# Volts? Amps? I need help with a power question



## kidzntoyz (Jun 8, 2011)

I am trying to run two point-to-point LGB trolley lines. I have purchased two Piko Reversing units, one for each line. My plan was to use a power source that I already have (I don't need to use a throttle as I will not be adjusting the speed of the trolleys once they get started). The power source states: input: 100-120VAC 3.0A and output: +24V 6.5A. I think I understand that it is the voltage and the amps combined that decide the speed at which the loco travels? I have adjusted the power down to 21 volts which is as low as it goes. Here is my dilemma... the Piko Reversing units each say "3 amps maximum". So if I am powering through two Piko Reversing units, does that mean I can have a maximum of 6A total (3A per unit)? I will be running at minimum two LGB 2064 Triebwagens and I also haven't been able to find how many amps they draw. I don't know anything about electricity, so any help would be appreciated. Thanks!


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## BigRedOne (Dec 13, 2012)

The amperage is a function of the load - the power supply will only deliver the amperage the load calls for. 

My LGB locomotive draws 0.7 amps with the train, and 1.0 amps when I added weight to the train. I think you'll be under 2 amps total operating the two trolleys, so you should be fine. If you're concerned, I'd add a 2.5 amp fuse between the power supply and each reversing unit (even if the trains don't draw three amps, a short curcuit from a derailing could.)


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## Treeman (Jan 6, 2008)

You may still need a throttle to slow them down. High voltage means higher speed.


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## kidzntoyz (Jun 8, 2011)

Should I assume that whatever speed one loco would travel on one track, the overall speed of two locos on two tracks would be less? And would the speed be determined by each individual model loco?


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## kidzntoyz (Jun 8, 2011)

I like the idea of the fuses ... and thanks for clarifying the amps question.


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## kidzntoyz (Jun 8, 2011)

Posted By BigRedOne on 23 Dec 2012 09:03 PM 
The amperage is a function of the load - the power supply will only deliver the amperage the load calls for. 

My LGB locomotive draws 0.7 amps with the train, and 1.0 amps when I added weight to the train. I think you'll be under 2 amps total operating the two trolleys, so you should be fine. If you're concerned, I'd add a 2.5 amp fuse between the power supply and each reversing unit (even if the trains don't draw three amps, a short curcuit from a derailing could.) 


So how do you figure out how many amps a loco is drawing? I do own a multimeter ... but knowing how to use it is something else.


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## Treeman (Jan 6, 2008)

Sounds like you will have constant voltage that will be too high. Running the second will not drop the voltage in this case.


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## Treeman (Jan 6, 2008)

Some multi meters can be connected in series with the load to measure current. Look for "A" on a dial set point on the meter with a DC for Amps, direct current.


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## BigRedOne (Dec 13, 2012)

Posted By kidzntoyz on 23 Dec 2012 09:39 PM 
Should I assume that whatever speed one loco would travel on one track, the overall speed of two locos on two tracks would be less? And would the speed be determined by each individual model loco? 


If you connected the two circuits in series, then each curcuit would see half the voltage (assuming each is the same resistance), but this would be a maximum of 12 volts. 12 volts does yield a reasonable speed to me. This is not the customary way to operate a model railroad, and adds potential for problems, but it would get you started with the components you have.


You can test the operation by connecting two tracks in series - one lead from the power supply goes to one rail of track one; the other rail of track one connects to one rail of track two; the other rail of track two returns to the power supply.

Typically, each section of track is conected in parallel to the power supply, such that each sees the full voltage output.


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## BigRedOne (Dec 13, 2012)

Posted By kidzntoyz on 23 Dec 2012 09:43 PM 
So how do you figure out how many amps a loco is drawing? I do own a multimeter ... but knowing how to use it is something else. 


Create a break in the circuit and connect your ampmeter in the break. Make sure your meter is capable of reading beyond the foreseeable currant draw, and that you are not creating a short circuit as you connect the meter - not all ampmeters are fused, and inexpensive ones often have low amperage capacity. 

I'm sure you're fine operating two trolleys on a 21 volt, 6 amp power supply. For me, 21 volt will be too fast, but that is personal preferance. Connecting in series might be just right, though.


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## Dan Pierce (Jan 2, 2008)

Fast running on a reversing unit would cause an engine to eventually strip its gears. 

Only engine I ever saw that 'coasted' fairly well was the LGB mogul, but these just took longer to strip the idler gear. 

Get a throttle and lower the voltage!!


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## chuck n (Jan 2, 2008)

On my point to point, I put a 10 ohm resister across a gap a foot or two in front of the diode gap that stops the engine. This reduces the speed of the engine by about half. The exact reduction depends upon the voltage on the main part of the track. This way the sudden stop isn't quite as jarring. You can put some numbers into Ohm's law and calculate the value of the resistor that would give you the final speed that you would like.

Chuck


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## toddalin (Jan 4, 2008)

Posted By kidzntoyz on 23 Dec 2012 08:48 PM 
The power source states: input: 100-120VAC 3.0A and output: +24V 6.5A. 
the Piko Reversing units each say "3 amps maximum". I don't know anything about electricity, so any help would be appreciated. Thanks! 



In theory your power supply can put out 24 volts at 6.5 amps (sounds like a Mean Well). It sounds like you want to take this as low as it goes (21) and use that to power the trains directly through two reversers without any other throttle to further reduce the voltage. 

First off, 21 volts will be way too fast and you will want some sort of throttle to get the trains to a more reasonable speed. I don't think that you could feasibly "series" the two reversers to halve the voltage because when one train stops, the other would also stop, even if still out on the line, or some other such nonsense could/would occur due to their interaction. Also, while you can use resistors to slow the train at the end of the line for a few seconds before it stops, you would not want a steady draw on a resistor, such as used to control the overall speed of the trains, as it would get VERY HOT.

With respect to the amperage rating. What Piko is telling you is that you do not want to use any engine on their system that will draw more than 3 amps, which is probably the rating of their relay contacts. Because your power supply can put out 6.5 amps and you will not draw more than 3 from either reverser, and no more than 6 for both reversers combined, you should be fine in that respect.


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## Dan Pierce (Jan 2, 2008)

The amp rating of a reverser can be the mosfet that creates the pulsed power such as the Aristo reverser, relay only creates the direction change.


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## lownote (Jan 3, 2008)

Dave bodnar has an article about using thermistors to slow acceleration:



http://www.trainelectronics.com/artcles/capacitor-thermistor-partII/thermistor.htm 


He has another article about using capacitors to slow deceleration. 

http://www.trainelectronics.com/artcles/capacitor/index.htm


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