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I Built and Used My First Incandescent Bulb Current-Limiter



 
 
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  #11  
Old December 21st 20, 10:41 PM posted to rec.audio.pro
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Posts: 38
Default I Built and Used My First Incandescent Bulb Current-Limiter

Don Pearce cannot stop Bull****ting wrote:

======================================
>
> I should add. The cold/hot resistance change is much greater in the
> NTC thermistor, which means that while it does a much better job of
> limiting the initial inrush current, its resistance once it reaches
> its final state will be only a few tens of milliohms, so it becomes
> essentially invisible to the circuit in operation.
>
> This would be a typical choice
>
> https://uk.farnell.com/ametherm/sl22...tor/dp/1703898
>

** Don just makes stuff up.

The presence or not of an NTC in an *amplifier" has no effect on the behavior of a "dim bulb"at switch on.

I deal with this stuff *every day* and Don does NOT !!!


....... Phil


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  #12  
Old December 21st 20, 11:04 PM posted to rec.audio.pro
Scott Dorsey
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Default I Built and Used My First Incandescent Bulb Current-Limiter

> wrote:
> Scott Dorsey wrote:
>
>===================
>> >
>> >But I would assume the bulb lighting up initially, is due
>> >to the initial in-rush current, that charges up the electrolytic
>> >filtering caps, on the outputs of the rectifiers?

>>
>> No. This is a "power-on thump" which is caused by the coupling capacitors
>> charging up, not the power supply.
>>

>
>** The OP never mentioned any " thump" and is not talking about one.


Yes, you are correct. From the original post, it seemed like he was using
a protection lamp on the speaker output (which is a common thing to do),
not on the AC line (which is also a fairly common thing for people to do
when they don't have a variac).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #13  
Old December 22nd 20, 01:06 AM posted to rec.audio.pro
Paul Dorman
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Posts: 55
Default I Built and Used My First Incandescent Bulb Current-Limiter

On 12/21/2020 3:04 PM, Scott Dorsey wrote:
> > wrote:
>> Scott Dorsey wrote:
>>
>> ===================
>>>>
>>>> But I would assume the bulb lighting up initially, is due
>>>> to the initial in-rush current, that charges up the electrolytic
>>>> filtering caps, on the outputs of the rectifiers?
>>>
>>> No. This is a "power-on thump" which is caused by the coupling capacitors
>>> charging up, not the power supply.
>>>

>>
>> ** The OP never mentioned any " thump" and is not talking about one.

>
> Yes, you are correct. From the original post, it seemed like he was using
> a protection lamp on the speaker output (which is a common thing to do),
> not on the AC line (which is also a fairly common thing for people to do
> when they don't have a variac).
> --scott
>


If you watched the video I posted, you'd see the
schematic is a very simple light bulb in series with
the "Hot" side of the AC line:

https://www.antiqueradio.org/art/DimbulbSketch.jpg

Yes, these are typically used when you don't have
a variac.

But audio turn-on "thumps" do not last a full
second! I stand by my theory that the initial in-rush
of current is the charging up of the electrolytic
filtering caps, on the outputs of the rectifiers.

But apparently, you are correct that light bulbs
are sometimes used in series with speakers, to protect
them:

https://trueaudio.com/st_prot1.htm

  #14  
Old December 22nd 20, 01:17 AM posted to rec.audio.pro
Paul Dorman
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Posts: 55
Default I Built and Used My First Incandescent Bulb Current-Limiter

On 12/21/2020 3:39 AM, Don Pearce wrote:
> On Sun, 20 Dec 2020 16:44:56 -0700, Paul Dorman >
> wrote:
>
>> This was used for a guitar amp that was continually
>> blowing slow-blow fuses instantly upon turning the amp
>> on.
>>
>> https://www.youtube.com/watch?v=k5oNQ1etN2c
>>
>> In my case, the bulb would briefly light up, and then
>> fade out within about a second. I read this meant the
>> amp was normal, and didn't have a short to ground, and
>> when I plugged the amp into the wall normally, I was able
>> to trouble-shoot it normally.
>>
>> But I would assume the bulb lighting up initially, is due
>> to the initial in-rush current, that charges up the electrolytic
>> filtering caps, on the outputs of the rectifiers?
>>
>> Because the initial 1 second flash only happened with a
>> linear power supply guitar amp, and did not happen with
>> my switched-mode guitar amp. With the latter, the bulb
>> never glowed noticeably, even at turn-on.

