Motor Current:
1)
Many MTH motors are capable of drawing up to as much as 3 Amps maximum loaded current before slipping. Some steamer motorss will draw up to 6 Amps.
A 2 motored unit can easily draw up to 6
Amps, which might be used when pulling a long string of cars, which
some operators do.
Large steamers with a big motor can also draw up to 6 Amps heavily loaded.
2)
The design of the ProtoSounds1 is limited to 2.5
amps of motor current solely because of the heat buildup of the 4
diodes on top of the rectifier.
This works just fine with short trains
of 4-6 easy rolling Aluminum passenger cars, or 8-12 freight cars.
The rectifier and relays are designed to handle 6 Amps.
However, under heavy loads, (currents above 2.5 Amps) the diodes being in such close proximity to the bridge rectifier will bake the board, causing roasting of the flux from
honey color to black, melting of the solder, melting diode plastic cases and
eventual destruction of the rectifier and finally the board. Along the way the board will warp.
3)
While the warping is no problem for the DCRUs, it can cause a voltage failure on ProtoSounds1's bottom board, and lead to possible destruction of the top board.
4)
One solution to the heat problem is to have the Hi-I Current upgrade installed.
See: AC&DC Motor Reverse Units: DC Motor Reveres Units, lines 1b1 & 1b2.
The Upgrade replaces the diodes on top with 2 chassis mounted rectifiers, which
dissipates the heat to the chassis. $30. Installation is $6.
4a)
With
a Hi-I upgrade, allowing for up to 6 Amps, yielding an increase of 3.5
Amps, one could add up to another 17 Al Passenger cars, for a total of
22 passenger cars. (3.5 Amps / 0.2 Amp per car = 17.5 cars). Now the
limit is one of torque & traction (not to mention the space),
rather than overheating of the reverse unit.
Note: Each dummy loco is approximately the load of 1.5 passenger cars.
4b)
The 1/2 Hi-I, 1 chassis mounted bridge rectifier: $15, Installation is $3.
The 1/2 Hi-I is a compromise, due to various space limitations and # of
cars. It uses 1 bridge rectifier and is good for up to
4.8 amps continuous motor current. It is good for up to 12 Aluminum
passenger cars or 24 freight cars.
We are talking about the current production easy rolling Al passenger
cars, not the '50s Lionel or the '80s Williams reproduction high
friction versions, etc.
5)
The other way to achieve the required power dissipation is to use more than 1 powered loco in the consist.
Note: Lighted passenger cars require current too. There will always be
a limit somewhere as to how many locos and cars can be on one train, as
set by the transformer's power/Voltage limits.
6)
The After Market QSI 3-rail Sound Systems manage with a maximum of 3.0
Amps for motor current, because the diodes are mounted
vertically.
7)
The loaded motor-current test, easily performed with a Z-4000:
1) Run the complete train at speed and note the Amperage and Voltage readings.
2) Stop the train and readjust the Voltage, if necessary, to return
to the same Voltage reading as during running and note the neutral
current.
3) The difference between the neutral current and the running current is the loaded motor current.
8)
The loaded motor-current test, performed with a precision resistor.
There is another way to measure current, which requires a 0.1 Ohm, 25 Watt resistor, and a 3.5 digit Digital Volt Meter with a 2 Volt AC scale.
Connect the resistor in series with the transformer lead going to the center rail. Connect the Volt meter across the 2 resistor terminals and multiply the Voltage reading times 10 to get Amps.
Ex: A reading of 200 milli Volts (0.200 Volts), times 10 represents, a current of 2 Amps.
9)
Some Volt Meters have AC current measuring capability, usually up to 10 Amps. However, using an external resistor protects your meter from any over current damage as well as allowing for more current that most meters will tolerate.
Take Voltage readings as before, for both the train running at speed, and stopped. The difference of the two readings is the motor current's resistor-Voltage, which is then multiplied by10 to get the motor current.
25 Watt, 0.1 Ohm, 1% resistors are available from STR for $7.50 each plus shipping. They are intended to be mounted on a sheet of aluminum to achieve the full rated heat dissipation.
10)
The exception to the 2.5 Amp current limit is the DCRU-MB made for Right-of-Way, which is limited to 1.5 Amps.
The exceptional Pittman high efficiency motors used in the Right-of-Way locos coupled with the ball bearing equipped (very easy rolling) Right-of-Way cars completely balance out the requirements and limitations for long trains and staying within the necessary current requirements.
Another way is to estimate:
11)
To get a better handle on estimating the current needed for your locomotive follow these rules of thumb.
To make any motor(s) of a loco turn requires about 1.5 Amps.
Each
aluminum passenger car added adds a load requiring an additional 200
milli Amp of motor current. Hence 5 Al passenger cars would require an
additional 1 Amp, making the total motor current 2.5 Amps.
Modern easy rolling freight cars are estimated to require abut 100 milli Amps each.
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