Digest for sci.electronics.repair@googlegroups.com - 16 updates in 4 topics

8:44 AM Penedão
thekmanrocks@gmail.com: Nov 15 04:10AM -0800

captainvideo:
 
Your problem is two-fold: distance, and
the all-digital broadcast requirement.
 
 
8 years ago, on NTSC(analog), distance
would not have been been such an issue.
You probably would have had snow on
a lot of channels, but you still had picture
and sound.
 
 
Now, on ATSC(digital), you don't get certain
stations at all, and frequent dropouts on
others.
 
This is why I maintain that ATSC is 'less
Green' than NTSC was: While with
digital stations can piggy-back channels
(4.2, 4.3, 4.4, etc.) they must BOOST
THEIR SIGNAL for people with same
OTA setup to receive them in the first
place. And increasing signal strength
meansUSING MORE ENERGY - something
the folks over at Alt.Video.Digital.Tv fail
to grasp.
 
You said you are using a 'parabolic' antenna
currently - I'm assuming that is dish-shaped.
 
Have you looked into a variation on this
form factor yet? It's all I'll ever use, even
just 35 miles away from my market:
 
https://m.lowes.com/pd/Channel-Master-Outdoor-Non-Amplified-Yagi-Type-Antenna/50005786?cm_mmc=SCE_PLA_ONLY-_-RoughPlumbingElectrical-_-SosHomeAutomation-Communication-_-50005786:Channel_Master&CAWELAID=&kpid=50005786&CAGPSPN=pla&k_clickID=35fefdd1-395a-47bd-a160-f2260ea5c961
Pat <pat@nospam.us>: Nov 15 10:36AM -0500

On Tue, 15 Nov 2016 04:10:07 -0800 (PST), thekmanrocks@gmail.com
wrote:
 
>meansUSING MORE ENERGY - something
>the folks over at Alt.Video.Digital.Tv fail
>to grasp.
 
You may fail to grasp it, too. When you hear about TV stations
(especially UHF stations) using millions of watts of power, they are
referring to ERP - Effective Radiated Power. That means the actual
power going into the antenna is much lower but the antenna has very
high gain. Rarely do stations use more than a few thousand watts of
actual power. The transmitter's actual power usage is a drop in the
bucket compared to all the other energy a TV station uses for lights,
cameras, HVAC, etc.
thekmanrocks@gmail.com: Nov 15 08:31AM -0800

Pat wrote: "You may fail to grasp it, too. When you hear about TV stations
(especially UHF stations) using millions of watts of power, they are
referring to ERP - Effective Radiated Power. That means the actual
power going into the antenna is much lower but the antenna has very
high gain. Rarely do stations use more than a few thousand watts of
actual power. The transmitter's actual power usage is a drop in the
bucket compared to all the other energy a TV station uses for lights,
cameras, HVAC, etc. "
 
________
Alright, say a typical medium market
station has historically transmitted
2,000W as a NTSC. 2009 they go
fully ATSC, still at 2,000W. Hundreds
of letters from viewers flood their
mailbox, and thousands of callers
jam their phone boards about not
being able to pick them up over the
air with their new TVs. Most are from
viewers in the outer one-third of the
station's transmission radius.
 
 
Station board deliberates, and
after a couple months decides to
increase transmitter wattage to 2,500W.
Viewer complaints plummet, while
greenhouse gas emmissions steadily
rise to generate additional electricity as
this scenario is mulitiplied across dozens
of medium markets and many major
markets.
 
Grasp that!
 
 
Yeah, I get that actual wattage is but
a fraction of ERP, but it still adds up
as many TV stations must increase their
signal strength to cover the same
audience area in digital as they did
via analog.
micky <NONONOmisc07@bigfoot.com>: Nov 14 08:42PM -0500

In alt.home.repair, on Tue, 15 Nov 2016 00:40:05 -0000 (UTC), Robert
>https://www.lowes.com/pl/Electrical-plugs-connectors-Cable-wire-connectors-Electrical/4294722553
 
>Just curious if I can get the hospital grade plugs at about the Lowes price?
 
