.
Well ... you need the ticket to use the transmit function of the
radio, but you don't need it to go to the hamfests. I've been going to
them for over 30 years (they've gotten smaller and fewer over that
period) and up until this year, I didn't have a license.
About three hamfests back, I won a door prize for the first time
-- a little handheld Yeasu FT250 2-meter transceiver, and decided that
the time had come. So I dove into a couple of sites giving the practice
exams to see how much I needed to learn, and after a little while at the
Technician (entry) level, I decided to try the General, and found that I
felt pretty good about that, too. I then tried the one for the Extra
class, and actually passed that (barely) the first try, so I kept diving
into that too. By the time the next local exams came up, I decided to
try for all three -- and passed all three. The Extra class was the one
which really needed my calculator quite a bit. (But, interestingly
enough, the actual exam I took did not need it -- it was pretty easy.)
In the practice, I had to refresh my memory on things like calculating
reactance at frequencies in capacitors and inductors, and calculating
resonant frequencies. Also a lot of summing resistance, inductance, and
capacitance at a given frequency (or just with the reactances given, and
figure out which of a number of labeled points on a graph it is.
Note that you can get up to 9 wrong on Technician and General
and still pass -- and up to 12 wrong on the Extra (50 questions instead
of 35). And they don't tell you what you got wrong.
My approach worked for me, since I had been an electronic
technician for a long time, and could easily spot the ridiculous answers
given (multiple-guess) and narrow things down fairly quickly, and make
pretty good guesses at some of the others, including what happens when
you combine more than one antenna in a particular way (I didn't know, but
I was able to guess a number of them.)
And then there are the "Smith Charts" -- graphical way of
solving complex reactance questions. I knew what they were for, but I
still don't know how to use them properly. I figured that I could pass
while getting *all* of those wrong. :-)
Here is one of the practice sites: http://aa9pw.com/radio/
and the other: http://www.eham.net/exams/
Both are built from the real questions used in the exams, and
each time you take one, you get a different collection of questions.
Both tell you what you got right and wrong, and what was right
if you got a question wrong. The first one tells you in order, while
the other one tells you in some sort of scrambled order.
The actual exam gave the same choices as the practice ones, but
the order of the choices (officially called "distractors") is different,
so you can't remember a question and say "That should be answer C". But
if you recognize the question and know *how* to answer it, you can spot
the right one.
The practice exams gave me the confidence to just go in, but
depends on what you already know. A lot of people I would suggest get
the books and read up and study. But take the practice exams first to
get an idea how much you need to learn.
Good Luck with your exam(s) (however many you choose to take.)
Note that to take the Extra class, you have to first take and pass
Technician and General. It does not have to be all in one day. If you
pass the earlier ones, you get a certificate which you can present when
you take later ones (they are often given at hamfests, and at other
locations.) Some places charge, others do it for free. The place I
picked turned out to be for free -- and I didn't know that until after I
had passed them all. :-) Those that charge charge per session, not per
exam, so if you take all three or just one the cost is the same.
Oh -- and if you pass one or more of the earlier ones, once you
get your license from that (less than a week in my experience), you
don't need to present the certificates. And you don't even need to wait
until you receive the license on paper -- as soon as your name and new
call sign are posted on the FCC site, you can start using the
transmitter.
FWIW -- I'm now KV4PH.
And so far, nothing with greater range than the little handheld
2-meter, which reaches from Vienna out to the Bluemont repeater (perhaps
45 miles -- but Bluemont has a *big* antenna tower on a mountain, so
that is a lot better than from handheld at ground level to another
handheld at ground level.
[ ... ]
I've measured the DC current or AC power most of my antique
electronics consume and written it on them for when they need work
later. Yesterday I extended the wiring to my 1950's TV antenna rotator
and then watched the power the controller drew when turned back on to
confirm I hadn't miswired it. Now I can unplug it where it comes into
the basement instead of going out in the rain when lightning is
predicted.
You live in that kind of area, eh?
Doesn't everyone? We get a lot of it during the summer. :-)
AFAIK, I've never lived where lighting struck wires or antennas. It
has never affected me personally during my 60 years so far. (Me glad,
BTW)
Interesting. I grew up in South Texas, and the old house had
lightning rods. And I remember them "thummm"ing when struck. And we
also had a few trees (not many in South Texas) hit and large chunks
split off. There was not much rain, but when there was, it was often a
serious thunderstorm, and I remember sitting on the porch watching it
approach -- and loved to watch it.
Here (Northern VA), lots more trees, and the ground is not as
level, so I usually can't watch a thunderstorm approach, except on the
weather radar put up by a couple of the TV stations. And while *I* don't
mind thunder, one of our cats runs under a particular solid chair at the
first sound of it. :-)
Oh yes -- and occasionally in the winter we get thunder-snow. :-)
Enjoy,
DoN.
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