A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth? This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

Little more than a scam


NT

On 22/10/2014 16:35, wrote:
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

Thanks. Not saying you are wrong, but I would have *thought* they would
have reasonable isolation between the two "sides".

It is this sort of thing

http://www.ebay.co.uk/itm/Durable-Ne...item3a89ecf7eb

except that if they came from Hong Kong, it was via Farness or RS.

On Wednesday, October 22, 2014 4:48:17 PM UTC+1, newshound wrote:
On 22/10/2014 16:35, wrote:
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

Thanks. Not saying you are wrong, but I would have *thought* they would
have reasonable isolation between the two "sides".
It is this sort of thing
http://www.ebay.co.uk/itm/Durable-Ne...item3a89ecf7eb
except that if they came from Hong Kong, it was via Farness or RS.

I dont see how relay isolation comes into it


NT

On 22/10/2014 18:28, wrote:
On Wednesday, October 22, 2014 4:48:17 PM UTC+1, newshound wrote:
On 22/10/2014 16:35, wrote:
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

Thanks. Not saying you are wrong, but I would have *thought* they would
have reasonable isolation between the two "sides".
It is this sort of thing
http://www.ebay.co.uk/itm/Durable-Ne...item3a89ecf7eb
except that if they came from Hong Kong, it was via Farness or RS.

I dont see how relay isolation comes into it


NT

Sorry, I thought you were implying that the high current on the
electronic "contacts" side of the relay was causing a high current or
voltage on the "virtual coil" side, the part which is connected directly
to the temperature controller. Ultimately the "mains" all comes from the
same consumer unit, but there are separate MCBs for each heater and for
the temperature controller. So if the heater element failure leads to
the busbar voltage bouncing around, that gets fed to the controller via
its MCB. Which is why I wondered whether a suppressor in that line might
help.

On Wednesday, October 22, 2014 6:50:21 PM UTC+1, newshound wrote:
On 22/10/2014 18:28, wrote:
On Wednesday, October 22, 2014 4:48:17 PM UTC+1, newshound wrote:
On 22/10/2014 16:35, wrote:
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

Thanks. Not saying you are wrong, but I would have *thought* they would
have reasonable isolation between the two "sides".
It is this sort of thing
http://www.ebay.co.uk/itm/Durable-Ne...item3a89ecf7eb
except that if they came from Hong Kong, it was via Farness or RS.

I dont see how relay isolation comes into it

Sorry, I thought you were implying that the high current on the
electronic "contacts" side of the relay was causing a high current or
voltage on the "virtual coil" side, the part which is connected directly
to the temperature controller. Ultimately the "mains" all comes from the
same consumer unit, but there are separate MCBs for each heater and for
the temperature controller. So if the heater element failure leads to
the busbar voltage bouncing around, that gets fed to the controller via
its MCB. Which is why I wondered whether a suppressor in that line might
help.

Insulation failure - excess current - dead relay. Simples.
If you do the maths on the surge idea you'll see its impossible.


NT

"newshound" wrote in message
o.uk...
On 22/10/2014 18:28, wrote:
On Wednesday, October 22, 2014 4:48:17 PM UTC+1, newshound wrote:
On 22/10/2014 16:35, wrote:
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a
bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its
fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

Thanks. Not saying you are wrong, but I would have *thought* they would
have reasonable isolation between the two "sides".
It is this sort of thing
http://www.ebay.co.uk/itm/Durable-Ne...item3a89ecf7eb
except that if they came from Hong Kong, it was via Farness or RS.

I dont see how relay isolation comes into it


NT

Sorry, I thought you were implying that the high current on the electronic
"contacts" side of the relay was causing a high current or voltage on the
"virtual coil" side, the part which is connected directly to the
temperature controller. Ultimately the "mains" all comes from the same
consumer unit, but there are separate MCBs for each heater and for the
temperature controller. So if the heater element failure leads to the
busbar voltage bouncing around,

That wouldn't happen with a resistive load like a heater.

that gets fed to the controller via its MCB.

The most it might see is a sag of the voltage as the element blows.
That shouldn't do it any harm with a controller.

Which is why I wondered whether a suppressor in that line might help.

