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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

why 12V?



 
 
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  #1  
Old March 7th 17, 08:37 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 1,458
Default why 12V?

So many things run on 12V DC. Firstly, why has that become the standard?
Is it all because of the nominal voltage of a car battery?
Secondly, wouldn't 24 or 48V be more convenient for many things?

I heard a few years back something about new cars being 48V in the near
future. Did it ever happen?

Bill
  #2  
Old March 7th 17, 08:57 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 1,458
Default why 12V?

On 07/03/2017 20:37, Bill Wright wrote:

I heard a few years back something about new cars being 48V in the near
future. Did it ever happen?


I just googled it. It didn't happen.

Bill

  #3  
Old March 7th 17, 09:21 PM posted to uk.tech.digital-tv
dave
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Default why 12V?

On 07/03/17 20:57, Bill Wright wrote:
On 07/03/2017 20:37, Bill Wright wrote:

I heard a few years back something about new cars being 48V in the near
future. Did it ever happen?


I just googled it. It didn't happen.


There was a plan in the 1980s to change cars to (I think) 32v. The idea
was to reduce the weight and cost of copper needed in a car by a factor
of about three. If the voltage was made any higher then
double-insulation and other safety measures would be needed, increasing
the cost. In the event the copper price reduced and the idea was shelved.
--
Dave

  #4  
Old March 7th 17, 09:43 PM posted to uk.tech.digital-tv
Woody[_5_]
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Posts: 1,581
Default why 12V?


"Bill Wright" wrote in message
news
So many things run on 12V DC. Firstly, why has that become the
standard? Is it all because of the nominal voltage of a car battery?
Secondly, wouldn't 24 or 48V be more convenient for many things?

I heard a few years back something about new cars being 48V in the
near future. Did it ever happen?


There seems to be or have been a number of 'standard' voltages.
6V was used on motorbikes and some cars - the 'Puddle Jumper' a.k.a.
Renault 4 for example - and those big torches of which the battery
formed part of the unit.
9V for portable radios - remember the PP3 and PP?
12V - nuff said
19V seems to be a very common voltage for laptop chargers
24V for commercial vehicles and trains(?)
48V for telephone systems and associated microwave links and nowadays
fibre equipments and always positive earth
90V used to be used for batteries in old portable valve radios
(remember them Bill?)
100V was also common - I used to have a SMPS mared 100/12 i.e. 100V
12A

I bet there's a lot more, but equally for battery supplies I would
think there is more 12V and 48V than anything else.


--
Woody

harrogate3 at ntlworld dot com


  #5  
Old March 7th 17, 10:21 PM posted to uk.tech.digital-tv
NY
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Posts: 933
Default why 12V?

"Bill Wright" wrote in message
news
So many things run on 12V DC. Firstly, why has that become the standard?
Is it all because of the nominal voltage of a car battery?


I would imagine so. 12V can easily be made out of six 2V lead-acid cells
(for a car) or eight 1.5V batteries (for a portable radio etc).

I'm not sure how 5V became the standard for USB power.

  #6  
Old March 7th 17, 11:11 PM posted to uk.tech.digital-tv
Graham C
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Posts: 166
Default why 12V?

On Tue, 7 Mar 2017 20:37:00 +0000, Bill Wright
wrote:

So many things run on 12V DC. Firstly, why has that become the standard?
Is it all because of the nominal voltage of a car battery?
Secondly, wouldn't 24 or 48V be more convenient for many things?

Bill


Slightly OT but I've been trying for years to find the reason behind
airfield runway lighting which is standardised at 6.6 amps.

Because of the high power necessary these are wired in series to cut
down on conductor requirements and provide constant brightmess down
the line. Most are dimmable but 6.6 amps corresponds to 100%
brightness. Clearly the wattage of the bulb determines the
brightness.

Originally during WWII each lamp was fed from a 1:1 transformer which
continued the circuit if a bulb filament failed. There were also
'thin-paper' cutouts and later zener type devices used to maintain the
circuit in the event of a lamp failure.

Even by the end of WWII constant current regulators were in use with
the thin-paper cut-out system to prevent the sytem going into 'domino
mode' if one, then two, then three lamps failes etc.

But why 6.6 amps?

GrahamC

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  #7  
Old March 7th 17, 11:37 PM posted to uk.tech.digital-tv
Graham.[_12_]
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Posts: 334
Default why 12V?

On Tue, 7 Mar 2017 22:21:58 -0000, "NY" wrote:

"Bill Wright" wrote in message
news
So many things run on 12V DC. Firstly, why has that become the standard?
Is it all because of the nominal voltage of a car battery?


I would imagine so. 12V can easily be made out of six 2V lead-acid cells
(for a car) or eight 1.5V batteries (for a portable radio etc).

I'm not sure how 5V became the standard for USB power.


TTL logic must figure strongly in the answer.


--

Graham.
%Profound_observation%
  #8  
Old March 7th 17, 11:48 PM posted to uk.tech.digital-tv
Graham.[_12_]
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Posts: 334
Default why 12V?

On Tue, 07 Mar 2017 23:11:59 +0000, Graham C
wrote:

On Tue, 7 Mar 2017 20:37:00 +0000, Bill Wright
wrote:

So many things run on 12V DC. Firstly, why has that become the standard?
Is it all because of the nominal voltage of a car battery?
Secondly, wouldn't 24 or 48V be more convenient for many things?

Bill


Slightly OT but I've been trying for years to find the reason behind
airfield runway lighting which is standardised at 6.6 amps.

Because of the high power necessary these are wired in series to cut
down on conductor requirements and provide constant brightmess down
the line. Most are dimmable but 6.6 amps corresponds to 100%
brightness. Clearly the wattage of the bulb determines the
brightness.

Originally during WWII each lamp was fed from a 1:1 transformer which
continued the circuit if a bulb filament failed. There were also
'thin-paper' cutouts and later zener type devices used to maintain the
circuit in the event of a lamp failure.

Even by the end of WWII constant current regulators were in use with
the thin-paper cut-out system to prevent the sytem going into 'domino
mode' if one, then two, then three lamps failes etc.

But why 6.6 amps?

GrahamC

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Why 6.3A for many valve heaters?

And why 3.14159265359 diameters in a circumference?

Go on Bill, tell us why?


--

Graham.
%Profound_observation%
  #9  
Old March 8th 17, 12:50 AM posted to uk.tech.digital-tv
Paul Ratcliffe
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Posts: 2,396
Default why 12V?

On Tue, 07 Mar 2017 23:48:00 +0000, Graham wrote:

Why 6.3A for many valve heaters?


FFS... 6.3V (and 0.3A typically).
  #10  
Old March 8th 17, 01:36 AM posted to uk.tech.digital-tv
Graham.[_12_]
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Posts: 334
Default why 12V?

On Wed, 08 Mar 2017 00:50:20 GMT, Paul Ratcliffe
wrote:

On Tue, 07 Mar 2017 23:48:00 +0000, Graham wrote:

Why 6.3A for many valve heaters?


FFS... 6.3V (and 0.3A typically).


I have to concede a definite brain fart there.



--

Graham.
%Profound_observation%
 




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