Digest for sci.electronics.repair@googlegroups.com - 17 updates in 4 topics

"Ron D." <ron.dozier@gmail.com>: Dec 09 11:14AM -0800

> t.....r@gmail.com says...
 
> > All domestic mains current loads are balanced, ie live & neutral carry the same & opposite current, resulting in nearly zero magnetic field. Pacemakers, like any life-critical medical equipment, are designed & tested to meet harsh real-world conditions & keep going.
 
Nope:
 
The neutral carries the "difference current" in the legs of a split phase system. It can be 180 or -180 out of phase (Said for ease of understanding). It can also be zero, but not likely,
 
The "difference current" is more accurate. While voltage is usually sinusoidal, current doesn't have to be. Voltage is what's regulated. inductive loads are one matter, but laptop switching power supplies is another.
Phil Allison <pallison49@gmail.com>: Dec 09 12:24PM -0800

Ron D. wrote:
 
 
> > > All domestic mains current loads are balanced, ie live & neutral carry the same & opposite current, resulting in nearly zero magnetic field. Pacemakers, like any life-critical medical equipment, are designed & tested to meet harsh real-world conditions & keep going.
 
> Nope:
 
** Fraid it is a yep.
 
Any mains appliance returns the same current down the neutral conductor it drew from the active. This mean very little mag field is generated by the appliance's own lead, assuming the two wires are closely paired or twisted.
 
 
 
... Phil
Ralph Mowery <rmowery28146@earthlink.net>: Dec 09 04:14PM -0500

In article <137d918d-cb77-4a4f-989b-66c8d7dbe141@googlegroups.com>,
pallison49@gmail.com says...
 
> ** Fraid it is a yep.
 
> Any mains appliance returns the same current down the neutral conductor it drew from the active. This mean very little mag field is generated by the appliance's own lead, assuming the two wires are closely paired or twisted.
 
I think you all are compairing apples and oranges.
 
One is thinking of a 240 volt system with 2 hots and the neutral, whrere
the neutral can have almost any ammount of current on it up to being
equal to what one side of the hot is using (120 volt devices).
 
Phil and the other are probably talking about a 120 volt device that has
only a hot and neutral. Which in that case the neutral must have the
same ammount of cuttent as the hot wire, unless there is a problem.
Fox's Mercantile <jdangus@att.net>: Dec 09 04:19PM -0600

On 12/9/18 3:14 PM, Ralph Mowery wrote:
> One is thinking of a 240 volt system with 2 hots and the neutral, whrere
> the neutral can have almost any ammount of current on it up to being
> equal to what one side of the hot is using (120 volt devices).
 
This is one of fallacies here in Ranger.
Around here, the thought is the Neutral to the breaker panel from
the meter can be smaller because it's not going to carry ALL of the
current because there will be an offsetting current from the other
hot leg.
 
They also tend to under size everything, because, you know, copper
is expensive. For example, my house has a 200 Amp service.
That should be #000 on all three legs and #4 for the ground.
When I got here, it was two #4 on the hots, #6 on the neutral and
#10 for the ground.
That was one of the first things I fixed.
 
 
--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
Ralph Mowery <rmowery28146@earthlink.net>: Dec 09 05:50PM -0500

In article <DMqdnZNXDrKSCJDBnZ2dnUU7-I3NnZ2d@giganews.com>,
jdangus@att.net says...
> When I got here, it was two #4 on the hots, #6 on the neutral and
> #10 for the ground.
> That was one of the first things I fixed.
 
Well you do not have to worry about ice forming on the power wires. I
think one chart showed about 105 deg C for the temperature rise with the
# 4 wire at around 200 amps.
Clifford Heath <no.spam@please.net>: Dec 10 12:33PM +1100

On 10/12/18 8:14 am, Ralph Mowery wrote:
 
> Phil and the other are probably talking about a 120 volt device that has
> only a hot and neutral. Which in that case the neutral must have the
> same ammount of cuttent as the hot wire, unless there is a problem.
 
Phil lives in Sydney. We use 240V single phase wiring, with a single hot
and a single neutral grounded at the panel. The RCD protection trips if
the currents on hot and neutral differ, even by milliamps for milliseconds.
 
