On 14/04/2018 11:42, The Natural Philosopher wrote:
On 14/04/18 09:34, newshound wrote:
On 13/04/2018 18:47, The Natural Philosopher wrote:
On 13/04/18 17:24, newshound wrote:


As you say, small mains transformer, a few resistors and of course
a 5 volt Zener on the ADC input.

Well i'd just clamp that to the 5V rails.

Clamp what? I'm confused.

The input.

resistor and reverse biased diode to +5V. If it goes above 5V the
diode clamps it to the suplly rail plus half a volt or so. Standsard
technique.


https://i.stack.imgur.com/LfzyT.png

is a perfect example

from a similar app.

https://electronics.stackexchange.co...erence-voltage


OK perhaps I am getting my Zeners and Shottkys mixed up, it is a long
time since I actually built anything like that. But that's the
principle I was trying to convey.

No: using a zener is a completely different technique. There you aim to
divert extra overvoltage current to ground. The clamp diverts it to the
power supply first.



Shottkys are only necessary to clamp fast transients, also: Ordinary
diodes work OK. Just put a small cap after the resistor.

Like this

http://vps.templar.co.uk/Odds%20and%...nput-stage.png


Thanks very much, that makes sense now!

A nodeMCU will almost certainly do everything you want including
logging to a remote database.

Problem is dealing with mains AC voltages and having to reduce them
first.




Isolating transformers isolate the mains and reduce them to safe levels.


Care to expand of that statement Dennis?..
--
Tony Sayer

On Friday, 13 April 2018 20:45:16 UTC+1, Cursitor Doom wrote:
On Fri, 13 Apr 2018 07:38:11 -0700, whisky-dave wrote:

Problem is dealing with mains AC voltages and having to reduce them
first.

Not really. Loads of suitable sub-min mains transformers in every local
recycling site; help yourself for free. Or just a couple of quid new from
China through Ebay.

Most small mains transformers are run very close to core saturation, so
any large transients are likely to be clamped by the transformer. This
could be overcome by putting a resistor in series with the transformer
primary so that it is running at a small fraction of mains voltage.
Have a load resistor on the secondary may improve the performance as well.

John

On 14/04/18 13:44, wrote:
On Friday, 13 April 2018 20:45:16 UTC+1, Cursitor Doom wrote:
On Fri, 13 Apr 2018 07:38:11 -0700, whisky-dave wrote:

Problem is dealing with mains AC voltages and having to reduce them
first.

Not really. Loads of suitable sub-min mains transformers in every local
recycling site; help yourself for free. Or just a couple of quid new from
China through Ebay.

Most small mains transformers are run very close to core saturation, so
any large transients are likely to be clamped by the transformer.

Oh dear. A pseudo authoritative statement from someone who doesnt know
the difference between voltage and current.



This
could be overcome by putting a resistor in series with the transformer
primary so that it is running at a small fraction of mains voltage.
Have a load resistor on the secondary may improve the performance as well.


Oh dear. Soemone who doesnt understand inductance either.


John



--
In todays liberal progressive conflict-free education system, everyone
gets full Marx.

On Saturday, 14 April 2018 14:42:10 UTC+1, The Natural Philosopher wrote:

Most small mains transformers are run very close to core saturation, so
any large transients are likely to be clamped by the transformer.

Oh dear. A pseudo authoritative statement from someone who doesnt know
the difference between voltage and current.

So do you disagree with my claim that small transformers are usually
run close to core saturation at their rated voltage?

Do you disagree with my expectation that grossly overdriving such a
small transformer (with the transient to be measured) will cause its
output to saturate and give an incorrect measurement result?

This
could be overcome by putting a resistor in series with the transformer
primary so that it is running at a small fraction of mains voltage.
Have a load resistor on the secondary may improve the performance as well.

Oh dear. Soemone who doesnt understand inductance either.

What exactly do you object to here? A resistively loaded transformer
looks like a resistor (apart from the leakage inductance) so in
conjunction with a series input resistor it will form a reasonable
potential divider thereby moving the operation well away from
saturation.

Please explain.

John

wrote:

On Saturday, 14 April 2018 14:42:10 UTC+1, The Natural Philosopher wrote:

Most small mains transformers are run very close to core saturation, so
any large transients are likely to be clamped by the transformer.

Oh dear. A pseudo authoritative statement from someone who doesnt know
the difference between voltage and current.

So do you disagree with my claim that small transformers are usually
run close to core saturation at their rated voltage?

Do you disagree with my expectation that grossly overdriving such a
small transformer (with the transient to be measured) will cause its
output to saturate and give an incorrect measurement result?

Saturation results from current flow. If the transformer has a high
impedance across the secondary saturation will not happen. (The voltage
output may not be precise for other reasons, but should be good enough
for the sort of transients that are going to affect a heating element.)



This
could be overcome by putting a resistor in series with the transformer
primary so that it is running at a small fraction of mains voltage.
Have a load resistor on the secondary may improve the performance as well.

Oh dear. Soemone who doesnt understand inductance either.

What exactly do you object to here? A resistively loaded transformer
looks like a resistor (apart from the leakage inductance) so in
conjunction with a series input resistor it will form a reasonable
potential divider thereby moving the operation well away from
saturation.

Please explain.

John
The load resistor will not improve anything. The resistor in series
with the primary will just make accurate voltage measurement impossible
because of the poorly defined and frequency dependent primary impedance
while providing no benefits.

