# How long would it take to charge a Tesla via USB?March 21, 2022 5:52 PM   Subscribe

I'm not a Science Guy so I have no idea how to go about answering this question. (I also keep trying to use Google to find an answer, but it keeps returning responses about how to charge USB devices from inside an electric car. THIS IS THE OPPOSITE OF THE QUESTION I'M ASKING.) So, Science Guys and Gals and Nonbinary Pals: Assuming an endless supply of juiced-up USB phone chargers (or whatever) and the proper connection to the car's battery, how long would it take to fully charge up your Tesla?
posted by AngerBoy to Technology (10 answers total) 3 users marked this as a favorite

Best answer: Looks like typical Tesla battery pack is 50-100 KwH (kilowatt-hours). A somewhat fast usb charger is 25 watts. If I'm doing the match right, that means 4000 hours assuming 100% efficiency for the largest battery pack. Real charging efficiency is probably more like 90%. And a very large step up in voltage would be needed from the low voltage (20v?) of the usb charger, further reducing efficiency. So 3-5000 hours depending on the battery capacity and charger capacity, maybe?
posted by jclarkin at 6:11 PM on March 21, 2022 [3 favorites]

According to the Googs, a model 3 has around 58 KW hours in its battery. Likewise, USB 3 charges at around 5 W. So, roughly 10,000 hours or 400+ days. For that kind of time you probably have to consider the self discharge rate and certainly have to consider driving some amount of stuff in the car, so it probably would actually be *dis* charging while it was connected.

But assuming a spherical Tesla, “more than a year.”
posted by Gilgamesh's Chauffeur at 6:12 PM on March 21, 2022 [8 favorites]

Perhaps the Googs misled me on the charging rate of USB—if it is really 20 W, then you could charge your spherical car in only a bit over three months! Sorry for the mis-estimate.
posted by Gilgamesh's Chauffeur at 6:15 PM on March 21, 2022 [1 favorite]

Best answer: This is a rough estimate: superchargers deliver "up to 120 kW" of DC power and take about 45 minutes to charge.

USB fast chargers are like 10W so that would be 540,000 minutes or 375 days.

Assuming it even allowed charging at 500 milliamps, I think the battery would discharge faster than it could charge.

On preview: close to other estimates.
posted by muddgirl at 6:16 PM on March 21, 2022 [3 favorites]

The most powerful USB charger you can get, by the USB spec, is 240W. A Tesla Model 3 Standard Range has 60kWh of usable battery, so theoretically you could do the math and work out how long it would take to charge (you could assume 95% efficiency or so).

But, in the real world, when a Tesla is charging it uses a certain amount of power to move coolant around, run computers, and so on. This thread suggests that overhead is 300W. So in the real world a Tesla would never actually charge via USB. If you could somehow bypass all that overhead and just charge the battery directly without the car using any energy at all, it would take about 11 days at 240W.
posted by ssg at 6:19 PM on March 21, 2022 [9 favorites]

TLDR: ranging 10 days to never; high certainty :)
posted by SaltySalticid at 6:25 PM on March 21, 2022 [1 favorite]

. USB chargers are between 5-48V and 0.5-5A, and multiplying those on the back of an envelope gives 2.5-240 Watts for USB 3.1 or newer
. by the power of algebra, that's 2.5-240 watt-hours per hour because there's 1 hours per hour.
. Tesla batteries range from 50-100 kilo-watt-hours which is 50,000-100,000 watt-hours.

100,000 watt-hours / 2.5 watts = 40,000 hours, because the watts cancel out. So small charger, no overhead, is 40,000hours/(24 hours/day) = 1,667 days for the big battery and the small charger.

50,000 watt-hours/240 watts = 208.33 hours = just under 9 days for the small battery and the big charger.

As others have noted, if the cost of charging is higher than the amount you can put in, you're trying to fill a leaky bucket that's leaking faster than you're pouring; then it's never going to work, dear Liza, dear Liza.
posted by adekllny at 6:30 PM on March 21, 2022 [4 favorites]

Teslas have a standby-current higher than USB charge power, so literally would never happen.
posted by doomsey at 7:16 PM on March 21, 2022 [2 favorites]

Assuming an endless supply of juiced-up USB phone chargers

Ooo, an endless supply, did you say? Recharge your Tesla in parallel. Just keep some fire extinguishers handy.
posted by They sucked his brains out! at 8:13 PM on March 21, 2022 [1 favorite]

Be realistic. Install the standard 220v household connection. It's a TESLA, not a hand-warmer!
posted by Goofyy at 12:18 PM on March 22, 2022

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