Battery Eliminator Boxes

Let's look at Battery Eliminator boxes that provide temporary electrical power. Comparing two members from the Canadian Tire Battery Eliminator series.

Car Boost

Both of these boxes contain a 12volt DC battery, like the one in an automobile. They can produce brief surges of high current to start an automobile engine. The little box can produce 600A and the larger can surge 1600Amperes. These numbers are written on the label.

One reason to have a device like this is to start an automobile engine where the car battery has been drained. Instructions say to clip red-clip to battery positive then touch black clip to ground terminal.

DC voltage is 12.91 volts between the red and black clips. Fire hazard! Do not put clips together!

Inverter

In North America we have an effeminate 120Volt alternating voltage. This is ten times the DC voltage of the battery inside the box. An inverter circuit generates pulses that go through a 10x transformer. Let’s look at the waveform of the output voltage.

That’s not a sinusoid. What is it? It is a staircase waveform of the right frequency (60Hz in North America) and, I assume, approximately 110volts RMS root mean square. An oscilloscope probe reduces the voltage for safety.

It has what we call "harmonics" in addition to the power. We have to be careful where we use this voltage. A lamp won’t care, a motor may burn out over a long period.

Be careful doing this measurement. Do not ground the Battery Eliminator, avoid grounding any live voltage. This box contains enough electrical power to start fires and injure people.

Output Power

Back to the label, again. The small device says it can output 120Watts. That’s enough for a lamp, more than enough to charge a phone. You can run a laptop or desktop computer. But no cooking appliances. Few motors. A lot of electrical devices will not run from the small battery eliminator.

The large device says 600Watts. Regular household circuits are rated at least 1500Watts so let’s think about what we can and cannot run with this power. Microwave ovens at 800Watts? Coffee machines taking 700Watts? No. A vacuum cleaner that needs 500Watts? Yes, but barely.

USB and Lighter

USB voltage is 5volts direct current. The standard lighter socket is pretty much the 12volts from the battery with some regulation circuitry. The power on either of these ports will be a fraction of what is used on the 3prong AC power ports.

Power Specs

How do we know how many watts it takes to operate a device? Look for specifications labels on the product or on a product information page. Typical values are easily found with a websearch. Remember that some devices are on-and-off, example of a refrigerator that draws high current for short periods and is off the rest of time.

A Kill-a-watt device is convenient and easy to get accurate power measurements.

How much power?

We're talking about a 12V battery that produces Watts over hours of time. Online specifications say this box can power a 25Watt LED lamp for five hours. An estimate of 125Watt-hours is reasonable.

Vacuuming an automobile at 400Watts consumed the eliminator's full charge in about 12 to 15 minutes. Watch your power use. Powering a cell-phone hotspot will be more power efficient than running a fiber modem.