whatever wrote:I understand your point snowchyld, the relationship between continuous and peak power can be a grey area, that is in the advantage of the ebiker if continuous power rating is used, peak can be pretty much anything the motor can handle before it burns up.
But there are I think numerous definitions used to relate continous and peak power, the rta paper doesn't say how they worked out 130watt continous, but there will be some hard and fast relationship/definition they have used...........................
Using Power = volts * amps * effeciency of motor
( volts= max battery voltage after charging, amps= max amps of controller, effeciency = efficiency of motor from manufacturer data ( done with hub motor testing equipment)
to calculate max amps that controller should be below to keep legal use:
P=v*I*E rearranging for current in amps gives I = P/(v*E) ( where P = 200watts )
For brushless non-geared motors: ( assume 83% peak effeciency )
24v system using sealed lead acid batteries: I = 200 / ( 26 * 0.83 ) = 9.3amps ( v= each sla batt =13v fully charged, effeciency 83% =0.83)
36v system using sealed lead acid batteries I = 200 / (39 * 0.83 ) = 6.2amps
48v system using sealed lead acid batteries I = 200 / ( 52 * 0.83 ) = 4.6amps
24v system using iron phosphate lithium I = 200 / ( 28.8 * 0.83 ) = 8.4amps ( 8 cells @ 3.6v)
36v system using iron phosphate lithium I = 200 / ( 43.2 * 0.83 ) = 5.6 amps ( 12 cells @ 3.6v)
48v system using iron phosphate lithium I = 200 / ( 57.6 * 0.83 ) = 4.2 amps ( 16 cells @ 3.6v)
24v system using lithium cobalt or manganese oxides I = 200 / ( 28.7 * 0.83 ) = 8.4amps ( 7 cells in series max voltage each cell 4.1v)
36v sytem using lithium cobalt or manganese oxides I = 200 / ( 41 * 0.83 ) = 5.6amps ( 10 cells in series max voltage each cell 4.1v)
48v system using lithium cobalt or manganese oxides I = 200 / ( 57.4 * 0.83 ) = 4.2amps ( 14 cells in seris max voltage each cell 4.1v)
How to test max amps of controller: put ammeter on battery wires lift wheel off the ground, go full throttle, put weight on the wheel onto the ground until wheel stops rotating, you can read max amps of controller reaches a peak just before wheel stops rotating.
( there are some losses in controller and windings but not enough to bother with)
Testing the max amps of your controller and then multiplying this by your voltage and peak efficiency wont give you a good idea of the max output of your motor, because most motors wont pull the controller's max amps when running at peak efficiency. case in point, when I floor my HT from a standstill, it pulls 40a for a while, but as the rpms increase, so does the efficiency (from a 0%) starting point, and the amps start dropping off once the (i think i have this part right) back emf voltage starts equalling the input voltage? anyway, to take the stall amps and multiply it by your voltage and efficiency would actually yeild a output of 0%, since efficiency at that point is 0 x imput. just above this, it may be far less than 200w, since efficiency near stall is generally in single digit %'s. ie 100v * 40A * 2% = 80w. an extreme case I know but it again shows the lack of thought given to these laws. I may be doing an elec. engineering course, but we've done little at this point in regards to motors, much of my knowledge comes from personal research... none of which has been particularly taxing or time consuming.
Im not sure if you meant your example as an example of what was used in the aforementioned court case (edit, looks like it was
), but if it was, its a sad and slightly frightening problem. the lack of understanding borders on becoming a joke. a poorly tuned (or should I say setup?) controller could create a motor with <30% efficiency without much trouble. think incorrect phase/hall wiring. the motor may still turn, thus 'have output power' but it may use 5x the power to reach the same speed. a more subtle source of lower motor efficiency is poor timing, if each phase is 'switched on' 25% later than it should, then some of the power going into the motor will be actually slowing it down, lowering its efficiency and therefore output power as a % of input. alternatively the motor could be poorly made or a lemon, and only have a max eff. of 50%... really, looking at input power is largely misleading, if not totally irrelevant.
What I'd find funny
if not for the fact that it'd never hold up in court
is that they state 'ungoverned max' of 200w, ie not limited by the controller or any other means. Technically, the ungoverned max of ANY brush less motor is going to be 0w, since they cannot operate without a controller. by taking the law as written we can run whatever governed power we wish, since it's only the ungoverned power that the law is concerned with. brush less motors are another issue, since they basically spin with a voltage applied across their terminals.