Re: Lead foot driver causes Curtis 1221C to complain

[Rod Hower <rodhower@ameritech.net>]

I'll give a real simple example of airflow.
I designed an AC inverter for Baldor motors and Drives.
It would put out 1.5 Hp on 460Vac without a fan.
With a 92mm sqare fan it can put out 5Hp at 460Vac.

Low RMP DC motor? check out the torque speed curves for
any motor, AC, DC or BLDC, low RPM and high torque is
very inefficient.  Once you get higher in RPM the efficiency
doubles (RPM etc depend on motor design)
This means you can easily get the same HP at twice
the efficiency if you gear your vehicle correctly.
My links for motor curves are at work, but I can
assure you that operating at the peak of the torque speed
curve makes a huge difference.  So this means appropriate
planning of shifting gears in a manual transmission EV.
(and appropriate cruising speed at the selected gear to
maximize efficiency on the torque speed curve)

Roger Daisley wrote:
> BRAVO, Lee!  You seem to understand the problem.  My comments and follow-up
> questions:
> ~~~~~~~~~~~~~~~~~~~~~~~
> Roger Daisley wrote:
> 
>>I recently acquired a VoltsRabbit running a Curtis 1221C, Prestolite
>>motor and 128-volts of flooded batteries.
>>
>>On warm days, the controller will abruptly cut back on current flow
>>and start to squeal at certain throttle positions. I assume it is
>>overheating.
> 
> 
> Yes. That's it exactly.
> 
> How are you shifting it? With EVs, you want to keep the motor at as HIGH
> an rpm as possible, for best cooling and efficiency. If you shift into
> higher gears to keep motor rpm lower, you also overheat the controller.
> So as a rule, you should be doing most of your driving in 2nd or 3rd
> gear; not 4th, and never 5th.
> 
> ???? Your advice surprises me. Yup, I have been under the inpression 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)
> 
> 
>>The controller and aluminum plate it's mounted on (Electro Automotive
>>design) is quite hot to the touch. Ideas that cross my mind are:
>>
>>Find a way for more air flow across the assy, but that seems
>>problematic as to "fixing" the problem.
> 
> 
> Even a small airflow has a dramatic effect on cooling. Where is the
> controller mounted, and what kind of airflow is it getting now?
> 
> ???? In my Rabbit, it's on the rt. front fender, inside, of course, behind
> the rt. headlight, probably exactly like yours.  There looks like virtually
> no airflow, other than what naturally "circulates around" in the engine
> compartment.  No fans, vents or ducts, other than as you mentioned, the
> "duct" created by the space between the inside fender wall and the bottome
> of the controller mounting plate.  Maybe I need to add a fan to blow some
> air in this area.
> 
> On my EV, the Curtis controller is mounted to a roughly 12" x 20" x 1/8"
> thick aluminum plate. This plate is mounted about 3/4" above the fender
> well, which serves as the bottom and left side of a "duct". A plastic
> cover goes over the top, and right sides, forming the top and right
> sides of this "duct". A 4.5" 12vdc muffin fan blows air lengthwise thru
> this duct. It has done a fine job of keeping the controller out of
> thermal limit.
> 
> 
>>Add cooling area or increased heat sink.
> 
> 
> Lots of people use a big finned heatsink. They are rather bulky and
> expensive, though, and they still need some airflow, whether from a fan
> or by being in the vehicle's windstream (like where the radiator
> normally goes).
> 
> ???? I wonder if it would be a good idea to recable the entire assy to the
> front of the car in the radiator area?
> 
> 
>>Some method of extracting the heat from the controller.
> 
> 
> You can also use liquid cooling. For example, attach metal tubing to the
> controller, and pump water or oil through it, which is in turn cooled by
> a radiator or heater core somewhere.
> 
> ???? Liquid?  I don't see any provision for liquid to be flowed through the
> controller.  I was thinking that maybe I could weld a second aluminum plate,
> spaced about 1/2" from the other, with fins welded on, closed on all sides,
> like a flat box, and circulated a coolant through that to a small radiator,
> such as a heater core.
> 
> Please keep the good ideas rolling in.  I'm about to convert an '86 VW
> Cabbie.  The current (no pun intended)  vehicle is my "testbed" and "organ
> donor".  I want to test all the good ideas and make all the mistakes here.
> 
> ???? BTW: I also have an new ADC motor from a Sparrow.  Would you go the the
> trouble and substantial expense of replacing the Prestolite motor with the
> ADC, when I transfer the equipment to the new car?
> 
> Roger Daisley
> Laguna Hills, CA
> 
> "Where Revolutionary New Ideas Are Not Always New or Revolutionary"
> 
>