http://en.wikipedia.org/wiki/Balun
A balun, pronounced /'bæl.ʊn/ ("bal-un"), is a passive
electronic device that converts between balanced and
unbalanced electrical signals. They often also change
impedance. Baluns can take many forms and their presence is
not always obvious. They always involve some form of
electromagnetic coupling.
Marshall Dudley wrote:
Wayne Fugitt wrote:
Morning Marshall,
Maybe you can tell me what I am missing or what I do not understand.
The only reason one measures the current is that he wants
to know the current flow in a specific circuit,
A finite circuit at a specific time and condition.
It may be a changing circuit, possibly a CS batch.
If one starts adding components such as a resistor, no matter the
size, he has changed the circuit, and the reading will be meaningless.
It is not meaningless, and can usually be determined, but is often
insignificant. For instance if one has a CS system which has a 10 K
resistor in series with 30 volts to provide a 3 mA current limit, and
you put a 1 ohm resistor in series to measure the current, it will drop
no more than 3 mV. That is insignificant to the circuit, and the 10,001
ohms will be in error by 1/100 of what a 1% resistor tolerance is.
The ratio of the change could be somewhat specific, but in most cases
it will not be. ( actually unknown )
This would be determined by the ratio of the resistance added to the
ratio of the original circuit.
Once again, if you are using a sufficiently low value resistor, the
difference is insignificant.
Just because someone made a mistake and connected the meter wrong, is
no need to think they could not still do it correctly.
Well, first I am not sure she was connecting it wrong, since I am not
sure what she was trying to accomplish. Was she trying to measure the
short circuit current of the power supply? If so the connection was
right, but the sequence of applying power, and/or selection of range was
wrong. If she was wanting to measure the current through a CS cell,
then the connection was wrong. But if connected right, could have the
same effect, if the wires in the cell were accidentally shorted together
unless she is using a limiting resistor. Using a small shunt resistor
and the meter on volts is less likely to cause a failure in the meter
than measuring mA current if something does go wrong.
I hate to see people advising beginners with makeshift methods, half
truths, and encouraging them to
wish, hope and pray, and go around in circles.
Then one year later, or two years later, they will still be confused
and not understand 1 , 1, 1
One Volt, One Ohm, and One AMP.
Lets see, what it V = I*R, I = V/R or R= V/I? Just kidding.
If they cannot understand that, when it is explained, or study it a
few minutes, then they should Abandon Ship, ASAP.
The only reason I can see to use a known resistor with a current meter
is to test the meter to see if it works.
No, you use a known resistor with a voltage meter. Stay away from the
current meter selection entirely, the voltage input is much more
overload tolerant than the current input.
Any one of us could make a simple drawing, or a picture or two showing
how to connect a volt meter or a current meter.
Likely 10,000 exist on the internet.
Once when installing a production line automation system I built, one
of my men connected a transformer backwards to
480 VAC. When he used the meter, it was destroyed, not beyond repair,
but beyond recognition. He was lucky that he did not loose a finger
or two, or more.
Yep, I evaporated the entire shaft of a screwdriver once when I
accidentally got it across the terminals of a car battery. For a while
I thought I was going to be both blind AND deaf. My sight came back,
but my ears still ring.
We all know, the higher the voltage, the less forgiving it actually
is, to equipment and to humans.
Maybe I missed the whole point about using the resistor.
Maybe.
>> It is a somewhat derogatory term
Some are transformers, putting out 24 or so volts AC, but most have a
diode bridge in them and a filtering capacitor to supply DC.
I think the term, "Wall Wart" means only one simple thing,
The people who use it have not a clue what they actually have. If
they did, they would use the proper term,
Power supply or Transformer. Plain and simple.
I use the term, and know darned well what they are, and what is in
them. I tend to use the term because I think they are ugly, and that
tends to convey that feeling. Using a term like power supply or
transformer is no better, when I hear power supply, I think of either a
bench supply, or one of the units that go into a computer. A transformer
can be anything from a balm antenna transformer to an HO train set
transformer, to a neon sign transformer to a huge one in a substation.
Wall wart describes the physical appearance and approximate size,
transformer or power supply describes the function. Neither alone really
gives a complete description, one would need to say a wall wart power
supply, or a wall wart rated at 24 VDC @ 500 mA for example.
It is one or the other, not a stupid Wall Wart.
I keep a precision 50 AMP meter shunt in my truck. I built it in a
nice plastic box with terminal strips installed on the box.
( for DC )
I can measure 3 amp full scale up to 300 amp full scale relative to
AC. No guessing at anything.
When you work on 480 / 3 phase inverters of 48,000 VA you cannot
afford to guess. 3 battery cabinets, 5 feet tall and 40 feet long each
. Awesome............
Some of the fuses cost $ 20.00 each. I have bought $ 200.00 worth of
fuses before I would go do a service call.
Not exactly Mickey Mouse stuff.
Yeah, those go off like a stick of dynamite when they blow.
Marshall
Wayne
======================
Marshall
faith gagne wrote:
What on earth is a wall wart?
Faith G
----- Original Message ----- From: "Clayton Family"
<clay...@skypoint.com>
To: <silver-list@eskimo.com>
Sent: Thursday, December 20, 2007 5:27 PM
Subject: CS>what did I do wrong?
Dear Esteemed and Learned List Members,
I was fooling around with a wall wart that is listed as 24V and
500mA, and had it hooked up in series with my radioshack
multimeter. It tested as 30.6V, and after I switched it to mA, the
meter failed.
Now it just reads micro volts and won't read anything else. Dang!
Maybe I had it on micro amps instead of milliamps, and would that
break it?
I need another multimeter! But I don't want to just turn around
and break this one too.
Thanks,
Kathryn
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