Thanks for your responses. Flecc you sound like you know what you're talking about. I would be risking a possible jail term if this is wrong - so you can understand me wanting to have a good answer!
I notice even on my 250W Oxygen it says 'peak' power comes in at a bit over 500W - so I assume it is down to the controller not allowing this to be a 'continuous' amount of power - am I close to the truth?
Anyways - I do like the look of the thing and with the amount I am saving through not running the R1 and the XJR then I have to spend that cash somewhere right? You are allowed two electric bikes right? There's no law against that is there??
None of our motors is in truth exactly according to the law, the fact being that a true 250 watts continuous maximum power would be useless. Manufacturers interpret the law on a more average basis of power delivered. In fact most legal e-bikes have a maximum power of between 400 and 600 watts, the odd ones exceeding 700 watts. These are called "peak" power and said to be only short term to avoid overheating, but in fact that's nonsense since they can operate at maximum level for the whole of their battery charge without overheating.
The situation is complicated by the two power expressions, gross power being the wattage derived from the battery voltage times the controller amperage capability, e.g. 37 volts x 14 amps = 518 watts. Since no system is 100% efficient, the net power that comes out as driving force is less by 15 to 25%, depending on the system, so that 518 watts can be anything from 388 to 440 watts of actual driving power.
However, even that is provisional, since battery voltages are nominal. A 37 volt lithium battery comprises 10 x 3.7 volt cells in series, but the 3.7 volts is nominal. Fully charged each cell is over 4.1 volts, but at end of charge it's dropped to only 3.2 volts meaning the battery of 10 cells changes from 41 volts to 32 volts as it's used each charge. Since this changes the calculations above, the power wattages change. Therefore the 388 to 440 watts of actual power mentioned above is really [336 minimum or 430 watts maximum] to [380 watt minimum or 488 watts maximum] actual power delivered.
So it's is rather like answering the question, "How long is a piece of string?"
The key thing is that that the manufacturer unequivocally states the bike is EU/UK legal, and that manufacturer is a respectable and known one. The laboratories which test e-bikes to the EN15194 standard appear to understand the true position and test to find declared bikes as legal. For example, one very well known manufacturer fits 16 amp controllers to his 37 volt e-bikes with motors of around 80% efficiency. That means gross power of 592 watts and net actual delivered power of 474 watts. They have been tested by an approved EN laboratory and found to be 250 watt legal with certificates issued!
It seems the European parliament is also aware of this nonsensical position, since they are recommending to the EU commission that the law be changed to remove all power restriction, relying only on the 15 mph speed limit in future. It remains to be seen whether that gets accepted.
P.S. You are allowed as many e-bikes as you like, we have members with several. I've owned three at one time, two of them declared legal e-bikes with peak gross powers of over 1000 watts!
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