Re: Lead foot driver causes Curtis 1221C to complain

["VanDerWal, Peter MSgt" <vanderwp@fhu.disa.mil>]

> ???? Your advice surprises me. Yup, I have been under the impression to
keep
> the motor turning slower because of back EMF and low efficiency.  I find
> that I'm shifting into the higher gears ASAP, while no tach, I'd guess the
> motor RPM is in the 750-2000 RPM range most of the time, usually in 3rd or
> 4th gear around in city traffic. (Pulls real nice. lol)
>  

I think if you follow Lee's advice most, if not all, of your overheating
problems will disappear.

I gather that you are misunderstanding the effects of back EMF and think
that it somehow reduces efficiency.  Back EMF is not a bad thing and it does
NOT reduce efficiency.  All it does is reduce the amount of current that
flows and under most circumstances this IMPROVES efficiency.

High currents are what you have to watch out for because not only do they
(generally) cause low efficiency, but all of that power that gets lost is
turned into heat.  Unless you want an electric heater, heat is generally a
bad thing.

Here is how it works.  I am going to assume you are familiar with Ohms Law (
E = I * R ) as well as the formula for figuring power ( P = E * I ).  SO to
figure out how much power you are loosing through a resistor (which is
effectively what your motor/controller are) then you can combine the two
formulas by substituting "E" like this ( P = (I*R) * I ) or as we like to
call it on this list I2R (Current squared times resistance).

So if you cut the current in half you reduce the I2R losses to 1/4 and since
these losses show up as heat, you reduce the heat generated to 1/4 the
amount.

So try to keep that motor spinning at 4000-5000 rpm and you will have much
less heat generated, as a side benefit the higher motor rpm means that it's
internal fan moves more air which helps keep the motor cooler and extends
it's life.

P.S. You can always shift up briefly during those times when you need more
"pull".  In series wound motors torque goes up nonlinearly with current so
twice the current usually means something more than twice the torque.
Theoretically twice the current should make four times the torque, but real
life motors usually have problems with magnetic saturation so they don't
typically see four times the torque.