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Re: AC offline to low-V supply, with a cap
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Bear in mind that this is a reverse engineering work in progress.  
Additional labels are now present on the schematic. The ground shown in
the bottom right side is the virtual ground. It's not the frame ground.
Here's a photo of the top side of the PCB:

http://crcomp.net/electronic/securitylight/pcbtopfront.png

The black wire and barely visible white wire are the 120VAC input. The
red wire is controlled by the blue relay at the upper middle of the PCB.
The relay's under command of a onboard microcontroller. (More about that
in a moment.) When the relay closes the red wire supplies 120VAC to a
pair of AC flood lights.  

The heart of the dropper shown in my schematic appears in the upper  
right hand corner of the PCB. In addition, the two large electrolytics  
to the left of the relay are the smoothing capacitors for the +24VDC and
+5VDC rails. R19 and ZD3 are SMD devices on the bottom of the PCB. (More
about that in a moment.)  

A PIR is under the three electrolytic capacitors beneath the relay. To
the right of the PIR is an LED and further right is the microcontroller,  
which is glob top encapsulated chip and therefore almost impossible for
me to access. The glob top chip shows up better in this photo:

http://crcomp.net/electronic/securitylight/pcbtopleft.png

My goal is to add a couple of features by modifying the PCB with the
replacement of the existing glob top microcontroller with a more user
friendly microcontroller. Here's a photo of the PCB bottom:

http://crcomp.net/electronic/securitylight/pcbbottom.png

The largest copper area on the middle left is the virtual ground shown
in my schematic. ZD3 is the middle of three devices shown on the upper
edge of the largest copper area. R19 is above it.

Acrylic paint and a small artist's brush was used to highlight the
power and ground traces. Green is for ground, cadmium red is for +24VDC,
and cadmium yellow is for +5VDC.  

Thank you, 73,

--  
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
We've slightly trimmed the long signature. Click to see the full one.
Re: AC offline to low-V supply, with a cap
Quoted text here. Click to load it



Bear in mind that this is a reverse engineering work in progress.  
Additional labels are now present on the schematic. The ground shown in
the bottom right side is the virtual ground. It's not the frame ground.
Here's a photo of the top side of the PCB:

http://crcomp.net/electronic/securitylight/pcbtopfront.png

The black wire and barely visible white wire are the 120VAC input. The
red wire is controlled by the blue relay at the upper middle of the PCB.
The relay's under command of a onboard microcontroller. (More about that
in a moment.) When the relay closes the red wire supplies 120VAC to a
pair of AC flood lights.  

The heart of the dropper shown in my schematic appears in the upper  
right hand corner of the PCB. In addition, the two large electrolytics  
to the left of the relay are the smoothing capacitors for the +24VDC and
+5VDC rails. R19 and ZD3 are SMD devices on the bottom of the PCB. (More
about that in a moment.)  

A PIR is under the three electrolytic capacitors beneath the relay. To
the right of the PIR is an LED and further right is the microcontroller,  
which is glob top encapsulated chip and therefore almost impossible for
me to access. The glob top chip shows up better in this photo:

http://crcomp.net/electronic/securitylight/pcbtopleft.png

My goal is to add a couple of features by modifying the PCB with the
replacement of the existing glob top microcontroller with a more user
friendly microcontroller. Here's a photo of the PCB bottom:

http://crcomp.net/electronic/securitylight/pcbbottom.png

The largest copper area on the middle right is the virtual ground shown
in my schematic. ZD3 is the middle of three devices shown on the upper
edge of the largest copper area. R19 is above it.

Acrylic paint and a small artist's brush was used to highlight the
power and ground traces. Green is for ground, cadmium red is for +24VDC,
and cadmium yellow is for +5VDC.  

Thank you, 73,

--  
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
We've slightly trimmed the long signature. Click to see the full one.
Re: AC offline to low-V supply, with a cap
On Fri, 8 Mar 2019 18:01:15 -0800 (PST), George Herold

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The load seems to consume quite a lot of current (several mA)
requiring quite large series capacitors. Typically capacitor input
supplies are used when only a few mA is required, so the capacitor is
smaller but still rated at sufficiently high voltage.


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I would suggest using a standard Y-cpacitors, which are tested for
2500 V for a few seconds.  

Assuming a "standard" 8/20 us lightning pulse with 2500 V peak, which
is about 300 V/us. With 0.56 uF capacitance, that makes 168 A peak
current through the capacitor i.e a practical short. Thus the 56 ohm
series resistor will take most of the transient. At 2500 V and 56
series resistor, the current would be 45 A and peak power dissipation
, of 112 kW lasting 28 uS or dissipating 3 J or actually half of that
considering pulse rise and fall times. Thus a 1 W resistor should be
sufficient, if there are several seconds between lightnings.
Unfortunately lightnings often consists of multiple hits within a few
hundred millisecond between them , so a few Watt resistor should be
used. A wire would resistor also has some inductance, limiting the
current.