No it wont. They don't do anything about sags in voltage.

The most they do is clip spikes and there shouldn't
be any spikes caused by the element failing to earth.

The failure of the ssrelay due to the element failing
may have killed the controller if you cant even turn
the controller on anymore. If you can still turn it on
but it no longer controls the load, its just the ssrelay
that's flailed on the overload as the element failed.

wrote in message
...
On Wednesday, October 22, 2014 4:48:17 PM UTC+1, newshound wrote:
On 22/10/2014 16:35, wrote:
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a
bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its
fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

Thanks. Not saying you are wrong, but I would have *thought* they would
have reasonable isolation between the two "sides".
It is this sort of thing
http://www.ebay.co.uk/itm/Durable-Ne...item3a89ecf7eb
except that if they came from Hong Kong, it was via Farness or RS.

I dont see how relay isolation comes into it

I assumed he meant that the controller is now completely
dead and that you cant even get it to come on anymore.

Instead of still coming on fine, but no longer
switching the load because the ssrelay has died.

On Wed, 22 Oct 2014 16:48:14 +0100, newshound
wrote:

On 22/10/2014 16:35, wrote:
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

Thanks. Not saying you are wrong, but I would have *thought* they would
have reasonable isolation between the two "sides".

It is this sort of thing

http://www.ebay.co.uk/itm/Durable-Ne...item3a89ecf7eb

except that if they came from Hong Kong, it was via Farness or RS.

Presumably you meant Shenzhen Farness Technology Co. Ltd., in which
case they probably _did_ come from Hong Kong.
--
J B Good

newshound wrote
wrote
newshound wrote

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

Thanks. Not saying you are wrong, but I would have *thought* they would
have reasonable isolation between the two "sides".

Not with the crap from china.

It is this sort of thing

http://www.ebay.co.uk/itm/Durable-Ne...item3a89ecf7eb

except that if they came from Hong Kong, it was via Farness or RS.

To protect from a short you need a very fast switch, but often when
elements start to faile the rise in current is not instant and it can cook
devices and make them fail that way.The best thing is some kind of current
monitor on each element I'd imagine.

As for suppressors. These are usually just inductive and capacitive filters
to try to stop switch transients and in the more modern machines, digital
and thyristor noises from going back into the mains.
In my view such things should already be in the in any case.


I had a thought, with all the current rubbish powerline adaptors for running
networks over mains cables, perhaps one could get a l plug in device to
render them useless on your mains phase and put an end to the interference
and make people use proper networks.
Brian

--
From the Sofa of Brian Gaff Reply address is active
wrote in message
...
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

Little more than a scam


NT

Brian Gaff wrote

To protect from a short you need a very fast switch, but often when
elements start to faile the rise in current is not instant and it can cook
devices and make them fail that way.

With a well designed controller it shouldn’t kill the controller.

The best thing is some kind of current monitor on each element I'd
imagine.

That's obviously one way.

As for suppressors. These are usually just inductive and capacitive
filters to try to stop switch transients and in the more modern machines,
digital and thyristor noises from going back into the mains.

And doesn’t do a damned thing about the
mains sagging due to a short in the element.

In my view such things should already be in the in any case.

Not that easy to do with small controllers tho.

I had a thought,

Too radical by far. n

with all the current rubbish powerline adaptors for running networks over
mains cables, perhaps one could get a l plug in device to render them
useless on your mains phase and put an end to the interference and make
people use proper networks.

Not even possible to do that with someone else's house wiring.


wrote in message
...
On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

Little more than a scam


NT

writes:

On Wednesday, October 22, 2014 4:32:02 PM UTC+1, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth?

No, its overload current flowing thru the ssrelay.

This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

Little more than a scam

I've had a couple of electronic timers start to act erratically when
used with washer or dryer. Probably because of sensitivity to spikes
caused by the appliance.
So in that limited case, suppressors might help.

--
Windmill, Use t m i l l
J.R.R. Tolkien:- @ S c o t s h o m e . c o m
All that is gold does not glister / Not all who wander are lost

On 22/10/2014 16:32, newshound wrote:
A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth? This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

They do not provide much protection. Little more than a scam.
--
Peter Crosland

Reply address is valid

On 22/10/2014 19:41, Peter Crosland wrote:
On 22/10/2014 16:32, newshound wrote:
A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth? This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

They do not provide much protection. Little more than a scam.

