RE: (ET) Using 4QD controllers

[Humphrey Timothy H Contr AFRL/IFEC <Timothy Humphrey rl af mil>]

No!

You'll lose efficiency.

The power lost in these motors is lost mainly to the heat from the current
in the armature. P=I^2*R. If you slow a motor down it will draw more
current. If you merely double the current, it will quadruple the current
burned up in the windings.

You still need the same amount of power applied to get the same work 
anyway.

Example: (not real life numbers)

Say I need 1 hp at 36rpm at the wheel.

Let's assume that there are no losses in the gearing.

I have a motor that turns 3600rpm at 36 volts and gives me my 1 hp. 

That tells me that it gives me 100rpm per volt (this works well with
permanent magnet motors and almost as well with sep-ex like we have. Does
Not Correlate with series wound motors.

OK, So I can gear it down 100:1 and my requirements are met.
The motor draws 21.33 amps at 36volts to produce 1hp. 768watts/36volts =
21.33amps
The power lost (dissipated) is 21.33amps * 21.33amps * .003ohms = 
1.36watts 

If I cut the motor speed in half by changing the gearing and the input
voltage.
The motor now draws 768/18= 42.67 amps to produce 1hp.
The power lost (dissipated) is now 42.67*42.67*.003= 5.46watts just to heat
the windings


However, you did double your top speed capability.

The above education came to me courtesy of many years lurking the EV list. 
I
hope I didn't screw it up too much.


Stay Charged!
Hump
I5/NY 


 


-----Original Message-----
From: Bob Murcek [mailto:rmurcek geisinger edu] 
Sent: Thursday, June 05, 2003 2:34 PM
To: elec-trak cosmos phy tufts edu; Timothy Humphrey rl af mil
Subject: RE: (ET) Using 4QD controllers


I have an E12 so I can't try this, but I'm wondering if the efficient
low-speed control provided by a PWM controller would make it possible to
just increase the motor pulley size to make up for the top speed lost by 
not
doing field weakening.  I.e., with the original contactor control you have
to run the motor at full speed or lose energy in the resistors; when you're
using a PWM controller you can run the motor at less than full speed at no
battery life penalty.  All you'd lose to a bigger motor pulley would be 
some
pulling power in 1st...Bob

>>> Humphrey Timothy H Contr AFRL/IFEC <Timothy Humphrey rl af mil> 
>>> 6/5/2003 2:16:28 PM >>>
Yes, and consequently, range(although not much, I believe).

My field weakening is not functioning on my I5. I have the knowledge and
capabilities to fix it, but it's absence doesn't bother me so much that I
feel a need too.  I expect to have a free moment sometime around the summer
of 2014, maybe I'll fix it then. ;-)

Stay Charged!
Hump
I5/NY


-----Original Message-----
From: john briese [mailto:goodguyforsure hotmail com] 
Sent: Thursday, June 05, 2003 12:36 PM
To: roden ald net; elec-trak cosmos phy tufts edu 
Subject: Re: (ET) Using 4QD controllers



So.....If I understand this correctly...(remember the only EE course I 
took 
I got a D in!!)
The 4 quadrant controller will give me reverse, will controll the field 
on/off, but I loose field weakening which will reduce top speed? John 
Briese