Frequently Asked Questions (FAQ)

(Electric Locomotives)

Q:  I've never built an electric loco before, where do I start?

A:  Decide on what you want to build. If you have never built one before, a less complex unit with 4 or 6 wheels would be a good choice, or a simple bogied design. A freelance rather than a true-to-scale model would probably be better to start with. Maximum speed should be 10~12kmph.

If you look at the insides of an electric locomotive, it may appear very complicated, sometimes leading to comments such as "Phew, I could never do that!" or similar, but you would be surprised how simple each part really is. The basic connections and circuits are quite simple and easy to understand, they just look complex when all squashed together in a small space! However, some understanding of basic electicity principles is highly desirable, look at a basic text book or look on the internet - there is plenty of tutorial material there. A knowledge of electronics is NOT required - just basic electrical knowledge.

Q:  Which is better 12V or 24V?

A:  Difficult to answer exactly, there is no absolute answer, but if 12V is used, for the same output power, the motor and battery currents involved will be doubled. 24V permits lower operating currents and usually a higher output power from the motor for a given size. On balance, either 12V or 24V can be used, but 24V is probably preferred.

Q:  Is it better to have one motor, or multiple smaller ones?

A:  Ideally it is better to drive each driven axle independently, similar to the prototype. However, one larger motor with a gear/chain transmission system has been successfully used. Multiple motors, with consequently more gears/sprockets, can push the cost up, and make the controls more complex.

Q:  Can I run 12V motors on 24V?

A:  Yes, they will run at approximately twice the speed, but they will be four times easier to burn out, and more than likely exceed the motor ratings. While possible, it is NOT recommended practice and should be avoided.
You can run any motor at less than its rated voltage without any problems (e.g. a 24V motor at 12V), they just run a bit slower.

Q:  Can I run my motors in series?

A:  Generally yes, but if one axle/motor slips, then the other motor will stop driving (or reduce its output power due to a differential effect), unless the wheels are coupled together somehow. Series connected motors can be used to permit 2x 12V motors to run from 24V. Parallel connection is more common.

Q:  What kind of battery should I use?

A:  Lead-acid batteries are usually the logical choice. Other newer battery types (such as Lithium or NiH) are slowly becoming available from electric car development, but not readily available commercially in small volumes yet. Batteries specifically designed for high power deep discharge traction or semi-traction use are preferred (golf cart batteries for example). A battery specifically designed for deep discharge applications is highly recommended.

Car batteries can be used for testing but will not give a long service life in this application, as they are designed for only short periods of discharge during starting and then continuous charging. Car batteries are not really suited to deep discharge applications like this. Deep discharge traction batteries are recommended, and will be more costly than car batteries, but will give superior performance for a longer period.

Q:  What size battery do I need?

A:  In general - as big a battery as will physically fit in your model! This gives maximum weight (good for traction) and the longest running time. Apart from that, it all depends on what running time you want, the particular motors you use and how much current they consume, how many motors etc. See this article on batteries for more information.

Q:  What type of motor is best?

A:  Permanent magnet motors are the most readily available and have been widely used with good results. A series wound motor is best for traction purposes but may be difficult to obtain. Shunt wound DC motors are least sutable for traction use. See this article on Electric motors for more information. But whatever motor is used, make sure it is rated for *continuous* (100% duty cycle) use at full power under load, not for intermittent use only, otherwise it will run much hotter than expected. Small motors high power output can be found on the market, but there is no 'free lunch' - they provide a high power for a short length of time and will run quite hot if used for too long, and must be rested for a long period to cool down. Not recommended for this useage.

Q:  How do I know which gears, sprockets to use?

A:  First off, you need to know the maximum speed of your motor, the diameter of the driving wheels, and then decide how fast you want to go [10~12kmph max suggested]. Then you calculate the overall reduction ratio required from motor to axle(s). Click here to calculate which gears or sprocket ratios you should use to achieve the desired speed.

Q:  What is the difference between dynamic and regenerative braking?

A:  Both of these types of braking use the traction motor(s) as a generator to generate energy from the braking effort which is connected to and dissipated in a load. With Dynamic braking, this energy is switched into a resistive load and dissipated as heat. With Regenerative braking, the energy is directed back into the batteries to help recharging. Regenerative braking also effectively ceases when the motors generate less than the battery voltage. These types of braking are quite effective at higher train speeds for slowing a train, but provide less and less braking effort as speed slows, and useless when stopped.

Note that dynamic or regenerative braking is only useful to slow or retard a train, they cannot stop a train, there is zero braking effort available from dynamic or regenerative braking at zero speed, and therefore cannot be used for parking or to hold a stationary train. A mechanical brake is still required (and very highly recommended) for stopping, and as a parking brake.

Q:  Can I use more than one controller on my loco?

A:  Yes, but usually with each controller controlling it's own separate motor (or motor group) load. Depending on the controller type/brand, you can operate controllers together and use one common throttle control (refer to the manufacturer's data sheets for your controller).

Connecting multiple controllers in parallel to get a higher current handling capacity is usually not viable, and will probably damage (destroy?) the controllers. Not recommended - Use a single higher-powered controller instead.