--

Roger Hayter

On 14/04/18 17:28, wrote:
On Saturday, 14 April 2018 14:42:10 UTC+1, The Natural Philosopher wrote:

Most small mains transformers are run very close to core saturation, so
any large transients are likely to be clamped by the transformer.

Oh dear. A pseudo authoritative statement from someone who doesnt know
the difference between voltage and current.

So do you disagree with my claim that small transformers are usually
run close to core saturation at their rated voltage?


Yes

Do you disagree with my expectation that grossly overdriving such a
small transformer (with the transient to be measured) will cause its
output to saturate and give an incorrect measurement result?

Yes.



This
could be overcome by putting a resistor in series with the transformer
primary so that it is running at a small fraction of mains voltage.
Have a load resistor on the secondary may improve the performance as well.

Oh dear. Soemone who doesnt understand inductance either.

What exactly do you object to here? A resistively loaded transformer
looks like a resistor (apart from the leakage inductance) so in
conjunction with a series input resistor it will form a reasonable
potential divider thereby moving the operation well away from
saturation.

Please explain.

I am not here to teach you basic electronics when you think you know it
all already


John



--
"The great thing about Glasgow is that if there's a nuclear attack it'll
look exactly the same afterwards."

Billy Connolly

On 14/04/18 19:06, Roger Hayter wrote:
wrote:

On Saturday, 14 April 2018 14:42:10 UTC+1, The Natural Philosopher wrote:

Most small mains transformers are run very close to core saturation, so
any large transients are likely to be clamped by the transformer.

Oh dear. A pseudo authoritative statement from someone who doesnt know
the difference between voltage and current.

So do you disagree with my claim that small transformers are usually
run close to core saturation at their rated voltage?

Do you disagree with my expectation that grossly overdriving such a
small transformer (with the transient to be measured) will cause its
output to saturate and give an incorrect measurement result?

Saturation results from current flow. If the transformer has a high
impedance across the secondary saturation will not happen. (The voltage
output may not be precise for other reasons, but should be good enough
for the sort of transients that are going to affect a heating element.)



This
could be overcome by putting a resistor in series with the transformer
primary so that it is running at a small fraction of mains voltage.
Have a load resistor on the secondary may improve the performance as well.

Oh dear. Soemone who doesnt understand inductance either.

What exactly do you object to here? A resistively loaded transformer
looks like a resistor (apart from the leakage inductance) so in
conjunction with a series input resistor it will form a reasonable
potential divider thereby moving the operation well away from
saturation.

Please explain.

John
The load resistor will not improve anything. The resistor in series
with the primary will just make accurate voltage measurement impossible
because of the poorly defined and frequency dependent primary impedance
while providing no benefits.

I admire your patience


--
"The great thing about Glasgow is that if there's a nuclear attack it'll
look exactly the same afterwards."

Billy Connolly

On 14/04/2018 13:29, tony sayer wrote:
A nodeMCU will almost certainly do everything you want including
logging to a remote database.

Problem is dealing with mains AC voltages and having to reduce them
first.




Isolating transformers isolate the mains and reduce them to safe levels.


Care to expand of that statement Dennis?..


What's to explain? they isolate the mains unlike autotransformers or
some other ways to drop mains voltage.
You aren't going to get a sever shock from a 6V isolating transformer
like you could from a potential divider using resistors.

On 13/04/2018 21:14, tony sayer wrote:



So let me get this right your trying to find out why a steam wallpaper
stripper is failing?.

I'd ask what make is it ?. Where is it made?

Modern Earlex, China I expect. 40 year old Earlex, UK I expect.

What's the actual specified mains voltage of the element in use for it?

220-240 volt

What the local mains voltage as measured over few days sampling

Today, it was 250. Sampling over a few days: THAT'S WHY I WANT A DATA LOGGER

and are
you in a rural overhead line fed area or urban underground?

As I said earlier, it's rural on overhead lines



And has the same thing happened to any like for like replacements?...

Half a dozen


Finally does it take any RCD trip out when it fails?.

Sometimes but not always. They are failing open circuit, some but not
all fail a megger test.

On Sat, 14 Apr 2018 09:28:08 -0700, jrwalliker wrote:

On Saturday, 14 April 2018 14:42:10 UTC+1, The Natural Philosopher
wrote:

Most small mains transformers are run very close to core saturation,
so any large transients are likely to be clamped by the transformer.

Oh dear. A pseudo authoritative statement from someone who doesnt know
the difference between voltage and current.

So do you disagree with my claim that small transformers are usually run
close to core saturation at their rated voltage?

Do you disagree with my expectation that grossly overdriving such a
small transformer (with the transient to be measured) will cause its
output to saturate and give an incorrect measurement result?

This
could be overcome by putting a resistor in series with the
transformer primary so that it is running at a small fraction of
mains voltage.
Have a load resistor on the secondary may improve the performance as
well.

Oh dear. Soemone who doesnt understand inductance either.

What exactly do you object to here? A resistively loaded transformer
looks like a resistor (apart from the leakage inductance) so in
conjunction with a series input resistor it will form a reasonable
potential divider thereby moving the operation well away from
saturation.

An effective way to avoid saturation issues when monitoring for
excessively high voltage excursions is to wire up an identical pair with
their 240v primaries in series and their low voltage (6 or 7 vac?)
secondaries in parallel (in phase current aiding) so as to help maintain
voltage balance between the primaries. Not only will this allow for 100%
excursions beyond the nominal 240vac supply, it should also allow high
frequency transients to be registered without molestation by saturation
effects. However, unless the transformers incorporate a 'grounded' inter
winding screen, high frequency transients can couple capacitively into
the secondary circuit, effectively magnifying their prominence.

