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Old May 22nd 19, 08:31 AM posted to uk.telecom.mobile
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Default Phone charger question

On 21/05/2019 19:49, Scott wrote:
On Tue, 21 May 2019 19:40:44 +0100, David Higton
wrote:

In message
Scott wrote:

Could you get a faster blowing fuse, or would that be a different
size? I thought the glass ones blew faster.


The trouble is that we wouold all like a fuse that will carry its rated
maximum current for ever, but blow fairly soon when called upon to pass
a current slightly over the rating.

With a hot wire as the active element, that's impossible. The wire has
to melt when the overload current passes, which means it'll already be
close to melting point when the rated current passes. Which means that
the element will oxidise over a period of days or weeks at maximum
current, and therefore blow unexpectedly.

Thanks. Worst case scenario then. If the charger burst into flames
would this ensure a fuse somewhere (either in the plug or at the
consumer unit) would trip? Would a burning charger set fire to a
wall?


Worst case a charger that bursts into flames and has no earth because it
is double isolated will continue to burn until there is an earth leakage
or the ring main circuit breaker trips for over current. I have to say
that chargers catching fire is very unusual - they should blow an
internal fuse before anything bad happens.

Battery packs are much more likely to start a fire if abused.
eCigs can go up in flames particularly well if left on charge too long.

I have seen 13A mains plugs turn into red hot glowing carbonised plastic
by water ingress to the socket where no ELCB was present. Fortunately
the red hot glowing embers from it were falling onto already wet carpet.

I assume the RCD / RCBO would not trip as there would be no leakage to
earth?


Eventually there will be when the insulation on the cables inside the
wall socket start to char.

--
Regards,
Martin Brown

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Old May 22nd 19, 12:15 PM posted to uk.telecom.mobile
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Default Phone charger question

On 21/05/2019 16:01, Scott wrote:
On Tue, 21 May 2019 14:17:09 +0100, Martin Brown
wrote:

On 20/05/2019 19:18, MissRiaElaine wrote:
On 20/05/2019 18:19, Graham. wrote:
Sorry this is a rehash of an earlier posting.* Is there a way of
testing a charger to make sure it is safe?* I bought one online (two
pin version so difficult to find).* The seller's feedback suggests it
may be counterfeit but actually all the indications are that it is
not.* It seems to have the right markings and the Apple technician
thinks it is almost certainly genuine.* Is there a conclusive test
without opening it up?* Best of all, is there an app for checking the
charger?


It's not unreasonable to be a little paranoid about this issue, the
following is chiefly about UK plugs and sockets.

The plug on every item we connect to the mains has to contain a
suitably rated fuse accessible to the user, but for some reason
wall-warts are exempt, so we have to take them on trust to have
suitable internal protection.

After all, when you plug your charger into a so-called 13A socket, it
is typically protected by a 32 amp breaker and therefore capable of
supplying about 7.5kW continuously.

That's something that has always worried me more than a little. I tend
to use a 4-way strip to power my chargers, at least that has a fused plug.


But unless you swap the fuse to a 3A one it will happily supply 26A for
several minutes before it blows. I know this because our local church
has managed in the past to melt extension cables by running two kettles
from one that is still rolled up until it melted internally. The fuse
was still OK since the building ELCB went first on earth leakage.

Could you get a faster blowing fuse, or would that be a different
size? I thought the glass ones blew faster.


You can get fast blow fuses but they sometimes fail on transients when a
normal device has an initial high peak current to charge its capacitors.

A common or garden fuse could survive a couple of minutes at twice its
nominal rating and for as much as a few seconds at 10x.

A fast blow will go at about 2x its nominal rating in under 1s. eg.

https://static.rapidonline.com/pdf/566630t_v1.pdf

--
Regards,
Martin Brown
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Old May 22nd 19, 06:49 PM posted to uk.telecom.mobile
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Default Phone charger question

In message
Scott wrote:

Worst case scenario then. If the charger burst into flames would this
ensure a fuse somewhere (either in the plug or at the consumer unit) would
trip?


You may be looking at this from the wrong direction.

It's very difficult to engineer a fault in a charger that causes enough
heat to be dissipated to cause a fire (and in any case, see below), yet
doesn't pull enough current to blow the internal fuse. Reaistically, a
charger can't develop such a fault. In the real world, faults will
cause the charger to simply stop working, possibly blowing the internal
fuse.

