[71 Ventura II]

OK, I wasted my afternoon trying to wire a 40a relay to power my new cooling fan. I verified the fan works on both low or high sides when connected straight to power/ground. I followed the instructions from the relay package and even tried wiring directions I found in an old issue of chevyhighperformance magazine. NO LUCK! confused2

The package said to use the terminals as follows: #87 "from power source", #85 "relay ground", #30 "for accessory", and #86 "from switch".
I hooked everything up no power to the fan! There's power getting to the relay but that's it.

The article read differenty recommending: #30 12 volt power source, #86 relay ground, #86 & #87 power out to accessories.
I hooked everything up no power to the fan! There's power getting to the relay but you know...

What am I missing? I was under the impression the "Relay" needs 12 volts in, a good ground, and then you send the power to the accessory. I must be missing something??? I'm trying to run an electric cooling fan from a late model Taurus could it be requieing more than the 40a rating or something? Confused! JD

P.S. What's the volt requirement to run the relay? I haven't verified the voltage getting to the relay yet as I just thought of it. But is there a min/max to operate the relay?

[wrenchmen]

lookie here..........http://forums.maxperformanceinc.com/...ighlight=relay

[71 Ventura II]

#30 battery power 12 volts
#87 goes to the fan
#86 ground
#85 needs 1/4+ volts to activate the relay

I just need to give a signal to #85 so it will transfer the power? Also, will my toggle switch act as the "fuse" or do I need to add one near the #30 terminal as well? JD

P.S. My relay has a different terminal diagram showing: #87 Power In, #30 to Lights or Horns, #85 Relay Ground, and #86 Switch. Is this normal and should I follow the printed diagram or follow the wiring from above? Geez this is strange! LOL JD

P.S. #2 I re-read the old thread numberous times and believe the terminals listed may be interchangeble? Since the relay gives specific instructions on which terminals to run I'll follow it. It looks like I'll just need to "loop" #86 & #87 together to activate the switch; while maintaining #30 to the fan and #85 for the ground. Thanks for the "link" it was very helpfull in understanding what makes the relay work. JD

[guccieng]

you do have a ground from the fan to chassis/battery, right?

[guccieng]

your post is confusing me: here's the skinny. a relay takes trigger voltage (from ignition switch) and grounds out via toggle switch or thermostat (that grounds out at certain temps). then you have big power in (from battery/alt) and big power out (to the fan). the fan will have to be grounded, too. 86 and 87 do not get connected.

[71 Ventura II]

Originally Posted by guccieng

your post is confusing me: here's the skinny. a relay takes trigger voltage (from ignition switch) and grounds out via toggle switch or thermostat (that grounds out at certain temps). then you have big power in (from battery/alt) and big power out (to the fan). the fan will have to be grounded, too. 86 and 87 do not get connected.

Curious, why can't you connect the "power in" with the "activation trigger"? On my switch it shows #87 BATT in and #86 as the Switch; since I'm controlling the BATT power via a toggle switch wouldn't it work?

After reading the old thread about relays I realized I did not have the switch wired to trigger the power to the fan. Yes I have the relay and the fan grounded to the core support. Once I power the "Switch" at the relay it will work great. JD

[guccieng]

the switch gets connected to the activation trigger through the relay. ignition hot goes to the relay, then through the relay. it needs a ground to make the 'big power' work. it finds a ground through a toggle switch or t-stat that grounds out the low power side of the relay making the big power work.

[guccieng]

batt power is not controlled via switch. lets back up. batt power is big power. it is hardwired. it goes to the relay with a big wire. the big power leaves the relay through a big wire to the fan. the fan is then grounded. the only other two wires left on the relay are for little power in and out. the power in is a switched 12v ignition hot wire. the out is to the switch, toggle or thermotstatic.

[Squidward]

This might help. See attached pic.

The +12v going to #86 through the switch doesn't need to be capable of carrying a heavy current load. 14-16 gauge wire should be plenty. Run this supply from a terminal on the fuseblock for an ignition ON source.

The load wire to the fan from #30 must be capable of carrying the rated curent load of your fan. I'm guessing 10 gauge should be ok without knowing your fan's amp rating, but since you have a 40A relay, I'm assuming it is less than 40. If it is >40, you need a bigger relay.