>Any suggestions?
 
I know where you can get them. Go to the corner of 4th and Center St.
and find a guy in a knit hat named Snake. Tell him Micky sent you and
he'll fix you up. Bring cash.
whit3rd <whit3rd@gmail.com>: Nov 14 05:59PM -0800

On Monday, November 14, 2016 at 4:40:07 PM UTC-8, Robert Bannon wrote:
> a hospital.
> https://static.grainger.com/rp/s/is/image/Grainger/5A076_AS01
 
> Googling, they're pretty expensive at $20 to $40 each!
 
You can get them cheaper, but 'hospital quality' implies lots of testing, including
guaranteed how-hard-they-hold-when-you-pull. There's lots of 'industrial' that's
just as rugged (and cheaper).
 
<https://www.lowes.com/pd/Hubbell-15-Amp-125-Volt-Black-White-3-Wire-Plug/3739267>
micky <NONONOmisc07@bigfoot.com>: Nov 14 10:54PM -0500

In sci.electronics.repair, on Mon, 14 Nov 2016 17:59:35 -0800 (PST),
 
>On Monday, November 14, 2016 at 4:40:07 PM UTC-8, Robert Bannon wrote:
>> I want to fix a half dozen or more 120VAC (USA) extension cords, all with
>> molded on connectors, both male and female by putting on something like
 
You're going to cut off the good connectors that are on there now? Are
these cords UL approved? If so, the connectors are as good as the wires
between them, so if you replace the connectors and not the wires the
wires will become or remain the weak link.
 
Add to that the possibillty that you'll nick the copper when putting the
connector on, or do something else that will make your installation less
than perfect.
 
Why do you thihk the current connectors are not good enough? Are you
running the cords higher than their rating? How do you know that the
connectors won't take the higher load but the wires between them will?
 
Not only that, if you step on the hard ones, I think you're more likely
to twist your ankle than with the molde-on ones, and if you drive over
one, I think you can break it, but not the molded on ones.
 
 
>You can get them cheaper, but 'hospital quality' implies lots of testing, including
>guaranteed how-hard-they-hold-when-you-pull. There's lots of 'industrial' that's
>just as rugged (and cheaper).
 
Yes, I think hospital quality includes what they pay for insurance in
case they burn down a hospital with 50 people too sick to get out in
time. (Plus all the expensive hospital electronics.)
 
When they burn down a normal factory, especially if it starts aas a
fire, usually everyone can get out. (Not sure about the hardware.)
Stormin' Norman <norman@schwarzkopf.invalid>: Nov 15 01:32PM

>https://www.lowes.com/pl/Electrical-plugs-connectors-Cable-wire-connectors-Electrical/4294722553
 
>Just curious if I can get the hospital grade plugs at about the Lowes price?
 
>Any suggestions?
 
Harbor freight has some decent male and female cord end connectors at a reasonable price, see:
 
http://www.harborfreight.com/125-volt-15-amp-male-plug-93686.html
 
If you absolutely must have hospital grade connectors, you can get the best deal buying them used on eBay.
"pfjw@aol.com" <pfjw@aol.com>: Nov 15 07:51AM -0800

Hubbell has what you want, and from various sources.
 
https://www.zoro.com/hubbell-wiring-device-kellems-plug-5-15p-15a-125vac-hbl8215c/i/G2507224/?gclid=CjwKEAiAgavBBRCA7ZbggrLSkUcSJACWDexATAkEd2KpgoIdzFk6y4s7uex_pvvMfRm01mKiQ2MekRoCLYHw_wcB&gclsrc=aw.ds for the male end.
 
https://www.zoro.com/hubbell-wiring-device-kellems-connector-5-15r-15a-125v-hbl5269c/i/G2032852/
 
for the female.
 
If this is what you want, search the various suppliers directly and then contact your local electrical supply house. They will sell these devices to 'civilians' around $10 or so, each.
 
Avoid the likes of Harbor Freight or other Chinese Junque outlets like the plague that they are.
 
