Most often toy train power requirements are calculated in watts. However, there are times when they are made and discussed in terms of amperes or amps.
In their “Product Reviews” section, Classic Toy Trains compares the amount of amps a locomotive being tested draws based on the voltage applied to the track.
In addition, although The Lionel Corporation’s How to Operate Lionel Trains and Accessories, 1957 and Lionel Train & Accessory Operating and Wiring Manual for “027,” “O,” Super “O”, 1967 discuss watts in relation to their toy train transformers, they then shift to estimating power requirements in amperes. They say:
“While electric power is normally calculated in watts, you can obtain a very close approximation of the requirements of your model railroad by adding up the current, in amperes, consumed by your equipment, …”
(Lionel Train & Accessory Operating and Wiring Manual for “027,” “O,” Super “O”, 1967, page 23)
Here is our best shot of as we understand it.
NOTE: The calculations of watts, amps, and volts below will look very precise, but they’re really just rough estimates and should be considered as such. Thats why the calculations in amps and watts come out different and why you should always round up to be safe.
Toy Train Transformers
First Let’s Talk Watts: Toy train transformers reduce household voltage to a safe level for operating toy trains. Toy train transformers are rated in watts. This is a measure of the amount of electric power the transformer can take from the household line without overheating. It is not a measure of the wattage the transformer can deliver to the layout.
A 15 amp, 110-volt household circuit can safely supply about 1650 watts of power (15amps x 110 volts). Plugged into that circuit, a 275-watt Lionel ZW* transformer takes 275 watts from it.
NOTE: Material we’ve reviewed indicates that up to 25 percent of a transformers rated wattage is used internally by the transformer to reduce the household voltage to a safe level for toy train use. The internal usage is reflected in a warming of the transformer.
The above material recommends that a transformer not be loaded to more than 75 percent of its rated wattage to prevent overheating and excessive power loss over an extended period of use.
Now Let’s Talk Amperes: As shown above, watts can be roughly calculated by multiplying amps by volts. Accordingly, amperes can be calculated by dividing watts by volts:
- (15 amps x 110 volts) = 1650 watts
- (1650 watts ÷ 110 volts) = 15 amps
Applying this formula, a 275-watt transformer, which supplies a maximum of 20 volts, can deliver 13.75 amps.
- (275watts ÷ 20 volts) = 13.75 amps
As discussed above, to prevent overheating and excessive power loss over an extended period of use, a transformer should not be loaded to more than 75 percent of its rated amperes.
- 13.75 amps x .75 = 10.3 amps
How Much is Enough?
Both the 1957 and 1967 Lionel instruction booklets provide amperage estimates based on the number of motors (1.25 amps per motor) and the number of steadily burning lamps (0.20 amps)
Total amperage requirements depend on how many motors and lights will be running at any one time on your layout. Also, locomotives and accessories that are not maintained will have higher requirements than those shown below. Here are some guidelines:
Total wattage requirements depend on how many lights, accessories, track signals and locomotives will be running at any one time on your layout. Also, locomotives and accessories that are not maintained will have higher wattage requirements than shown in the table.
Here are some guidelines:
- Include the locomotive that draws the most amps. If two or more locomotives will be running at the same time, include the combination that draws the most.
- Include operating accessories that will most likely be operating when the locomotives are running.
- Include automatic track signals that will most likely be operating when the locomotives are running.
- Include lamps in passenger cars, cabooses and other illuminated cars that will most likely be on the track when the locomotives are running. Include the combination that draws the most.
- Include lamps in switches and switch controllers.
- Include lamps in streetlights, floodlight towers, non-operating accessories and buildings.
Lets Do The Math
| Sample Layout Equipment | Quantity | Requirements In Amps | Total Amps |
| Locomotives | |||
| One Motor and Whistle | 1 Loco | 1.25 amps | 1.25 |
| Two Motors and Whistle | 1 Loco | 2.5 amps | 2.5 |
| Acccessories | |||
| Operating Accessories | 3 accessories | 1.25 each | 3.75 |
| Automatic Track Signals | 2 signals | 1.25 amps each | 2.5 |
| Lamps (6 volts) | |||
| 4 x (2 lamp Floodlights) | 8 lamps | 0.20 amps each | 1.60 |
| 2 x (2 lamp Passenger Cars) | 4 lamps | 0.20 amps each | 0.80 |
| Lamps (12 volt small) | |||
| 5 Streetlights | 5 lamps | 0.20 amps each | 1.00 |
| 6 x (2 lamp Floodlight towers) | 12 lamps | 0.20 amps each | 2.40 |
| 2 x (4 lamp Floodlight towers) | 8 lamps | 0.20 amps each | 1.60 |
| Lamps (12 volt large) | |||
| 14 x switches | 14 lamps | 0.20 amps each | 2.80 |
| 7 x switch controllers | 7 lamps | 0.20 amps each | 1.40 |
| Lamps (18 volts) | |||
| 1 x Caboose | 1 lamp | 0.20 amps each | 0.20 |
| Estimated Total Amps | 21.80 | ||
- Add 25 percent to the Estimated Total Watts to account for the wattage used up internally by the transformer:
- 21.8 x 1.25 = 27.25 amps
- Round up to the next 100 watts to cover any miscalculations and to allow for expansion:
- 27.25 amps rounds up to 30 amps
- This 30-amperage requirement can be spread over a number of transformers. For example, one for track power to run the locomotives and lights in cars and switches and another for accessories floodlights, streetlights etc.
- Where more than one transformer is used, make sure they are in phase with each other.
- But if its still not enough to justify getting the transformer or transformers you REALLY want, just add more. Like they say:
A true toy train enthusiast needs at least one ZW!