Open Frame and Enclosed Power Supply Buyer's Guide

The Power

Selecting the right power supply for any project

By Robert Cong

The difference between open and enclosed power supplies is simple: one has an open frame which allows the components to be exposed to the elements, and the other has an enclosed which protects it from the elements. From there, the options are numerous.

Open Frame Power Supply
Mean Well LPP-150-12 150W Open-Frame Power Supply

Enclosed Frame Power Supply
Mean Well RS-150-12 150W Enclosed Power Supply

So why choose an open-frame power supply and risk the possibility of damage to the supply or accidentally being shocked? One very important factor: cooling. Just as a pie fresh out of the oven cools much faster when placed out in the open rather than wrapping it in foil, an open-frame power supply keeps much cooler than an enclosed one, leading to less power loss. Some applications may have the power supply sit out of the way and never be in the vicinity of any harmful environmental factors, so choosing an open-frame supply would be ideal. The selection for open-frame power supplies include linear, medical switching, and single or multiple-output.

Medical switching supplies go through the most stringent testing procedures in order to be approved for use in the highly-sensitive medical and healthcare fields. All devices in the environment must be operational in accordance with their standards in order to avoid any harm to the patients and operators. Such standards include very low leakage current and very low electromagnetic interference (EMI).

A feature that some open-frame supplies have is ultra-miniature size. This may be a critical feature in some applications that need to save as much space as possible. The average size of one these supplies is just 2.5"L x 1.8"W. While it may not be able to provide as much power as other supplies, they are perfect for smaller applications.

For those applications that require a supply with physical protection from environmental harm, there are enclosed power supplies. Enclosed power supplies include DIN-Rail power supplies, LED power supplies, DC/AC inverters, and DC/DC converters. Information on LED power supplies can be found here. For now, let's focus on DIN-rail and general AC-to-DC enclosed power supplies.

Enclosed AC-to-DC power supplies come in single, double, triple, and quadruple-output forms. They come in varying sizes, usually proportional to the power output of the supply. Just as with open-frame supplies, they have many different features that need to be considered when searching for a specific power supply: 5G vibration testing, power factor correction function, built-in remote sense function, built-in on/off control, parallel function, and protection. See the table below for information on each of these features.

5G Vibration Testing G is the acceleration of gravity (9.8m/s2) and 5G is 5 times that amount. During this test, the supply is powered up at specific parameters and secured onto a vibration machine. The supply is vibrated at an acceleration of 5G on each axis (x, y, z). This is done to simulate any major occurrences, such as an earthquake, and ensure that the supply will continue functioning in such crucial circumstances.
Built-in active Power Factor Correction (PFC) Power factor correction provides for a higher ratio of real power to apparent power. This means the higher the ratio, the more the amount of power provided is actually being utilized and outputted.
Built-in Remote Sense Prevents the dropping of the voltage level at the output load. Provides for more accurate voltage outputs and precise measurements.
Built-in Remote On/Off Allows the supply to be switched on or off using a digital or analog signal.
Parallel Function Allows the user to connect multiple power supplies together in parallel for added voltage and/or current depending on the wiring configuration.
Short-Circuit Protection Protects the supply from accidental short-circuits. If a short occurs, the supply will typically shut down the supply or hiccup the output. It may automatically recover or need to be re-powered, depending on supply design.
Over-Voltage Protection When the input voltage being applied is much higher than the supply is designed to take, damage to the supply may result. Some types of this protection shut down the supply once it senses a voltage that is too high and re-powers back on to recover.
Overload Protection When a very large load is applied, the supply may try to stay in constant current mode, but that may be harmful to the supply if it is unable to continuously provide that amount of current. This function helps sense for loads that are too large.
Over-Temperature Protection Heat is one of the biggest problems facing the efficiency of a power supply. When the temperature gets too high for safe operation, this function shuts down the supply and may recover automatically once the temperature drops to a safe level.
100% Full-Load Burn-In Test This tests if the power supply unit can deliver its rated output at high temperatures. This is helpful in making sure that the supply is able to function at its maximum potential even in hot, harsh conditions.

Table of Common Features in a Power Supply

DIN rails are standard metal rails used to mount equipment while saving valuable workbench space. DIN-rail power supplies have a custom-formed shape specifically made for quick and simple mounting onto DIN rails over your workbench. These supplies come only in single-output, but take varying input voltages from universal full range AC inputs to high-voltage, 3-phase inputs. Some also have a slim design to save DIN-rail space, and UPS (uninterruptible power supply) system function to always have a backup for your critical applications that always need power. Depending on your application and environment, DIN-rail power supplies can be the perfect solution to having the power you need while keeping the actual supply out of the way. Pair them up with some DIN-rail timers to precisely control your power in various time ranges.

240W DIN-Rail AC-to-DC Power Supply
Mean Well SDR-240-24
240W DIN-Rail AC-to-DC Power Supply

Check out even more mounting brackets and accessories for all of your power supply mounting and space-saving needs.

Mounting Bracket Accessory
Mean Well MHS013 Mounting Bracket Accessory

Enclosed Frame Power Supply
Mean Well DRL-01 "L" Mounting Bracket

When deciding on an open-frame or enclosed-frame power supply, you must always look at your specific application first. Find out how much power output is needed, and then based on environmental factors, choose between an open or enclosed frame. Find out if multiple outputs will be needed, and if specific agency approvals or mounting specifications are critical to the application. Once the critical aspects are noted, you can then look for the extra features to most effectively power your application.

AC-to-DC Open-Frame Power Supplies
Breakdown of AC-to-DC Open-Frame Power Supplies

Enclosed Frame Power Supply
Breakdown of AC-to-DC Enclosed-Frame Power Supplies

Now that you have an idea of all the various types of open and enclosed power supplies, you can make a better decision on what products are best for you. Remember, knowledge is power, and power is needed in every application.

Now that you know what to look for, make sure you have all the parts you need. If for some reason you can't find what you need, just write us a note and we'll do our best to find it for you.

Have more questions? Send an email to: [email protected].

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