Portable Lithium Battery AC Output


This summer I did a lot of work down at Toronto Harbourfront. I brought my laptop and various receivers and micro-controllers with me. When the sun was shining, I used a portable 80W solar panel to power everything and on cloudy days I used a portable 85W lithium battery pack. I didn’t get a chance to use the AC output of the battery pack, so I decided to test it using an old short wave receiver as a load. The receiver has 10 tubes, so it takes at least 100W to 150W which is more than the battery is rated for, but it is a good test.

Test Waveforms

Fig.1 AC Wall Outlet Voltage 123Vrms
Fig.2 AC Wall Output Voltage 348Vp2p = 123Vrms x 1.414 x 2
Fig.3 Lithium Battery AC Output 112Vrms
Fig.4 Lithium Battery AC Output 294Vp2p

Figure 1 shows the standard AC wall voltage in Toronto as measured on a voltmeter = 123Vrms. Figure 2 shows the same voltage as viewed on a scope = 348Vp2p
123Vrms = 123 x 1.414 x 2 Vp2p = 348Vp2p

Figure 3 shows the AC voltage output of the lithium battery = 112Vrms. Figure 4 shows the same voltage as measured on a scope = 294Vp2p
294Vp2p = [(294/2)^2x (5.5/8.5)]^0.5 = 118Vrms

To calculate the rms voltage, the stair step is squared, so the peak voltage is 147^2V. This lasts for about 5.5units of 8.5units, then the average is calculated and the square root taken. Note that the cursors are a bit high, so the 118Vrms is probably close to 112Vrms on the meter.

Figure 5 shows the YouTube video of the successful test of powering the radio.

Fig.5 AC Test of Lithium Battery Pack

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By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.