Electric fans to alternator

diesel_lv

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I'm going to try another set of fans on my '67 Coronet, 496. I'm in Fort Mohave AZ where our summers are regularly over 115 n often see 125. These new fans pull 40 amps at start each and then run at about 22 amps. I've got a serpentine pulley setup w a 140 amp alternator. My question is, should I run my power wire ro my relays directly from the alternator? Reason for asking is thinking about how much amps would be going through the relay just below the firewall wiring bulkhead. Thanks in advance.
 

Ironbuilt

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In a short answer, NO. I would run the power from my alternator to the battery stud on a starter relay with a minimum 4 ga. wire, 2 ga. if you have it. Ground the casing of the alternator with the same 4 ga. wire. The battery positive should also go to that stud. From there, power the relays, minimum 50 amp with 10 gauge wire. With that amp draw, use nothing less than 10 gauge wire. If you are using manual toggle switches, make sure they are rated for 50 amps minimum. Grounds are the single most important part of your setup. Use 10 gauge wire minimum and be sure that your block has a good ground strap to the frame. I would avoid the thermostats that come with electric fans and run each fan off of it's own toggle.
 

diesel_lv

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In a short answer, NO. I would run the power from my alternator to the battery stud on a starter relay with a minimum 4 ga. wire, 2 ga. if you have it. Ground the casing of the alternator with the same 4 ga. wire. The battery positive should also go to that stud. From there, power the relays, minimum 50 amp with 10 gauge wire. With that amp draw, use nothing less than 10 gauge wire. If you are using manual toggle switches, make sure they are rated for 50 amps minimum. Grounds are the single most important part of your setup. Use 10 gauge wire minimum and be sure that your block has a good ground strap to the frame. I would avoid the thermostats that come with electric fans and run each fan off of it's own toggle.
Ok, that's what I've got right now, 4ga from alternator to stater relay and then a new, "factory" battery cable w the new "factory" wire from relay to battery. All wires are 10ga. 50 amp breakers then 75 amp relays for each fan. The fuel injection triggers on n off. All Metripac connectors. I'll have to check on the ground for the alternator though. Fan grounds are also 10ga. Thanks.
 

6872n73

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Running it to the battery would be best with a circuit breaker. If the battery is in the trunk I would go to the starter.
 

Ironbuilt

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Ok, that's what I've got right now, 4ga from alternator to stater relay and then a new, "factory" battery cable w the new "factory" wire from relay to battery. All wires are 10ga. 50 amp breakers then 75 amp relays for each fan. The fuel injection triggers on n off. All Metripac connectors. I'll have to check on the ground for the alternator though. Fan grounds are also 10ga. Thanks.
Make sure with an alternator that powerful (140 amp) that you ground the case.
How are you planning to operate the new fans? Thermostat? Toggle?
 

diesel_lv

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Make sure with an alternator that powerful (140 amp) that you ground the case.
How are you planning to operate the new fans? Thermostat? Toggle?
It is triggered by the fuel injection ECM. My normal highway temps in 120° weather is about 175° so I'm setting the on temp at 195° and the off at 185°. Also on when a/c is on. I've been using this alternator for a little over a yr now but I'll check my ground cable tomorrow.
 

1STMP

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PICO Wiring 5522PT
These are pull switches, but they're
reasonably priced and.....75 amps.
 

Nacho-RT74

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In a short answer, NO. I would run the power from my alternator to the battery stud on a starter relay with a minimum 4 ga. wire, 2 ga. if you have it. Ground the casing of the alternator with the same 4 ga. wire. The battery positive should also go to that stud. From there, power the relays, minimum 50 amp with 10 gauge wire. With that amp draw, use nothing less than 10 gauge wire. If you are using manual toggle switches, make sure they are rated for 50 amps minimum. Grounds are the single most important part of your setup. Use 10 gauge wire minimum and be sure that your block has a good ground strap to the frame. I would avoid the thermostats that come with electric fans and run each fan off of it's own toggle.

IF YOU HAVE AMMETER, IS WRONG TO HOOK UP ANYTHING TO THE BATT POST!

It will melt down the bulkhead faster and will stress out the ammeter without need for that!

EVERYTHING must be sourced from alt side of ammeter, and yes, of course, a bigger capacity alt must be used, able to feed everything your car needs at the lower speed as posible ( iddle )
 

F4R/T

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If you are worried about putting the load on the toggle switches you can always add a relay to carry the switched load , I like that for constant/ heavy loads including pumps and fans.
 

Ironbuilt

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IF YOU HAVE AMMETER, IS WRONG TO HOOK UP ANYTHING TO THE BATT POST!

It will melt down the bulkhead faster and will stress out the ammeter without need for that!

EVERYTHING must be sourced from alt side of ammeter, and yes, of course, a bigger capacity alt must be used, able to feed everything your car needs at the lower speed as posible ( iddle )
He's running EFI and a 140 AMP alternator, not to mention a full array of electronic ignition products. I am quite sure that he did away with that dinosaur ammeter a long time ago and installed a reliable voltmeter in it's place.
 

Mike67

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I ran a #4 from my battery, positive and ground, from the trunk to a 6 or 8 circuit fuse block mounted on my inner apron.
From there it goes to my 60amp relays which are controlled by the Spal Fan Controller via the ignition power.
I dont have a current pic but this is when I first started to assmble everything. But afded another relay and lowered the block to make room for my PS reservoir.

20200101_190139.jpg
 
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