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Default AC Current Sensing Relay GFCI Mod

A GFCI can be modified to be used as an AC current sensing circuit
to turn on/off another receptacle when a load attached to the
sensing receptacle (the GFCI) is turned on/off. It takes a very
simple modification to the GFCI: cut one trace and add a resistor,
mechanically block the GFCI internal contacts always on, and
solder on 2 pieces of hookup wire to power an external relay,
available from Digikey for $3.46.

The attached pictures show the modifications made to a Leviton
"smartlockpro" GFCI receptacle model 7599-RW, available at
HomeDepot. A short piece of hookup wire (red in the pictures)
slides into the solenoid armature mechanism to hold the contacts
up (up = away from the PCB). The solenoid plunger is discarded.
The pictured 220K resistor could be replaced with a 100K - see
the text below. When the mod is finished, reassemble the GFCI
receptacle with the hookup wire routed through holes drilled in
the bottom of the receptacle and wire it as below:

---Hot------------------+
| Controlled
Modified | Receptacle
GFCI |
----- | -----
---Neut---+---| | | | | | o |
| | o | | | | | |
| | T | | | ' |
| | R | | | o |
| | | | | | ---o---| | | |---+
| | o |---+----^ ----- |
| ----- " |
| - | | + " |
| | +--[2.2K]---+-------+ |
| | | | + |
| | [Rly] [10uf] |
| | D1 | | |
| +---|--------+-------+ |
| |
+-----------------------------------+

NOTE: the AC input to the modified GFCI *must* have one side
to the LINE terminal and the other side to the LOAD terminal.

Relay: 48V 8.96 mA coil Digikey Part# Z2825-ND - contacts rated
16A at 250VAC
Cap 100 volts or higher. I used a 10 uF 100 volt unit because
that's what I had close to hand.

The added 220K resistor keeps the GFCI circuit from detecting
the imbalance it creates by its own current draw, and allows
"vampire" power devices - like a TV with a remote - to be powered
from the sensing (GFCI) receptacle. Providing the vampire draw is
low enough, the relay will not energize until the TV is turned on.
With higher draw vampire devices, replacing the 220K resistor with
a 100K results in a "window" tested with a 4 watts and an 11 watt
bulb. Turning on the 4 watt bulb did not energize the relay;
turning on the 11 watt bulb did.

Ed


Hmmm ... this won't post with all (3) the attachments.
I'll post a reply to this with the "GFCI disassembled"
picture.

Attached Thumbnails
AC Current Sensing Relay  GFCI Mod-gfci-contact-shim-jpg  AC Current Sensing Relay  GFCI Mod-gfci-sensing-mods-jpg  
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Default AC Current Sensing Relay GFCI Mod

ehsjr wrote:



Hmmm ... this won't post with all (3) the attachments.
I'll post a reply to this with the "GFCI disassembled"
picture.


Here's the third picture. I could have avoided the problem
by making the pics smaller, but the shim is a little hard
to see so I went with full size.

I'll post the circuit operation description if anyone wants it.

Ed

Attached Thumbnails
AC Current Sensing Relay  GFCI Mod-gfci-disassembled-jpg  
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