Question { 5491 }

what is cutoff voltage?

Answer

In electronics,
the cutoff voltage is the electrode voltage value that
reduces the dependent variable of an electron tube
characteristic to a specified low value
In batteries,
the cutoff (final) voltage is the prescribed lower-limit
voltage at which battery discharge is considered complete.
The cutoff voltage is usually chosen so that the maximum
useful capacity of the battery is achieved. The cutoff
voltage is different from one battery to the other and it's
highly dependent on the type of battery and the kind of
service in which the battery is used. When testing the
capacity of a NiMH or NiCd battery a cutoff voltage of 1.0
V is normally used. 0.9V is normally used as the cutoff
voltage of an alkaline cell. Devices that have too high
cutoff voltages may stop operating while the battery still
has significant capacity remaining

Premature voltage cut-off--

Some portable equipment does not fully use the low-end
voltage spectrum of a battery. The equipment cuts off
before the designated end-of-discharge voltage is reached,
leaving some battery power unused.

A high cutoff voltage problem is more widespread than is
commonly assumed. For example, a certain brand of mobile
phone that is powered with a single-cell Lithium-ion
battery cuts off at 3.3V. The Li‑ion can be discharged to
3V and lower. With a discharge to 3.3V, only about 70
percent of the expected 100 percent capacity is used
(source wikipedia)

Question { IIT, 4902 }

wat is syncronization . wat parameter will take for
syncronization.

Answer

sychronisation is important when parrallel operation of two
generators or when we connect a generator to grid.
The generator supply must only be connected to a live
grid,
1. Phase angle difference
2. Voltage differnece
3. frequency diffenrence (slip)
between the generator and grid voltage are within
permissible limits and the phase sequence of both generator
and grid rotating field should be identical.

Question { 10750 }

how to calculate the speed of a induction motor without
using tacho meter?

Answer

IN COMMON MOTORS SLIP=4%
IN THAT CASE A MOTOR WITH SYNCHROUNOUS SPEED 1500RPM WOULD
BE A SHAFT SPEED = 1440 RPM
I think Mr. Kiru is correct

Question { Emerson, 6204 }

What is the Diff. btw Fire Alarm System & VESDA System??????

Answer

The VESDA system uses an aspirator to sample air from
various strategic points within the room and this is
continuously monitored for products of combustion. The
system is highly sensitive and can detect very early stages
of burning, before a fire has time to develop

An automatic fire alarm system is designed to detect the
unwanted presence of fire by monitoring environmental
changes associated with combustion. In general, a fire
alarm system is either classified as automatic, manually
activated, or both. Automatic fire alarm systems can be
used to notify people to evacuate in the event of a fire or
other emergency, to summon emergency forces aid, and to
prepare the structure and associated systems to control the
spread of fire and smoke.

Question { Emerson, 8016 }

What is meaning of Float Charging of Batteries???

Answer

"A method of maintaining a rechargeable battery in a fully
charged condition by continuous, long-term, constant-
voltage charging, at a level sufficient to balance self-
discharge. also called trickle charging. " (source-
babylon dictionery.com)



Trickle charging, also called float charging, means
charging a battery at the same rate as it is self-
discharging, thus maintaining a full capacity battery. Most
rechargeable batteries, particularly nickel-cadmium
batteries or nickel metal hydride batteries, have a
moderate rate of self-discharge, meaning they gradually
lose their charge even if they are not used in a device.
One must be careful, however, that if a battery regulator
is not employed, the charge rate isn't greater than the
level of self-discharge, or overcharging and possible
damage or leakage may occur ( source wikipedia)