MODEL 821A - 3.0 AMP PWM WALKAROUND MEMORY THROTTLE
Fully assembled and tested - see bottom of page for more details
The model 821 is the big brother
to the model 852B PWM
throttle. This is definitely the best choice for heavy duty model
railroading. Since 1990, the predecessor model 820 and the new 821A have been,
and remain as, one of today's best dollar for dollar model railroad throttle
values. The number one choice for clubs and large layouts, the 821 boasts the
ability to dish out up to 3 amps continuous pulse width modulation current without batting an eye.
Internal current overload and over temperature protection features make sure
that this hard working throttle stays on your layout and not at the repair shop!
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The 821A circuit is a proven
performer. For multiple lash-ups, precise controlled yard work, and steady
mainline running, the 821 is the best choice you can make. This throttle
will operate on AC or DC input voltage making it ideal for outdoor shows
or for running off of just about any power pack you have laying around.
Even the most stubborn motors will show improved performance and response.
HO, N and Z scale voltages can be "dialed in" with an adjustment
on the main printed circuit board. And, contrary to popular myth, PWM will
not harm your motors. Easy setup and comprehensive instructions make
this a natural choice for the "electronically challenged". Isn't
it about time you had a throttle you derived pleasure from? |
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Pulse width
modulation throttles overcome friction and inertia by
"kicking" the motor with full throttle voltage for a
short period of time. The voltage rises to full amplitude very
rapidly and shuts down to nothing equally as fast. No slow rise
and decay times mean less motor heating. But even better, the
motor starts to spin immediately and PREDICTABLY. PWM throttle
settings produce repeatable and predictable speed changes without
jump starts and motor stall at low speeds. This means no more
overcompensating on the throttle control knob in the yard when
you're trying to couple to a cut gently or when you're trying to
take up coupler slack.
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The 821A
throttle consists of 2 parts. First is the hand control, designed for one
handed operation. The high impact styrene control box measures 2"
wide, 4" long and 1" deep. That's small enough to fit
comfortably in the palm of your hand. The hand control unit is equipped
with "SPEED" and "MOMENTUM" controls as well as a
"DIRECTION" toggle switch. The handset cord is 6' long and is un-terminated, which means that you will select and supply the 4 pin mating
connector of your choice to interface with the 821A's main printed circuit
board assembly. |
Directions are included so that
you can customize your 821A handset by adding "BRAKING" and
"MOMENTUM DEFEAT" features at a later date. The memory feature allows
you to locate several operator stations around your layout and move the handset
from one location to another on the fly without affecting your train's speed or
direction of travel. This is a highly sought after feature for large club and
home layouts.
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The main
printed circuit assembly is designed to mount under the layout, out of the
way. The massive finned aluminum heat sink keeps the output device from
over-heating under the most demanding conditions like those 4 and 5 unit
multiple lash-ups! Digitally generated signals process the handset's DC
control voltage to produce clean PWM voltage to give you the ultimate in
locomotive control.
The system
requires 12 to 18 volts AC or DC power. This means you can use a car
battery at outdoor shows to power your throttle! How many throttles can do
that? It's just another built in feature of this marvelous throttle. |
A PRIMER ON PWM
Most modelers are familiar with the concept of proportional voltage throttles.
But, what about PWM?. Take a look at the voltage pulse diagrams
below. When you start at the low end of the PWM control knob,
output voltage will rise from 0VDC (the blue dashed line) to full
output voltage (the red dashed line-for the sake of explanation
let's say this is 12VDC). This happens 60 times per second for
this throttle design. It can be varied on other designs. The
first wave is 10% pulse duration. This means that full DC voltage
is present for 10% of one sixtieth of one second. The pulse
duration is actually less at the bottom end of the control
setting, but 10 % is a nice place to start to explain what's
happening here. At the 10% setting the locomotive will be
travelling at typical slow yard speeds. Turn it up to 25% and the
speed increases. The voltage doesn't increase, only the amount of
"on" time does. 50% and 90% settings increase the speed
of the locomotive proportionaly. The throttle design presented
here varies the pulse duration from 0% (no voltage) to 100%
(which is pure DC) at full setting.
Real locomotives
use PWM speed control methods to turn their motors as do most
heavy industrial DC motors. Even VCRs, tape decks and CD players
use some form of PWM control to control motor speeds. Sadly, it
seems that proportional voltage control systems proliferate in
the world of model railroading.
If you have never
experienced the pleasure of absolute control in the operation of
a locomotive powered by a PWM throttle, you're truly missing out
on one of the better aspects of model railroading. It's kind of
ironic that people will spend upwards of $100 on the purchase of
a quality locomotive and refuse to
dish out a few extra bucks to realize the full potential of their
new toy with a great throttle.
PRICE
EACH - FULLY ASSEMBLED & TESTED
USD $72.00
SHIPPING
EXTRA
To order this item, send
an e-mail to me and I'll
supply you with details.