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limiting inrush current at the relay


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jaxzin 
Copper - Posts: 87
Copper spacespace
Joined: December 16, 2006
Posted: April 06, 2013 at 2:05 AM / IP Logged  
Hi all.
Im needing a special relay to drive a radiator fan from a Ford Taurus. At startup the inrush current can be as much as 130A, steady state is about 35-37A.
At my relay on the output I need a current limiter. Am considering a NTC thermistor ( inrush current limiter ). this one here.
Would this work? Placed on the output of the relay with a diode?
Inrush current limiter
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 06, 2013 at 2:13 AM / IP Logged  
No
1 fan or 2?
jaxzin 
Copper - Posts: 87
Copper spacespace
Joined: December 16, 2006
Posted: April 06, 2013 at 2:29 AM / IP Logged  
1 fan
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 06, 2013 at 2:30 AM / IP Logged  
Does it have separate low and high speed windings?
jaxzin 
Copper - Posts: 87
Copper spacespace
Joined: December 16, 2006
Posted: April 06, 2013 at 2:35 AM / IP Logged  
Yes I am planning on using the high speed for engine cooling and the low speed for A/C operation.
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 06, 2013 at 2:45 AM / IP Logged  
Is it 130 amps when starting the low speed? There is a way to start it in low speed and then seconds later turn to high. This should make it much easier on your system. Any idea of the current draw at low speed startup?
jaxzin 
Copper - Posts: 87
Copper spacespace
Joined: December 16, 2006
Posted: April 06, 2013 at 3:04 AM / IP Logged  
Low speed is about 80 something. Still too much as the vehicle I plan to put it on only has a 100A alternator.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: April 06, 2013 at 5:03 AM / IP Logged  
I wouldn't worry about the inrush current as relays and fuses etc will generally ride thru that. As long as the relay is rated for the normal full load current plus a bit extra (typically 20-30%).
Contact arcing etc (being an inductive load) is a different issue, but I'd suggest suck it & see.
PS - those NTC thermistors are not suitable, they are for different applications - not current "limiting".
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: April 06, 2013 at 8:57 AM / IP Logged  
There's something wrong here, the Taurus should only draw about 85 amps to start the engine in warm weather, so 130 amp fan draw, sorry but feel free to prove me wrong.
jaxzin 
Copper - Posts: 87
Copper spacespace
Joined: December 16, 2006
Posted: April 06, 2013 at 10:12 AM / IP Logged  
howie ll wrote:
There's something wrong here, the Taurus should only draw about 85 amps to start the engine in warm weather, so 130 amp fan draw, sorry but feel free to prove me wrong.
It's the current spike when set to run from a dead stop that is over 100 amps but only for a few miliseconds.
Taurus Fan Inrush current spike video
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