Peter Wieck
Melrose Park, PA
John Robertson <spam@flippers.com>: Nov 14 05:21PM -0800

> son's machine and he can do whatever he wants with it, no matter what
> kind of help dad wants to give.
> Eric
 
Did you look at the Mouser link I included a few posts ago? They list
400 and 500VDC Photoflash caps. Mind you, you need to order one to two
hundred.
 
http://ca.mouser.com/Passive-Components/Capacitors/_/N-5g7r?Keyword=photoflash&FS=True
 
Here is a surplus place with photoflash caps, not cheap, but they are in
stock:
 
https://www.surplussales.com/capacitors/Electrolytics/eaf.html
 
However, if you use the part number you will probably find a stocking
distributor...
 
JustRadio sells good caps, but they aren't photoflash rated - pretty
safe bet on that!
 
John :-#)#
 
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
mike <ham789@netzero.net>: Nov 14 05:24PM -0800

On 11/14/2016 3:15 PM, Ralph Mowery wrote:
>> I found 220 mfd 450 caps at JustRadio.com. I'm not sure if these will
 
> The 220 mfd will work fine where the 200 mfd caps are used. Many of
> them have a large tolerance of 20 to 50 %or more.
 
Might be helpful to take a peek below the obvious.
 
Take a close look at the pix of the capacitors at the mouser link.
Compare the solder pins to the size of the buss bars in the welder.
At least you'll be able to say you thought about the consequences
of tiny pins and dubious solder connections. That compounds if you
go with fewer larger caps. All that energy into the weld
came from the caps. It's just as easy to melt the solder at that
end.
 
Don't go too crazy with the cap values. My spot welder is calibrated
to deliver energy based on the voltage and cap value.
If the cap is different, the calibration can be off by that ratio.
If your meter has a square-law scale, that can make a significant
difference in calibration at one end or the other. You can't
just add a resistor to fix it. But you can put a post-it note
on the panel and do the scale factor in your head.
 
If you don't have a schematic, create one. It only takes one
wrong assumption to make a lot of smoke.
 
Beware saturation in the output transformer. Mine has a core reset
pulse between firings. If that part of your system is broke,
you can saturate the core. At best, that can take your diagnostics
down the wrong path. At worst, more smoke that takes out the parts
you just fixed.
 
Are we having fun yet?
whit3rd <whit3rd@gmail.com>: Nov 14 05:45PM -0800


> I found 220 mfd 450 caps at JustRadio.com. I'm not sure if these will
> discharge fast enough.
 
For a welding purpose, 100l milliseconds is very fast (no functioning
capacitor you are likely to find would have too high ESR for this job).
 
ESR gets to be important with low voltage high current, where a fraction of
a volt of ripple is a malfunction. Fraction of a volt difference on a 450V capacitor
charge is negligible.
Clifford Heath <no.spam@please.net>: Nov 15 03:54PM +1100

On 15/11/16 12:45, whit3rd wrote:
>> discharge fast enough.
> For a welding purpose, 100l milliseconds is very fast (no functioning
> capacitor you are likely to find would have too high ESR for this job).
 
I agree that the speed doesn't matter, but low ESR caps have wiring that
will survive higher currents. No sense having a whopping cap
with internally-fused connections.
 
I also have a bench-top spot welder, from my father who was an
orthodontist. It has a 110V input (so we needed a transformer
from 240V), and that feeds via a small Variac into a selenium
rectifier. I suspect the caps need replacing (again - they were
last done 25 years ago) and I have a bunch of 300V photoflash
caps from disposable cameras that I hope will suffice.
 
The welding contacts are an anvil and an upper contact connected
to the foot pedal, via an adjustable pressure-operated switch
that fires the contacter. That leaves both hands free to hold and
position the work. When you press down hard enough, the thing
fires, very cute.
 
What I don't know is how to determine the maximum energy I can
dump through the output transformer without saturating it.
Anyone know how I can tell (other than just keeping the
capacitance below the original value)?
 
