AHD RRampMeter
Application Notes, Helpful Hints
PDF Document
As a result of my involvement in “Command
Control” Systems for 16 years, it became apparent that model
railroaders needed a simple to use, accurate tool to measure
volts and amps for their Railroads. The advent of DCC with
its unconventional waveform further amplified the need. I
conveyed the concept and format to Larry Maier, a model railroader,
and electrical engineer who is also a vital contributor to
our DCC development efforts. His resulting design speaks
for itself. Jim Scorse from NCE Corp also made some great
suggestions.
The maximum DCC and DC voltage is approximately 23 volts
(covers the complete specified NMRA voltage range). The maximum
DCC and DC current is approximately 9.2 amps. The maximum
AC voltage is about 17 volts while the maximum AC current
is about 6.5 amps. AC signals have a higher ratio of the
maximum signal value to the RMS signal value than does the
DCC and DC signal. These values may vary slightly from unit
to unit due to component tolerances. The accuracy is between
2%-3% full scale. Two status indicator LEDS indicate either
DCC or AC voltage, no indication on LEDS means DC voltage
is present. When measuring DCC and AC voltages and current,
any polarity will work. When measuring DC voltage, proper
polarity is necessary. If you attempt to measure a DC voltage
and there is no readout, simply reverse the connection polarity
and you will get the proper readout. Units with battery or
an external DC power supply will display DC voltage and current
irrespective of polarity.
Version IV RRampMeterHP is same as III but designed for
large scale high voltage and current applications with the
following specs: DCC: 38.6 v and 18-20 Amps; AC: 27.6 v and
18-20 Amps; DC: 38.6 v and 18-20 Amps
Amperage must be measured in series by connecting the left
set of contacts or clip leads to the input power supply or
power source while the right set of contacts or clip leads
are connected to the load or isolated track section where
current is to be measured (Fig 1). The RRampMeter may be
connected in the reverse direction without damage, but the
display will show the current used by the RRampMeter in addition
to the load current (about 0.03 to 0.04 for no load) (Fig
4). The voltage display also will not account for any voltage
drop in the RRampMeter itself.
Voltage can be measured from the left or right set of contacts
or clip leads. If measuring voltage only, then either end
of the RRampMeter may be used accurately.
We do not recommend soldering directly to the buss bars
that connect the adjustable contacts as this may interfere
with the operation of the adjustable contacts (Fig 2).
For Panel or Fascia mounting, Version (1) can be used. You
will have to cut out holes in your fascia for the LEDS and
the Indicator Lights. Four mounting holes are provided on
the circuit board for mounting. You can also use Version
(2) and mount the enclosure cover to your Fascia if you prefer
a dressier appearance (Fig 3). For mounting templates see,
Fig’s 6 and 7.
The RRampMeter is designed to read true RMS voltage and
current. The RMS values are proportional to the power being
supplied to the layout. An average reading meter (most inexpensive
meters found in electronic stores, hardware stores, etc.)
WILL NOT agree with the RRampMeter. The RRampMeter is displaying
the correct values.
Some DC power supplies use pulsed power for low speed. The
RRampMeter will read this signal at its correct RMS value,
but will display the AC PRESENT light. Once the supply transitions
to full DC, the RRampMeter will continue to display the correct
values, but the DCC PRESENT and AC PRESENT lights will both
be out.
If the current display shows more than 0.00 amps when only
the booster is connected to the left hand input, then the
display value may be adjusted to 0.00 by turning R44 until
the display just transitions from 0.01 to 0.00.
When using a battery, the RRampMeter will not show 0.00
volts with no signal connected. This is because the open
contacts on the input actually pick up some voltage from
the surroundings (power lines, DCC on the tracks, etc.).
In addition, the circuitry used cannot quite reach 0.00.
The RRampMeter is calibrated to read correctly above several
tenths of a volt.
The RRampMeter will measure voltages down to approximately
7.00 volts without using the 9V battery option. For DCC,
this is more than adequate. To measure lower voltages, the
battery option must be used. If the battery is connected,
one position of the switch will turn the RRampMeter on using
the battery. The other position will disconnect the battery
and allow the RRampMeter to be powered from the input voltage.
Either position may be used with the battery connected.
If the RRampMeter is operated at currents in excess of 5
amps on a continuous basis, then it must be mounted in such
a way as to allow free air circulation for cooling.