Given that washing machines, dishwashers, tumble dryers are built down
to a price in a very competitive market, I wonder why the (presumably
competent) designers include them. (I could believe it is driven by RFI).

On Wednesday, October 22, 2014 7:50:52 PM UTC+1, newshound wrote:
On 22/10/2014 19:41, Peter Crosland wrote:
On 22/10/2014 16:32, newshound wrote:

A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth? This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

They do not provide much protection. Little more than a scam.

Given that washing machines, dishwashers, tumble dryers are built down
to a price in a very competitive market, I wonder why the (presumably
competent) designers include them. (I could believe it is driven by RFI).

They mostly don't include them. When they are used they're part of a circuit that does something of use and works, very different to simply sticking one across the mains and being excessively optimistic.


NT

"newshound" wrote in message
o.uk...
On 22/10/2014 19:41, Peter Crosland wrote:
On 22/10/2014 16:32, newshound wrote:
A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth? This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

They do not provide much protection. Little more than a scam.

Given that washing machines, dishwashers, tumble dryers are built down to
a price in a very competitive market, I wonder why the (presumably
competent) designers include them.

Because they are all covered by warranty and it’s a lot
cheaper to include them than do the warranty claims.

(I could believe it is driven by RFI).

It isnt, particularly now with digital free to air TV.

newshound wrote

A Brewer mate of mine has a temperature controller which switches
a bank of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too.

I suppose it could have been a spike on the incoming mains,

That wouldn't happen at the same time the element failed.

or perhaps local spikes associated with the element failing to earth?

Not spike so much as just too much current for the controller.

This made me wonder whether it would be worth adding a
suppressor to the supply to the controller (a basic West 6100 type).

Wouldn't help IMO. The problem is that the controller isnt
designed properly and couldn't handle the element failure.

I see from ebay that there are plenty of suppressors
for washing machines for about a tenner. Would it
be worth adding one of these?

Pointless IMO.

Or are they more about keeping "machine" noise off the mains?

They are as pointless as those ones that purport to protect
your desktop and other stuff like TVs from mains spikes.

On 22/10/2014 20:33, Rod Speed wrote:

They are as pointless as those ones that purport to protect your desktop
and other stuff like TVs from mains spikes.
While the devices themselves may not be particularly useful, the point
is the promise by the manufacturer to repair attached equipment...
Of course it's pointless to buy any without such a "promise"

Lee wrote
Rod Speed wrote

They are as pointless as those ones that purport to protect your desktop
and other stuff like TVs from mains spikes.

While the devices themselves may not be particularly useful, the point is
the promise by the manufacturer to repair attached equipment...

Trouble is that hardly any of them ever pay out on a claim.

Of course it's pointless to buy any without such a "promise"

And pointless to buy ones with such a "promise" too,
because those are nothing like as cheap as the ones
the OP asked about and don’t pay out anyway.

In article ,
newshound writes
A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth? This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

My first thoughts were that mains front ends of these things are pretty
robust and unlikely to pass transients to the electronics. Yes, some
domestic mains thermostats use dodgy capacitive droppers that could pass
transients but for something a bit more industrial, I'd expect a fully
isolated supply of a simple transformer or switched mode type.

You also mention that they are on separately MCB'd spurs so I'd expect
fully separate cables so no shared neutral path and earths only commoned
at the MCB box. All good practice.

I'd expect the solid state relays to be opto isolated too no path there
either but I hope that signal or driver cables are not bundled together
with load cables.

Only thing left are the temperature sensors. Are these robust in
stainless sleeves or some kind of surface mounted device. I suppose it
is possible that the failure to earth on the heater found an alternate
path for at least some of the fault current through the sensor, blowing
the interface. Do you think that might be possible? Again, sensor cables
should not be bundled with power.