In countries with non-polarized mains plug, series Y-capacitors are
used in both L and N lines.

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Who needs isolation transformers on the service bench when servicing
AC/DC radios or tube televisions ;-).  Just make sure that you plug in
the mains plug in the correct way so that internal metallic chassis is
directly connected to the mains neutral wire. With the plug inserted
the other way, you have direct 220 V phase voltage at the chassis.
  
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A Class II (double insulated) device never has a ground connection.  

It seems that the circuit diagram is incorrectly drawn.


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Re: AC offline to low-V supply, with a cap
snipped-for-privacy@downunder.com wrote:

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** Unfortunately, most SMPS and the like have no link from supply neutral to  circuit common  -  only floating the AC supply and linking the AC side common to ground internally allows free use of a scope to trouble shoot the PSU.  


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** 100% not true.  

The vast majority of domestic audio and video equipment is Class II insulated these days - HOWEVER the metalwork and circuitry become linked to ground in normal use by being interfaced with any non Class II item.  The scope on your bench is one such.  



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** The one you can now see or the one that was made to vanish ??  

  

....  Phil  






Re: AC offline to low-V supply, with a cap
On Sat, 9 Mar 2019 01:34:29 -0800 (PST), Phil Allison

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Yes, true for single phase full wave rectifier. Either use  insulated,
battery powered, floating test equipment, such as DVMs and battery
powered oscilloscopes.  

Even better especially with higher voltage and higher power
electronics, use voltage transformers (and current transformers) to
bring the potentials down to a grounded test equipment.
  
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Class II only refers to the mains connection, it does not require
galvanic separation on audio, video or data connections.  

Isolation of external connections is required only if the internal
circuits are forced to some dangerous (live) voltages, such as the
mains phase voltage in a AC/DC device. For a tube TV, very few
external connections were available, typically only an external
speaker connection, since there were already an audio output
transformer.  

Connecting an audio tape recorder would require an expensive adaptor
(audio transformer), not to mention video connections, before
multi-MHz optoisolators become available.  

Big isolated knobs were use or at least plastic potentiometer axes.

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Re: AC offline to low-V supply, with a cap

snipped-for-privacy@downunder.com wrote:


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** Battery powered scopes are potentially lethal on the work bench.  

  I know cos I own one, an MS15 by Non LinearSystems.  


 ( snip crap)  


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** Utter bullshit. What drugs are you on ???  

Class II is all about user safety and exposed metalwork must be "double ins
ulated " from the AC supply and earth.  

Never seen the notice: "Double Insulated - do not earth" ???  
-----------------------------------------------------------



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ns.  
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** Irrelevant and not what I wrote.

The essential requirement is that there is NO connection to supply ground b
y whatever means. Such connection not only eliminates the safety inherent i
n class 2 it also allows a horror situation in which multiple, interconnect
ed Class II items all become electrocution hazards because of one faulty it
em, miswired lead or outlet.  




....  Phil  





Re: AC offline to low-V supply, with a cap
On Sat, 9 Mar 2019 12:27:44 -0800 (PST), Phil Allison

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You seem to confuse with SELV
https://en.wikipedia.org/wiki/Extra-low_voltage#Separated_or_safety_extra-low_voltage_ (SELV)
Safety/Separated extra-low voltage i.e. voltages below 50 Vac or 120
Vdc, in which no external connections allowed.

I was referring to ordinary Class II LV circuits, not SELV.




Re: AC offline to low-V supply, with a cap
On Saturday, 9 March 2019 20:27:47 UTC, Phil Allison  wrote:
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 by whatever means. Such connection not only eliminates the safety inherent
 in class 2 it also allows a horror situation in which multiple, interconne
cted Class II items all become electrocution hazards because of one faulty  
item, miswired lead or outlet.  

2 errors there.

1. The essential aspect of 'double insulation' is the extra measures taken  
to prevent hazardous voltages appearing on external metal parts. 'Double in
sulation' should not be taken literally, as while some parts are required t
o be literally double insulated, some are not. Earthing a double insulated  
(or to be more precise a class 2) appliance does not negate the safety feat
ures of double insulation.

2. Earthing/grounding a class 2 metal cased device & connecting several tog
ether does not make it a shock hazard. That claim is just confused.

Time for you to rant now.


NT

Re: AC offline to low-V supply, with a cap
On Sunday, March 10, 2019 at 5:38:10 AM UTC-4, snipped-for-privacy@gmail.com wrote:
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nd by whatever means. Such connection not only eliminates the safety inhere
nt in class 2 it also allows a horror situation in which multiple, intercon
nected Class II items all become electrocution hazards because of one fault
y item, miswired lead or outlet.  
Quoted text here. Click to load it
n to prevent hazardous voltages appearing on external metal parts. 'Double  
insulation' should not be taken literally, as while some parts are required
 to be literally double insulated, some are not. Earthing a double insulate
d (or to be more precise a class 2) appliance does not negate the safety fe
atures of double insulation.
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ogether does not make it a shock hazard. That claim is just confused.
Quoted text here. Click to load it

When is it not time for Phil to rant?  

