I'm in the process of considering an e-bike conversion & have been reading up as much as I can. I came across the thread from 2012 discussing the UK law & power ratings of motors.
I'm no expert but I think some are confusing the power rating of the motor with power consumption. Someone said that their 250 watt rated motor was reading 620 watts on the 'Cycle Analyst' display when they were going up hill using maximum power setting. As I understand it (40 years after leaving school where I should have learnt it!) the 620 on the readout was the consumption rate of the available power. A 36 volt X 10Ah battery = 360 watt hours of available energy so a reading of 620 indicates that that level of power consumption could be available for just 35 minutes. Remember there is a huge difference between maintaining a steady slow speed on the level, and climbing a hill quickly - try doing it without a bike! As a sufferer of ME / post viral fatigue I'm very aware that the weaker you are, the more noticeable the difference in energy requirement is between say, level walking & uphill running. The same applies to motors; a low voltage motor may not be able to drive up more than a gentle gradient but be capable of sustaining some distance on the level - think mobility scooters and vintage cars. A powerful modern car might be capable of spectacular acceleration and pulling power but it will not go further because it uses up more of its stored energy in the fuel tank.
I'm no expert but I think some are confusing the power rating of the motor with power consumption. Someone said that their 250 watt rated motor was reading 620 watts on the 'Cycle Analyst' display when they were going up hill using maximum power setting. As I understand it (40 years after leaving school where I should have learnt it!) the 620 on the readout was the consumption rate of the available power. A 36 volt X 10Ah battery = 360 watt hours of available energy so a reading of 620 indicates that that level of power consumption could be available for just 35 minutes. Remember there is a huge difference between maintaining a steady slow speed on the level, and climbing a hill quickly - try doing it without a bike! As a sufferer of ME / post viral fatigue I'm very aware that the weaker you are, the more noticeable the difference in energy requirement is between say, level walking & uphill running. The same applies to motors; a low voltage motor may not be able to drive up more than a gentle gradient but be capable of sustaining some distance on the level - think mobility scooters and vintage cars. A powerful modern car might be capable of spectacular acceleration and pulling power but it will not go further because it uses up more of its stored energy in the fuel tank.
