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Choosing the correct power supply for your application

 

There are many manufactures of power supplies that support the hobby marketplace. Pricing and quality can vary quite a bit. The important consideration is ensuring the correct type of supply is matched to the project you intend to use it for.

Here at Ngineering, we manufacture many different electronic products that support Lighting, Lighting Effects, Constant Voltage and Sound Effects.

For customer convenience and flexibility, nearly all of our products include an on-circuit voltage regulator which allows the product to operate over a wide range of input voltage (usually DC voltage).

While these voltage regulators provide very precise output voltages to ensure our products operate as expected, they do need clean input (DC) voltage of a known value to operate correctly.

Clean input  (DC) voltage can be defined as voltage that does not have a noise component larger than a few millivolts (thousandths of a volt), or a AC voltage component, or is pulsed DC voltage.

Known value can be defined as a supply that outputs a given voltage that is not dependant on the load (current in Amps (or milliamps) that is placed on the supply.

 

Power supply potential problems:

Wall-warts: Characteristically named because when they are plugged into a house electrical outlet they look like a "bump" or "wart" sticking off the wall. These are typically available everywhere and a very inexpensive ($5-$15). They are also very simple in design, essentially a voltage dropping transformer and a couple of diodes. They reduce the house voltage (~117-120 volts AC) to the output defined (5, 9, 12, 18 volts, etc.) and the diodes convert the AC to a somewhat "unclean" DC voltage. The main problem with these devices is that they do not have internal voltage regulation so the stated output voltage is nothing close to the actual voltage (known value) when a load is applied. We have seen 12-volt "wall-warts" that measure well over 20-volts when tested with a volt meter. Their output voltage is usually stated based on the load (in Amps or miiliamps) they can support. Additionally, because they have minimum AC to DC rectification, the DC output contains AC "noise". Both of these problems can be catastrophic for powering LEDs. Since LEDs draw very low operating current, they will not "load-down" a supply very much. As a result, connecting an LED with a current protecting resistor to a "12-volt" wall-wart can easily turn the LED into a flashbulb! (excessive input voltage).

MRC power supplies: Model Rectifier Corporation (MRC) has made many wonderful power supplies for the model railroad hobby market for many, many years. However, many of their supplies intended for track powering non-DCC (analog) model railroading applications have found their way into projects they were not intended for. Because they have sold so many supplies over many, many years a high percentage of model railroaders have at least one, or two setting around in their spare parts bins. Here's the problem... Many of their products have a feature called "momentum". The DC motors used in model locomotives have difficulty operating smoothly at lower track voltages because they don't operate as efficiently as they do at higher voltages. As a result they can be "jerky or stuttering". MRC's solution was to provide pulsed DC to the motor so it would receive a higher voltage but for short durations of time. This pulsing worked very well to help solve the "stuttering" problem with the DC motors. However... this type of DC voltage is a disaster for a circuit that has a voltage regulator expecting to receive clean DC. Basically, what happens is that each time the regulator receives a pulse of DC it tries to "start". It goes into a continuous restart mode and never get the circuit fully functioning properly.

Older power supplies: Train "transformers" and power supplies have been around for more that 75 years. Many are still in use today. Again...however... these supplies have a couple of components that age over time and can fail or become weaker. Electrolytic capacitors have a lifespan and can become "leaky" over the years. These are usually fairly large "can-like components that hold an electrical charge and act as a filter to smooth out rectified DC voltage to make it clean. The most common types are oiled-filled or paper-wound. The one exception is tantalum electrolytic capacitors (made with the rare-earth material, tantalum). These do not exhibit the aging problem but are of much smaller size and capacitance value and are typically not used in these higher amperage power supplies. The other component is the germanium diode. Most of these were replaced by silicon diodes and diode bridges many years ago, so their existence would be quite rare.. When the big capacitors age, the DC output from the supply becomes less clean and more bumpy (similar to the pulsed DC described above). Very old supplies should be considered suspect.

DCC track power: this type of track power is rapidly becoming the "standard" for model railroad operations because it provides such exceptional support for operational control. With DCC, several (or many) locomotives can be operated on the same section of track, individually at different speeds and in different directions, at the same time. However... (here we go again) The DCC signal that is applied to the track is pulsed DC including  "packets" of information that decoders located in each locomotive translate to perform commands properly. This signal is also somewhat similar to AC voltage in that it goes both +DC and –DC.. Depending on the modeling scale this signal may have a different voltage value, but when one rail is say +12 volts, the other rail is –12 volts (a difference of 24 volts). For this signal to be used as a DC power source, it must be rectified (usually a 4-diode bridge rectifier) and then passed through a capacitor (or capacitors) to filter out any remaining noise (bumps). Most DCC decoders include these components to create a DC voltage for their accessory functions. We have several products (N8101 for example) that also do this.

A simple test: If you have one of our products and are experiencing unexpected behavior, try substituting the power supply you're using for a fresh, 9-volt battery. If the "problem" goes away and everything seems to act normally, your power source was the problem. Batteries are the cleanest DC voltage available.

 

Types of projects:

LED Lighting: LEDs are marvelous devices and we carry many, many different ones. From an electrical standpoint, they are diodes and require DC voltage to operate properly. Different colored LEDs have different device voltages and their brightness is determined by the amount of current (in milliamps) that flows through them. For this reason, they require a supply that provides clean DC voltage of known value to ensure they perform as expected. More information about determining specific LED parameters can be found here, here, and here.

LED Lighting Effects: Our Lighting Effect Simulators have on-circuit voltage regulators that allow them to operate over a wide range of DC input voltage. This flexibility lets the product family work in many different environments and modeling scales for DC, DCC and battery applications. We presently have nearly 50 different special effects.

Our N80XX family of Simulators is best suited for static applications (structures, etc.) and dynamic applications that are DCC track powered. Their input voltage range is 6-18 volts DC. They require clean DC input voltage and when track powered, draw very little current so they can be powered directly by a DCC decoder's accessory function output. This family includes a Schottky barrier diode to protect the circuit against reverse input voltage polarity.

Our NLA80XX family is a lower input voltage version intended for analog (non-DCC) track power with an input voltage range of 3.2-16 volts DC. These also require clean DC input. This family also includes a Schottky barrier diode to protect the circuit against reverse input voltage polarity.

Our NLD80XX family is a lower input voltage version intended for either battery powered RC modeling products, or several of the DCC sound decoders now on the market that have 3.3-volt outputs for their accessory functions. Their regulator will support an input DC voltage of 3.2-16. This family does not include a Schottky barrier diode, so care must be take to avoid incorrect input voltage polarity.

Constant Voltage: Our constant voltage products (on our Lighting Accessories page) provide a constant output voltage for LED lighting when DC input voltage varies widely. These are intended to support regulated LED brightness for dynamic (track powered) rolling stock applications in the analog (DC) environment. Several include capacitors that will "cleanup" a noisy or "dirty" DC voltage such as flicker caused by gaps or dirty track.

Sound Effects: Our Little Sound and Little Bigger Sound products have on-circuit voltage regulators on both the sound module and our external Audio Amplifier (used with Little Bigger Sounds) that will accept DC input voltages between 7 and 20-volts. This offers great flexibility but these regulators need clean DC at their inputs to properly function.

 

Ngineering Power Supplies: This is shameless marketing, but we do offer fully regulated and filtered power supplies that operate within 2% of their stated output voltage over the full load range, and... they're not expensive. If you're interested, the link is here.

 

 

 

 

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