Ryan and Rich, I apologize for taking so long to get back to you about
this. I have just come up for air, found I have a chance to address
this, and even found a drawing I already made (attached). Here's how it
works (refer to the drawing and to the control board schematic):

The OEM controller connects the light green wire to the OEM fan to +14V
when the OEM battery temperature reaches around 89-96 deg F. This
control leaves that connection in place but taps it and runs it to J8F
pin 1. Once the fan is so energized, proportional control is affected
by varying the current to the violet line to the negative terminal of
the OEM fan. The voltage of this line is monitored, and a DTC (system
error) is asserted if the fan has become an open circuit. Control is
effected by removing the violet line from the OEM fan and running it
instead to J8F pin 3. J8F pin 5 is then run to the OEM fan. A diode
(actually 3 in-line 3A diodes in parallel to handle 5A) between pin 3
and pin 5 allows the OEM control to operate the fan normally when the
control board is unplugged (J8F plugs into J8M on the control board).

The control board has a 2.2K resistor between pins 1 and 3 of J8, a
controlled pullup from pin 1 to +14V, and a controlled pulldown from pin
5 to chassis ground. When not in PHEV mode, the control board does
nothing. When in PHEV mode, pin 5 is always pulled down to ground.
This causes the fan to run at full bore whenever there is power on pin 1
(normally when the OEM battery temperature is above 89-96 deg F). At
the cost of some passenger compartment noise, this keeps the OEM battery
temperature below 100 deg F instead of around 114 deg F, thereby keeping
it cool enough for EV mode, which will not work when the OEM battery's
temperature is above 104 deg F, to continue to be enabled. It would no
doubt be possible to proportionately control the fan to this lower
temperature, too, but this system is not yet that sophisticated.

The pullup on J8 pin 1 is to allow the PHEV system to force the OEM fan
ON when desired and the OEM battery temperature is below 89-96 deg F. A
recommended use of this feature is to force the fan ON when the OEM
battery temperature is so low that discharge current limit (DCL) is
below 100A, thereby (sometimes severely) limiting EV mode current. If
the driver, as would be expected, is using the cabin heater, the fan can
speed up the heating of the OEM battery by blowing cabin air over it,
thereby enabling EV mode sooner than without forcing the fan ON.

I hope this clarifies control of the OEM battery fan. Jack, as usual,
please add this explanation (and drawing) to the documentation.

--
+++++++++++++++++++++++++++++++++++++++++
Ron Gremban, rgremban@...
California Cars Initiative, a nonprofit organization:
http://www.CalCars.org
Moderator & Technical Lead
http://www.priusplus.org
PRIUS+ PHEV Conversion Group: http://groups.yahoo.com/group/priusplus
Newsletter: http://groups.yahoo.com/group/calcars-news
Do-it-yourself PHEVs: http://www.eaa-phev.org/wiki/PriusPlus
+++++++++++++++++++++++++++++++++++++++++

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