Only now looking back at the West 6100 I see it is a pretty small device
so they may have cut corners on the supply side but the wide supply
range 100-265V AC does suggest a proper SMPS. I see from the manual that
they do suggest using a mains isolating transformer to isolate the unit
from transients and while I assume you have the mains unit (suitable for
a 1:1 mains isolating transformer), the 24V AC unit may be less
susceptible if fed from a 240/24V transformer.

Other than looking at the sensor path for the failure, I'd be more
inclined to look at transformer isolation on the supply rather than use
MOVs as they are pretty unreliable. I suspect that the washing machine
suppressors you mention are EMC filters rather than transient
suppressors and whilst they are effective in reducing RF interference on
other electronics, they are not intended or designed to remove damaging
transients. Post a link to one though and I will let you know what I
think it is.

The manual has other noise/transient suppression suggestions.

Full manual he

http://www.west-cs.co.uk/assets/Manu...al-English.pdf


or http://preview.tinyurl.com/lzmb7fs

Good luck!
--
fred
it's a ba-na-na . . . .

On 23/10/2014 13:19, fred wrote:
In article ,
newshound writes
A Brewer mate of mine has a temperature controller which switches a bank
of domestic immersion heaters in a hot water tank via solid state
relays. One of the elements has just failed to earth (blowing its fuse).
The failure seems to have taken out the temperature controller too. I
suppose it could have been a spike on the incoming mains, or perhaps
local spikes associated with the element failing to earth? This made me
wonder whether it would be worth adding a suppressor to the supply to
the controller (a basic West 6100 type). I see from ebay that there are
plenty of suppressors for washing machines for about a tenner. Would it
be worth adding one of these? Or are they more about keeping "machine"
noise off the mains?

My first thoughts were that mains front ends of these things are pretty
robust and unlikely to pass transients to the electronics. Yes, some
domestic mains thermostats use dodgy capacitive droppers that could pass
transients but for something a bit more industrial, I'd expect a fully
isolated supply of a simple transformer or switched mode type.

You also mention that they are on separately MCB'd spurs so I'd expect
fully separate cables so no shared neutral path and earths only commoned
at the MCB box. All good practice.

Yes, correct


I'd expect the solid state relays to be opto isolated too no path there
either but I hope that signal or driver cables are not bundled together
with load cables.

Not bundled together, but I will have a look at the routing, there may
be a couple of "crossovers".


Only thing left are the temperature sensors. Are these robust in
stainless sleeves or some kind of surface mounted device. I suppose it
is possible that the failure to earth on the heater found an alternate
path for at least some of the fault current through the sensor, blowing
the interface. Do you think that might be possible? Again, sensor cables
should not be bundled with power.


MI thermocouple, I think it is in a pocket but not quite sure. Sensor
cables not bundled with power. I will check for resistance to earth in
case the pocket/clad has a water leak.


Only now looking back at the West 6100 I see it is a pretty small device
so they may have cut corners on the supply side but the wide supply
range 100-265V AC does suggest a proper SMPS. I see from the manual that
they do suggest using a mains isolating transformer to isolate the unit
from transients and while I assume you have the mains unit (suitable for
a 1:1 mains isolating transformer), the 24V AC unit may be less
susceptible if fed from a 240/24V transformer.

That's a very good idea. I have a cheap ( £30) West clone on order for
delivery tomorrow for fitting over the weekend. I don't think I have an
isolating transformer among my collection of useful stuff, but I'll
order one in case it happens again.


Other than looking at the sensor path for the failure, I'd be more
inclined to look at transformer isolation on the supply rather than use
MOVs as they are pretty unreliable. I suspect that the washing machine
suppressors you mention are EMC filters rather than transient
suppressors and whilst they are effective in reducing RF interference on
other electronics, they are not intended or designed to remove damaging
transients. Post a link to one though and I will let you know what I
think it is.

Won't bother with them then. I had already speculated that they might be
there for RFI (which I guess is part of the standards these days).


The manual has other noise/transient suppression suggestions.

It's not otherwise an electrically noisy environment.


Full manual he

http://www.west-cs.co.uk/assets/Manu...al-English.pdf



or http://preview.tinyurl.com/lzmb7fs

Good luck!

Thanks for all the helpful suggestions.

