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relay, two temperature controlled fans


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75blazer 
Member - Posts: 2
Member spacespace
Joined: May 28, 2014
Location: Illinois, United States
Posted: May 28, 2014 at 3:26 PM / IP Logged  
Hello,
I have tried to figure this out on my own by searching the forums and I find myself getting overwhelmed trying to paste different ideas together. Since it is evident that many on this board are much smarter than I am, I figured I give this a go.
I want to run 2 electric cooling fans. I want 1 to turn on with a temp probe in the cool side of the radiator and the other to turn on with a temp probe in the water neck (different temps, I was thinking 200 on at the water neck and 185 on at the cool side of the rad). Additionally, I want them both to turn on when I switch on the AC. FURTHER, when switching on from the AC, I'd like to have 1 of them on a 1 or 2 second delay to soften the blow to the electrical system.
Am I nuts or does this make sense?
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: May 28, 2014 at 9:20 PM / IP Logged  
Is this for a liquid cooled vehicle? If so, why 2 fans? And why not 2 sensors for one fan?
If you want to limit the cooling (ie, higher radiator-out temperature provided in (engine out) temp is not exceeded), why not PWM the fan? (But normally engine-in temps are not regulated; cooling usually operates based on engine outlet temperatures. Controlling both usually requires control systems with an engine-independent pump.)
75blazer 
Member - Posts: 2
Member spacespace
Joined: May 28, 2014
Location: Illinois, United States
Posted: June 02, 2014 at 1:33 PM / IP Logged  
It's an old Chevy V8. The shroud/fan kit I intend to use is a dual fan setup, thus the 2 fans. Regarding PWM, in a nutshell, I think it's just too complicated for me. I can wire up relays, programming chips on the other hand, I'm not so sure.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: June 02, 2014 at 5:27 PM / IP Logged  
The easiest is probably to use diodes between the temp switches and fan relays and cross/inter connect them in whatever combination you want.
One output (probably for the outlet fan) could go thru a delay - maybe a 555 circuit or a readymade DEI (DEI 528T?).
FYI - the diodes are used to isolate different circuits whilst allowing interconnection - see DIODES above. (EG - maybe the 'negative door trigger' in your case where driver & passenger door are your in & out sensors, and the brown to alarm -ve input goes to your out fan relay (85) via the delay and another diode goes from your in sensor to the other fan relay.

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