# How much will it cost me to top up my e-bike?September 2, 2021 11:09 AM   Subscribe

My electricity bill is R\$ 14,20 for 100 kWh (110V AC). The charger is 90W, and the output is 36V DC 2A. The battery is 36V DC with a capacity of 10.4 Ah. How much will a full recharge cost?
posted by Tom-B to Science & Nature (3 answers total) 1 user marked this as a favorite

Best answer: 36V × 10.4Ah = 374Wh. Allow a bit of slop for charger inefficiency and say that a full charge will eat 500Wh = 0.5kWh (it will be a bit less than that because the battery will typically not be going from 0% to 100% charge, probably more like 10% to 100%). So a full charge will cost 0.5kWh × R\$14.20/100kWh = R\$0.07.
posted by flabdablet at 11:19 AM on September 2, 2021 [1 favorite]

36V × 10.4Ah = 374.4Wh = 0.3744 kWh
Cost of electricity per kilowatt hour...
R\$14.20 / 100 kWh = R\$0.142 / kWh
Total cost to charge the e-bike to capacity from zero...
0.3744 kWh × (R\$0.142 / kWh) = R\$0.053
The wattage and output voltage of the charger aren't material to the question. As flabdablet notes, there will be some lossage along the way, but almost certainly not enough to add more than a few centavos.
posted by letourneau at 11:22 AM on September 2, 2021 [1 favorite]

Best answer: Back of the envelope: 36V 2A DC is 72 watts, so let's assume the charger is 80% (90 watts AC -> 72 watts DC) efficient which seems ballpark right. It would take 5.2 hours @ 2 A to get 10.4 AH DC, so 5.2 hours at 90 watts AC is 468 watt-hours, which is ~0.5KWH. On preview: different approach, same answer.
posted by true at 11:22 AM on September 2, 2021 [1 favorite]

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