In our hyper connected world chock full of mobile phones and other devices, battery charging is a routine task we probably don’t think much of. However, on a larger scale, as it is applied to EVs and PHEVs, understanding the basic principles behind how a battery is charged helps define how the charging infrastructure is best utilized.
How quickly a battery charges is dependent on how much power that battery is getting. Power, measured in watts, is a function of voltage (volts) and current (amps). Putting that into a context, the standard household electrical outlet is wired for about 120 volts and is typically on a 15 or 20 amp breaker, the amount of power that outlet will produce is about 2,000 watts, or 2 kilowatts.
EV and PHEV battery packs are measured in watts or kilowatts (1,000 watts). Since the Tesla EV is the most commonly known electric vehicle we will use one for our example. The Tesla roadster has a 53 kilowatt battery pack. To figure out rough charging time simply divide the battery pack by the by the 2 kilowatts, the car will charge in about 27 hours. That’s obviously a bit too long to be practical. Fortunately, we are not limited to our simple household plug, most homes have at least 240 volts coming in to the electrical panel and commercial properties somewhat more than that.
The automotive industry has settled on some basic standards for EV and PHEV car charging which are segmented into three “levels” each at higher power outputs.
• Level I – 120 volts at 16 amps provides about
• Level II – 208 / 240 volts at 30 amps which provides about 7.2 kilowatts of power
• Level III – also referred to as a quick or fast charge is 400 volts at 125 amps providing 50 kw
With a quick glance at the above table it should be obvious that Level II charging will satisfy most daily users needs. The level II charging standard will be the backbone of any charging network.