Some (few) buildings have two separate 240V phases wired to different
circuits inside the house, but nothing gets connected between the phases.
 
Clifford Heath.
Phil Allison <pallison49@gmail.com>: Dec 09 07:30PM -0800

Ralph Mowery wrote:
 
 
> One is thinking of a 240 volt system with 2 hots and the neutral, whrere
> the neutral can have almost any ammount of current on it up to being
> equal to what one side of the hot is using (120 volt devices).
 
** If a 240V load is connected across the two phases, then the current is each wire is the same.
 
The principle is simple: a current carrying loop that is closed down on itself ( ie the wires are paralleled) or twisted cannot radiate a mag field.
 
 
.... Phil
tabbypurr@gmail.com: Dec 10 02:04AM -0800

On Sunday, 9 December 2018 19:14:44 UTC, Ron D. wrote:
 
> Nope:
 
> The neutral carries the "difference current" in the legs of a split phase system. It can be 180 or -180 out of phase (Said for ease of understanding). It can also be zero, but not likely,
 
> The "difference current" is more accurate. While voltage is usually sinusoidal, current doesn't have to be. Voltage is what's regulated. inductive loads are one matter, but laptop switching power supplies is another.
 
 
I think you'll find house sockets are wired single phase.
 
 
NT
Fox's Mercantile <jdangus@att.net>: Dec 10 05:42AM -0600


> I think you'll find house sockets are wired single phase.
 
> NT
 
Actually, the term "Split Phase" is accurate.
The source is a center tapped 240 volt winding.
-180 0 +180 degrees.
Either side to center (neutral) is 120v, and across both sides (hot)
is 240v.
The usual problem is when people insist on calling it 2-phase due to
the +/- nature of it.
It is not, the primary is single phase.
 
The real problem occurs in a 3-phase Wye system.
A-N, B-N and C-N are each 120 volts. Until someone who doesn't know
how it works, takes A-B and tells the consumer it's 240v. And then
typically table saws go up in flames, because they REALLY do no like
running at 208 volts with a 120 instead of 180 phase shift across
the windings.
 
 
 
 
--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
Look165 <look165@numericable.fr>: Dec 10 01:01PM +0100

120*(3^^0.5) gives 207V, not 240.
 
Fox's Mercantile a écrit :
tabbypurr@gmail.com: Dec 10 04:22AM -0800

On Monday, 10 December 2018 11:42:17 UTC, Fox's Mercantile wrote:
> The usual problem is when people insist on calling it 2-phase due to
> the +/- nature of it.
> It is not, the primary is single phase.
 
3 phase has an angle between each phase of 360/3 = 120 degrees.
2 phase has an angle between each phase of 360/2 = 180 degrees. And that's what you have with the US domestic 120/240 system.
 
 
> typically table saws go up in flames, because they REALLY do no like
> running at 208 volts with a 120 instead of 180 phase shift across
> the windings.
 
Naturally some people don't understand some things, nothing new there.
 
 
NT
Fox's Mercantile <jdangus@att.net>: Dec 10 06:26AM -0600

On 12/10/18 6:01 AM, Look165 wrote:
> 120*(3^^0.5) gives 207V, not 240.
 
207.84 or commonly called 208.
 
I said uneducated electricians THINK that two 120v phases
running 120 degrees instead of 180 degrees apart equals
240 volts.
 
As a service manager in a tool store, I had to explain that
running a 5 HP table saw motor on 208 volts was NOT covered
under warranty and they should make their "electrician" pay
for the repairs.
 
--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
MOP CAP <email@domain.com>: Dec 09 05:13PM -0800

In a selenium rectifier the big plates are BOTH rectifiers and heat sinks!
Seen the hugh vacuum chambers in which the were made.
CP
tabbypurr@gmail.com: Dec 10 02:02AM -0800

> >are extremely fussy about that.
 
> I plan to leave it on the chassis for looks, but replace it.
> My voltage is real low, so it seems it's weak or worse....
 
and about to go into toxic fumes mode.
Jeff Liebermann <jeffl@cruzio.com>: Dec 09 11:37AM -0800

On Sun, 9 Dec 2018 10:14:11 -0500, Ralph Mowery
>I am not that much of a touch typist. I can do the letters and a few
>common punctuations,but have to look for some of the other symbles. I
>never look at the mouse once I find it and get it in my hand.
 
