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GFI Outlet Chirps

A

analogman

Jan 1, 1970
0
I have a GFI outlet that gives off a faint chirping sound. Took me a
while to find out where the sound was comming from. Sounds like a
little bird. Any ideas?
 
N

NSM

Jan 1, 1970
0
| I have a GFI outlet that gives off a faint chirping sound. Took me a
| while to find out where the sound was comming from. Sounds like a
| little bird. Any ideas?

Replace it? All I can think of is that it's going into fault mode
repeatedly.

N
 
S

Simon Cussonnet

Jan 1, 1970
0
Chat do you mean by "Sounds like a little bird" ? Crooo Crooo, Twiiiitt
twiiiiitt or chip chip chip ?

The electronics of those GFIs are generally supplied by the mains through a
capacitor (470 nF or more). Sometimes the plastic film capacitors crackle
because crossed by 50 or 60 Hz current or pulses. It may occur especially
where electric appliances are driven by signals superimposed to the mains
(ie. 175 Hz pulses used to turn on the water heaters). Does your GFI
"whistles" at specific hours ?

Please be more precise, also in the type of GFI (sensitivity) you have, 230
V 50 Hz or 115 V 60 Hz ?
 
C

CJT

Jan 1, 1970
0
analogman said:
I have a GFI outlet that gives off a faint chirping sound. Took me a
while to find out where the sound was comming from. Sounds like a
little bird. Any ideas?

Maybe a cricket has crawled inside.
 
A

Asimov

Jan 1, 1970
0
"CJT" bravely wrote to "All" (12 Nov 04 23:15:48)
--- on the heady topic of "Re: GFI Outlet Chirps"

CJ> From: CJT <[email protected]>

CJ> analogman said:
I have a GFI outlet that gives off a faint chirping sound. Took me a
while to find out where the sound was comming from. Sounds like a
little bird. Any ideas?

CJ> Maybe a cricket has crawled inside.

Buddy Holly and the GFI's!?

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.
 
J

James Sweet

Jan 1, 1970
0
analogman said:
I have a GFI outlet that gives off a faint chirping sound. Took me a
while to find out where the sound was comming from. Sounds like a
little bird. Any ideas?

While I'm normally all for repairing things, in this case I'd recommend you
just replace it, it's a permanently connected line operated device, even the
extremely remote chance that it causes a fire is not worth it given the
cheap cost of replacement.
 
A

analogman

Jan 1, 1970
0
I have no intention of repairing the unit. This is more of a
curiousity than anything else sparked by another question I read here
somewhere.

The "chat" is more of a "Twiiiitt, Twiiiitt, Twiiiitt..." and the unit
is a 115V/60Hz. I am unaware of any nearby appliances running when I
hear this and my water heater is gas fired. No power connected to it
as it uses a pilot to ignite. Does it Twiiitt at specific hours? Not
sure. I think it happens all the time. It's very faint and I don't
hear it unless the house is very quiet. It's a Home Depot Cheapo
installed by previous owner! Gee, maybe I should make sure the
polarity is correct! ;-)
 
S

Simon Cussonnet

Jan 1, 1970
0
I've been building hi-sensitivity electronic GFIs for years, 15 years ago
and didn't heard such a phenomenon !
The sensor is a toroidal core, made with high permeability alloy either a
rolled band for the 100 mA diffs or stacked washers when high perfs and
stability are required (5 or 10 mA sensitivity).
Under circumstances the rolled band might vibrate but at the mains frequency
60 Hz. Twiiiit suggest something like 1 kHz or more. As I already said the
caps may crackle, again at 60 Hz. I really can't see what could cause this
noise.
Basically the principle is the following:
The sensing core is put over the two (three or four) wires in order to sense
any current imbalance between the wires. The wires play the role of the
primary winding of a current transformer. The secondary is made of very
small wire (1000 to 2000 turns), connected to a low impedance input
amplifier (Norton Amp). Its output triggers a thyristor connected to a kind
of relay, which armature pulls a lock to open it. This lock is mechanically
closed by the lever the operator pushes on. The power supply is provided by
a capacitor connected to the mains, in series with a small 27 Ohms resistors
(to limit the surge current) and one zener diode connected to the other
line, another diode, forward biased is connected to the zener, feeding an
electrolytic capacitor also returning to the other line. THe current is
rectified by the zener forward biased and the voltage is limited by the
zener value. The second diode avoids the filtering capacitor to be
discharged within the zener during the opposite alternance.
There's no DC/DC converter ! so no hi-pitch audible frequency.

I'm curious to learn more ! Any link to the GFI spec ?

Thanks
 
J

JURB6006

Jan 1, 1970
0
I've been building hi-sensitivity electronic GFIs for years,

OK, but realize this, when a common mode signal comes along, that transformer
has a whole new set of specs., i.e. very low impedance and the inductance is
pretty much nullified. What's left is going to resonate higher.

Now for the stretch. . . . . .

Any large unit using a switched mode power supply near enoungh to cause a
transient on the AC line could trigger a reaction of some type. Now even if the
SMPS didn't radiate, I've seen some where there is no resistor going to the
rectifier. There is when you first fire it up, but then a relay closes and
shunts it out. If it has pretty healthy rectifiers that happen to switch fast,
that will put a transient on the line, especially under a higher load and
especially when they feed like an 820uF filter cap. Iv'e seen some things that
rectified the line into two 470s in parallel. If the diodes are switching fast
and the ESR of the main filters is/are low. . . . . . . . . .

I know this is far fetched, perhaps barely plausible, but explain it some other
way, I'll listen. This is however all that I can think of right now.

JURB
 
S

Simon Cussonnet

Jan 1, 1970
0
The usually used diode is an 1N4001 in addition to an input Zener 1.3 W
rated. Its forward and reverse currents are rather low and must be limited
by a small resistor in order the junction doesn't blow when the capacitor is
charging the first time. There's no transformer hence when the 470 nF is
discharged, the current is limited only by the resistor. Believe me it's
absolutely necessary because of the low allowed volume and the small size of
the diodes !

470 nF 27R 1N4001
o----||---------rrrrrr------+ ---->|--------+---- +Vd to the electronic
circuits
| k | +
mains Z 15V === electrolytic cap (470 µF 20
Vdc)
| zener |
o---------------------------+----------------+--- 0



On another hand, you're right. On SMPS the diode bridge is connected
directly to the mains (there's no series capacitor as shown above) and its
output is connected to the filtering capacitors . With the hi-surge current
diodes used in SMPS' bridge rectifiers, the resistor between the bridge and
the capacitors can be so low that the PCB tracks and the ESR are high enough
to limit the current to withstandable values for every guy. In that case,
the volume and the costs can deal with the diode performances.


About the current transformer,
When the circuit is perfectly balanced between the two lines of the mains,
there's no differential current into the transformer. It's far from
saturation. The inductance is pretty high. But there's also another
constraint, it must have a very low magnetizing current unless significant
non-linearity occurs at low current. Its purpose is to detect some milliAmps
over a balanced pair of let say 20 Amps currents. It also needs to be
balanced over a large range of frequencies otherwise, if not able to reject
transients, the GFI may trigger.
 
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