Further on the topic of flammability: chargers should be built out of
components and materials that don't support combustion.

Would a burning charger set fire to a wall?


Directly: no, unless the wall is made out of something very unusual.
Even wood or wood cladding could reasonable be expected to require
more heat than a charger could generate, in order to start burning.

Indirectly: the relevant safety standards prohibit even the possibility
of flaming material falling out of the enclosure (I'm thinking about
falling onto something flammable below and the result propagating
further). Chargers of the types you're talking about don't normally
have any holes through which burning stuff can fall anyway.

The above all relates to things that are designed and type tested to
conform to relevant safety standards such as EN 60 950, UL 60950, etc.
It all goes out of the window for fake devices.

David
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Old May 23rd 19, 02:15 PM posted to uk.telecom.mobile
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Default Phone charger question

On 22/05/2019 19:49, David Higton wrote:
In message
Scott wrote:


Would a burning charger set fire to a wall?


Directly: no, unless the wall is made out of something very unusual.
Even wood or wood cladding could reasonable be expected to require
more heat than a charger could generate, in order to start burning.


The only way where it might is if the socket itself is compromised to
the point where it begins to char and bridged live to neutral. The
classic highly filled white plastic socket will char to red hot carbon
under these conditions as will an overloaded 4 way adaptor.

Indirectly: the relevant safety standards prohibit even the possibility
of flaming material falling out of the enclosure (I'm thinking about
falling onto something flammable below and the result propagating
further). Chargers of the types you're talking about don't normally
have any holes through which burning stuff can fall anyway.

The above all relates to things that are designed and type tested to
conform to relevant safety standards such as EN 60 950, UL 60950, etc.
It all goes out of the window for fake devices.


Flaming material should never happen. Glowing red hot char can though
and surprisingly quickly. I have seen a couple of examples.

I doubt that a well designed charger would ever fail by bursting into
flames, but the thing being charged is potentially much more suspect.
The infamous exploding Galaxy Note 7 for example:

https://www.wired.com/2017/01/why-th...ept-exploding/

Most battery packs are supposed to have in circuit protection against
faults but sometimes they don't get it exactly right.

--
Regards,
Martin Brown
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Old May 27th 19, 08:55 AM posted to uk.telecom.mobile
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Default Phone charger question

On Wed, 22 May 2019 19:49:17 +0100, David Higton
wrote:

In message
Scott wrote:

Worst case scenario then. If the charger burst into flames would this
ensure a fuse somewhere (either in the plug or at the consumer unit) would
trip?


You may be looking at this from the wrong direction.

It's very difficult to engineer a fault in a charger that causes enough
heat to be dissipated to cause a fire (and in any case, see below), yet
doesn't pull enough current to blow the internal fuse. Reaistically, a
charger can't develop such a fault. In the real world, faults will
cause the charger to simply stop working, possibly blowing the internal
fuse.

Further on the topic of flammability: chargers should be built out of
components and materials that don't support combustion.

Would a burning charger set fire to a wall?


Directly: no, unless the wall is made out of something very unusual.
Even wood or wood cladding could reasonable be expected to require
more heat than a charger could generate, in order to start burning.

Indirectly: the relevant safety standards prohibit even the possibility
of flaming material falling out of the enclosure (I'm thinking about
falling onto something flammable below and the result propagating
further). Chargers of the types you're talking about don't normally
have any holes through which burning stuff can fall anyway.

The above all relates to things that are designed and type tested to
conform to relevant safety standards such as EN 60 950, UL 60950, etc.
It all goes out of the window for fake devices.

Well, exactly. I was asking about the worst case scenario for a
counterfeit product.


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Old May 28th 19, 04:15 PM posted to uk.telecom.mobile
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Default Phone charger question

Graham. wrote:

The plug on every item we connect to the mains has to contain a
suitably rated fuse accessible to the user, but for some reason
wall-warts are exempt, so we have to take them on trust to have
suitable internal protection.


The plug fuse is intended to protect the cable, for instance if it's damaged
and shorting the conductors together. Wall-warts don't have a mains cable to
protect, so they don't need a plug fuse.

