On Tue, 23 Sep 2014 23:44:01 +0100, Jeremy Nicoll - news posts
wrote:

Johny B Good wrote:


A plug in energy monitor will give you a chance to check the weekly total
consumption of things like fridges / freezers (any white goods items that
are run on an intermittent weekly basis).

... this isn't so easy for appliances that are built-in


Prioritise: make sure there isn't a 'phantom load', make sure the meter's
not over-reading

It's a few years since I last tried to work out what causes base load here.
The puzzles are

- central heating system: the boiler unit has a segment timer on
the front driven by an internal electric motor; it's normally
bypassed but still driven. There's an external electronic
programmer as well; sometimes I have the latter turn heating
on for some hours but have the segment timer in use too so
that the heating is on, say, for every third 15 minute period
over those hours. The boiler also of course has its main
PCB and - when heating is on - the pumps. I don't imagine it
uses much, but it's on all the time...

Its supply is via a fused spur unit.

All valid considerations. I agree these sort of fixed connected loads
are problematical with regard to verifying their actual consumption.
Digital controllers usually only take a watt or two, the CH pump
usually somewhere in the region of 50 to 100 watts (the old Grundfoss
UPS 15-60 3 speed pump I pulled from my CH system a few years ago is
rated at 45, 70 and 105 watts for the three speed options - can't
recall what the replacement is rated at). The Honeywell motorised
diverter valve takes 6 watts and I'd expect less than a watt for a
motor driven time switch.

The most practical way to get such readings, without intercepting the
feed to connect a watt meter, is to shut everything else off and
monitor the suppliers KWH meter for a sufficiently long sampling
period (counting disk revs or led blinks) to at least keep the error
down to less than 10%. In the case of the CH, this might take half an
hour or so (circa 100 watt load, mainly the pump).


- alarm system - half a dozen PIRs, 2 smoke detectors, 2 control
panel/keypads with illuminated displays, active siren boxes on
two sides of the house with tell-tale LED flashes... all on a
wired system.

And, like the boiler, no simple way to intercept the mains supply
to measure it. I have wondered if anyone makes a plug that one
could use on a flying lead to insert into the spur's fuse holder
to break out a connection?

You might be able to make one up but the main problem will be
accessing the neutral connection (although you could get away with
using a handy earth bonded point as a substitute neutral - the meter
draws only microamps from the neutral for the voltage sensor). It'll
be tricky enough making up a fuse cartridge 'plug' to divert the live
via the meter's current sensor but doable with a little ingenuity.



- halogen hob; it's connected via T&E to a kitchen oven supply; if
I bought the sort of energy monitor that's meant to be clipped
to meter tails could I get a reading by clipping that around the
T&E?

That may work ok if the voltage probe relies on a galvanic connection
to the live (or has that as an option. Some of these clamp on current
sensors designed to clamp around meter tails also use the clamp itself
to sense the live voltage via capacitive coupling which may be
compromised when clamped round a thinner cable (reduced coupling of
the electric field (voltage) which will give a lower reading than
actual.


- ovens ... timer is on all the time; surely this uses hardly any
power, but it's quite old technology so maybe it wastes more
than I'd expect. ISTR the supply is from a 13A socket but it's
hidden behind kitchen units.

It's unlikely to be more than a watt or two when 'switched off'. If
you really need to 'know', you can always fumble around to gain access
to the 13A socket.



- PIR-controlled outside light, permanently wired into a lighting
circuit... though there's an isolator switch... Can one use the
sort of plug-in energy monitor that's meant to be plugged into a
13 A socket to measure power used by a light - there must be a
L & N running through the isolator to the light so presumably I
could divert them to a 13A socket, plug in the monitor & connect
flex from a 13A plug to the outward part of the light's supply?

That's certainly a workable solution. It just needs a modicum of care
and common sense. Presumably the main aim here is to log the
consumption over a few days of use (you know what the lamp takes, you
just don't know how much run time it'll typically be clocking up - the
rest of the circuit standby consumption is unlikely to be more than a
watt or two, but you'll be able to verify this to remove such
'mystery' from your estimates)

When I installed the security light a couple of decades ago, I picked
up the power from the top floor ring main via a 5A fused connector
unit. I just didn't fancy having a 500W halogen switch on surge
risking a blown lighting fuse on the upstairs and basement lighting
circuit (or, for that matter, the ground floor lighting circuit).

If I wanted to connect an 'energy meter' I'd have to use a cheap
extension lead as a 'breakout box for the plug in meter and wire it
into the FU box for the duration.



- bell transformer, meant to be illuminating a bell-push, but I
think the bulb's blown... so presumably the transformer uses
nothing at all, or a negligible amount?

Some of the older ones could be using as much as 4 or 5 watts just
keeping themselves at nice and toasty 40 to 50 degrees. A good quality
bell transformer could well be wasting as little as half a watt or
less with the lamp in the illuminated bell push consuming a further
half watt or so with the bell itself perhaps taking no more than
another watt or two on each press of the bell push.

My solution for the front door bell was to use a battery powered
ex-GPO trembler bell (with a wireless bell push wired, via blocking
diode across the bell push contacts so the 3 x 9v PP3 battery pack
bought in poundland didn't backfeed into the 12v powered wireless
sender unit used to signal the repeater 'bell unit' I keep in my
upstairs office - the GPO trembler bell is mounted right onto the
front door frame).

I think I replaced the decade or so old 16 by AA cell 24v battery
pack with the PP3 pack just over a year ago. I certainly expect the
poundland '27 volt' battery to last at least 12 months or more, making
the running cost far cheaper than a typical mains powered bell (even
the most efficient of mains powered illuminated bell push doorbells is
going to struggle to compete with that level of economy :-)

Again, if you want to check the actual consumption of the mains
powered bell, you're going to have to intercept the mains feed to plug
in your 'energy monitor'. for the stakes involved (around a fiver's
worth on the annual electricity bill), I'd be inclined to leave this
exercise on the back burner for now.

Getting a handle on your PIR controlled flood lighting, however,
would, imo, be worth the hassle involved since it is potentially a
higher stakes game (a 3 to 5 hundred watt lamp running for 3 to 10
minutes at a time, maybe a few dozen times a night can add a
significant amount of running cost comparable to your daily use of the
electric kettle!).
--
J B Good