>
> You will find that the bulb has a rather finite lifetime.Instead use
> the part designed for the job, a negative temperature coefficient
> (NTC) thermistor. Any switched mode power supply is most likely to
> already have one fitted, which is why your bulb seems to do nothing.
>


While a thermistor might also prevent a fuse from blowing out,
it doesn't give you a visual sign that there is a short-to-ground in
the circuit being tested.

The light bulb turns on when there is a short to ground.

  #15  
Old December 22nd 20, 01:37 AM posted to rec.audio.pro
Paul Dorman
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Posts: 55
Default I Built and Used My First Incandescent Bulb Current-Limiter

On 12/21/2020 3:39 AM, Don Pearce wrote:
> On Sun, 20 Dec 2020 16:44:56 -0700, Paul Dorman >
> wrote:
>
>> This was used for a guitar amp that was continually
>> blowing slow-blow fuses instantly upon turning the amp
>> on.
>>
>> https://www.youtube.com/watch?v=k5oNQ1etN2c
>>
>> In my case, the bulb would briefly light up, and then
>> fade out within about a second. I read this meant the
>> amp was normal, and didn't have a short to ground, and
>> when I plugged the amp into the wall normally, I was able
>> to trouble-shoot it normally.
>>
>> But I would assume the bulb lighting up initially, is due
>> to the initial in-rush current, that charges up the electrolytic
>> filtering caps, on the outputs of the rectifiers?
>>
>> Because the initial 1 second flash only happened with a
>> linear power supply guitar amp, and did not happen with
>> my switched-mode guitar amp. With the latter, the bulb
>> never glowed noticeably, even at turn-on.

>
> You will find that the bulb has a rather finite lifetime.Instead use
> the part designed for the job, a negative temperature coefficient
> (NTC) thermistor. Any switched mode power supply is most likely to
> already have one fitted, which is why your bulb seems to do nothing.
>


It's not clear to me that a thermistor would prevent a fuse from
blowing in a guitar amp, or any other circuit, that has a short
to ground. Because while the resistance may be high initially, while
the thermistor is cold, the resistance will go low as it heats up,
allowing the fuse to blow.

A thermistor also doesn't give you a visual indication that a
short-to-ground is in the circuit under test, as a light bulb does.

Remember a light bulb in series with the AC line, is mainly a
trouble-shooting tool.
  #16  
Old December 22nd 20, 01:43 AM posted to rec.audio.pro
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Posts: 38
Default I Built and Used My First Incandescent Bulb Current-Limiter

Paul wrote:
===========
>
> But audio turn-on "thumps" do not last a full
> second! I stand by my theory that the initial in-rush
> of current is the charging up of the electrolytic
> filtering caps, on the outputs of the rectifiers.
>

** PSU electros normally charge fully in two cycles of AC power.
The presence of a 75 or 100W lamp in series makes that take longer.
With a tube radio, it is the heater current surge that takes a few seconds.
With large iron core transformers, they are the main culprit with single cycle surges up to 150amps.


> But apparently, you are correct that light bulbs
> are sometimes used in series with speakers, to protect
> them:
>
> https://trueaudio.com/st_prot1.htm
>

** LOL - it is never a supply voltage lamp that is used.

12 and 24V halogen bulbs *are* used but only rarely to protect a woofer or whole speaker .