Steve

On Thursday, October 23, 2014 9:08:08 PM UTC+1, newshound wrote:
On 23/10/2014 13:19, fred wrote:
In article ,
newshound writes

Other than looking at the sensor path for the failure, I'd be more
inclined to look at transformer isolation on the supply rather than use
MOVs as they are pretty unreliable. I suspect that the washing machine
suppressors you mention are EMC filters rather than transient
suppressors and whilst they are effective in reducing RF interference on
other electronics, they are not intended or designed to remove damaging
transients. Post a link to one though and I will let you know what I
think it is.

Won't bother with them then. I had already speculated that they might be
there for RFI (which I guess is part of the standards these days).

C&L are normally used for rfi, MOVs arent effective at that.


NT

In article ,
newshound writes
On 23/10/2014 13:19, fred wrote:

I'd expect the solid state relays to be opto isolated too no path there
either but I hope that signal or driver cables are not bundled together
with load cables.

Not bundled together, but I will have a look at the routing, there may
be a couple of "crossovers".

Crossovers aren't a problem, you need a significant close coupled path
to induce noise (a trivial problem) and even more coupling to induce
damage.

Only thing left are the temperature sensors. Are these robust in
stainless sleeves or some kind of surface mounted device. I suppose it
is possible that the failure to earth on the heater found an alternate
path for at least some of the fault current through the sensor, blowing
the interface. Do you think that might be possible? Again, sensor cables
should not be bundled with power.

MI thermocouple, I think it is in a pocket but not quite sure. Sensor
cables not bundled with power. I will check for resistance to earth in
case the pocket/clad has a water leak.

Thermocouple input is really low level so there will be a sensitive
amplifier in the path which could have popped but you mentioned a total
failure (display out) which makes me think again of a supply transient.
In a compact can, space is at a premium so as I said, they may have cut
corners on input components close to limits so that may be a place to
look at again.

Only now looking back at the West 6100 I see it is a pretty small device
so they may have cut corners on the supply side but the wide supply
range 100-265V AC does suggest a proper SMPS. I see from the manual that
they do suggest using a mains isolating transformer to isolate the unit
from transients and while I assume you have the mains unit (suitable for
a 1:1 mains isolating transformer), the 24V AC unit may be less
susceptible if fed from a 240/24V transformer.

That's a very good idea. I have a cheap ( £30) West clone on order for
delivery tomorrow for fitting over the weekend. I don't think I have an
isolating transformer among my collection of useful stuff, but I'll
order one in case it happens again.

Once you are behind an isolating transformer (significant impedance to
the mains) I'd be more inclined to stick a MOV transient suppressor on
the device's supply terminals. Something like this perhaps:

http://cpc.farnell.com/blah/dp/RE03686

The manual has other noise/transient suppression suggestions.

It's not otherwise an electrically noisy environment.

Noise & (damaging) transients couple via the same mechanisms so there
may still be some useful advice there, just ignore the stuff that you
don't think is applicable.

Thanks for all the helpful suggestions.

You're welcome, all you have said points to a well thought out
installation so it may be a challenge to track down the failure
mechanism. Next step might be to carry out an insulation test on the
remaining elements to pre-empt the next failure (after disconnecting the
relays and new controller of course :-)
--
fred
it's a ba-na-na . . . .

On 23/10/2014 22:06, fred wrote:
In article ,
newshound writes
On 23/10/2014 13:19, fred wrote:

I'd expect the solid state relays to be opto isolated too no path there
either but I hope that signal or driver cables are not bundled together
with load cables.

Not bundled together, but I will have a look at the routing, there may
be a couple of "crossovers".

Crossovers aren't a problem, you need a significant close coupled path
to induce noise (a trivial problem) and even more coupling to induce
damage.

Only thing left are the temperature sensors. Are these robust in
stainless sleeves or some kind of surface mounted device. I suppose it
is possible that the failure to earth on the heater found an alternate
path for at least some of the fault current through the sensor, blowing
the interface. Do you think that might be possible? Again, sensor cables
should not be bundled with power.

MI thermocouple, I think it is in a pocket but not quite sure. Sensor
cables not bundled with power. I will check for resistance to earth in
case the pocket/clad has a water leak.

