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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.

current limited rechargables?



 
 
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  #1  
Old November 21st 13, 11:34 PM posted to uk.tech.digital-tv
Mike[_19_]
external usenet poster
 
Posts: 114
Default current limited rechargables?

In article ,
Roderick Stewart wrote:

However, it's physically possible to connect lots of PP3s in a zigzag
arrangement which puts them in series.


You have to zig-zag the batteries to get AC, I think ...

http://www.instructables.com/id/Mini...ricity-backup/

Darwin in action? At least insulate the terminals.
--
--------------------------------------+------------------------------------
Mike Brown: mjb[-at-]signal11.org.uk | http://www.signal11.org.uk

--- news://freenews.netfront.net/ - complaints: ---
  #2  
Old November 22nd 13, 05:14 AM posted to uk.tech.digital-tv
Andy Burns[_8_]
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Posts: 215
Default current limited rechargables?

Mike wrote:

Roderick Stewart wrote:

it's physically possible to connect lots of PP3s in a zigzag
arrangement which puts them in series.


You have to zig-zag the batteries to get AC, I think ...

http://www.instructables.com/id/Mini...ricity-backup/

Darwin in action? At least insulate the terminals.


Thirty-odd years ago I saw someone who had a rather neat arrangement of
200 NiCads in series in a length of drain pipe, with a 13A socket on the
end, he used it as a portable power supply for a BBC Micro. Presumably
the Beeb's internal PSU was switch mode and happy to chop-up 240V DC?

  #3  
Old November 22nd 13, 11:33 AM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
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Posts: 2,208
Default current limited rechargables?

On Thu, 21 Nov 2013 23:34:25 +0000 (GMT), lid (Mike)
wrote:

You have to zig-zag the batteries to get AC, I think ...

http://www.instructables.com/id/Mini...ricity-backup/

I suspect the person responsible for this probably does think so.

There have been a few stories in the press about Apple phones and
laptops catching fire, and I now realise there could be more to these
stories than I first thought. You wouldn't expect somebody ignorant
and rich enough to afford an Apple device to go cheapskate rather than
buy the official accessories, but money can't buy you brains.

Rod.
  #4  
Old November 22nd 13, 04:21 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
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Posts: 853
Default current limited rechargables?

On Fri, 22 Nov 2013 05:14:00 +0000, Andy Burns
wrote:

Mike wrote:

Roderick Stewart wrote:

it's physically possible to connect lots of PP3s in a zigzag
arrangement which puts them in series.


You have to zig-zag the batteries to get AC, I think ...

http://www.instructables.com/id/Mini...ricity-backup/

Darwin in action? At least insulate the terminals.


Thirty-odd years ago I saw someone who had a rather neat arrangement of
200 NiCads in series in a length of drain pipe, with a 13A socket on the
end, he used it as a portable power supply for a BBC Micro. Presumably
the Beeb's internal PSU was switch mode and happy to chop-up 240V DC?


Surely you meant 260V DC. Unless the smpsu was designed for universal
mains voltage use (90 to 265 V ac) like a laptop charger, 240VDC would
be below the minimum threshold for a smpsu rated for 230v AC supplies.

Otoh, he might have been considering the inevitable risk of reverse
charging a cell or six in the string by specifying a per cell endpoint
voltage of 1.3v, hence the use of only 200 cells as opposed to 217
cells for an endpoint voltage of 1.2v per cell.

Of course, this was for a smpsu that didn't have a PG signal (at
least, I don't believe such auxiliary control signals arrived until
the advent of the IBM PC) so may well have still provided usable power
right down to an HT voltage of just 240VDC.

If you wanted to try the same trick with a desktop PC (a DC input
jack via an extra ht blocking diode fitted to the ATX PSU) you'd
definitely have to supply a minimum DC voltage of 261 volts or else
the PSU would negate its PG line and place the CPU into a halt/reset
state.

When using sealed rechargable cells, it's best to use a more
managable sized string with a high efficiency converter to generate
the nominal 300vDC required in the HT module of an ATX psu (assuming
the 5vSB is also fed by this common HT source rather than its own
independent HT module - but an extra blocking diode should allow you
to overcome even this eventuality).

Since the ratio of min to max HT voltage just exceeds 1.42:1 in a
standard 230VAC ATX psu (260v min to 374v max DC HT voltage) you can
use a simple (but very high efficiency) unregulated squarewave
converter using a transformer with a step up turns ratio of 26 off of
a 12v SLA battery with virtually no risk of reverse charge damage
(about 10.2v endpoint cut out voltage - the same value typically used
by UPSes).

Whilst such protection might seem to of limited use if you can't
likewise power the monitor, you do at least have the luxury of
sufficient time to replace the blown plugtop or ring main fuse (or
allow time for the mains to resume from a, hopefully, short outage or
even to fire up a standby generator) before having to trigger a normal
shutdown via a brief press of the on/off button (better that than
suffer a sudden loss of power mid- compute).

The overall conversion efficiency is probably on a par with a cheap
quasi sinewave (aka, modified squarewave) UPS so the main advantage of
this approach is that it offers the time rich, cash poor, individual
an affordable alternative to the classic UPS approach.

The transformer can be easily handwound using a suitable ferrite core
and the rest of the handful of components required can be bought at a
fraction of the cost of a cheap UPS.
--
Regards, J B Good
  #5  
Old November 22nd 13, 04:44 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
external usenet poster
 
Posts: 853
Default current limited rechargables?

On Fri, 22 Nov 2013 11:33:59 +0000, Roderick Stewart
wrote:

On Thu, 21 Nov 2013 23:34:25 +0000 (GMT), lid (Mike)
wrote:

You have to zig-zag the batteries to get AC, I think ...

http://www.instructables.com/id/Mini...ricity-backup/

I suspect the person responsible for this probably does think so.

There have been a few stories in the press about Apple phones and
laptops catching fire, and I now realise there could be more to these
stories than I first thought. You wouldn't expect somebody ignorant
and rich enough to afford an Apple device to go cheapskate rather than
buy the official accessories, but money can't buy you brains.


I think you'll find that's more to do with dangerous counterfeits
rather than to do with using high voltage DC as a substitute for mains
power.

However, with universal mains voltage devices (90 to 265v AC), there
is a risk of overloading a single pair of rectifier diodes in the
bridge circuit when feeding them with the lowest working DC voltage
since the current isn't shared between the two pairs of rectifier
diodes in the bridge. It's unlikely to be an issue with a phone
charger but it can certainly be one for a laptop charger.

Counterintuitively, this danger disappears with DC voltage feeds of
260 to 370 volts (the current through the diodes becomes half what it
needs to be at the low end of the input voltage range for the rated
power output which keeps it within the diodes' continuous current
rating.
--
Regards, J B Good
  #6  
Old November 22nd 13, 05:42 PM posted to uk.tech.digital-tv
Dave Plowman (News)
external usenet poster
 
Posts: 5,339
Default current limited rechargables?

In article ,
Johny B Good wrote:
There have been a few stories in the press about Apple phones and
laptops catching fire, and I now realise there could be more to these
stories than I first thought. You wouldn't expect somebody ignorant
and rich enough to afford an Apple device to go cheapskate rather than
buy the official accessories, but money can't buy you brains.


I think you'll find that's more to do with dangerous counterfeits
rather than to do with using high voltage DC as a substitute for mains
power.


Think Boeing Dreamliner.

--
*The sooner you fall behind, the more time you'll have to catch up *

Dave Plowman London SW
To e-mail, change noise into sound.
 




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