yycwrangler wrote:Can anyone help me out with the math. So my ebike battery is 500 watts. It says it will take 5 hours to charge. So in simplistic terms I need a charging system that can provide 100watts/hr for 5 hours. If my wife has her ebike with us then 200w/hr. Most of these investor gens say 1700 or so watts running. Does that mean 1700w/hr..if so, I should have plenty of juice to charge the bikes and also the battery for led purposes.
Al
Watts is a unit of measure for power, the speed of doing work. It is equivalent to horsepower. One horsepower is 746 watts. A toaster that takes 750 watts takes 750 watts while it is on. Watts per hour doesn't make sense. If a lawnmower engine produces 3.5 horsepower it doesn't matter how long it takes to mow your yard. It is just 3.5 horsepower. After toasting an entire loaf of bread the toaster continues to use energy at the rate of 745 watts.
If your ebike charger takes 500 watts for 5 hours it takes 500 watts the whole time. At the end your energy use will have been 2500 watt hours or 2.5 kilowatt hours. The electric company charges about ten cents per kilowatt hour. If you also charge a second bike the two chargers, each taking 500 watts, will require 1000 watts if run at the same time.
If you charge them one at a time you use energy at the rate of 500 watts for 10 hours. If you charge them at the same time the total energy, 5000 watt hours, gets transferred at twice the speed, 1000 watts for half the time.
The cheapest Harbor Freight generator is good for 700 watts continuously. It can charge one bike. Your 200 watts per hour calculation for 2 bikes doesn't work.
A generator rated to produce 1000 watts continuously should work, theoretically. A 2000 watt generator will be less likely to overheat and more likely to actually work at high elevation. The 1000 watt generator might be louder. The 120 volts produced might drop to 110 or 105. The bikes might take longer to charge. The total fuel consumed might be higher.
Actually, the battery chargers don't run at a constant rate. Lithium batteries are much better than lead acid but the charger power requirement will vary with the battery state of charge and the battery current will vary too.
Another way to look at it is to consider the cruise ship going from Miami to Mexico. It is going 20 knots. After an hour it is still going 20 knots. If you say it's going 20 knots per hour does that mean it is going 40 knots after an hour? After an hour of 20 knots it will have gone 20 nautical miles but it is still going 20 knots. Knots per hour doesn't make sense for cruise ships. After 20 hours it is not going 400 knots.