Thermocouple input is really low level so there will be a sensitive
amplifier in the path which could have popped but you mentioned a total
failure (display out) which makes me think again of a supply transient.
In a compact can, space is at a premium so as I said, they may have cut
corners on input components close to limits so that may be a place to
look at again.

Only now looking back at the West 6100 I see it is a pretty small device
so they may have cut corners on the supply side but the wide supply
range 100-265V AC does suggest a proper SMPS. I see from the manual that
they do suggest using a mains isolating transformer to isolate the unit
from transients and while I assume you have the mains unit (suitable for
a 1:1 mains isolating transformer), the 24V AC unit may be less
susceptible if fed from a 240/24V transformer.

That's a very good idea. I have a cheap ( £30) West clone on order for
delivery tomorrow for fitting over the weekend. I don't think I have an
isolating transformer among my collection of useful stuff, but I'll
order one in case it happens again.

Once you are behind an isolating transformer (significant impedance to
the mains) I'd be more inclined to stick a MOV transient suppressor on
the device's supply terminals. Something like this perhaps:

http://cpc.farnell.com/blah/dp/RE03686

The manual has other noise/transient suppression suggestions.

It's not otherwise an electrically noisy environment.

Noise & (damaging) transients couple via the same mechanisms so there
may still be some useful advice there, just ignore the stuff that you
don't think is applicable.

Thanks for all the helpful suggestions.

You're welcome, all you have said points to a well thought out
installation so it may be a challenge to track down the failure
mechanism. Next step might be to carry out an insulation test on the
remaining elements to pre-empt the next failure (after disconnecting the
relays and new controller of course :-)

Can I be cheeky and ask whether this would be a suitable isolating
transformer?

http://cpc.farnell.com/block/tim60/t...0va/dp/TF01496

The controller that I have on order is only 5 VA but I can't seem to
spot anything with a lower rating than 60.

TIA!

On Thursday, October 23, 2014 10:51:17 PM UTC+1, newshound wrote:

Can I be cheeky and ask whether this would be a suitable isolating
transformer?
http://cpc.farnell.com/block/tim60/t...0va/dp/TF01496
The controller that I have on order is only 5 VA but I can't seem to
spot anything with a lower rating than 60.

Not really, 'Regulation: 83.5%' means V_out will be up by 55/60 x 16.5% giving 276 volts at 240 in (if mains strays higher it'll go even further up).


NT

In article ,
newshound writes

Can I be cheeky and ask whether this would be a suitable isolating
transformer?

No problem, only 2 mins to check.

http://cpc.farnell.com/block/tim60/t...0va/dp/TF01496

The controller that I have on order is only 5 VA but I can't seem to
spot anything with a lower rating than 60.

Yes, I suppose they generally are used for more industrial type loads or
power tools.

Neat and easy mounting but I'm afraid the load regulation is a bit ****
(100-83.6 = 16.5%), meaning that on a 240V supply you could see 287V at
light loads which is way too high, and that's before you get any
tolerances or surges on the incoming supply. Sadly, it looks like we
could be more likely to pop your unit than protect it.

Good news however is that your unit appears to have a true switch mode
power supply wide input range of 100-240V ac, meaning that you could run
the unit from a single 115V winding instead of connecting it to the
series connected 230/240V ones. That would give you say 120-144V at the
input which would be fine and if it was a supply transient that killed
it then you have even more headroom to play with (plus any differential
transient would be reduced in half by the transformer).

This is dependent of course on your cheapie replacement also having the
same wide input range (100-240V) so do check that.

I'd make sure that the installation is labelled clearly to say that the
unit is operating at 115V deliberately and that it must not be used with
the windings series connected (240+ V).

The reduction in input voltage probably means that you wont need a MOV
but if you decide to belt and brace it then put this lower voltage item
on the 115V output of the isolating transformer:

http://cpc.farnell.com/blah/dp/RE03666 (150V ac nominal).

If your new unit is 240V only than sadly we should prob leave the iso
transformer behind (there are tricks to reduce the supply voltage before
the transformer but let's not get too tricky I think). I couldn't find a
multitapped isolating transformer on a quick search.

HTH

--
fred
it's a ba-na-na . . . .