Do you still plug in your laptop to 120V power? Tote the “brick” everywhere you work?

Or have you discovered the simplicity and convenience of a USB-C connection?

I was recently asked if we could incorporate a power inverter and 120V outlets into the design of our height-adjustable Console Desks. This was not the first time this question was asked.

The rationale for the inclusion of the inverter and outlets was to accommodate users who are slow to adopt changes in technology. My answer was affirmative from one perspective.

Technically speaking, we can, of course, include the features into the desk. It is not free, so perhaps we can realize a bit more revenue and profit for each unit we sell.

That doesn’t mean I endorse the concept.

Start at the Wall Outlet

Let’s take a step back and look at this from a system perspective starting at the 120V AC power outlet on the wall. This is where we plug in our Charging Center. The Charging Center has power supplies that convert the AC power to DC power to charge our QIKPAC Carry batteries. The batteries are then mounted onto our Console Desk, where they power the height-adjustment mechanisms, the USB connections included in the QIKPAC Carry, and the optional wireless phone charger.

All is rational at this point, as the mobility and other benefits enabled by the battery system create an excellent value proposition for our Console Desk products.

To connect a Power Inverter, a spare port on the underside of the QikPac Desk Dock could be used to direct DC power to the inverter. The inverter then generates 120V AC power that is delivered to outlets attached to the desk. The technology-resistant users that plug into the AC outlets do so by plugging in their laptop power supplies, the “brick”, which takes AC power and immediately converts it straight back to DC power for the actual operation of their laptop.

By now, you may have inferred where I am going with this. If we follow all of this, we go from AC to DC to AC to DC power. Each of these steps involves some power loss (a.k.a. heat) so efficiency is comparatively poor compared to the AC-to-DC, USB-C approach.

By the Numbers

The power supplies in the Respond! Charging Center are about 91% efficient when they convert AC power to DC power to charge the battery. The QIKPAC battery is about 98% efficient in its operation. An inverter is about 89% efficient when it converts DC power to AC power. The typical laptop computer is about 85% efficient when it converts AC power to DC power.

To calculate the overall efficiency, we multiply the individual efficiencies, or 0.91 x 0.98 x 0.89 x 0.85 = 0.67. In other words, the overall system efficiency with an inverter included is about 67%. Or said another way, this approach uses 33% of the electricity from the wall outlet to create unwanted heat that adds to the air conditioning load.

Not only does this add operating expense, but it is also a bad sustainability practice to waste 33% of the power between a wall outlet and DC input for desktop computing equipment.

In practice, the efficiency might actually be worse. Inverters continue to operate and draw power even when nothing is plugged in. If the occupant of the desk with an inverter is using the USB-C connections, the inverter will be operating and wasting electricity.

How efficient is the Respond! power configuration?

The power supplies in the Charging Center are about 91% efficient. The QIKPAC battery is about 98% efficient. The USB-C outlet is about 96% efficient. Since the desktop computing equipment can plug directly into the USB-C port, there are no further components required,

When the components are considered together as a system, the overall efficiency is 0.91 x 0.98 x 0.96 = 0.86. In other words, 86% efficient with about 14% lost to unwanted heat. The inefficiencies when an inverter is added to the configuration are more than double the solution that directly uses the USB-C connection.

Note that the Respond! power system is actually more efficient than the typical 85% efficient AC-to-DC laptop power supply that is based on older engineering designs.

About Older Computers

Some of you might ask, “What about users that have older equipment that is not USB-C compatible?”

To answer this question, you might want to compare the cost of adding inverters and outlets against the cost of new computers. My hunch is that there will be a compelling argument to be made for upgrading equipment.

I know managers that will look at this issue and suggest that accommodating users reluctant to switch to USB-C power is not a technical issue at all. Instead, they will see it as a leadership issue solved by encouraging their workforce to do the right thing. If top leadership wants sustainable practices in their businesses, they can get them.

Old habits may die hard, but the future is more important than the past.