Dual Electric Fan people..... i have a question
05-26-2010, 07:52 PM
#1
Thread Starter
Dual Electric Fan people..... i have a question
For you guys running dual fans, has anyone made a time switch so the fans run for a few min after shut off? like a turbo timer, but for fans? The under hood temps here in Albuquerque are killing me.
Duc
Duc
05-26-2010, 08:01 PM
#2
Race Car
On '87+ 928's, the fans do run after shutdown if the intake temperature and/or the A/C refrigerant temperature is above a certain threshold. I believe they are triggered by a temp switch on top of the S4 intake (a simple hot/not hot switch). It may not be that hard to wire in a similar switch for earlier cars retrofitted with the dual-fans.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
05-26-2010, 08:37 PM
#4
Race Director
the fan control program is quite complicated...there are many different "maps" that take into account AC, temp, load cooling flaps to determine fan speed on a variable level.....too complicated for me...since all the brains also consume some voltage...so you never get full voltage at the fans..... even on a street car I would just remove all that stuff and install a simple on-off switch like the OB's use for the AC fan....rig a simple fuse-relay and your done.....100% voltage at a point you determine.....
05-26-2010, 08:41 PM
#5
Race Car
The only problem with having the dual-fans running 0% or 100% and nothing inbetween is that at 100% voltage those fans are spinning really really fast and drain lots of current. Such a duty cycle on the fans is not really necessary 90% of the time. Maybe have a two-stage setup with two relays?
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
05-26-2010, 09:34 PM
#6
Rennlist Member
I have replaced the engine driven fan and the front AC fan with 2 x 11" assy from SPAL. Its wired off the original bottom radiator sensor at the moment, and this will run with ignition in the accessory position, until the sensor turns off. Typically for me, after parking up, this is under 2 minutes, in a coolish climate. The position of this sensor is not at all optimal for real temperature control, so I am going to fit a top hose sensor soon.
jp 83 Euro S AT 52k
jp 83 Euro S AT 52k
05-26-2010, 10:04 PM
#7
Three Wheelin'
Join Date: Mar 2010
Location: Colorado Springs, CO USA
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the fan control program is quite complicated...there are many different "maps" that take into account AC, temp, load cooling flaps to determine fan speed on a variable level.....too complicated for me...since all the brains also consume some voltage...so you never get full voltage at the fans..... even on a street car I would just remove all that stuff and install a simple on-off switch like the OB's use for the AC fan....rig a simple fuse-relay and your done.....100% voltage at a point you determine.....
So, complicated may be a reason to remove all the controllers, but not being able to run the fans at as high a speed as a switch should not be.
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05-27-2010, 12:31 AM
#10
Rennlist Member
928motorsports makes an adaptor that goes in the top hose, and can take a temp switch. I have a home made one ready to go into mine to drive the electric fans....here..
http://www.928motorsports.com/parts/...endermount.php
Difficult to make one cheaper than that. Unless you have to buy your own M22x1.5 tap.
A friend here in Oz (with electric fans) tracks his car regularly, but using the bottom radiator sensor, was always having temp control issues, and getting coolant blowing out the overflow. Since fitting a sensor in the top hose, such problems seem to have disappeared....
jp 83 Euro S AT 52k
http://www.928motorsports.com/parts/...endermount.php
Difficult to make one cheaper than that. Unless you have to buy your own M22x1.5 tap.
A friend here in Oz (with electric fans) tracks his car regularly, but using the bottom radiator sensor, was always having temp control issues, and getting coolant blowing out the overflow. Since fitting a sensor in the top hose, such problems seem to have disappeared....
jp 83 Euro S AT 52k
Last edited by jpitman2; 05-27-2010 at 12:58 AM.
05-27-2010, 01:45 AM
#12
Rennlist Member
One switch with two circuits will do it more cheaply and compactly. There are many available in the same format & thread size - see here :-
http://www.busdepot.com/details.jsp?...ber=251959481K
The std 928 switch is M22x1.5 thread, as are many at that site.
jp 83 S
http://www.busdepot.com/details.jsp?...ber=251959481K
The std 928 switch is M22x1.5 thread, as are many at that site.
jp 83 S
05-27-2010, 07:53 PM
#13
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Just an observation or two:
-- Electric fans are not free when it comes to power to run them. The motors are not perfectly efficient, and the alternator used to convert the power to run them is not perfectly efficient. Bottom line is that it costs you an addtional 10-20% in conversion losses, sometimes more, to go to electric from direct-drive mechanical fans.
-- The temp sensor/switch location in the 928 is at the bottom of the cold side of the radiator, and functionally regulates the temperature of the coolant returning to the engine. It does not regulate engine temp, is not directly sensitive to engine temp or instant load changes. There's a delicate temp control balance between the effects of the fan on return temp and the effects of that return temp and engine load in the way the thermostat works that ultimately decides what the water temp is on the way back to the top of the radiator.
Changing to a cooler fan switch to get the fans running faster or earlier may or may not change the readings on the dash gauge.
Now back to our regularly scheduled "my car seems to run hotter in the summertime" discussion.
-- Electric fans are not free when it comes to power to run them. The motors are not perfectly efficient, and the alternator used to convert the power to run them is not perfectly efficient. Bottom line is that it costs you an addtional 10-20% in conversion losses, sometimes more, to go to electric from direct-drive mechanical fans.
-- The temp sensor/switch location in the 928 is at the bottom of the cold side of the radiator, and functionally regulates the temperature of the coolant returning to the engine. It does not regulate engine temp, is not directly sensitive to engine temp or instant load changes. There's a delicate temp control balance between the effects of the fan on return temp and the effects of that return temp and engine load in the way the thermostat works that ultimately decides what the water temp is on the way back to the top of the radiator.
Changing to a cooler fan switch to get the fans running faster or earlier may or may not change the readings on the dash gauge.
Now back to our regularly scheduled "my car seems to run hotter in the summertime" discussion.
05-27-2010, 10:13 PM
#15
Rennlist Member
Just an odd fact. FWIW
85 and 86 condensor fan has two speeds.
On the passenger fender near the radiator is a resistor.
If the intake tube temperature sensor trips, it runs the fan via a circuit that includes this resistor. The speed is less than if the fan is triggered by another sensor.
You can see this slower speed operation by bridging the two connectors on the intake tube sensor.
85 and 86 condensor fan has two speeds.
On the passenger fender near the radiator is a resistor.
If the intake tube temperature sensor trips, it runs the fan via a circuit that includes this resistor. The speed is less than if the fan is triggered by another sensor.
You can see this slower speed operation by bridging the two connectors on the intake tube sensor.