Yes, we are talking PID now and I can probably design something that would
do the job. I suspect you could too since you brought up PID.

But I wonder if the solution can be done a little less "high tech" and all
12V powered?

For example, there are a set of known parameters for pulling a long hill:

1. You would want to know that the transmission was not in high gear.
2. You would want to know that the engine was above a certain RPM, let's say
above 3500 RPM for arguments sake?
3. You would want to know that the engine was making power - throttle open &
not coasting down a ling hill in lower gear to conserve breaks.
4. You would want to know that the vanagon met these two parameters for a
specific period of time - maybe 15 seconds?

Once these four tests were met you would switch on the fan or an auxiliary
fan to pull all the heat you could from the radiator.

Once test 1, 2 or 3 were no longer true for 15 seconds, you would switch the
auxiliary control off. If this were a separate auxiliary fan it would turn
off but if it were the main fan the fan would still be managed under the
vanagon's system control.

Tom
www.stir-plate.com

-----Original Message-----
From: Alistair Bell [mailto:albell@shaw.ca]
Sent: Sunday, April 25, 2010 11:28 AM
To: Tom Hargrave
Cc: vanagon@GERRY.VANAGON.COM
Subject: Re: PWM controller , was Water Cooler System Design Flaw
Workaround?

we're talking pid now :)

ab

On 25-Apr-10, at 9:06 AM, Tom Hargrave wrote:

This being the case, something may be worth designing that turned on the fan
earlier based on temperature change, like for example when pulling a hill,
to give the cooling system a jump start on cooling.

Tom
www.towercooler.com