Nothing will protect you from a device that's maliciously engineered. The
protective earth is no use if the metal case isn't connected to it (or is
connected via a thin bit of wire). Double insulation won't help if the
device isn't actually double insulated (for instance, the screws in the
plastic case are live).

After all, when you plug your charger into a so-called 13A socket, it
is typically protected by a 32 amp breaker and therefore capable of
supplying about 7.5kW continuously.


That's true. But you can't dissipate 7.5kW inside a wall-wart for very long
before it melts, fuse or no fuse. A proper design would have a thermal
cutout. A malicious design won't, but there's not much that can be done
about that.

Theo
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Old May 28th 19, 06:28 PM posted to uk.telecom.mobile
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Default Phone charger question

On 28/05/2019 17:15, Theo wrote:

The plug fuse is intended to protect the cable, for instance if it's damaged
and shorting the conductors together. Wall-warts don't have a mains cable to
protect, so they don't need a plug fuse.


A plug fuse protects a cable if the conductors short out, but what
protects the conductors inside a charger or whatever if *they* short out..?

As far as I'm concerned, if it's plugged into a ring main, it needs a
fuse. I don't trust manufacturers to include a fuse or a thermal cutout,
I want to be able to see for myself that the device has adequate protection.


--
Ria in Aberdeen

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Old May 29th 19, 09:53 PM posted to uk.telecom.mobile
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Default Phone charger question

In message
Scott wrote:

On Wed, 22 May 2019 19:49:17 +0100, David Higton
wrote:

In message
Scott wrote:

Worst case scenario then. If the charger burst into flames would this
ensure a fuse somewhere (either in the plug or at the consumer unit)
would trip?


You may be looking at this from the wrong direction.

It's very difficult to engineer a fault in a charger that causes enough
heat to be dissipated to cause a fire (and in any case, see below), yet
doesn't pull enough current to blow the internal fuse. Reaistically, a
charger can't develop such a fault. In the real world, faults will cause
the charger to simply stop working, possibly blowing the internal fuse.

Further on the topic of flammability: chargers should be built out of
components and materials that don't support combustion.

Would a burning charger set fire to a wall?


Directly: no, unless the wall is made out of something very unusual. Even
wood or wood cladding could reasonable be expected to require more heat
than a charger could generate, in order to start burning.

Indirectly: the relevant safety standards prohibit even the possibility
of flaming material falling out of the enclosure (I'm thinking about
falling onto something flammable below and the result propagating
further). Chargers of the types you're talking about don't normally have
any holes through which burning stuff can fall anyway.

The above all relates to things that are designed and type tested to
conform to relevant safety standards such as EN 60 950, UL 60950, etc. It
all goes out of the window for fake devices.

Well, exactly. I was asking about the worst case scenario for a
counterfeit product.


I don't think it can ever be possible to answer that question.

David
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Old May 30th 19, 04:05 PM posted to uk.telecom.mobile
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Default Phone charger question

MissRiaElaine wrote:
A plug fuse protects a cable if the conductors short out, but what
protects the conductors inside a charger or whatever if *they* short out..?

As far as I'm concerned, if it's plugged into a ring main, it needs a
fuse. I don't trust manufacturers to include a fuse or a thermal cutout,
I want to be able to see for myself that the device has adequate protection.


I don't think it makes a lot of difference if you can dissipate 7.5kW (32A
breaker), 3kW (13A fuse) or 0.75kW (3A fuse). If you do any of those inside
a wallwart package, the end result is a fire. The fuse doesn't help you.
And there's good reasons why, if your device is supposed to take 20W, a
100mA fuse is a nonstarter.

If you want protection against overheating but don't trust the device,
you're going to have to fit your own thermal cutout to the outside of the
package.

Theo
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Old June 3rd 19, 06:45 PM posted to uk.telecom.mobile
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Default Phone charger question

On 30 May 2019 17:05:31 +0100 (BST)
Theo wrote:

If you want protection against overheating but don't trust the device,
you're going to have to fit your own thermal cutout to the outside of
the package.

If you're not sure where to put it, run the PSU hard until part of the
case starts to melt, as happened to a 99p from China phone charger that
I bought. That's where to put the thermal sensor. :-)



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