RailPro > RailPro Specific Help & Discussion
Large Scale Power
TJMac:
Awesome info thank you! Another question, the instructions for the large scale module say not to exceed 12amps....is that the engine under load or the system as a whole (IE: the power supply should be less than 12amps)?
So something like this?
15-18 volts
10 amps
Watts will be 150-180
Electricity is NOT my thing :o
Alan:
12 amps is the most current a single LM3 can handle for a brief instant. 8 amps is the most current a single LM3 can handle for an extended period of time. You must use some sort of circuit protection to disconnect the power if the current exceeds 12 amps through a single LM3. That could be a circuit breaker or a fuse. I would think a 12A fuse on the locomotive would be the most cost effective solution.
The power supply rating should be (total motor stall current of all locomotives that will run simultaneously) * 2.
For example:
Loco 1 stall current = 5A
Loco 2 stall current = 8A
Loco 3 stall current = 6A
Total stall current = 19A
x 2 = 38A
Use a 40A power supply
TJMac:
I think I got it....I think. How do I calculate the stall current of my locos....or can I?
Thanks again!
Tom
Alan:
Sooner or later you have to set the loco stall current on the HC so that it will control the loco correctly. Follow the instructions in the HC manual. The stall current will display on the screen.
If you do not yet have power you can directly measure the loco motor resistance with an ohmmeter by placing the test leads on the drive wheels or on the motor leads. Then use Ohm's Law to determine what the amperage will be at whatever voltage power supply you plan to use. Amps = Volts / Ohms. You may need to spin the motor armature slightly by hand to find the lowest resistance reading (motor brushes spanning two commutator strips).
Examples:
Power supply voltage = 18V
Meter reads 6 ohms across loco wheels
18 / 6 = 3
Stall current at 18 volts = 3 amps
Power supply voltage = 24V
Meter reads 6 ohms across loco wheels
24 / 6 = 4
Stall current at 24 volts = 4 amps
atsfguy:
Alan,
Are you saying to measure resistance between drivers to obtain the wattage to feed into Ohm’s law?
I played with electronics way back in the 60s but my Army career interveened and I missed out on lots of good stuff coming on in the 70s.
Correct me if I am mistaken but I thought one had to actually stalll the loco in order to measure stall current. Your method, if I understood correctly, is much simpler and easier. Easy is better!
Thanks for everything you do in this forum, it is much appreciated.
Cecil Collum
atsfguy
US Army, retired
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