Rick C.

Re: AC offline to low-V supply, with a cap
On Sun, 10 Mar 2019 07:27:11 -0700, gnuarm.deletethisbit wrote:

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 When everyone else in the thread has, metaphorically, perfected the art  
of walking on eggshells without cracking them?


--  
Johnny B Good

Re: AC offline to low-V supply, with a cap
On Tue, 12 Mar 2019 17:12:49 -0700 (PDT), George Herold

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The double insulated application class is Class II (not Class 2).

Phil seems to mix Class II with Class III, which is a SELV (Separate
Extra-Low voltage) contraption, in  which no other connections are
allowed.  

One classical example is work lights for working _inside_ a metallic
container, which requires an ELV lamp (typically less than 24 Vac) fed
by an external isolation transformer with primary and secondary in
separate slots. The secondary side connection is two pole only and a
special type connector is used to allow only a simple lamp to be
connected to the isolation transformer. Possibly also a fixed cable
connection between isolation transformer and lamp to prevent other
connections to the ELV line.


Re: AC offline to low-V supply, with a cap
snipped-for-privacy@downunder.com wrote:
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The dropper's a polyester capacitor that's identical to these capacitors:  
https://www.ebay.com/itm/0-56uF-560nF-250V-Red-Polyester-Capacitors-564-10pcs-/302218260256
    Part of the load's a relay coil that draws 15mA @ 24VDC. Although  
it's unknown how much the glob top, 22-pin microcontroller draws, the
venerable 20-pin PIC16F84 draws up to 100mA.    
    It took me a few minutes to figure out that gschem crops the  
schematic to the visible area when you zoom-in and export a PNG to a  
website. The PNG was re-exported to my website afterward.

Thank you, 73,

--  
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
We've slightly trimmed the long signature. Click to see the full one.
Re: AC offline to low-V supply, with a cap
Quoted text here. Click to load it

Allow me to summarize my research to make it easier for readers to
understand.

AC outdoor security lights typically use a dropper because there's
usually not a handy outdoor electrical outlet available or a wall wart.  
Even when an outlet is available, wall warts are not used because  
criminals will just unplug it to defeat security. The security light  
shown below is UL approved and sold through outlets such as Home Depot:

https://www.homedepot.com/p/Defiant-180-Degree-White-Motion-Sensing-Outdoor-Security-Light-DF-5416-WH-A/203716654

The dropper subcircuit inside of one looks like this:

http://crcomp.net/electronic/securitylight/085-5411-MB.png

The ground shown in the bottom right side is the virtual ground. It's  
not the frame ground. Here's a photo of the top side of the PCB:

http://crcomp.net/electronic/securitylight/pcbtopfront.png

The black wire and barely visible white wire are the 120VAC input. The
red wire is controlled by the blue relay at the upper middle of the PCB.
The relay's under command of a onboard microcontroller. (More about that
in a moment.) When the relay closes the red wire supplies 120VAC to a
pair of AC flood lights.  

The heart of the dropper shown in my schematic appears in the upper  
right hand corner of the PCB. In addition, the two large electrolytics  
to the left of the relay are the smoothing capacitors for the +24VDC and
+5VDC rails. R19 and ZD3 are SMD devices on the bottom of the PCB. (More
about that in a moment.)  

A PIR is under the three electrolytic capacitors beneath the relay. To
the right of the PIR is an LED and further right is the microcontroller,  
which is glob top encapsulated chip and therefore almost impossible for
me to access. The glob top chip shows up better in this photo:

http://crcomp.net/electronic/securitylight/pcbtopleft.png

My goal is to add a couple of features by modifying the PCB with the
replacement of the existing glob top microcontroller with a more user
friendly microcontroller. Here's a photo of the PCB bottom:

http://crcomp.net/electronic/securitylight/pcbbottom.png

The largest copper area on the middle right is the virtual ground shown
in my schematic. ZD3 is the middle of three devices shown on the upper
edge of the largest copper area. R19 is above it.

Acrylic paint and a small artist's brush was used to highlight the
power and ground traces. Green is for ground, cadmium red is for +24VDC,
and cadmium yellow is for +5VDC.  

FWIW, Todd Harrison produced a video ( https://youtu.be/11Yve2ijWyk )  
that shows how to convert a readily available medical grade isolation  
transformer into a tech iso transformer. In the video Harrison also  
reviews safety considerations apropos to dropper supplies.

Thank you, 73,

--  
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
We've slightly trimmed the long signature. Click to see the full one.

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