Re: Lead foot driver causes Curtis 1221C to complain

[Lee Hart <leeahart@earthlink.net>]

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.

> 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?

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).

> 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.
-- 
Lee A. Hart                Ring the bells that still can ring
814 8th Ave. N.            Forget your perfect offering
Sartell, MN 56377 USA      There is a crack in everything
leeahart_at_earthlink.net  That's how the light gets in - Leonard Cohen