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It has been many years since my electronics days, but I believe a diode does have a fixed voltage drop. I think it's around .7 volts if I remember correctly. So it does regulate the voltage in some respects.
Anthony Watson www.watsondiy.com www.mountainsoftware.com
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HerHusband presented the following explanation :

Yes, that is a forward voltage drop across the junction. The voltage depends on the materials used in the device. The regulation function of a diode is usually a reverse voltage taking advantage of the breakdown characteristic. IOW a reversed diode as a shunting device. The same can be used as a reference diode to control a transistor regulator. Zener diodes come to mind for this.
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On 6/4/2016 8:01 AM, HerHusband wrote:

A "regular" silicon diode has *about* a 0.7V forward drop. Though the actual drop is dependant on the current flowing through the junction (as current increases, the drop increases -- but only slightly; not proportionately as with a purely resistive device). There's a "knee" in the V-I curve at that point (but, all knees are "rounded" to some extent!)
LED's, OTOH, have a much higher forward drop. Some of the high efficiency ones are as LOW at ~1.7-1.9V. Most, however, tend to be higher -- ~2.1 for Red/Yellow/Orange and closer to 3.4 for the Blue/White devices.
(Even these are just ballpark numbers as it depends on the dopants used)
Germanium ("Is there life on Germanium?") diodes have forward drops in the 0.2V range. Schottky diodes are in the 0.15-0.45V range.
And, of course, you can get zeners at all sorts of voltage ranges (but, these are operating in reverse bias when zenering)
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On 06/04/2016 10:01 AM, HerHusband wrote:

The (forward) voltage drop depends on the semiconductor material. .7V for silicon diodes, around 2V for LEDs.
Reverse voltage drop can vary greatly according to design. I've see about 3V (for a LED) to 1KV (1N4007 IIRC).
With either polarity, voltage exceeding that will cause current to flow. This is called "breakdown" and is not harmful unless the diode's maximum current is exceeded. A LED is normally operated in forward breakdown (necessary for it to light).
A diode is a voltage regulator. If you connect a LED (and nothing else) to a car battery, the LED will try to bring the battery down to 2V, and try to handle nearly infinite current. I did this once and didn't even see any light before there was a POP and half the LED disappeared. You need a resistor that drops the excess voltage (10V here) without exceeding the LED current (typically 30mA).

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On Sat, 4 Jun 2016 15:01:11 -0000 (UTC), HerHusband

blue have higher forward drops in that order, up to about 3.8 for ultra blue. The white ones are closer to 4 volts - 3.7 to 3.8 rings a bell. A silicone diode is around.0.7 volts, and a Shotky diode is closer to 0.3 or 0.4 volts. A galena diode only drops about 0.2, and a selenium rectifier diode drops about 1 volt per cell.
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On 06/04/2016 06:47 AM, Stormin Mormon wrote:

A very simple definition that is sort of correct but leaves out a lot of stuff.
A diode has a threshold voltage. It the supplied voltage is less than that, there will be no current. Otherwise the diode will conduct. It will conduct as much as needed to limit the voltage across it to the threshold. This means a diode may conduct excessive current if nothing is done to limit it. This is frequently a resistor in series.
An important thing about a diode is that the threshold is different for each polarity. That simple definition is correct when the voltage is between one threshold and the other.
When the diode is in series, it will have a voltage drop equal to the threshold voltage (which threshold depends on polarity).
BTW, I know that semiconductor junctions are even more complex than that.
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On Sat, 4 Jun 2016 07:47:27 -0400, Stormin Mormon

That's only half the definition. It has both forward and reverse voltage drops, and forward current draw is determined by the voltage drop and the supply voltage.
As long as the supply voltage does not excede the forward voltage drop by ant significant amount, the current will remain within limits.
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On 06/04/2016 07:59 PM, snipped-for-privacy@snyder.on.ca wrote:

Supply voltage (voltage across the diode) WILL be equal to voltage drop. That is the diode acting as a voltage regulator. That explains the need for a resistor with a LED.