The RRampMeter is a great 9V battery tester. Just connect
the battery across the track inputs.
You may be surprised at how much booster voltage is lost
in track feeders, long stretches of track, and control switches.
The RRampMeter is telling the truth.
The RRampMeter will work with common rail systems. If you
want to measure the current in a single track block, connect
the common rail feed to J1-1 (J4-1 or J6) and the remaining
side of the booster to J1-2 (J4-2 or J7). A single output
connection may be run from J2-1 (J5-2 or J9) to the desired
block. If you want to measure the TOTAL current on the common
rail feed, connect the common rail to J1-2 (J4-2 or J7) and
the remaining side of the booster to J1-1 (J4-1 or J6). The
common rail is then connected to J2-1 (J5-2 or J9).
We have tried the RRampMeter in conjunction with the programming
track with mixed results. In some cases, the current drawn
by the RRampMeter to operate itself may be sufficient to
upset the programming sequence. If you want to operate the
RRampMeter with the programming track, it may be necessary
to use the battery option.
If you plan to use the RRampMeter without the case in a
situation where it will be handled, it may be wise to glue
Y1 and C1 (located on the back of the board) to the printed
wiring board to prevent an accidental component removal.
We find that a touch of “Crazy Glue” or equivalent is ideal
for this purpose.
J4 and J5 are optional and sized for a two terminal header
for use with a connector. The DigiKey part number is ED1817-ND.
The mating plug is DigiKey part number ED1717-ND. You may
also solder wires directly to these holes for a permanent
installation.
If you are installing the RRampMeter as a permanent fascia
display, a piece of red clear plastic or lighting gel in
front of the display will improve the contrast.
Why the RRampMeter
Maintaining and analyzing the electrical system of a layout
requires accurate measurements of the voltage and amps.
When dc was used a standard meter was all that was needed
for these measurements. With DCC use of a standard meter
most of the time will not give you an accurate measurement.
Tests have show that meters not designed to read the DCC
wave forms can be off by as much as ±50%. Even meters that
are “true RMS” may not be designed for the frequency range
of DCC. The RRampMeter was designed to fill the need for
a highly accurate DCC meter to measure of both voltage
and amps. The RRampMeter is designed as a flexible tool
to monitor and analyze the electrical operation of a layout.
It is designed to work not only DCC power but to make accurate
measurements of ac and dc. The RRampMeter has an amazing
2% accuracy. Because the original 10 amp range of the RRampMeter
was not adequate for large scales a 20 amp version was
added to the line.
Available Models
A total of four models of the RRampMeter are available. There
are three models are available in the 10 amp range and
one for large scale with a 20 amp range. The standard meter
is rated at up to near 10 amps and up to 23 volts DCC or
dc and 6 amp at up to 16 volts on ac. The new Version VI
RRampMeter for large scale trains have a capacity of up
to about 20 amps. The three basic models are [A] a bare
module design for panel mounting, [B] mounted in a plastic
case and [C] mounted in a plastic case with the option
of battery power. All of the meters are powered by the
input voltage. The voltage must be greater than 7 volts
to operate. Versions III and VI come with a backup 9 volt
battery to operate the meter when the input voltages of
less than 7 volts. The meter can be used either as a portable
meter or mounted permanently in a panel. Screw terminals
are supplied with the meter that can be soldered to the
back side of the meter’s circuit board.
RRampMeter Circuit Modules
Version I - Bare Module RRampMeter Module; 7 to 23 volts
10 Amp (DCC)
Version II - RRampMeter with enclosure and clip leads; 7 to 23
volts 10 Amp (DCC)
Version III - RRampMeter with enclosure, clip leads and 9 volt
battery backup; 0 to 23 volts 10 Amp (DCC)
Version IV - RRampMeter with enclosure, clip leads and 9 volt battery
backup; 0 to 23 volts 20 Amp (DCC)
Panel Meter
A meter mounted near the system or booster will let you monitoring
the power supplied to the layout. This will let you can
determine how well your system or booster is regulating
voltage under load. You can also measure just how close
you are to the maximum power limit of the booster or system.
This will indicate the operation of the system/booster,
but not the voltage drop of the wiring and rails of the
layout.
Track Voltage
Voltage is read by connecting to the two terminals on the
left side of the meter. The end of the circuit board has
an area that allows you to put the meter directly on the
rails to measure the voltage. In order to measure amps,
the current must flow through the meter by connecting a
load to the two terminals on the right side of the meter.
