Onan LTC Series User Manual

DESCRIPTION
The
Onan
series
LTC
(load
transfer
control)
is
designed fot
use with Onan
2-wire, 24-voLt, remote-starting,
generating
plants
installed for standby service.
The
LTC
controls
generating plant
operation, supply of c-ommercial and emer-
gency power
to the load.
It
assures a supply
of
emergency
power
during
commercial
power
failures.
CIRCUTT
&
COMPONENTS
The basit:
LTC
includes:
1.
Load
transfer switch that connects either
the commer-
cial or
emergency
power
to the load.
2. Relays
to start and stop
the
generating
plant
and control
the bansfer
switch.
3.
A
battery
charga which
maintains
starting
batteries
at
full-charge.
NOTE:
Use
the
wirin! dia(,ran
lumished
with
the
control
in
conjunction
with
flis
explanation
(wirin{
diagams
explained in
[vtaintenance Section).
0perotion
-
(Mechonicolly
Held
Tronsfer
Swirch):
The frans-
let
switch is electrically
operated and
connects
the load to
commercial or emergency
power
source. An
LTC's
current
rating is
determined by
the transfer switch capacity.
All transfer
srvitches contain
two separate
sets
of
contacts;
one
set connects the
commercial iine
to rhe
load,
the
other
connects the emergency
power
to the load.
A
pull-in
coil
(when
energized by line
power)
pulls
in
the
lineside
con-
tacts.
A
mechanical latch
then
locks
the
contacts
closed
and opens a micro-switch
that
disconnects the
pull-in
coil.
This
eliminates hum
during normal operation.
Another
coil
(energized
by
plant
output)
operates
the
mech-
anical latch
release, disconnecting
the line-side
contacts.
These contacts must
unlatch
and
drop
out before
the
gen-
erator
contacts
can
close.
Power supplied to this
coil also
pulls
in
and
holds
the
generator
contacts closed.
Both
mechanical
and electrical inter-locks prevent
contacts from
closing
at the same
time.
The 6asic control
circuit
consists
r.;f
I
hre,e relavs:
1.
Start-stop
relay
2.
Transfer switch
pilot-relay
3.
Instant
transfer relay
In addition,
it
may
contain
some optional relays.
The
start-
stop
relay
controls
starting
and
stopping
of
the
generating
plant.
When the relay
de-energizes
its
contacts
signal
the
engine
control to
start and
run
the
plant.
The
transfer
switch
pilot-relay
controls
the mechanical
latch
release
coil
and
the
generator
side of
the
bansfer
switch.
When
the
pilot-relay
energizes,
it releases
the latch
and
connects
the
coil
that
pulls
in
the
generator
side of the
transfer
switch.
The
instant
transfer
relay
conhols
the lineside
of the
trans-
fer
switch
and
also
the
generator
side.
Whenever
this relay
is
energized
from
line power,
it
breaks
the
circuit
to the
generator
side
and energizes
the line-side
of the transfer
switch.
Normally
(with
cominercial
power
on)
the
transfer
switch
line-side
is
closed.
The
start-stop
relay
and
instant
trans-
fer relay
are
energized;
the transfer
switch
pilot-relay
is
de-energized.
When
conrmercial
power
fails,
the
start-stop
and instant
transfer
rr:li1s
de-energize.
This
closes
the
start-stop
relay
contact,
signaling
the
plant
to
start.
When
voltage
builds
up, the
hansfer
switch
pilot-relay
pulls
in,
energizing
the latch
r.lisconnect
coil
and generator-side
coil.
The main
line
contacts
open,
generator
contacts
close,
and
the
gen-
erator
supplies
power
to
the load.
When
commercial power
returns,
the instant
hansfer
relay
closes
which
disconnects
the
generator
side coil of
the
transfer
switch
and
allows
the line.side
to
pull
in immedi,
ately.
At
the
same
time, the
start-stop relay
energizes
to
stop
the
generating
plant.
High
Rote Bottery
Chorger: This
charger
includes
a
high
rate
of
about 2-amps
to
boost low
batteries
and
a
low rate
(100
-
500
milliamp,
adjustable with
rheostat) to maintain
batteries
once
charged. Both are controlled
by
a toggle
switch
on the
inner
panel.
A
light
indicates
when the high
rate
is on;
the
meter indicates
the low rate
charge
cunent.
Load
Tlzrnsfet
Control
LTC800-1200
is contained in
two
separate cabinets,
one cabinet
contains the
control relays,
battery charger, and
optional equipment.
The
other cabinet
contains
the transfer
switch.
The
transfer switch
is
rated at
8ft)- or
120Gamps
and has non-tripping
circuit breakers
actuated
by
small electric
motors.
A
mechanical interlock
(on
the
back of
the switch)
prevents
line and
generator
contacts
from
being
closed
at the same
time.
5-.

Onan LTC Series Specifications

General

Brand	Onan
Model	LTC Series
Category	Controller
Language	English