Thanks for the info. It's about the same for me. The common
characters I can type without looking. The shifted characters require
my looking at the keyboard.
 
>lenses come with it. Mine came with a 10x and 20x lense. I almost
>always use the 10x lense. I bought a 5x but found the one i got did
>not seem to have a large a field of view as the 10x.
 
I rather prefer adjustable power in the head (0.7x to 3x) as in the
Bausch and Lomb scopes. I have a variety of eyepieces but WF10X is
what works best for PCB work.
 
>I don't have any problem at all looking through the scope and working.
>AT 68 I do not seem to have any major problems with the shakes.
 
I'm at 70. No shakes. However, I do have some problems adjusting to
working under the microscope or HUD. I probably need more practice.
 
>rework station from China that has the hot air wand and soldering
>pencil. If I was using the equipment to make money,I would get something
>better.
 
I have the bad habit of buying used test equipment and tools. None of
my microscopes were purchased new. A few of my objective lenses and
eyepieces were purchased new, but most came with the used scopes. If
I were still doing this professionally, I would not have time to do
the necessary repairs on the used equipment and probably would have
bought something that was ready to use.
 
>There is a fellow on youtube (Louis Rossman) that works on Apple
>computers and at one time he was pushing that scope for the price.
 
"Amscope SE400-z microscope, a must have tool for repair technicians."
<https://www.youtube.com/watch?v=m4LaZsS5V7s> (7:45)
 
>have any use for the camera. His newer scopes have a way of mounting
>the camera where he can still see through both lenses and a 3 rd lense
>for the camera.
 
In the above video, he uses his Android phone through one eyepiece. He
has some other scopes, one of which is a trinocular microscope, which
has a third tube for the camera (but less working range).
 
For photos, I have one of these:
<https://www.amscope.com/cameras/0-3-mega-pixel-usb-live-video-microscope-imager-digital-camera.html>
I should have bought one with a 0.5x lens, but decided to go cheap.
Big mistake because the image width is about half the width as viewed
through the eyepiece.
 
 
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
"Ron D." <ron.dozier@gmail.com>: Dec 09 09:00AM -0800

I had an EICO FET TVM. I still have it. D Cell for the ohmeter and a 9V battery for the voltmeter.
 
Mine had the phone plug as yours does and also. The probe was quite large in diameter and could turn to insert/remove the resistor (whatever value it was).
 
I think it was AC/Ohms and DC,
 
I doubt the cabeling matters and RG-58 would probably suffice.
 
If you keep your voltages down, RG174 is about 1/2 the diameter (0.1") of RG-58
 
RG58/59; http://www.scp-sa.es/resources/upload/files/categorias/148/esp/RG58_RG59.pdf
 
RG59 is TV stuff with a solid core.
 
RG174 https://www.awcwire.com/productspec.aspx?id=rg174-coaxial-cable is good for 1500 VRMS and it quite flexible.
 
If had to actually make a probe and it made a difference as to whether the resistor is in the tip or the plug, You can get a BNC for the probe end.
 
But then some of the standard probes could likely easily accommodate a series resistor inside. Especially some of the adjustable probes like these: https://www.fluke.com/en-us/product/accessories/test-leads/fluke-tl40
"Ron D." <ron.dozier@gmail.com>: Dec 09 09:02AM -0800

On Sunday, December 9, 2018 at 12:00:36 PM UTC-5, Ron D. wrote:
 
> RG174 https://www.awcwire.com/productspec.aspx?id=rg174-coaxial-cable is good for 1500 VRMS and it quite flexible.
 
> If had to actually make a probe and it made a difference as to whether the resistor is in the tip or the plug, You can get a BNC for the probe end.
 
> But then some of the standard probes could likely easily accommodate a series resistor inside. Especially some of the adjustable probes like these: https://www.fluke.com/en-us/product/accessories/test-leads/fluke-tl40
 
You can get RG174 and other cable by th foot. e.g. https://www.showmecables.com/bulk-rg174-coaxial-cable-26-awg-per-ft
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