True “RMS”
Most common meters can read both ac and dc, but can not accurately
read DCC power. In order to accurately read DCC power a “true
RMS” meter, like the RRampMeter is needed. This is due
to the shape and frequency of the DCC signal. Even many “true
RMS” are not designed for the high frequency of the DCC
wave form. The RRampMeter automatically detects and switches
to the type of power it is measuring.
Two LEDs indicate DCC or ac, no LED on indicates dc.
Layout Voltage Loss
When the rail voltage to a decoder drops the train speed
can also drop along with lights dimming. There are many
places in the path from the booster to the decoder where
voltage can be lost. The voltage from the booster or system
may have a small drop as more current is drawn. The wiring
from the booster to the rail will also lose some voltage.
Devices like circuit breakers and block detector can add
to the voltage loss. Nickle Silver rail is not as good
a conductor electricity as copper wire and can be a significant
part of the voltage loss. Rail joiners can also cause a
loss in voltage. To determine the layout voltage loss the
voltage must be measured at the rails when current is flowing.
Without a current flow there is little to no voltage loss.
It is almost impossible to get a good stable voltage reading
using a train running as a current load. The best way to
measure the loss is with some type of steady load. An automotive
lamp turns out to be a good device to use as a steady load.
They are cheap and easily available. A couple of pieces
of wire with clips can be soldered the lamp. (See photo)
Depending on your scale and booster rating one of the following
automotive lamps should work. The #912 draws about 1 amp
the #1141 about 1.5 amps and the #1156 about 2.25 amps.
(Due to the low cold resistance of a lamp, the 1156 lamp
can cause low powered systems like the Zephyr to shut down
[overload]. The 912 should be OK for this test.) Choose
a lamp that is near the maximum current used in a block,
not the current used by the layout.
The first test should be to determine the voltage loss of
the system or booster. [A] Measure the output voltage of
the booster at a point close to the booster with no trains
running. If you have an RRampMeter connected as a panel meter
close to the booster this reading should work. [B] Next connect
the load to the rails load (lamp) to the rails with the meter
still next to the booster. The difference between the two
readings will give you the voltage loss of the booster at
this current. [C] Read the voltage at the rails with out
a load. [D] Read the voltage at the rails with the load.
The lamp can be connected the terminals of the RRampMeter
so a number of reading can be made in the same block. You
may be surprised at the voltage loss at different points
of the same block. This can be due to the poor conductivity
of Nickle Silver rail. Poor connections of rail joiners is
another thing to look for. Wire that is under size is also
a cause of voltage loss. When making measurements of loss
across things like rail joiners and connections the voltage
is so low that the RRampMeter with the battery option make
be needed. It is best to keep the voltage loss due to wiring
and rails under 1 volt. More than a couple of volts can cause
slowing of locomotives and in extreme cases even cause the
decoder to drop out. There is a wire chart that shows the
length of wire for a ½ volt drop due to wire resistance.
The chart shows the voltage drop for 1, 2, 5 and 10 Amps.
This is a chart for one way resistance. If you wire out to
the rails and back (double the length ) this chart becomes
a 1 volt chart.
Which Size Wire?
The 20 to 18 gauge wire should be used only for Z and N scales.
This size can be used for short track feeders in larger
scales. The 16 gauge works for most small layouts with
short runs. The 14 to 12 gauge for larger layouts in most
scales. The 8 to 10 should be reserved for older O scale
and G scale layouts. This larger size wire becomes a bit
cumbersome to work with.
Stranded wire can be used anywhere, but solid should only
be used where it will not be flexed or moved.
Voltage loss for ½ volt for different currents and wire
size.
|
Wire Size
|
1A
|
2A
|
5A
|
10A
|
|
8
|
796
|
398
|
159
|
80
|
|
10
|
501
|
250
|
100
|
50
|
|
12
|
314
|
157
|
63
|
31
|
|
14
|
198
|
99
|
40
|
20
|
|
16
|
124
|
62
|
25
|
12
|
|
18
|
78
|
39
|
16
|
8
|
|
20
|
50
|
25
|
10
|
5
|
Monitoring Current
If your layout uses common rail wiring and you have more
than one booster you can monitor the current from both
boosters. Run the common of both booster through the meter
and this will get you an indication of total layout current.
NOTE this will only work with common rail wiring. |
Wig-Wag, LLC
