X-FORD MAN
Member
- Joined
- May 26, 2001
I want to run both my fan and water pump off the fan switch of my FAST, will the driver handle the current of two relays?
TIA!
TIA!
Can you run two relays on the FAST fan curcuit
- Thread starter X-FORD MAN
- Start date
Yes, the relays require very, very little current. No problem for the FAST.
You could also run the 12V+ from the output of the first relay to the input/trigger of the 2nd relay, so the FAST only triggers one relay (the first relay powers the fan plus the second relay).
On the other hand, why do you want to run your water pump only part-time? I would be very worried about hot spots and overheating. I would think you would want to run the water pump separately. I assume this race-only?
-Bob Cunningham
You could also run the 12V+ from the output of the first relay to the input/trigger of the 2nd relay, so the FAST only triggers one relay (the first relay powers the fan plus the second relay).
On the other hand, why do you want to run your water pump only part-time? I would be very worried about hot spots and overheating. I would think you would want to run the water pump separately. I assume this race-only?
-Bob Cunningham
I may be incorrect, but I think the FAST shuts off the fan at WOT. I know DFI and stock ecm do this. I used to trigger my water pump relay off the fuel pump relay. This way, you never forget to turn it on, it's always on when the engine is running, and it doesn't pull the battery down when the key is on/engine off.
Craig Smith
That was easy!
- Joined
- May 25, 2001
Actually, I would not run two relays off of the same output. Some relays draw a little more than one might think. I do agree completely though that the water pump should ALWAYS run if the engine is on. I would guess that you would wreck the motor trying to cycle the water pump based on engine temp.
And yes, the ECU will shut the fan output off above 80% TPS. At WOT, maintaining battery voltage is more critical on an EFI car than it is on a carbed car. The fan is often a huge drain on the charging system, and it's more important for the fuel pump and injectors to work properly than it is for the fan to work at WOT, especially since most cars are rarely at WOT for more than, say, a 1/4 mile pass.
And yes, the ECU will shut the fan output off above 80% TPS. At WOT, maintaining battery voltage is more critical on an EFI car than it is on a carbed car. The fan is often a huge drain on the charging system, and it's more important for the fuel pump and injectors to work properly than it is for the fan to work at WOT, especially since most cars are rarely at WOT for more than, say, a 1/4 mile pass.
X-FORD MAN
Member
- Joined
- May 26, 2001
Having the water pump motor turn on and off with the FAST fan switch is simulating a thermostat right??? I wanted to run this configuration to cool my car down in the pits, with the engine off I could key the ignition and have the fan and water pump run till it reached my predetermined shut down temperature. This way I wouldn't forget and leave it running and kill the battery. But now knowing the FAST cuts out the fan at 80% TPS, this configuration is out of the question.
Craig, On runs, I have data logged as low as 12.1 volts, what is the lowest voltage you've seen without any ill effects to the FAST.
Thanks Guys!
Craig, On runs, I have data logged as low as 12.1 volts, what is the lowest voltage you've seen without any ill effects to the FAST.
Thanks Guys!
If this were my car, I would try to rig it up so it runs something like this:
- Electric water pump comes on with the fuel pump (i.e. the fuel pump relay turns on the water pump relay)
- Fan comes on with the FAST unit
- The water pump can *also* come on with the fan
Depending on how you wire it, you might need two relays in parallel for the water pump, or maybe a single relay and some diodes so stuff doesn't come on inadvertantly. It will take some thinking, but it is certainly possible.
-Bob Cunningham
- Electric water pump comes on with the fuel pump (i.e. the fuel pump relay turns on the water pump relay)
- Fan comes on with the FAST unit
- The water pump can *also* come on with the fan
Depending on how you wire it, you might need two relays in parallel for the water pump, or maybe a single relay and some diodes so stuff doesn't come on inadvertantly. It will take some thinking, but it is certainly possible.
-Bob Cunningham
- Joined
- May 28, 2001
X Ford regarding voltage minimums at WOT.
I have seen the voltage drop to 11.8 volts on a WOT blast and it did not affect the ECM or injectors. There is a volt booster and a 220 amp alternator on the car. This was using the datalog on a dyno. The fan was running too.
Be careful with voltage and FAST systems. You need a solid 12 volts coming from the charging system to run the ECM correctly. I have seen where low voltage would cause us to run the injectors more to compensate and once we fixed the problem all of a sudden we were rich across the board on the fuel map.
I like Cals' idea about running the fuel pump and water pump from the same circuit.
From runs on the track, I have seen the temp go up because the fan switches off but once you pass the lights and are in the return lane the motor was cooling back down.
Hope this helps
I have seen the voltage drop to 11.8 volts on a WOT blast and it did not affect the ECM or injectors. There is a volt booster and a 220 amp alternator on the car. This was using the datalog on a dyno. The fan was running too.
Be careful with voltage and FAST systems. You need a solid 12 volts coming from the charging system to run the ECM correctly. I have seen where low voltage would cause us to run the injectors more to compensate and once we fixed the problem all of a sudden we were rich across the board on the fuel map.
I like Cals' idea about running the fuel pump and water pump from the same circuit.
From runs on the track, I have seen the temp go up because the fan switches off but once you pass the lights and are in the return lane the motor was cooling back down.
Hope this helps
TwinTurboIroc
New Member
- Joined
- Mar 5, 2002
So Craig....if you dont think it is safe to run 2 relays off the fan circuit, would it be ok to have the one relay trip the other to turn on both fans?