Clifford Heath.
mike <ham789@netzero.net>: Nov 14 10:56PM -0800

On 11/14/2016 8:54 PM, Clifford Heath wrote:
> Anyone know how I can tell (other than just keeping the
> capacitance below the original value)?
 
> Clifford Heath.
That's not a simple question.
The first order approximation is that CURRENT is what
creates the magnetic field that saturates the transformer.
If you put a scope current transformer on the primary,
load the secondary with the resistance and inductance of
your welding setup, crank up the voltage until you see
a sharp rise in the slope of the current pulse. That's
the too-much point. What happens when you add more caps
is dependent on the transformer characteristics.
Energy is linear in caps but quadratic in volts.
 
25 years ago, I was tasked with fixing an OEM forward
converter that would randomly self-destruct.
I built a fixture to synchronize the load transient with
the switching frequency. I could watch the primary current
head for the sky on the scope as the load transient crossed the
switching point.
Took it to the vendor site and proceeded
to blow up power supplies until they conceded that they had
a board layout problem to fix.
 
After the weld, the field will be sitting somewhere on the
B-H curve of the core. The next weld might be very dependent
on where you left it last time.
 
This is a page from my Unitek CD spot welder. Shows how they
reset the core.
 
http://imgur.com/ZeZerGx
 
I experimented with a microwave oven transformer battery tab
welder. I was hitting it with a timed pulse. Repeatability
was horrible.
When I synchronized the pulse with the line and gave it an
integral number of full cycles, the starting point on the
B-H curve was consistent and the welds got much more repeatable.
 
There was considerable discussion on exactly when you should terminate
the pulse, but mine was constrained to somewhere near zero current by
the triac.
Clifford Heath <no.spam@please.net>: Nov 15 08:34PM +1100

On 15/11/16 17:56, mike wrote:
> On 11/14/2016 8:54 PM, Clifford Heath wrote:
snip
> a sharp rise in the slope of the current pulse. That's
> the too-much point. What happens when you add more caps
> is dependent on the transformer characteristics.
 
Thanks, that all makes sense. I'd like a bit more capacity
if I can get it.
 
I'll have a look and see if it has a core reset current too.
 
Clifford Heath.
 
Chris Jones <lugnut808@spam.yahoo.com>: Nov 16 12:03AM +1100

On 15/11/2016 17:56, mike wrote:
> That's not a simple question.
> The first order approximation is that CURRENT is what
> creates the magnetic field that saturates the transformer.
Be careful, remember there is a secondary current and its magnetic field
will largely cancel that of the primary, so looking at the primary
current is a red herring unless the secondary is open-circuit.
 
The rate of change of flux in the core will be proportional to the
primary voltage. What you need to look at is actually the integral of
primary voltage with respect to time, as this will give you the change
in the flux in the core. The longer the pulse lasts, the less voltage it
will take to cause saturation. (For similar reasons, 60Hz mains
transformers will saturate at a lower voltage if used on 50Hz mains.)
You could get more energy into the weld if you increse the voltage of
the primary pulse and decrease the duration, because the dissipation in
the weld is proportional to the integral of v sqared with respect to
time, whereas the change in the flux in the core is proportional to the
integral of v (not squared) with respect to time. Also, make sure that
the core starts out with maximum flux in the opposite direction. This
might be achieved with a reset pulse as others have pointed out,
provided the core material is one that will retain the magnetisation. If
not, you could perhaps feed a reverse current through the primary using
a low voltage power supply, to build up reversed flux just before the
main welding pulse. That might make the switching a bit more complicated.
"Tmachcinsk@aol.com" <Tmachcinsk@aol.com>: Nov 14 05:50PM -0800

Thank you for your concern. You are correct the picture convergence is actually very good. Just off a very little bit at the very bottom of the screen. Not the end of the world but would be nice to make it perfect seems to be just the bottom corners off a little bit. The v regulator on the power supply for the convergence board was replaced by me about 4 years ago. That may be why it is off. Thanks Ted
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1 Response to Digest for sci.electronics.repair@googlegroups.com - 16 updates in 4 topics

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