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  #1 (permalink)  
Old 12-03-2018, 10:39 AM
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Default Fan

Bulldog here again I have a question about my electric fan on my small block ford . it has a switch for on an off i keep it on all the time but with the weather cold now should I turn it off and let it cycle on its on ? Thanks and every one have a great Christmas . Bulldog
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  #2 (permalink)  
Old 12-03-2018, 11:31 AM
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Even in the summers here I let mine run off the switch. I had an on/off switch but only used it when I brought the car home and put it in the garage I would then turn the fans on for a few minutes to get rid of the heat surge.

Ron
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Old 12-03-2018, 12:36 PM
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Quote:
Originally Posted by Ron61 View Post
Even in the summers here I let mine run off the switch. I had an on/off switch but only used it when I brought the car home and put it in the garage I would then turn the fans on for a few minutes to get rid of the heat surge.

Ron

That's pretty much what I do. I'll usually flip the manual switch a couple of minutes before I expect shutting it off to minimize the amount of time the fans run after I shut it off. Other than that the fans run off the thermo-switch / controller.
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Last edited by cycleguy55; 12-03-2018 at 09:02 PM..
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Old 12-03-2018, 07:54 PM
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Default Fans

Thanks guys I can always count on yall for the answers.
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Old 12-04-2018, 02:17 PM
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Default fan relay

Hi,
carry an extra fan relay in the car, mine blew in the border lineup and the HOT engine blew water all over everything as my fan relay failed, actually melted. so try pushing you cobra 1/8 mile as there is no turnouts in the lineup
P
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Old 12-05-2018, 10:20 AM
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Quote:
Originally Posted by HighPlainsDrifter View Post
Hi,
carry an extra fan relay in the car, mine blew in the border lineup and the HOT engine blew water all over everything as my fan relay failed, actually melted. so try pushing you cobra 1/8 mile as there is no turnouts in the lineup
P
When my fan relay failed I discovered it in a nearly inaccessible location - on the top of a cross bar above the pedals. Accessed through the wheel well after removing access panels. Aaaarrrggghhh!!

When I replaced it I installed a pair of relays in parallel. Each of the relays has sufficient capacity to handle the load on its own, but sharing the load I'm hoping they last forever.
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Old 12-05-2018, 12:24 PM
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Isn't most of the issue associated with the Relays overheating directly attributable to wire size and the soundness of each connector for the circuit? There are Relays capable of carrying far more amperage than any automotive load requirement in any vehicle, just look at the average electric hybrid these days with relays carrying amperage in excess of 700amp.

The heat factor is directly associated to the amperage carrying ability of the wire, and the quality of ALL connections. One of the biggest faults in many aftermarket wiring assemblies is the use of "crimp on" electrical connectors at many locations through a single circuit and not soldering these connectors during electrical build-up. Each of these connections, if even slightly faulty, contribute to additional resistance in the circuit and overall heat buildup within the circuit.

A good practice is to check your wire amperage capacity for both gauge AND length per Ohms law and then build in a safety or overage factor based on highest amperage expected including start-up additional loads. All electrical motor components peak higher amperage demand at initial start up then return to normal continual operating amp loads.

And do not minimize the quality of all of the connections within a circuit. I personally solder all connections, even if I'm using crimp type connectors, then heat shrink with dielectric grease within the heat shrink tubing for water/weather resistance, discarding the colored plastic crimp insulation. This is very easy, quick, and inexpensive but ensures the most stable and weather resistant electrical connections in a circuit for a very long time. Also, do not forget to use a quality dielectric grease on all spade type connectors to minimize poor conductivity at the male/female spade connection.

If you are overheating relays, I'd suggest to review the overall circuit amperage load with all items running especially at start-up, factor in an overage for safety (probably 15%), check that the wire and relays are rated for these amperage loads and make sure all connections are sound, preferably soldered and heat shrunk.
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Old 12-05-2018, 12:35 PM
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Why is the size of an automotive wire so important? When electricity passes through a wire, The wire resists the electricity and some of it is converted into heat that is absorbed by the wire. This lost energy is realized in the form of a voltage drop at the end of the wire. In its simplest terms, you can think of 12 Volts as during 12 units of work. If you're wire has a 2% voltage drop, then the wire is using up 0.24 volts, or units of work. That leaves 11.76 volts, or units of work left. So if you put a volt meter on your battery and read 12 volts, when you put your volt meter on the end of the wire, you will read 11.76 volts. If you are running 20 amps through your wire then your wire is absorbing 4.8 watts of power. Now let's say your wire has a 20% voltage drop. The voltage reading on your volt meter at the end of the wire will only be 9.6 volts, and the wire is absorbing a whopping 48 watts of power!

Automotive Wire Recommended Amperage Capacity Chart - 2% Voltage Drop
Recommended Length and Amperage for Automotive Wire while maintaining a 2% or less voltage drop at 12 volts
Automotive Wire Size 5 Amps 10 Amps 15 Amps 20 Amps 25 Amps 30 Amps
20 Gauge Wire (AWG) 4.5 ft 2.2 ft 1.6 ft .
18 Gauge Wire (AWG) 7.3 ft 3.7 ft 2.4 ft 1.8 ft
16 Gauge Wire (AWG) 11.5 ft 5.8 ft 3.8 ft 2.9 ft 2.3 ft 1.9 ft
14 Gauge Wire (AWG) 18.4 ft 9.2 ft 6.1 ft 4.6 ft 3.7 ft 3.1 ft
12 Gauge Wire (AWG) 29.4 ft 14.7 ft 9.8 ft 7.4 ft 5.9 ft 4.9 ft
10 Gauge Wire (AWG) 46.8 ft 23.4 ft 15.6 ft 11.7 ft 9.4 ft 7.8 ft
8 Gauge Wire (AWG) 74.4 ft 37.2 ft 24.8 ft 18.6 ft 14.9 ft 12.4 ft
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Old 12-05-2018, 12:46 PM
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In the above examples, if your fan circuit is running at 20amp demand, 14 gauge wire can be a maximum of 4.6 feet in length AND the connections need to be very sound to not contribute to additional voltage drop.

Since the fan relay circuit is probably closer to 6 to 8 feet in length, a 20 amp circuit REQUIRES a minimum of 12 gauge wire with sound connections and a relay capable of carrying 20amp plus. 10 gauge wire is probably a better choice in combination with soldered connections and dielectric grease on all spade connections.
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Old 12-05-2018, 01:08 PM
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As a kind of funny side note, for any of you that have ever worked on a 60s era british sports car with Positive Earth electrical systems. One of the contributing factors for the British selecting Positive Earth electrical systems was the cost and weight savings they could achieve with Positive Earth.

Using the chassis or body of the vehicle to carry the positive electrical surge of electrical demands, then the actual wiring carrying the ground back to the battery.

These systems were an absolute mess and thrown to the trash heap of OEM technology after a few years. My dad exposed me to these at a very young age as he raced several MG Midgets in the late 60s early 70s that also included the infamous "Lucas Electrical" components. One of the first thing he would do to each car was to convert the entire MG electrical system to negative earth and properly size wiring for all circuits accordingly. Positve Earth Lucas electrical fuel pumps were notorious to only last a year or two, many failures directly attributable to poor chassis electrical connections and the resistance and heat build up that accompanied this system. Poor connections, either due to age or weather exposure put the nail in the coffin of positive earth electrical architecture 50 years ago.
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Old 12-06-2018, 09:28 AM
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Default Fans

Really goodinfro thanks again guys. Bulldog
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