If this is just a temporary setup, you can use a PC or laptop to record
the waveform using an audio recording application. Unless you need to
detect extremely high frequency transients, you can choose an 8 or 16 bit
mono sampling rate of 8 or 16 or 22.05 KHz to save disk space if planning
on logging for more than 12 hours worth (Heads Up! 24 hours in 16 bit
stereo at a 44.1KHz sample rate produces a 7GB file! DAMHIK, IJK).

If your main interest is checking for extreme voltage excursions rather
than high voltage spikes. adjust the recording level on the 50Hz
fundamental to -10dB FSD otherwise choose -20dB FSD if you're looking for
high voltage spikes (sub millisecond transients). A -10dB setting allows
you to see overvolting events just in excess of +200% and a -20dB setting
will let you identify spikes as large as 2.4KV without clipping (assuming
the transformer assembly can deal with such spikes).

A quick 'n' dirty way to check whether there were any 'events' worth
zooming in on, is to ask the audio app to calculate a normalisation
factor for the whole period. A normalisation factor of 9dB on a recording
level of -10dB FSD represents a 12.2% voltage boost. OTOH, a
normalisation boost value of 9.172dB represents a 10% overvolting event
on a -10dB recorded level.

HTH & GL!

--
Johnny B Good

In article ,
dennis@home wrote:
On 14/04/2018 13:29, tony sayer wrote:
A nodeMCU will almost certainly do everything you want including
logging to a remote database.

Problem is dealing with mains AC voltages and having to reduce them
first.




Isolating transformers isolate the mains and reduce them to safe levels.


Care to expand of that statement Dennis?..


What's to explain? they isolate the mains unlike autotransformers or
some other ways to drop mains voltage.
You aren't going to get a sever shock from a 6V isolating transformer
like you could from a potential divider using resistors.

a 6v transformer is just a transformer. Isolating transformers do just that
_ they isolate - mains level voltage on the output. Used to be an
essential workshop item when dealing withn live cahssis equipment.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

In article , newshound
wrote:
On 13/04/2018 21:14, tony sayer wrote:



So let me get this right your trying to find out why a steam wallpaper
stripper is failing?.

I'd ask what make is it ?. Where is it made?

Modern Earlex, China I expect. 40 year old Earlex, UK I expect.

What's the actual specified mains voltage of the element in use for it?

220-240 volt

What the local mains voltage as measured over few days sampling

Today, it was 250. Sampling over a few days: THAT'S WHY I WANT A DATA
LOGGER

and are
you in a rural overhead line fed area or urban underground?

As I said earlier, it's rural on overhead lines



And has the same thing happened to any like for like replacements?...

Half a dozen


Finally does it take any RCD trip out when it fails?.

Sometimes but not always. They are failing open circuit, some but not
all fail a megger test.

ask your supply co to install a voltage logger.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On 14/04/2018 21:12, charles wrote:
8

a 6v transformer is just a transformer. Isolating transformers do just that
_ they isolate - mains level voltage on the output. Used to be an
essential workshop item when dealing withn live cahssis equipment.


Not all transformers are isolating!
Why do you suppose I said an isolating transformer rather than an auto
transformer or any other type with a single coil?

On Saturday, 14 April 2018 19:29:43 UTC+1, The Natural Philosopher wrote:

The OP is convinced that slow voltage surges are the problem not
fast high-voltage transients. However, this is just an
assumption - there might be fast transients causing insulation
breakdown. Nobody actually knows.

Therefore it would make sense to try and achieve a reasonable
bandwidth if it can be done with little extra effort.

It might be something completely different such as corrosion of the
elements.

Its an interesting problem. I will have a rummage around for a
suitable transformer and make some measurements and report back
in a few days.

John

dennis@home wrote:

On 14/04/2018 21:12, charles wrote:
8

a 6v transformer is just a transformer. Isolating transformers do just that
_ they isolate - mains level voltage on the output. Used to be an
essential workshop item when dealing withn live cahssis equipment.


Not all transformers are isolating!
Why do you suppose I said an isolating transformer rather than an auto
transformer or any other type with a single coil?

Not all, but nearly all! Except for special applications for
autotransformers, most applications require not only isolation but an
insulation resistance tested to some insulation resistance standards,
if only to avoid killing people who touch the secondary circuit and/or
tripping RCDs when the secondary circuit is permanently or transiently
connected to earth. Reference to an "isolating transformer" tends to
imply one used *only* for isolation with a one to one ratio of turns.


--

Roger Hayter

On Saturday, 14 April 2018 21:03:15 UTC+1, Johnny B Good wrote:

An effective way to avoid saturation issues when monitoring for
excessively high voltage excursions is to wire up an identical pair with
their 240v primaries in series and their low voltage (6 or 7 vac?)
secondaries in parallel (in phase current aiding) so as to help maintain
voltage balance between the primaries. Not only will this allow for 100%
excursions beyond the nominal 240vac supply, it should also allow high
frequency transients to be registered without molestation by saturation
effects. However, unless the transformers incorporate a 'grounded' inter
winding screen, high frequency transients can couple capacitively into
the secondary circuit, effectively magnifying their prominence.

A very good approach if two identical transformers are available.

John

wrote:

On Saturday, 14 April 2018 19:29:43 UTC+1, The Natural Philosopher wrote:

The OP is convinced that slow voltage surges are the problem not
fast high-voltage transients. However, this is just an
assumption - there might be fast transients causing insulation
breakdown. Nobody actually knows.