Ground #85, and give #87 a heavier wire (just like the one connected to 30). If it was me, I'd run a wire from the alternator + term, through an inline fuse, and to #87.

I don't have your relay or packaging with me, but I used your supplied package info. Sorry if my idea differs from others. Hope it works out.

Use the top chart in this link for determining wire size/insulation type based on how much current your fan draws.
http://www.wiktel.com/standards/ampacit.htm

[71 Ventura II]

I looped a smaller wire between the main power and switch terminals so when I trip the toggle the fan comes on. The "Switch" terminal actuates the transfer of power once it sees 1/4 volt of power. Other than blowing the 20a fuse on the test drive it seems to work? I replaced the fuse with a 30a plus wired in and inline 30a fuse between the BATT terminal at the fuse box and the toggle switch. I turned on the fan and let it run for 10 minutes without issue. I'll keep my eyes on the setup to see if any of the wires get hot or anything. Thanks for all the feedback! JD

["QUICK-SILVER"]

Originally Posted by 71 Ventura II

I looped a smaller wire between the main power and switch terminals so when I trip the toggle the fan comes on. The "Switch" terminal actuates the transfer of power once it sees 1/4 volt of power. Other than blowing the 20a fuse on the test drive it seems to work? I replaced the fuse with a 30a plus wired in and inline 30a fuse between the BATT terminal at the fuse box and the toggle switch. I turned on the fan and let it run for 10 minutes without issue. I'll keep my eyes on the setup to see if any of the wires get hot or anything. Thanks for all the feedback! JD

Your wiring harness and fuse box wasn't designed for the kind of load that fan puts on it when it starts up. It takes a lot more amps to start the fan than it does to run. The reason for using relays is so you don't run that kind of power through the factory wires. The fan starting is more than the power supply wire to the fuse box is suppose to do. Much less running the fan plus what the car uses; like headlights, wipers, heater fan, etc..
Blowing the 20 amp fuse was at the limit of what the wires could safely handle over a period of time. The 30 is going to add a lot more heat to the wires before the fuse blows.

To get full benefit of the relay, you need to mount it (the relay) between battery + and fan or between alternator + post and fan.(maybe starter post if you have a trunk mount battery) Then use the cars wires to trigger/trip the relay, kind of like what you've already done. Just run new heavy wire from power supply to relay, and the same from relay to fan. Use a piece of fuse link or high amp fuse in the power wire to the relay in case the fan ever shorts out.

If the fuse box melts, it might take out more than the accessory batt terminal in the fuse box.
This is serious stuff as in fire hazzard that needs done right.
I'd hate to hear anything bad happened to you or the car because you didn't have good directions.
Don't put this off, you've got to fix this right.

[71 Ventura II]

Originally Posted by "QUICK-SILVER"

Your wiring harness and fuse box wasn't designed for the kind of load that fan puts on it when it starts up. It takes a lot more amps to start the fan than it does to run. The reason for using relays is so you don't run that kind of power through the factory wires. The fan starting is more than the power supply wire to the fuse box is suppose to do. Much less running the fan plus what the car uses; like headlights, wipers, heater fan, etc..
Blowing the 20 amp fuse was at the limit of what the wires could safely handle over a period of time. The 30 is going to add a lot more heat to the wires before the fuse blows.

To get full benefit of the relay, you need to mount it (the relay) between battery + and fan or between alternator + post and fan.(maybe starter post if you have a trunk mount battery) Then use the cars wires to trigger/trip the relay, kind of like what you've already done. Just run new heavy wire from power supply to relay, and the same from relay to fan. Use a piece of fuse link or high amp fuse in the power wire to the relay in case the fan ever shorts out.

If the fuse box melts, it might take out more than the accessory batt terminal in the fuse box.
This is serious stuff as in fire hazzard that needs done right.
I'd hate to hear anything bad happened to you or the car because you didn't have good directions.
Don't put this off, you've got to fix this right.

Thanks for the directions! I just found this thread since the moderators moved it! The information is very timely indeed, I went out tonight to let the car run to test the new cooling fan. Well there's both good and bad to report...

