Our E-Bikes come in 250 watt, 300
watt, and 500 watt versions. In our
Seattle store, we stock almost exclusively 500 watt versions. Our central city has the steepest streets of
any major city in the world, except Hong Kong (no, not San Francisco). If you want to know why, Google "Henry
Yesler" or, "skid road." Many Seattle city
streets have 12 to 15% grades.
If you are going to ride in the
country around here, like our airplane owner and boat owner customers, or if
you live in an area of the country with milder or no hills, 300 watts is more
than fine. But, some people will always
want maximum acceleration and speed, and if you are so inclined, 500 watts is
always fun, if not always necessary.
The confusion comes from sellers
and manufacturers who state or advertise "our bike has a 350 watt motor but
actually puts out 750 watts." There is a
good chance they aren't lying, but there is a cost behind that boast.
Before we get into the electrical
engineering, an analogy might be helpful.
Picture a dam with a reservoir behind it and a pipe running out the
bottom. The amount of push out of the
pipe will depend on the height of the water; this is analogous to what the
voltage of the battery is. The diameter
of the pipe will determine how much water can come shooting out the pipe at a
given reservoir height (which we have already defined as volts). That pipe diameter is analogous to amps,
which is controlled on an e-bike by the controller. Now, imagine that at the far end of the pipe
is a water wheel which captures all of the energy of the water shooting out of
the pipe. The work that that water wheel
can do is measured in watts, just like the work the motor on the Prodeco and
its competitors is measured in watts.
Horsepower is actually just another name for watts. 1 horsepower is the same as 746 watts. To determine watts (the measure of the work
done by the water wheel at the reservoir or the electric motor on the e-bike)
we multiply volts (the height of the reservoir above the pipe, representing the
voltage of the battery) times amps (the diameter of the pipe, representing the
controller). Since a 36 volt battery
actually charges up to 37.4 volts and discharges down to close to 36.0 volts
before it quits, if you have a 20amp controller, then, like a pipe of a
certain size at the bottom of the reservoir that moves up and down about 5%,
you have between 748 watts (when the battery is at its very peak charge of 37.4
volts) and 720 watts (when the battery is discharged to 36 volts).
There is rating system for the
power of DC motors, no doubt formulated many decades ago by some electrical
engineering society, quite possibly in Germany or England. I have looked for it and can't find and
welcome input from you. Anyway, at a
motor's rated output, it will run extremely efficiently and just about forever
if it is properly made.
Almost all manufacturers,
including Prodeco, drive their motors at more than the rated power. For instance, Prodeco uses a 20 amp
controller on its 500's. If you press the
thumb control all the way down, you will get between 720 and 748 watts,
depending on the state of charge in your battery as discussed above. Watts times volts is the formula. So we are allowing our customers to goose
their motors about 45 per cent above rating.
Experience tell us that because of the conservatism of the rating
system, there is no harm. That is why
they have the longest warranty (2 years) in the business.
The competitor who boasts of 750
watts from a 350 must, by the laws of physics, also have a 20 amp controller
(same reservoir, same pipe, just a much smaller wheel to handle it all). BUT, they are letting their customers goose
their motors 117% over rating! If you
visually look at the difference in size between that 350 and the Prodeco 500,
you will probably think that is an awful lot of juice going through not much
metal. Our experiments show that pushing
them that hard negatively effects both mileage and battery life.