Is my maths correct

[aaannndddyyy]

I have a ping 48 volt 12 amp battery (So that’s 48 * 12 = 576 watts).

At the moment I have an Ezee Sprint geared motor, rated at 350 watts at 36 volts, which has been running at 48 volts for the last 6 months without any problems and stays cool with good toque and will cruse at 20 mph for 30 + miles or around 1.5 hours run time which is perfect for city ridding.

I am now looking at making a bike that will be used outside the city and will need a range of at least 20 + miles and a top speed inxs of + 30 mph.

500W Hi Speed Electric Bicycle Bike Hub Conversion Kit on eBay, also Bicycle Parts, Cycling, Outdoor Sports, Sporting Goods (end time 06-Jun-09 05:00:57 BST)
If I buy the 500 watt direct drive motor will it run at peck efficacy for around 1 hour?
And cruse at around 25 mph, 25 mph + 1 hour = 25 + miles per charge?.

OR

1000 W 48 V Electric Bicycle Bike Hub Conversion Kit on eBay, also Bicycle Parts, Cycling, Outdoor Sports, Sporting Goods (end time 05-Jun-09 05:02:20 BST)
a 1000 watt direct drive motor will run at peck efficacy for around half an hour?
And cruse at around 30 mph, 30 mph + 30 mins = 15 + miles per charge?

If my maths is correct neither of these motors fits the bill.

 

[Tiberius]

I have a ping 48 volt 12 amp battery (So that’s 48 * 12 = 576 watts).

Hi Andy,

Its better with batteries to work in Ah (Ampere-hours), so a 48 V 12 Ah battery has a nominal energy of 576 Wh (Watt-hours).

Ping batteries are only rated for discharge up to 2 C. Ie, a 12 Ah battery should not be run at more than 24 A. Allowing for a voltage drop that's a peak power from the battery of about 1000 W.

Motor ratings are difficult. You really need more info about the motors to do any meaningful calculations. But if you can get the motors matched to the bike and running at relatively efficient voltages and speeds, then here are some rules of thumb.

Power consumption depends on how much you pedal and how much you used the throttle. Typical figures would be 10 Wh/mile at low speed, 15 Wh/mile at 20 mph rising to more like 30 Wh/mile at 30 mph. Each rider will be different, though.

From the Wh/mile figures and the battery capacity, you can estimate the range at different speeds.

HTH,

Nick