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02-09-09, 07:53 AM
#23
safe
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Our Math Agrees...

You are having trouble with how I presented the math... but the math is correct because our results are in agreement. I divide by losses in order to work backwards to how much actual battery energy is required to create the power needed.

Downhill (5% negative slope for 10 miles)

Freewheel - 10 miles / 24.35 mph = 0.41 hours (net power gain/loss is zero)

Regen - 10 miles / 15.00 mph = 0.67 hours (behind by 0.26 hours)

Recaptured Energy = 0.133 hp * 746 watt/hp = 99.22 watt

99.22 watt * 0.67 hours = 66.48 Wh * 0.7 (motor losses) = 46.5 Wh

46.5 Wh * 0.9 (battery losses) = 42 Wh (this is the energy recovered)

Uphill (5% positive slope for 10 miles)

Freewheel - 10 miles / 7 mph = 1.43 hours

Power Needed - 0.187 hp * 746 watt/hp = 139.5 watt / 0.7 (motor losses) = 199.3 watt

199.3 watt * 1.43 hours = 285 Wh

Regen - Must do 10 miles in 1.43 hours - 0.26 hours = 1.17 hours (or less)

10 miles / 14.5 mph = 0.69 hours (which bets the freewheel)

Power Needed - 0.443 hp * 746 watt/hp = 330.5 watt / 0.7 (motor losses) = 472 watt

472 watt * 0.69 hours = 326 Wh

...but we get to subtract the "savings" so the actual value is:

326 Wh - 42 Wh = 284 Wh

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But my point was that you are forced to increase the power level by a factor of:

0.443 hp / 0.187 hp = 2.36 = 236% the power output.

In many cases when you are forced to run at a higher power level you lose efficiency and that's what made the issues that followed after it apply.

.

Last edited by safe; 02-09-09 at 09:43 AM.