Therefore it would make sense to try and achieve a reasonable
bandwidth if it can be done with little extra effort.

It might be something completely different such as corrosion of the
elements.

Its an interesting problem. I will have a rummage around for a
suitable transformer and make some measurements and report back
in a few days.

John

Just to generalise, and by no means to accuse the OP, the commonest
cause of submerged element failure is probably allowing the water level
to get too low, or possibly displaced sideways if the vessel is not kept
horizontal.


--

Roger Hayter

Roger Hayter wrote:

dennis@home wrote:

On 14/04/2018 21:12, charles wrote:
8

a 6v transformer is just a transformer. Isolating transformers do just
that _ they isolate - mains level voltage on the output. Used to be
an essential workshop item when dealing withn live cahssis equipment.


Not all transformers are isolating!
Why do you suppose I said an isolating transformer rather than an auto
transformer or any other type with a single coil?

Not all, but nearly all! Except for special applications for
autotransformers, most applications require not only isolation but an
insulation resistance tested to some insulation resistance standards,
if only to avoid killing people who touch the secondary circuit and/or
tripping RCDs when the secondary circuit is permanently or transiently
connected to earth. Reference to an "isolating transformer" tends to
imply one used *only* for isolation with a one to one ratio of turns.

FAOD, I should have said nearly all *mains* transformers. There are of
course other kinds.


--

Roger Hayter

On Sat, 14 Apr 2018 21:13:38 +0100, charles wrote:

ask your supply co to install a voltage logger.

Just report the "high" voltage, 250 is only 3 short of the permitted
maximum. The DNO for here jumps pretty damn quickly at reports of
wide voltage variation and/or approaching the limits.

If they do install a logger you don't get to see the data.

High voltage will shorten the life incandescant bulbs quite a bit. We
used to get through a bulb every week or two. Bought a UPS plugged it
in it went straight into voltage reduction mode. Measured voltage,
250 ish, rang DNO, engineer at door two hours later, transformer
tapping adjusted next or the day after, bulb consumption fell
noticabley...

I wouldn't expect a 1? 2? kW water heating element to be as sensitive
to voltage as light bulbs unless it's really cheap and nasty. Or made
such that 240 is the max rather than nominal voltage...

--
Cheers
Dave.

On 14/04/18 21:03, Johnny B Good wrote:
An effective way to avoid saturation issues

THERE ARE NO SATURATION ISSUES UNTIL CURRENT IS DRAWN

WE ARE NOT DRAWING POWER

--
€œIt is hard to imagine a more stupid decision or more dangerous way of
making decisions than by putting those decisions in the hands of people
who pay no price for being wrong.€�

Thomas Sowell

On 14/04/18 23:35, wrote:
On Saturday, 14 April 2018 21:03:15 UTC+1, Johnny B Good wrote:

An effective way to avoid saturation issues when monitoring for
excessively high voltage excursions is to wire up an identical pair with
their 240v primaries in series and their low voltage (6 or 7 vac?)
secondaries in parallel (in phase current aiding) so as to help maintain
voltage balance between the primaries. Not only will this allow for 100%
excursions beyond the nominal 240vac supply, it should also allow high
frequency transients to be registered without molestation by saturation
effects. However, unless the transformers incorporate a 'grounded' inter
winding screen, high frequency transients can couple capacitively into
the secondary circuit, effectively magnifying their prominence.

A very good approach if two identical transformers are available.

THis is like renewable energy.

Solving nonexistent problems in the most expensive and complicated way
possible

It's a CRAP approach


John



--
€œIt is hard to imagine a more stupid decision or more dangerous way of
making decisions than by putting those decisions in the hands of people
who pay no price for being wrong.€�

Thomas Sowell

On 14/04/2018 23:42, Roger Hayter wrote:
Roger Hayter wrote:

dennis@home wrote:

On 14/04/2018 21:12, charles wrote:
8

a 6v transformer is just a transformer. Isolating transformers do just
that _ they isolate - mains level voltage on the output. Used to be
an essential workshop item when dealing withn live cahssis equipment.


Not all transformers are isolating!
Why do you suppose I said an isolating transformer rather than an auto
transformer or any other type with a single coil?

Not all, but nearly all! Except for special applications for
autotransformers, most applications require not only isolation but an
insulation resistance tested to some insulation resistance standards,
if only to avoid killing people who touch the secondary circuit and/or
tripping RCDs when the secondary circuit is permanently or transiently
connected to earth. Reference to an "isolating transformer" tends to
imply one used *only* for isolation with a one to one ratio of turns.

FAOD, I should have said nearly all *mains* transformers. There are of
course other kinds.



You can say what you like now, but this is a DIY group and some people
won't know what an isolating transformer does or why to use one. Only a
fool expects everyone in a public audience to understand what they say.
Don't give out advice on dangerous stuff unless you make it clear.

Its the same with the advice for 12V supplies people give out, there are
12V supplies that are isolated from the mains but there are some that
aren't and you really don't want the ones that aren't for "projects".
Its hard to tell on ebay/amazon what is and isn't live so I tend not to
buy them when cpc is just as cheap.

The Natural Philosopher wrote:

On 14/04/18 21:03, Johnny B Good wrote:
An effective way to avoid saturation issues

THERE ARE NO SATURATION ISSUES UNTIL CURRENT IS DRAWN

WE ARE NOT DRAWING POWER

Absolutely. The only reason for using a transformer capable of
supplying significant power is to obtain one with proper mains voltage
insulation. Otherwise any small signal 50:1 transformer with a suitable
low frequency bandwidth would do the job.


