Hello,

A couple of weeks ago I was asking about replacement cable for a hair
dryer. It was rated at 1440W and we couldn't make our minds up whether
6A cable would be suitable or whether to use 10A just to be sure.

I have now changed the cable. I used 10 A and it was not too fat to
fit, so that was good. I could only get "normal" 10 A flex. Does
anyone know where I can get heat resistant 10A flex from?

The hairdryer was only held to gether by one screw! Inside the cable
was soldered to a PCB on which was mounted a switch for off, heat 1,
heat 2.

I made the mistake of removing the old wire and then realising that I
could not remember which terminal was live and which was neutral! I am
pretty sure I got it right because I followed the PCB tracks and wired
the live to the switch, I hope

Any way I have tested it a few times and it seems ok. Would it make a
difference if they were back to front? Next time I must remember to
make a note or take a photo of what is where first!

From the other end of the PCB run three tiny wires to the fan and
heater. These wires are so tiny! I have seen door bells using thicker
wires!

I really cannot understand why the mains cable has to be so thick when
the current then runs through what is practically fuse wire! Why is
this? Surely these tiny wires do not carry 6A?

Inside the nozzle there is an element wrapped round a body. On the
body I could see some components but could not quite work out what
they were because thy were obscured by the element.

I am not sure if one was a bi-metallic strip to perhaps act as an
overheat cut off?

I think there was a resistor, presumably to lower the fan speed on
the first setting.

But what were all the other bits (diodes etc) for?

Thanks in advance,
Stephen.

In article ,
writes:

Any way I have tested it a few times and it seems ok. Would it make a
difference if they were back to front?

In most of Europe, they will be back-to-front half the times the
hair drier is used.

From the other end of the PCB run three tiny wires to the fan and
heater. These wires are so tiny! I have seen door bells using thicker
wires!

I really cannot understand why the mains cable has to be so thick when
the current then runs through what is practically fuse wire! Why is
this? Surely these tiny wires do not carry 6A?

It probably doesn't matter if those wires get hot.

Inside the nozzle there is an element wrapped round a body. On the
body I could see some components but could not quite work out what
they were because thy were obscured by the element.

I am not sure if one was a bi-metallic strip to perhaps act as an
overheat cut off?

I think there was a resistor, presumably to lower the fan speed on
the first setting.

But what were all the other bits (diodes etc) for?

A common design uses a low voltage DC motor, in series with the
element. The motor therefore requires a bridge rectifier.
A common design fault with this scheme is the use of a 50V bridge
rectifier on the basis that the motor is only something like 10-20V.
Motor commutators are not perfect, and there will be momentary
periods when it's open circuit, resulting in 240VAC across the
bridge, which can blow it. I've replace 3 such bridge rectifiers
over the last ~20 years, and always replace with mains ones which
then don't blow again.

Speed/power control is done either by having a tap on the element,
or by using a diode to half wave rectify (or some combination of
both). You can't just have a cold fan in these designs though, as
the heater is required to drop the voltage for the fan.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 22 Mar 2008 09:06:21 GMT, (Andrew
Gabriel) wrote:

A common design uses a low voltage DC motor, in series with the
element. The motor therefore requires a bridge rectifier.
A common design fault with this scheme is the use of a 50V bridge
rectifier on the basis that the motor is only something like 10-20V.
Motor commutators are not perfect, and there will be momentary
periods when it's open circuit, resulting in 240VAC across the
bridge, which can blow it. I've replace 3 such bridge rectifiers
over the last ~20 years, and always replace with mains ones which
then don't blow again.

Speed/power control is done either by having a tap on the element,
or by using a diode to half wave rectify (or some combination of
both). You can't just have a cold fan in these designs though, as
the heater is required to drop the voltage for the fan.

Thanks for the informative reply. I did see diodes so they could be
for either of the purposes you describe but I didn't have a proper
study to find out more.

Thanks, Stephen.