by David Norton, TDK-Lambda Americas
Designers can avoid reliability problems by acquainting themselves with the way connector pin materials stand up to repeated use and corrosion.
Examine the input and output connectors on most open-frame power supplies and you’ll likely find parts from a supplier like Molex or JST. These connectors are inexpensive, readily available, reliable and easy to use. In addition, use of these readily available parts makes it easier for designers to second-source a power supply, if necessary, when some standardization exists.
Many power supply manufacturers will specify the name of the mating connector series in their product documentation. But they will often leave it up to the user to determine the actual part numbers. This usually provokes a call to power supply tech support for a recommendation.
An example illustrates why power supply makers adopt this practice. Consider the industry standard low-power 2×4-in. single output power supply. The Molex KK 09-50-3041 housing is widely specified as an output mating connector. Made of nylon, it has a friction lock and four circuits: two for the plus output and two for the minus output.
When looking for the mating pin, one has to be a little more careful. The suggested pin for the connector is available in two materials: brass and phosphor bronze.
Brass is a common material for contacts and pins. It is inexpensive, has good conductivity and is generally dependable in a benign, low-temperature environment like an office. Brass loses flexibility as it ages and, under repeated stress, is subject to crystallization, which significantly lowers it conductivity. However, most power supplies don’t undergo repeated connect/disconnect cycles, so loss of conductivity usually isn’t a problem.
Phosphor-bronze mating pins should be considered for more challenging environments. Phosphor bronze is an alloy of copper with 3.5 to 10% of tin and a phosphorus content of up to 1%. The phosphorus serves as a deoxidizing agent during melting. These alloys are tough, strong and have a low coefficient of friction. They are particularly helpful for applications at higher temperatures because heat can make brass contacts lose their spring properties. If there is some vibration, the lack of spring in a bronze pin can cause reliability problems. Phosphor-bronze contacts do not lose their spring. However, brass is more conductive than phosphor bronze, so check current rating capability.
Phosphor bronze is more expensive than brass, currently about $0.13 compared to $0.05 for brass (1,000-piece pricing from a distributor). For a 2×4-in. power supply, the additional few cents could add $0.56 to the bill-of-material cost. Designers should consider the environment and desired field life. As a note, on higher power 2 X 4-in., open-frame power supplies, there are alternatives to the single-point-of-contact KK style pins like those used with the Molex 09-50-1041 housing (SPOX series). These have multiple points of contact for lower resistance.
There are several other metals that can be found in power connector pins and plugs. Here are a few details about how other metals compare:
Beryllium copper is often used for its excellent conductivity and thermal properties. It has the best electrical conductivity of any spring alloy of comparable hardness. It beats other copper-based spring alloys in terms of resistance to fatigue and strength. So it is generally a candidate for applications experiencing numerous insertion and withdrawal cycles. But it costs more than any other basic contact material.
Nickel-silver alloys are actually copper alloys with nickel and often zinc. The typical makeup is 60% copper, 20% nickel and 20% zinc. These alloys resist oxidation but may be susceptible to stress corrosion, though not to the extent of brass.
Several materials can be used for plating connector pins. Gold is an excellent conductor and has a low contact resistance. Hard gold platings are applied in applications characterized by numerous insertion/withdrawal cycles. Gold can be impregnated with graphite to handle super-high insertion/withdrawal needs.
Of course, gold is expensive, so alternative plating materials have been developed. Silver is a general-purpose plating for power contacts. But it tarnishes when exposed to air. The resulting oxide layer can be problematic for low-level circuits, less so for power contacts. Like gold, silver has become expensive, so suppliers have developed alternatives.
Nickel is slow to react with air, so it resists corrosion and is relatively conductive. It often serves as an undercoat for contacts destined for high-temperature-use to prevent migration of plating materials. It also has good wear resistance.
Tin has good conductivity and is relatively inexpensive. But it has poor wipe resistance and best suits connectors that experience few mating cycles.
Finally, rhodium is sometimes found in connectors that need exceptional wear qualities. It is not as conductive as gold or silver, but its conductivity is generally acceptable when the material is deployed as a thin plating.
TDK-Lambda Americas
www.us.tdk-lambda.com
When choosing the correct power cord for household appliances and office devices, people often make costly mistakes by blindly selecting products they think will suit their needs. However, choosing the wrong products can only cause more problems and bring more expenses.
On the other hand, most people simply go with the longest and cheapest option, which is also wrong. The trick to making an informed decision and intelligent purchase is to know how to choose the suitable power cable for your specific needs.
To do that, you’ll need to inform yourself of the main factors to consider when deciding which extension cord power cord and extension cable to use. There is a wide range of hardware specifications to take into consideration when buying new power cables.
You need to consider why you need power cables. Each device, appliance, and workstation in your home and office requires a matching power cord. With that in mind, let’s get deeper into details regarding power cords to help you make the right decision.
Two of the most common power cable options you’ll find in almost every household and office are two-prong NEMA 1-15 and three-prong NEMA 5-15. Two-prong NEMA 1-15 is the perfect choice for various devices such as TVs, charger cords, lamps, electric fans, and so on.
However, NEMA 1-15 cords aren’t grounded; therefore, they can’t be used for supporting high-powered devices such as microwaves and refrigerators. You’ll need NEMA 5-15 for that. It is a three-prong power cord that comes with a round pin for ground wire use.