--

Roger Hayter

On 14/04/2018 23:59, Dave Liquorice wrote:
On Sat, 14 Apr 2018 21:13:38 +0100, charles wrote:

ask your supply co to install a voltage logger.

Just report the "high" voltage, 250 is only 3 short of the permitted
maximum. The DNO for here jumps pretty damn quickly at reports of
wide voltage variation and/or approaching the limits.

If they do install a logger you don't get to see the data.

High voltage will shorten the life incandescant bulbs quite a bit. We
used to get through a bulb every week or two. Bought a UPS plugged it
in it went straight into voltage reduction mode. Measured voltage,
250 ish, rang DNO, engineer at door two hours later, transformer
tapping adjusted next or the day after, bulb consumption fell
noticabley...

I wouldn't expect a 1? 2? kW water heating element to be as sensitive
to voltage as light bulbs unless it's really cheap and nasty. Or made
such that 240 is the max rather than nominal voltage...

This is one of the mysteries, there are a couple of incandescent bulbs
and AFAIK they are not prone to failure. These are 2.3 kW heaters. As an
alternative to logging data, I suppose I could knock up a diac/triac
"dimmer" to drop the power by (say) 10%.

On 15/04/2018 12:12, newshound wrote:
On 14/04/2018 23:59, Dave Liquorice wrote:
On Sat, 14 Apr 2018 21:13:38 +0100, charles wrote:

ask your supply co to install a voltage logger.

Just report the "high" voltage, 250 is only 3 short of the permitted
maximum. The DNO for here jumps pretty damn quickly at reports of
wide voltage variation and/or approaching the limits.

If they do install a logger you don't get to see the data.

High voltage will shorten the life incandescant bulbs quite a bit. We
used to get through a bulb every week or two. Bought a UPS plugged it
in it went straight into voltage reduction mode. Measured voltage,
250 ish, rang DNO, engineer at door two hours later, transformer
tapping adjusted next or the day after, bulb consumption fell
noticabley...

I wouldn't expect a 1? 2? kW water heating element to be as sensitive
to voltage as light bulbs unless it's really cheap and nasty. Or made
such that 240 is the max rather than nominal voltage...

This is one of the mysteries, there are a couple of incandescent bulbs
and AFAIK they are not prone to failure. These are 2.3 kW heaters. As an
alternative to logging data, I suppose I could knock up a diac/triac
"dimmer" to drop the power by (say) 10%.

I'm with Dave here. As long as the unit doesn't become dry I wouldn't
expect it to be sensitive on voltage. Methinks a failing batch.

The fact incandescent bulbs can cope with the higher voltage just
confirms these thoughts.

It is possible your DVM reads high. Some are very poor at measuring rms
voltage.

On 14/04/2018 23:42, Roger Hayter wrote:
wrote:

On Saturday, 14 April 2018 19:29:43 UTC+1, The Natural Philosopher wrote:

The OP is convinced that slow voltage surges are the problem not
fast high-voltage transients. However, this is just an
assumption - there might be fast transients causing insulation
breakdown. Nobody actually knows.

Therefore it would make sense to try and achieve a reasonable
bandwidth if it can be done with little extra effort.

It might be something completely different such as corrosion of the
elements.

Its an interesting problem. I will have a rummage around for a
suitable transformer and make some measurements and report back
in a few days.

John

Just to generalise, and by no means to accuse the OP, the commonest
cause of submerged element failure is probably allowing the water level
to get too low, or possibly displaced sideways if the vessel is not kept
horizontal.


You are both making reasonable points. Roger, I don't *think* we are
suffering from low water level or tilting, but this is something that I
can't be absolutely certain about. John, I don't *think* it is fast
transients causing insulation failure because then I would be expecting
it to "blow" other stuff like fluorescent lights, phone chargers, the
electronics of the washing machine, etc. But I could be wrong. I
originally thought it must be something in the local water chemistry.
Seeing 250 volts on my single measurement makes me more inclined to
think it is worth doing some logging.

On 15/04/2018 12:19, Fredxx wrote:
On 15/04/2018 12:12, newshound wrote:
On 14/04/2018 23:59, Dave Liquorice wrote:
On Sat, 14 Apr 2018 21:13:38 +0100, charles wrote:

ask your supply co to install a voltage logger.

Just report the "high" voltage, 250 is only 3 short of the permitted
maximum. The DNO for here jumps pretty damn quickly at reports of
wide voltage variation and/or approaching the limits.

If they do install a logger you don't get to see the data.

High voltage will shorten the life incandescant bulbs quite a bit. We
used to get through a bulb every week or two. Bought a UPS plugged it
in it went straight into voltage reduction mode. Measured voltage,
250 ish, rang DNO, engineer at door two hours later, transformer
tapping adjusted next or the day after, bulb consumption fell
noticabley...

I wouldn't expect a 1? 2? kW water heating element to be as sensitive
to voltage as light bulbs unless it's really cheap and nasty. Or made
such that 240 is the max rather than nominal voltage...

This is one of the mysteries, there are a couple of incandescent bulbs
and AFAIK they are not prone to failure. These are 2.3 kW heaters. As
an alternative to logging data, I suppose I could knock up a
diac/triac "dimmer" to drop the power by (say) 10%.

I'm with Dave here. As long as the unit doesn't become dry I wouldn't
expect it to be sensitive on voltage. Methinks a failing batch.

The fact incandescent bulbs can cope with the higher voltage just
confirms these thoughts.