GOOD: The new fan kicks "A" because I let the car run in the driveway for 10-15 minutes W/fan running the temps never topped 135 degrees!!! I turned the fan off to let the temp climb to 140 degrees then turned the fan back on to see how it would handle the heat; it quickly dropped the temp back down to 135 degrees! I really like the fan!

BAD: The power consumption of the new fan must be very high! Not just on start up but the entire time this thing is pulling some power big time. The power robbing fan is enough to cause the MSD 6AL to malfunction? Literally you have to raise the idle of the engine to get it to idle when the fan is on; when you turn the fan off the idle rpm raises by nearly 400 rpm's! What in the world would cause such a voltage drop when the fan is turned on? With the fan ON I had the car idling +- 1050 rpm really steady and when the fan is turned off it jumps the idle to 1400 rpm's. Very strange to me what gives???

I'm going to change the power feed wire for the fan straight to the positive battery terminal ASAP. I can't use the + term on the one wire alternator for fear the high output of the 100a unit may hurt the relay or something. The trigger wire may or may not change I'm not sure if it would gain a benefit from the current configuration. The wires from the factory fan look to be 10 gauge so I assume I need to match that size for the fan power wire? OR does it depend how far the run is from the BATT power source to the relay? JD

[george kujanski]

The RPM change is most likely due to the load on the alternator. Generating the power required to run the fan puts a load on the alternator, which the engine needs to drive.

It's all about energy.....the fan requires a lot of it, the alternator provides the electrical energy, the engine provides the mechanical energy to drive the alt.

A 62A alternator requires 3 HP to drive at full output...a datapoint I remember from my days designing charging systems.

Consider this: assume a mechanical fan requires 1 HP to drive. The engine supplies about 1 HP to drive the fan.

Now take a electrical fan that requires 1 HP to drive. The alt provides that 1 HP, but it requires 2 HP from the engine to produce the 1 HP out to drive the fan. An alternator is generally less than 50% efficient.

George

[71 Ventura II]

Originally Posted by george kujanski

The RPM change is most likely due to the load on the alternator. Generating the power required to run the fan puts a load on the alternator, which the engine needs to drive.

It's all about energy.....the fan requires a lot of it, the alternator provides the electrical energy, the engine provides the mechanical energy to drive the alt.

A 62A alternator requires 3 HP to drive at full output...a datapoint I remember from my days designing charging systems.

Consider this: assume a mechanical fan requires 1 HP to drive. The engine supplies about 1 HP to drive the fan.

Now take a electrical fan that requires 1 HP to drive. The alt provides that 1 HP, but it requires 2 HP from the engine to produce the 1 HP out to drive the fan. An alternator is generally less than 50% efficient.

George

Interesting info, I will change the power lead to my fan away from the fuse box instead going straight to the batt. If the RPM drop/increase remains the same then it will validate the alternator output as the culprit. fwiw I have a powemaster 100a "one wire self-exciting" alternator. Thanks! JD

[guccieng]

the drop in rpm has more to do with the strength of your motor at idle than the alt. the 100 amp alt is more than enough, it's the motor that has to turn it. try retuning your idle circuit.

you can run the power lead from the alt to the fan. you should only do this with a heavy gauge wire (10 is good) if you have a good heavy gauge wire going to the battery. the battery is needed to provide 'surge' power when the fans kick on. if you don't have a good lead to the battery, mount the fan lead straight to the positive battery post.

i'm not sure how you got the idea of running power from the fusebox to the fan; the whole point of the relay is to separate 'big power' from 'little power'. please, DO NOT run the fan through the fuse box!!! if you do, i can only pray you have good fire insurance.

also, what thermostat are you running? it sounds like you're not running one at all if the temp topped out at 135. get a good 180 t-stat.

[george kujanski]

At idle, the engine is providing only a few HP, so a change of 1 or 2 HP from an alternator load is a substantial percentage of the total.

Since the idle speed is not controlled (by the computer as in modern cars), the load increase causes a RPM drop.

George

[HJones1313]

I'd just like to add my 10c worth to this deal. It's extremely important that you find the correct fuse rating for your new fan, and stick with it. The answer is not just stick a higher-rated fuse in. If the fuse blows, something's wrong.....