Evening Marshall,
>> At 01:24 PM 12/21/2007, you wrote:
Thanks for all the details.
It is not meaningless, and can usually be determined,
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.
Looks like you made a meter shunt. Of course I meant for the original
task someone wanted to do. If they could not measure the CS batch current,
....... likely they could not do much else,
The statements you made are all technically correct and actually need no
comment.
Some don't even realize why, but I appreciate your comments more than anyone.
I can understand them, and relate most to field situations.
>>Lets see, what it V = I*R, I = V/R or R= V/I? Just kidding.
Likely you can write your own formulas. I can write some but I like to
have them programmed into my HP 15 C. Very fast and often saves me
hundreds of dollars, in a few cases, thousands of dollars.
Yep, I evaporated the entire shaft of a screwdriver once when I
accidentally got it across the terminals of a car battery.
Everyone needs to do it once. I tried to discharge some capacitors in a
carrier
current transmitter. Surely the power was still on. I hate the think the
capacitors could do that with the charge only, but maybe so. Mine did not
evaporate, I had a little left.
>> 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.
The Wall Warts.
faith gagne wrote: What on earth is a wall wart?
I wonder if he knows yet. I better make a few statements. <grin
Some might think I barely know what one looks like. Nothing could be
further from the truth.
Likely I have used more than anyone on the list, maybe more than any 10
people unless they sell them, build them, or steal Wall Warts for a living.
I don't mean dozens, or even hundreds, I mean Thousands of the critters.
Most have a major manufacturers name, fully labeled with all
specifications, and the size peaks out at 40 Volt Amps. A few may exist
that are 45 or 50 Volt Amps but I have never seen one. If I need 50 VA,
100 VA, or more, I select a chassis mounted transformer, and fuse it as I
see fit.
The inherent problem, in standby service, it that the larger Wall Warts
will come loose from the receptacle. The better and larger ones have a tab
with a hole that allows the receptacle cover plate retaining screw to be
inserted to hold the Wall Wart into place.
My favorite way to install a Wall Wart is to add a receptacle in my own
cabinet, which is very convenient for light, drill motor, soldering iron,
ect, ......... and mount the Wall wart inside the cabinet.
One system I installed in the mid 70's cost my customer over 10 grand. It
was powered by one wall wart. A 40 VA Transformer.
No mater the application, I have always disliked the critters for one
simple reason.
They are a compromised and cheap solution to a problem that in most cases
disserves better.
A genuine power supply in a plastic or metal case, with a 3 wire grounded
plug indicates someone did not cut corners, save a few cents or a dollar or
two, and did the job right.
Today we use many UL listed power supplies. Most have 4, 6, 8, or more
fused outputs. They last 4 to 8 years, 24 / 7 service and deliver the full
load they are designed to deliver.
When these fail, we never repair them. We replace them with a New Unit.
Not that I can't, but when Life Safety and a building full of people, many
sleeping,
depend on the devices, if something fails, I want it to be something the
factory did, ....... not something I repaired.
Relative to Wall Wart Definitions, .............
>> It is a somewhat derogatory term
About as good as one can get.
Power Supply and Transformer are generally accepted terms.
They can be from an ounce or two, a pound or two, hundreds or pounds or
thousands of pounds in size.
Size, use, and origin does not change the definition.
I suggest that the proper term be used instead of "Wall Wart".
I was going to comment on Fault Current a bit, but this critter is long
enough already.
Fault Currents are mean, nasty, noisy, dangerous, destructive,
explosive, and often kill people.
Generally all this is handled at an engineering level, manufacturer
labels, various codes, and not of concern to field personnel.
Other than, Project Managers, Project Engineers, and Electrical Inspectors.
Out of thousands of such people I have known, none run around measuring it.
If you measure it, or attempt to do so, it will be the end of most two bit
devices.
Could be the end of the meter and the end of the user also.
Certainly it is not worth measuring on a Wall Wart. I have a 12 VDC power
supply that delivers 100 amps. I did design and build a load testing
device. This is not the fault current. It has custom heat sinks, special
air tunnels, and fans for each tunnel.
I certainly do not want to know the Fault Current. I hope it never happens.
Was going to include testing of GFCI devices, but that is another story.
Wayne
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