It is possible your DVM reads high. Some are very poor at measuring rms
voltage.

This one read 240V at home. But I will try again with the Robin PSC/loop
tester which is probably more accurate.

On Sun, 15 Apr 2018 10:17:43 +0100, Roger Hayter wrote:

The Natural Philosopher wrote:

On 14/04/18 21:03, Johnny B Good wrote:
An effective way to avoid saturation issues

THERE ARE NO SATURATION ISSUES UNTIL CURRENT IS DRAWN

Which statement is total and utter ********. :-)


WE ARE NOT DRAWING POWER

Essentially true in this case but totally beside the point.


Absolutely. The only reason for using a transformer capable of
supplying significant power is to obtain one with proper mains voltage
insulation. Otherwise any small signal 50:1 transformer with a suitable
low frequency bandwidth would do the job.

Wow! Here's me thinking that it's only TNP that doesn't properly
understand basic electrical theory. :-)

Saturation issues have nothing to do with drawing power via a
transformer's secondary. The problem arises out of the magnetization
current increasing (due to either insufficient turns or else,
equivalently, excess voltage) to the point that the magnetic flux in the
core reaches a level that saturates the magnetic core material used.

There is an art to manufacturing an old fashioned wallwart transformer
as cheaply as possible such as those often hot running chinese wallwarts
where they've calculated not only the thinnest of wire to be used but
also the minimum number of turns required for the nominal voltage rating
without inducing excessive saturation effects. As a consequence, such
transformer designs leave no margin whatsoever for over-volting events in
the mains supply.

The heating effect in such transformers under no-load conditions is
typically a watt or two both from I squared losses due to the saturation
peaks causing transient reductions in the primary inductance which
results in corresponding current spikes and the increased hysteresis
losses in the core material itself.

In my search to find some figures on the magnitude of 'magnetisation
current' compared to the full load current, I noticed some interesting
animated graphs of core saturation effects in this wikipedia article

https://en.wikipedia.org/wiki/Transformer#Real_transformer.

Unfortunately, I wasn't able to find figures for transformer
magnetisation current which ISTR as being typically an order of magnitude
or so less than that due to their maximum load current ratings.

Using a pair of transformers wired as I suggested is an effective way to
eliminate any question regarding transformer saturation effects for the
sort of over-volting events being monitored. It's an arrangement that
allows for a 100% over-volting event to be measured without saturation
effects spoiling the integrity of the measurement of an event that would
instantly fry incandescent lamps and heater elements alike.

It doesn't matter that the transformers are only operating at half their
designed voltage rating. The arbitrarily low secondary voltage is simply
a faithful, low voltage, galvanically isolated replica of the mains
voltage being monitored anyway, the level of which will be calibrated so
that 240v corresponds to -10 or -20 dB of FSD in the audio recording
itself. Using an audio recording application to log the mains waveform is
just a quick 'n' dirty way to see whether or not there is anything of
interest to be logged in the first place.

--
Johnny B Good

On 16/04/18 00:54, Johnny B Good wrote:
On Sun, 15 Apr 2018 10:17:43 +0100, Roger Hayter wrote:

The Natural Philosopher wrote:

On 14/04/18 21:03, Johnny B Good wrote:
An effective way to avoid saturation issues

THERE ARE NO SATURATION ISSUES UNTIL CURRENT IS DRAWN

Which statement is total and utter ********. :-)


WE ARE NOT DRAWING POWER

Essentially true in this case but totally beside the point.


Absolutely. The only reason for using a transformer capable of
supplying significant power is to obtain one with proper mains voltage
insulation. Otherwise any small signal 50:1 transformer with a suitable
low frequency bandwidth would do the job.

Wow! Here's me thinking that it's only TNP that doesn't properly
understand basic electrical theory. :-)

Saturation issues have nothing to do with drawing power via a
transformer's secondary. The problem arises out of the magnetization
current increasing (due to either insufficient turns or else,
equivalently, excess voltage) to the point that the magnetic flux in the
core reaches a level that saturates the magnetic core material used.

There is an art to manufacturing an old fashioned wallwart transformer
as cheaply as possible such as those often hot running chinese wallwarts
where they've calculated not only the thinnest of wire to be used but
also the minimum number of turns required for the nominal voltage rating
without inducing excessive saturation effects. As a consequence, such
transformer designs leave no margin whatsoever for over-volting events in
the mains supply.

The heating effect in such transformers under no-load conditions is
typically a watt or two both from I squared losses due to the saturation
peaks causing transient reductions in the primary inductance which
results in corresponding current spikes and the increased hysteresis
losses in the core material itself.

In my search to find some figures on the magnitude of 'magnetisation
current' compared to the full load current, I noticed some interesting
animated graphs of core saturation effects in this wikipedia article

https://en.wikipedia.org/wiki/Transformer#Real_transformer.

Unfortunately, I wasn't able to find figures for transformer
magnetisation current which ISTR as being typically an order of magnitude
or so less than that due to their maximum load current ratings.

Using a pair of transformers wired as I suggested is an effective way to
eliminate any question regarding transformer saturation effects for the
sort of over-volting events being monitored. It's an arrangement that
allows for a 100% over-volting event to be measured without saturation
effects spoiling the integrity of the measurement of an event that would
instantly fry incandescent lamps and heater elements alike.

It doesn't matter that the transformers are only operating at half their
designed voltage rating. The arbitrarily low secondary voltage is simply
a faithful, low voltage, galvanically isolated replica of the mains
voltage being monitored anyway, the level of which will be calibrated so
that 240v corresponds to -10 or -20 dB of FSD in the audio recording
itself. Using an audio recording application to log the mains waveform is
just a quick 'n' dirty way to see whether or not there is anything of
interest to be logged in the first place.

