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This looks like a dream Home
Automation scenario: buy a Wi-Fi smart plug, put a 1.5 ton Split AC
in it and your Digital Assistant will do you a favor to cool the
entire house before you reach back.
You might have seen the box
reading "16A Heavy Duty" so a 1.5 Ton Split AC will surely
draw 7-8A current when running in a steady state. So math doesn't
lie, it should work?
This is not true; if you're
going to put a 1.5 Ton AC in a plastic smart plug then the internal
relay is going to either fuse or melt, or at the worst case start a
fire. Let us understand, with reasons from Electrical Engineering why
this 16A rated smart plug isn't going to do what it's supposed to and
why its rating is technically a half-truth.
1.
The Resistive Vs Inductive Load Trap
This is a secret gem of Home
Automation industry that they don't tell the consumers. If a
manufacturer writes that this smart plug can handle 16A it only means
that it can handle a 16A pure resistive load, for example heater,
water heater, iron, electric kettle, or anything like that. But an
air conditioner has an inductive load(it consists of an electrical
motor which runs the compressor) and this causes a phase lag between
the voltage and current (meaning power factor is less). Thus the tiny
switch in a smart plug takes stress 10 to 100 times more compared to
a water heater. There are strong chances that the 16A resistive rated
relay would at best handle a 8A inductive load.
2.
Inrush current (Compressor Kick)
Even if it's not an inverter
based 1.5 Ton AC that draws just 8A in a steady state, you'll have a
suddenly immense spike in the current as the compressor kicks in,
just to overcome the inertia of the gas. At that instance your AC
will draw something between 25-35 A current. This huge 30A electrical
surge will hit the tiny metal contact within an electro mechanical
switch called a relay. Every time your AC kicks in this burst of
current creates an arc across the contact that over the time burns
the contacts out. Thus it will either cause the relay to fuse shut
(the AC running constantly) or create a resistance between the
contacts, making it glow red.
3.
The Joule heating effect (P = I^2R)
Thus even if it's an inverter
1.5 Ton AC that starts up with a soft start to prevent the rush of
current it would burn eventually due to the cheap, weak relay and
poor construction. Any well built smart plug has a sturdy connection
and good spring to hold a strong pin to the AC female socket. In your
case, the one you bought is most likely a low quality one where the
spring is weak, the brass pin is extremely thin and has flimsy
contacts that don't press hard enough against the socket pins. The
electrical formula, P=I^2R, implies that this high current along with
the resistance of poor connection will generate an immense heat. As
the smart plug is basically a sealed plastic box that has your Wi-Fi
chip and a power supply inside, it lacks the provision of allowing
the heat generated inside to escape out. Hence the internal
temperature is bound to rise up to more than 150 degrees Celsius in
about 4 hours and melt the plastic socket around the pins.
4.
The Bottom Line - Making Your AC Smart
Do not use plug-in adapters
for motor loads (water pumps, air conditioners etc). If you really
want to make your AC smart, you must install a High Capacity Smart
Contactor or Heavy Duty Smart module directly in to your distribution
board or electrical panel that is internally built with a rugged
contact resistant to arcs. Such smart modules include a substantially
powerful, silver alloy internal contact for taking care of electrical
arcs.
After all this, you can safely
use them for a lamp, television or a kettle. Using a 1.5 Ton AC in a
smart plug is hazardous and basically an electrical accident. Ditch
the smart plugs and hardwire the motor loads directly to the
distribution panel.