There is a wide selection of wire gauges for household and office extension cables. Which one you choose depends on the application. If you need to support heavy-duty items, you’ll need a thicker gauge cable. Thicker gauge cables allow more power to flow through it and are an excellent option for distances.
There are four standard wire gauge sizes for NEMA 5-15 plugs:
It’s always better to go with a thicker gauge cord than the recommended. Some people prefer thinner gauge wire with a right-angle power cable, but this solution could cause more issues because your devices and appliances do not have enough power to run. If you want to avoid malfunctioning and devices burning out, choose a thicker gauge cable.
Outer jacket is one of the essential factors when choosing the suitable power cable for your unique needs. For example, if you plan to use a power cord outdoors in colder temperatures, a regular power cord might become much harder to work with due to coldness.
Colder temperatures tend to stiffen up the power cable, making them hard to manage and use. In such situations, power cords with all-weather outer jackets are a much better solution. When choosing a power cord for outdoor use, go with the SJEOW standard for power cables.
SJEOW stands for:
Now, since you have some basic understanding of important things to know about power cords, let’s move on with the best tips and practices for choosing the correct power cord for your needs, as well as safety tips for working with power cords.
Here are some points to consider for choosing a suitable cable.
Since you can never correctly guess how long a power cord should be for a specific use, it’s always better to buy a longer cable to get some extra room for error. Longer wires are always helpful, more convenient, and safer too.
Of course, you can always connect one cable to another. Still, you risk adding electrical resistance between your device and the outlet that can cause voltage drops, making your devices and power tools run at lower power. Since this can start a fire, melt your cords, and cause other problems, you can avoid all this by simply buying a longer cable.
In applications where more power is needed, thicker cords always work better. The thicker the wires, the more power the cable can safely carry. This is vital for electrical applications over longer distances.
Any cable should run low-power devices and gear like stereo, battery chargers, and lights. However, if you want to safely run power tools like wet/dry vacs, saws, and drills at peak power, you’ll need a cord for maximum power.
Here is how to choose the correct length and thickness:
You can always make sure you have the correct power cord by checking the amperage rating on the packaging. We recommend you go with a 15 A rating. Avoid indoor/outdoor cables rated for 10 A or 13 A.
15 A fuses or breakers are pretty standard in most residential and commercial electrical panels. You can plug in any equipment or tool with a 15 A cable. More importantly, if the cable is pushed beyond its limits, it will cut off the power.
When it comes to contractor cables, anything up to 300 V will do as it meets workplace safety requirements. In terms of residential voltage in the US, 125 V or 130 V will do just fine.
Some power cables are simply designed to be more flexible and allow for a broader range of applications. The flexibility of use is crucial for applications at lower temperatures.
The more flexible a power cord is, the more usable it is in tight spaces, easier to store correctly, and stretch across your home or workspace. Opt for power cords listing temperatures below freezing as they are generally more flexible to work with.
Multi-outlet cables, also known as a banana tap, are commonly seen in residential and commercial properties. However, we don’t recommend using them for running work lights and power tools and equipment due to being easy to overload. If you require serious power, we recommend general-purpose cords with one outlet per cord.
The best option is to go with the less robust indoor cords for lower-power gear like wireless speakers, lamps, and phone chargers. However, most current building codes, including UL, don’t allow the use of extension cables in a permanent installation due to regular wear and tear making them a real fire hazard. Use them for digital devices and appliances that don’t require much power. Keep in mind that indoor cables aren’t weather resistant.
Let’s quickly cover the three types of extension cords- light-duty, medium-duty, and heavy-duty.
These power cords, designed for light-duty devices, aren’t grounded and come with two plug prongs. You can use them for devices up to 7 amps and other light-duty appliances like clocks, lamps, etc. Recommended cord length:
Usually grounded, medium-duty cords come with the third wire and can power three plug grounded appliances. You can use them for computers, TVs, and any other similar device that requires up to 10 amps of power.
Recommended cord length:
Heavy-duty power cords fit the bill if you need cables that can support 10 to 15 amps of power. These are grounded cables that come with the grounding plug prong and include a third wire. They also have three-slot plugs for powering grounded appliance cables. These cords are perfect for heating appliances and power tools.
Recommended length:
If you’re looking for the best power cables for outdoor purposes that can also resist moisture, look for the cords with a built-in ground-fault circuit-interrupter (GFCI) protection that prevents shock hazards.
Taking precautions while working with power cables is extremely important. Since we cannot stress this enough, here are a few quick tips to keep you safe:
When you look at a power cord, you can see that it’s nothing more than a bundle of insulated electrical wires. While there’s nothing suspicious about that, the problem is that the electrical current flowing through those wires generates a lot of heat that can quickly turn a simple power cord into a real hazard.
If a power cord overheats, it can melt the plastic insulation and cause fires, short circuits, and more. In most situations, you’ll just power a device or an appliance by plugging it directly into a power outlet using its factory cable.
However, in situations where you don’t have a proper factory cord sized appropriately for the electrical current load and demand, you’ll need to work with what you have. If you exceed the safe load capacity, the consequences could be disastrous. In such cases, always take help from an expert.
We sincerely hope this guide helps you choose the suitable power cable for your commercial and residential needs. Even though it may sound a bit complicated initially, it’s isn’t that hard to get into it once you know what to look for. Keep these tips in consideration when buying power cables, and don’t forget to stay safe while working with power and extension cables.
If you don’t have anyone around who’s an expert in this field, it’s best to consult an electrician when you are tampering with electricity for the first time. So, be well prepared, and there should be no worries.