...... Phil
  #17  
Old December 22nd 20, 01:46 AM posted to rec.audio.pro
Paul Dorman
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Posts: 55
Default I Built and Used My First Incandescent Bulb Current-Limiter

On 12/20/2020 8:01 PM, wrote:
> Paul wrote:
> ============
>>
>> But I would assume the bulb lighting up initially, is due
>> to the initial in-rush current, that charges up the electrolytic
>> filtering caps, on the outputs of the rectifiers?
>>

>
> ** The largest part of the " inrush surge " is down to the iron transformer core *magnetising* and losing nearly all of its inductance at switch own.
> Can take 20 cycles of AC power for the core to unmagnetise too.
>
> SMPSs usually surge hard at a switch on too, yours must be an exception.
>


The iron transformer is magnetizing every cycle, which
would be 60 times a second, for 60Hz AC.

If the secondary was open, and not connected to anything,
then the back EMF would be high enough, to prevent the light
bulb from turning on, due to the low current draw.

When the secondary is wired to the rectifiers, there is
now a load, and the large filtering caps need to be charged up,
which I believe is the reason the light bulb turns on briefly,
for about one second.

  #18  
Old December 22nd 20, 01:49 AM posted to rec.audio.pro
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Posts: 38
Default I Built and Used My First Incandescent Bulb Current-Limiter

Paul wrote:
=============
>
> It's not clear to me that a thermistor would prevent a fuse from
> blowing in a guitar amp, or any other circuit, that has a short
> to ground. Because while the resistance may be high initially, while
> the thermistor is cold, the resistance will go low as it heats up,
> allowing the fuse to blow.
>

** Under a short circuit condition , NTC thermistors *explode*
like a fire cracker spreading debris all over the place.

> Remember a light bulb in series with the AC line, is mainly a
> trouble-shooting tool.


** Of course, a very primitive one that works only sometimes.

Tube radios and tube amps are the main use.

May SS amps will refuse to work with a lamp in series.


..... Phil

  #19  
Old December 22nd 20, 01:56 AM posted to rec.audio.pro
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Posts: 38
Default I Built and Used My First Incandescent Bulb Current-Limiter

Paul wrote:
============
>>
> > ** The largest part of the " inrush surge " is down to the iron transformer
>> core *magnetising* and losing nearly all of its inductance at switch own.

>
> > Can take 20 cycles of AC power for the core to unmagnetise too.
> >
> > SMPSs usually surge hard at a switch on too, yours must be an exception.
> >

>
> The iron transformer is magnetizing every cycle, which
> would be 60 times a second, for 60Hz AC.
>


** But not at *switch on * !!!!!!!!!

The phenomenon is called " inrush surge" and is a *whole subject* on its own.

This article from my colleague Rod Elliott may give you a hint.

https://sound-au.com/articles/inrush.htm


..... Phil


  #20  
Old December 22nd 20, 02:13 AM posted to rec.audio.pro
Ralph Barone[_3_]
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Posts: 53
Default I Built and Used My First Incandescent Bulb Current-Limiter

> wrote:
> Paul wrote:
> ============
>>>
>>> ** The largest part of the " inrush surge " is down to the iron transformer
>>> core *magnetising* and losing nearly all of its inductance at switch own.

>>
>>> Can take 20 cycles of AC power for the core to unmagnetise too.
>>>
>>> SMPSs usually surge hard at a switch on too, yours must be an exception.
>>>

>>
>> The iron transformer is magnetizing every cycle, which
>> would be 60 times a second, for 60Hz AC.
>>

>
> ** But not at *switch on * !!!!!!!!!
>
> The phenomenon is called " inrush surge" and is a *whole subject* on its own.
>
> This article from my colleague Rod Elliott may give you a hint.
>
> https://sound-au.com/articles/inrush.htm
>
>
> .... Phil
>
>
>


Section 4 of your linked article talks about transformer inrush, which is a
definite concern for equipment with large power transformers. We had an
event a couple years ago when energizing some 500 MVA, 500 kV transformers
at the wrong point on wave resulted in a large outage and actual
destruction of some other equipment in the vicinity.

 




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