Re: Lead foot driver causes Curtis 1221C to complain

[Roger Daisley <roger@daisley.com>]

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"