500w E Bike ins

[Ocsid]

I am not overly convinced the "legality" or not makes the rider immune to any civil claim for personal injury from third parties, by far the biggest "life changing impact" to which we are exposed.

I am though pretty sure the technical minutia of any bike used that we have managed to insure for that risk, will be of great interest to the insurer facing multi million, or even down to multi thousand pound claims.

 

[joelectric]

Buy a 250w sticker from ebay , attach to motor and use bike as is.

 

[Az.]

I am not overly convinced the "legality" or not makes the rider immune to any civil claim for personal injury from third parties, by far the biggest "life changing impact" to which we are exposed.

Immune? No, but legality impacts if you can be insured or not.

 

[fe02man]

I had to get my ebike kit and then work all this out too. The problem with using watts as the limiting metric for motors is that the watts expended is a result of work demanded and available power. For DC current the calculation for watts is simply Volts X Amps. source..
but that just reveals the Maximum available.

So my '250w' motor fed with 15a from my 36v battery can output upto 36x15=540watts of power.. Now my bike came fitted with a 15a controller, I could easily upgrade to a 17a or 22a controller, perfectly legally and connected to my motor with 250w etched on its body.. Much more power available...
all i need do to keep the bike legal is apply the 15.6 mph speed limit.

btw my 36v battery fully charged is 42v so when fully charged my legal ebike has upto 630W available power..

Even more grunt can be achieved by using a 48v battery (56v fully charged) though that would probably require a controller upgrade too. 56x15= 840w and with a 22a controller well over 1000w .. from a legal 250w motor!

That's a very helpful explanation,

 

[saneagle]

That's a very helpful explanation,

What he said is not the full story, and it's important that you get the rest if you want to understand how power works in an ebike.

When he mentioned his motor can output 540w of power because his controller takes 15A from the 36v battery, that's false. The controller has an efficiency of about 90% and the motor has an efficiency curve that ranges from about 50% to 80% in normal use, though it can go much lower. In that case his motor outputs somewhere between 243w and 389w, which you can see is much lower than the 540w.

Next, is the effect of back emf, which is a bit weird. As soon as a motor starts to spin, it becomes a generator. The voltage it generates is opposite to the battery voltage, so the net voltage in the motor gets cut down. Basically, the fast you go, the less current you can get pushed through the motor.

Between efficiency and back emf, typically, max power comes at around 75% of the motor's unrestricted max rpm.

Lastly, the battery voltage is not 36v. It starts at around 42v and decreases to about 31v when empty, so you only get about 75% as much power when the battery is down compared with when it's full.

 

[fe02man]

Carole Nash was the goto insurer for vintage and custom M/bikes back when i dabbled....

They will not insure ebikes of 500w.

 

[Woosh]

They will not insure ebikes of 500w.

that's not surprising. No insurance company will insure an illegal bike.
If you want to ride with ordinary cyclists or without helmet, you have to stay with 250W kits.

 

[fe02man]

that's not surprising. No insurance company will insure an illegal bike.
If you want to ride with ordinary cyclists or without helmet, you have to stay with 250W kits.

I understand fully where you are coming from and appreciate your comments. But l am going to speak to DVLA; having read their notes and see where it goes. I will keep you informed