If the supply voltage exceeds the forward voltage drop by ANY amount, the current will be infinite* (as the diode tries to regulate E by conducting until supply voltage drops to the diode's forward voltage).
* - limited only by the power source's capacity.
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On Fri, 3 Jun 2016 06:25:02 -0400, Stormin Mormon

will be less and the light output moderately less. Doesn't matter how "stiff" the battery is as long as the output voltage is low enough that the LED does not draw too much current.
3 aaa alkalines top out at about 4.5 volts. Lithiums are 3.7 nominal - freshly charhes possibly as much as 4.2 for a very short time
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On 06/03/2016 01:11 AM, Don Y wrote:
[snip]

I remember the last 3 (more than an hour or two) outages here and they were about 8 years apart.
BTW, during the last outage (from the tornado) wired phone service was out too but my cell phone (Verizon wireless) was OK.

That reminds me of when I was working behind a relative's console TV (this was before LCD so it was really big). Light was dim back there but barely adequate.
She decided to turn on a nearby lamp and dim became BLACK.
[snip]
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On 6/3/2016 10:33 AM, Mark Lloyd wrote:

Our utilities are below grade so seldom affected. Our last outage was a distribution transformer for the neighborhood catching fire. Before that, IIRC, a fire in a cable vault.
In 20+ years, I think we've lost power 3 or 4 times. (lost natural gas supply once -- THAT was interesting!)

Most of my kit hides under things -- under dressers, tables, beds, etc. And, most of the time, this is "just fine" (TmReg).
But, on those occasions when you need to plug/unplug a cable or needs to survey the contents of a box (without moving it as it's tethered to <whatever>), a light is essential. OTOH, you're only using it for a few seconds so even the crappiest "batteries" will last a long time!
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On 6/3/2016 1:53 PM, Don Y wrote:

Our electric is on poles, the wires weave through miles of half-dead maple trees. Consequently, every summer we get a thunderstorm or two that takes out power for 2-5 days. Before power company deregulation, we almost *never* had power outages...and when it did go out, the outage lasted less than 6 hours. The idiots that passed the power deregulation laws ought to be electrocuted!
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On 6/3/2016 6:14 PM, Tax Payer wrote:

Similar situation. Ours is underground but before it goes to our street it is above ground with lots of trees. That's why I bought a generator and had a transfer panel put in several years ago.
I've complained to the power company many times about their not keeping up the access trimming but even after they do it we could still lose it in a bad storm. Last one blew a big tree down that not only took down wires but took down a pole.
My system is too small to handle the whole house. I was mainly interested in furnace, well and freezer. Newer systems can handle the whole house by proper managing although not everything can be on at once.
I have to bring in gasoline but if we had natural gas I would use that as fuel source.
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On 6/3/2016 6:14 PM, Tax Payer wrote:

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Per Bill M Moore, Esq.:

Consider that the power company is losing revenue every minute those lines are down.
Dunno about rural areas, but that is beeeeeg money in a densely-populated area.
--
Pete Cresswell

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On 06/03/2016 05:14 PM, Tax Payer wrote:
[snip]

I live in one of the few areas around here that don't have deregulation. One difference is rates are much lower (I pay about half what people in a nearby city pay).
BTW, when figuring rates, I skip all the misleading stuff and just divide total bill by usage.
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I put all of "my" lines underground, but the power company's cables are all on poles.
We typically lose power a few times each winter, usually due to wind storms blowing trees onto power lines. Occasionally ice will take down a line, or someone will take out a pole with their car.
Most outages only last a few hours, but once we had an outage that lasted a day and a half.
Anthony Watson www.watsondiy.com www.mountainsoftware.com
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On 6/3/2016 9:48 PM, HerHusband wrote:

When I lived in the midwest, everything was overhead. I could count on an outage in my neighborhood every month or two. A drunk taking out a pole; an ice-laden branch falling on the wires; high winds; etc.
We've had so few, here, that they come as a real "surprise"!
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Don,

We occasionally get what I call "annoyance" outages. That's when the power blips off for a minute or two before coming on again. Just long enough to screw up all the clocks in the house, annoying. :)
Thankfully, most of our clocks are battery operated now, and the UPS for my computer sails right through those.
Anthony Watson www.watsondiy.com www.mountainsoftware.com
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Hi Anthony,
On 6/4/2016 7:45 AM, HerHusband wrote:

I had an ISP thast must have been plagued with a similar problem (or, a software bug) as I noticed that if I was pulling down an ISO at certain times of the overnight that the connection would "reset".
I knew it wasn't anything on my end (as I'd be sitting there, at the time -- doubtful they had staff on site at all hours of the night!)

I've been trying to replace all of our clocks with designs of my own (I like clocks!). Part of the design process is to include "time services" so they automatically track a common reference (that *they* elect, if the previous "reference" is unavailable).
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