I give up. What is the use of a degree in it and a year spent designing
transformers?


--
Canada is all right really, though not for the whole weekend.

"Saki"

In article , dennis@home
scribeth thus
On 14/04/2018 13:29, tony sayer wrote:
A nodeMCU will almost certainly do everything you want including
logging to a remote database.

Problem is dealing with mains AC voltages and having to reduce them
first.




Isolating transformers isolate the mains and reduce them to safe levels.


Care to expand of that statement Dennis?..


What's to explain? they isolate the mains unlike autotransformers or
some other ways to drop mains voltage.
You aren't going to get a sever shock from a 6V isolating transformer
like you could from a potential divider using resistors.

Isolating transformers are generally known to isolate a direct mains
connection.....
--
Tony Sayer

In article , charles
scribeth thus
In article ,
dennis@home wrote:
On 14/04/2018 13:29, tony sayer wrote:
A nodeMCU will almost certainly do everything you want including
logging to a remote database.

Problem is dealing with mains AC voltages and having to reduce them
first.




Isolating transformers isolate the mains and reduce them to safe levels.


Care to expand of that statement Dennis?..


What's to explain? they isolate the mains unlike autotransformers or
some other ways to drop mains voltage.
You aren't going to get a sever shock from a 6V isolating transformer
like you could from a potential divider using resistors.

a 6v transformer is just a transformer. Isolating transformers do just that
_ they isolate - mains level voltage on the output. Used to be an
essential workshop item when dealing withn live cahssis equipment.


Indeed they were, still got one 240 in and 240 out at around 5 kW..
--
Tony Sayer

In article , tony sayer
wrote:
In article , charles
scribeth thus
In article , dennis@home
wrote:
On 14/04/2018 13:29, tony sayer wrote:
A nodeMCU will almost certainly do everything you want including
logging to a remote database.

Problem is dealing with mains AC voltages and having to reduce
them first.




Isolating transformers isolate the mains and reduce them to safe
levels.


Care to expand of that statement Dennis?..


What's to explain? they isolate the mains unlike autotransformers or
some other ways to drop mains voltage. You aren't going to get a sever
shock from a 6V isolating transformer like you could from a potential
divider using resistors.

a 6v transformer is just a transformer. Isolating transformers do just
that _ they isolate - mains level voltage on the output. Used to be an
essential workshop item when dealing withn live cahssis equipment.


Indeed they were, still got one 240 in and 240 out at around 5 kW..

Mine's not a big as that, but still quite heavy.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On Friday, 13 April 2018 20:45:16 UTC+1, Cursitor Doom wrote:
On Fri, 13 Apr 2018 07:38:11 -0700, whisky-dave wrote:

Problem is dealing with mains AC voltages and having to reduce them
first.

Not really. Loads of suitable sub-min mains transformers in every local
recycling site; help yourself for free. Or just a couple of quid new from
China through Ebay.

All you do then is reducing the overvolage to a level you might not detect with an ardunio.

On 16/04/18 11:24, whisky-dave wrote:
On Friday, 13 April 2018 20:45:16 UTC+1, Cursitor Doom wrote:
On Fri, 13 Apr 2018 07:38:11 -0700, whisky-dave wrote:

Problem is dealing with mains AC voltages and having to reduce them
first.

Not really. Loads of suitable sub-min mains transformers in every local
recycling site; help yourself for free. Or just a couple of quid new from
China through Ebay.

All you do then is reducing the overvolage to a level you might not detect with an ardunio.


????

Hsa the government been putting somnething in the water supply?


--
"In our post-modern world, climate science is not powerful because it is
true: it is true because it is powerful."

Lucas Bergkamp

On Friday, 13 April 2018 22:22:14 UTC+1, dennis@home wrote:
On 13/04/2018 15:38, whisky-dave wrote:
On Friday, 13 April 2018 15:23:29 UTC+1, dennis@home wrote:
On 13/04/2018 10:24, newshound wrote:
On 13/04/2018 07:48, Halmyre wrote:
On Thursday, April 12, 2018 at 1:59:45 PM UTC+1, newshound
wrote:
On 12/04/2018 12:51, The Nomad wrote:
On Thu, 12 Apr 2018 12:37:06 +0100, newshound
wrote:

For reasons I won't bore you with, I'm interested in
building a cheap, simple data logger to monitor mains
voltage, ideally two channels (live to earth and neutral
to earth). In the dim and distant past I have designed
and built such things more or less from scratch, but
surely someone has already done this.

I havn't used either Arduino or Pi before, but I assume
one or other would be the obvious starting point.

However ATM google isn't giving me a strong lead.
Thoughts?

A quick google came up with:

https://openenergymonitor.org/forum-archive/node/58.html

https://circuitdigest.com/microcontroller-projects/arduino-ac-voltmeter




https://www.briandorey.com/post/ardu...e-and-current-
logging

Avpx

Thanks, that second one looks like a good basis.

Won't the capacitor smooth out any transients you might want to
observe?

I am looking for transients longer than maybe a second or so.
Obviously, might need to experiment with capacitors a bit.

You need a simple mains transformer to a few volts and feed it
into the A-D converter on an arduino and do some maths on the
samples.

How often will it sample and what sort levels of spikes and
transcients. And don't forget the ADC can only really 'see' DC
voltages.

AC is just DC with an offset.

