RE: (ET) Ammeter observations

["Markus Lorch" <mlorch vt edu>]

> As for the constant current by gear, that is believe it or 
> not, completely expected.  Why?  Because it's the load on the 
> motor that determines the current draw.  The more Tq it must 
> supply, the higher the currents will be.  With lower gearing 
> the current will be lower due to decreased Tq demands, 
> conversely with higher gearing.

I can agree with this part.  However higher (vehicle) speed 
requires more amperage should be drawn as our voltage stays
the same. (except for the first 4 speeds where the resistors
lower the voltage)

> 
> You might ask what about the electrical speed selector?  
> Well, you did not alter the load (Tq requirement), you only 
> reduced the voltage applied.  Your WATTS are lower, but so is 
> your speed, while the amps remained the same.  That's why you 
> choose the GEAR for the right speed with the "speed" selector 
> in full. 

Now I see where our confusion comes from. The E12 must only 
control speed using resitors. Thus this is not true for the E20s
as they have field weakening (and your fields are constant as
generated by PMs) so your constant amperage is explained. In
E20s the speeds above 4 weaken the fields, increase speed
and thus increase amperage. Higher speed at constant voltage
requires higher amperage.  
Your recommendation translated to an E20 would be: "you
choose the GEAR for the right speed with the speed selector (pedal)
in 4", plus I noticed that it is slightly better power usage
to use a smaller gear with some field weakening than a larger
gear with resistors to achieve the same speed. 

> EVs are no different.  You want to apply the greatest 
> possible voltage at the lowest possible amperage for the 
> greatest range. 

Thats right. The reasons are twofold 
1. higher voltage, lower amperage = less loss in the wiring
2. at lower amperage your batteries last longer (this is the BIG reason)

Markus