[#10082 - October 2008]
I need to monitor when my sump
pump in the basement goes on and
off. The pump draws 10A l20 VAC.
Figure
2A
note AN954. It has just what you want
(with no transformer)! You can get it at
www1.microchip.com/downloads
/en/AppNotes/00954A.pdf or http://
tinyurl.com/no-xformer for a shorter
path.
The schematic in Figure 1 (of
AN954) uses five small parts and uses
a capacitor to limit the current and
drop the excess voltage that the zener
and your 10 mA load doesn't use.
Figure 5 uses only four. This circuit
is like Figure 1, but uses a resistor
instead.
Figure 10 = Figure 1 but uses eight
parts as it has more safety features
built in.
Figure 11, likewise, is the same as
Figure 5 using nine parts.
And Figure 12 uses four parts and
uses a bridge rectifier for better
efficiency and output voltage stability.
Have fun, safely!
Brian German
Thief River Falls, MN
of the other outlets. When the pump
turns on, it will activate the other
device you have plugged in the SLAVE
outlet. Cost is $20 plus what you
spend on the alarm device.
There are also computer grade
power strips called "Smart Strips" that
do basically the same thing as the
Craftsman Auto Switch. The difference
is the Craftsman device was designed
with high current motor loads in mind.
Perfect for your situation.
The first solution has the
attraction of being cheaper. But it will
only tell you if the pump switch is on
and not if the sump motor is running.
The second — while more expensive —
will detect if the pump is running.
Tim Naami
Poplar Grove, IL
#2 Dave Johnson’s website
provides the perfect answer. www.dis
covercircuits.com/DJCircuits/pump
motormon2.htm
The circuit (Figure 3) can turn on
a light or sound a beeper, whenever
an AC line powered pump motor turns
on. It is designed to detect the motor
current using a small inductor placed
on the outside of the motor’s power
cable. No direct wire contact is
needed.
Wesley K. Miller
Dillsburg, PA
+3v
+
1/3N LITHIUM CELL
APPROX. 3uA
CURRENT DRAW
APPROX 5 YEARS
OPERATION
#1 If your sump system has a separate pump and float switch plugs, this
is easy. The float switch plugs into the
wall and then the pump plugs into the
back of the float's plug. Simply unplug
the pump from the switch, add a multi
plug adapter (one plug to three) and
plug the pump back in. In one of the
remaining plugs, add some sort of
device that makes a loud noise when
powered on. You could plug in an AC
adapter and run low voltage wiring to
another part of the house to activate a
flashing light and/or some sort of siren
or bell. Cost is about $2 plus what you
decide to spend on the alarm device.
If your sump system has a single
plug, you can get a device from Sears
called a "Craftsman Auto Switch"
(Sears item #00924031000) Mfr.
model #24031). Other places that sell
power tools have these controllers but
I'm familiar with the one from Sears.
This device plugs into the wall outlet
and you plug your control equipment
(such as a table saw) into the MASTER
outlet. There are two slave outlets that
supply power to such devices as lights
or vacuums. When you turn on the
saw, the vacuum cleaner is automatically powered on, as well. In this case,
you plug your pump into the MASTER
outlet and using the same concept as
before, plug in an alarm device to one
+ 10uF
C1
Figure 3
CABLE
+3v
+3v
+3v
C
L1
4.7M
R1
1M
R7
BE
0.76V
MOUSER
434-03-104J
OUTPUT SINKS
CURRENT WHEN PUMP
IS RUNNING
OUT+
22K
R2
22M
R3
470pF 0.1uF
C4 C C6
B
2N3904
0.1uF E Q1
C3
5
1
OUT-
100mA MAX
100mH
L1
0.75V
52
4148
4_
1
3+
LMC7215 D1
U1
1.0uF
MUST USE C2
UNSHIELDED
INDUCTOR
1.5M 0.1uF 220K
C5
R4 R5
0.1uF
C7
D
G
ZXM61N02F
S Q2
4.7M D
R6
GS
APPROX 0.10 AMPS PUMP MOTOR
CURRENT NEEDED
X100
10mV PEAK SENSITIVITY
#3 A GFCI receptacle contains all
the electronics you need, except for
an LED and a 10K resistor. It can be
modified to light the LED anytime
the pump runs. The modification
consists of opening the circuit at
the SCR that energizes the
solenoid and placing a 10K resistor
and LED in series across the
opened circuit. The one I just
tested required disassembling the
GFCI, cutting one circuit trace,
drilling two holes in the back of the
GFCI, running two wires through
the holes and soldering them to
the circuit board, and reassembling
the GFCI. The LED and resistor
are connected to the wires.
Disassembly and reassembly must
be done with care so that nothing
is damaged. When reassembling,
there are two movable contacts
December 2008 95