Yeah sure it is.

Idiot.

In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction.


Offset has nothing to do with it.


Only a couple of resistors required to set the voltage range to be
within the ADC input range.

doesn't help much though, in fact depending on these spikes you might
not 'see' much after reducing it through a transformer and
rectifier.

So we have something else you don't know much about.

but still a lot more than you do.
DC is NOT AC with an offset.


A nodeMCU will almost certainly do everything you want including
logging to a remote database.

Problem is dealing with mains AC voltages and having to reduce them
first.


Isolating transformers isolate the mains and reduce them to safe levels.

Isoltaing transformers isolate that is why they are called Isolating
transformers. It is NOT always about reducing to a safe level, because there are pulse isolating transformer nothing to do woith isolating for safety reasons.

http://uk.farnell.com/wurth-elektronik/760301301/gate-driv-transfrmr-1-1-1-750uh/dp/2431618?mckv=z8r992i2_dc|pcrid|78108291069|&gross_ price=true&CATCI=pla-131232739029&CAAGID=14983516629&CMP=KNC-GUK-GEN-SHOPPING-WURTH_ELEKTRONIK&CAGPSPN=pla&gclid=EAIaIQobChMIyIX t7cu-2gIVY7HtCh3HSw7qEAQYASABEgJiZvD_BwE&CAWELAID=12017 3390000290019

No who knows nothing.
isolating transformers aren't just about safer voltages.

On Saturday, 14 April 2018 20:39:07 UTC+1, newshound wrote:
On 13/04/2018 21:14, tony sayer wrote:



So let me get this right your trying to find out why a steam wallpaper
stripper is failing?.

I'd ask what make is it ?. Where is it made?

Modern Earlex, China I expect. 40 year old Earlex, UK I expect.

What's the actual specified mains voltage of the element in use for it?

220-240 volt

What the local mains voltage as measured over few days sampling

Today, it was 250. Sampling over a few days: THAT'S WHY I WANT A DATA LOGGER

A data logger won;t fix the problem, niether will buying an ardunio whether it's fakeardunio from ebay or the latest verion with wifi/bluetooth it'll be a waste of money, if you know you have 250V when you should really only have 230V then that is what needs sorting, an ardunio can't sort this problem out.



and are
you in a rural overhead line fed area or urban underground?

As I said earlier, it's rural on overhead lines

Perhaps you need a flying ardunio then ;-)


And has the same thing happened to any like for like replacements?...

Half a dozen

time to stop measuring the problem and start sorting it.


Finally does it take any RCD trip out when it fails?.

Sometimes but not always. They are failing open circuit, some but not
all fail a megger test.

On Monday, 16 April 2018 11:30:35 UTC+1, The Natural Philosopher wrote:
On 16/04/18 11:24, whisky-dave wrote:
On Friday, 13 April 2018 20:45:16 UTC+1, Cursitor Doom wrote:
On Fri, 13 Apr 2018 07:38:11 -0700, whisky-dave wrote:

Problem is dealing with mains AC voltages and having to reduce them
first.

Not really. Loads of suitable sub-min mains transformers in every local
recycling site; help yourself for free. Or just a couple of quid new from
China through Ebay.

All you do then is reducing the overvolage to a level you might not detect with an ardunio.


????

Hsa the government been putting somnething in the water supply?

Not sure who puts stuff in the water.

On Mon, 16 Apr 2018 11:04:01 +0100, charles wrote:

In article , tony sayer

wrote:
In article , charles
scribeth thus
In article , dennis@home
wrote:
On 14/04/2018 13:29, tony sayer wrote:
A nodeMCU will almost certainly do everything you want
including logging to a remote database.

Problem is dealing with mains AC voltages and having to reduce
them first.




Isolating transformers isolate the mains and reduce them to safe
levels.


Care to expand of that statement Dennis?..


What's to explain? they isolate the mains unlike autotransformers or
some other ways to drop mains voltage. You aren't going to get a
sever shock from a 6V isolating transformer like you could from a
potential divider using resistors.

a 6v transformer is just a transformer. Isolating transformers do just
that _ they isolate - mains level voltage on the output. Used to be
an essential workshop item when dealing withn live cahssis equipment.


Indeed they were, still got one 240 in and 240 out at around 5 kW..

Mine's not a big as that, but still quite heavy.

Heavy! I should say so! Based on my collection of 360VA transformers
which each weigh 16 Lbs or so. I'd estimate a 'Ballpark' figure for that
5KVA transformer to be somewhere around a couple of CWT! :-)

--
Johnny B Good

"whisky-dave" wrote in message
...
Today, it was 250. Sampling over a few days: THAT'S WHY I WANT A DATA
LOGGER

A data logger won;t fix the problem, niether will buying an ardunio
whether it's fakeardunio from ebay or the latest verion with
wifi/bluetooth it'll be a waste of money, if you know you have 250V when
you should really only have 230V then that is what needs sorting, an
ardunio can't sort this problem out.

It doesn't *solve* the problem, but it supplies evidence of the fact that
there is a problem and the times when it occurs, which will (hopefully)
persuade the electricity supply company to investigate and rectify.

What intrigues me is that a fairly small over-voltage of 10V (*) is shorting
the life of the wallpaper stripper element so much. You'd expect other
heating elements (kettle, immersion heater, electric fire, cooker) would
suffer the same fate.


(*) http://www.twothirtyvolts.org.uk/pdf...n_230Volts.pdf says
230V + 6% -10% (so 216V to 253V) with a nominal voltage of 240V