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G8MNY  > TECH     30.11.19 11:00l 119 Lines 5491 Bytes #1 (0) @ WW
BID : 33772_GB7CIP
Subj: Saveplug Motor Economiser
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 191130/0947Z @:GB7CIP.#32.GBR.EURO #:33772 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                (Updated Jan 13)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

PRINCIPLE
These plugs can reduce the power used on fridge/freezer compressors & central
heating pump motors. They reducing the mean supply voltage & a shaded pole AC
electric motor or a capacitor start AC motor, will normally run at reduced
voltage with very little reduction of mechanical output.

Output W               full speed     Input W
100% ┤       .˙   .---────────────── ├ 400%
     │    .˙'  ' Ů95%          'OVER │         A stalled motor looks
 75% ┤ .˙'      'Ţ           .' HEAT ├ 200%    like a transformer with
     │'         Ů'          ˙        │         a shorted secondary & it
 50% ┤ High I   Ţ '˙ . . . 'Saturated│ 100%    takes about 4-15 times
     │ Stalled |     Normal    core  │         the normal power/current.
 25% ┤        /                      ├ 50%
     │ __..-─'                       │
  0% ┼────┬────┬────┬────┬────┬────┬─┴ 25%
    140  160  180  200  220  240  260
                 RMS AC Volts

N.B. In a compressor situation, the motor can easily be stalled by powering off
& on just after the pressure builds up. To stop motor burn outs there is a
built in thermal switch to turn off the power for a few minutes, letting the
gas pressure leak away & the motor restarts again from no back pressure. (This
is why you can't reliably run a 100W motor on a small 600W generator/UPS!)

WAVEFORM
    _                        _
  /~ ~\                    |~ ~\
 │     │  Supply           │    │  Load
│       │         │      __│     │__       __
         │       │                  │     │
          │     │                   │    │
           \_ _/                    |_ _/
             ~                        ~
On resistive loads the waveform looks something like this, but motors are not
resistive!

The power saving is not all it seems, as the slightly higher pulse currents can
also increase the motor copper losses & with the plug heat as well may negating
any saving.

CIRCUIT
  ┌───────────────────────────────────────────────────────────E
  │
  │            ┌────────────┬──────────┬───┬─────────────┐
  │            │           100k       _│_ _│_            │
  │            │       Diac ├────┐    /_\ \_/            │
  │            │         ___│___ │  ┌──┤   ├──┐          │
  │            ├─150─┐   /_\_\_/ │  │ _│_ _│_ │         15k
  E            │     │      │    │  │ \_/ /_\ │ u22      │    APPLIANCE
               │ T2__│___   ├────)──)──┴───┘  ├──┤├─┐   _│_
PLUG           │   /_\_\/  180   │  │ u1      │     │   \_/­OK
               │     │ \____│   === ├─┤├──390─┴─10M─┤    │LED
N   L          │     │      │  u1│  │              _│_  _│_
│   │          │ T1  │     100   │ 22k             \_/  \_/
│   │ FILTER   │ │<│/       │    │  │               │    │
│   │          ├─┤ ├─────┬──┴────┴──┴───────────────┴────┴────L
│   └──┬──()))─┤ │>│    ===
│ u22 === :::  └─────33R─┘ u22
└──────┴──()))────────────────────────────────────────────────N

OPERATION
Mains is fed through a filter in to power Triac T1 a BTA15, it is triggered by
the smaller Triac T2 a 2N6073. This in turn is triggered by the Diac. (this can
be just 2 identical low voltage transistors back to back). The u1 cap charges
up through the 100k, reaches the Diac's breakdown voltage T2 triggers & then
T1. T1 triggering also removes the power to T2 & hence T1 gate drive. T1 stays
conducting until that half cycle AC current goes to zero (due to motor
inductance this will be later than the AC voltage zero).

The bridge rectifier & load across the Diac is some stabilising circuit for
peak loads.

Note the fraction of mains removed is always about the same & not voltage
regulated (pity). On 250V in you get about 230V RMS out.

POWER SAVED
To determine this any power measurement needs a good true RMS power meter, it
is no good using a mean or RMS amp & volt meter! For complex wave shapes phase
angles between I & V, instant multiplication of these must be done. With modern
uProc meters this is now possible to good accuracy!
       ┌─────┐         ┌──────────┐
Mains ─┤True ├─────────┤Appliance │   Get the full range of
       │Power│         │under test│   Powers used, including
       │Meter│         └──────────┘   stalled/start motor power.
       └─────┘
       ┌─────┐ ┌─────┐ ┌──────────┐   Get the full range of
Mains ─┤True ├─┤Saver├─┤Appliance │   Powers used, including
       │Power│ │plug │ │under test│   stalled/start motor power.
       │Meter│ └─────┘ └──────────┘   Check the motor always starts!!
       └─────┘
Power savings will very much depend on the normal mains supply voltage & the
amount of over saturation that occurs in that make of motor at that voltage.

Typical savings on say a 100W 220V motor on max EU 253V might be 50W with 5W
warming the plug. The same motor on 230V might be 10W with 4W lost in the plug.
A less saturated 230V motor on 253V might not see any saving. You do need to
measure it to know if it is worth while fitting the plug!

RADIO NOISE
The plug is well filtered to the mains side, but none to the motor, so the
wiring to that needs to be short if LF QRM is to be kept low.


See my tech buls on "UK 13A Fused Mains Plug", "Maplin Mains Meter 2000MU-UK"
"AC Theory", "Transistors, SCRs & TRIACs", "Variacs", "Economy Turn ON Timer"
& "Meter Movement Types".


Why don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


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