Wiring thermo fans to run directly off alternator

[Ribfeast]

Hi guys, just wondering if there is any harm in running my thermo fans directly off the alternator instead of the battery?

[Grant]

No but make sure you use a fuse to protect the theros and the alternator.

[Hen]

Your alternator (fat white wire) is connected directly to your battery +ve terminal (through a big fuse).

So I see there being approx zero difference.

Any reason you suggest this?

Hen

[Ribfeast]

I think I am getting some losses through the power cables on the way to the battery via fuses boxes etc (18yo car). Plus the battery is in the boot. I have a 60A fuse on the fans, might go smaller actually. Someone said it might create a greater load on the alternator or regulator, but I can't see how? The alternator becomes the main voltage and earth point for the car while it is running right?

[sideshow]

90% of fans i wire goto the alternator

12 inch or smaller fans will draw less than 20 amps and startup and probably 10 or 12 at running speed

i have a 16 in thermo and headlights dip when it turns on

i have run fater cables for pos and neg vbut it still does it

think its just the initial hit that does it

nothing u can do about it

maybe get a massive alternator but then u still have to spin it faster

spinin an alternator faster at idle gives better charge when idling
but recently had a guys car where the belt was slipping with a new smaller pulley
so fixing one prob caused another

[mrshin]

Also, where are you taking the 'sense' wire from?

[Ribfeast]

Great info man Fans now wired directly to alternator. Voltage out of the ciggy socket still gets as low as 11V though, seems to happen after the car has warmed up a fair bit. Maybe the regulator in the alternator is getting heatsoak?
Have you come across any aftermarket alternators for 1JZ?

[chris davey]

When my car is running again I am going to do some logs but my microtech shows that sometimes under power it goes down to about 12.0v instead of around 13.8v. Near new battery. Would this be pointing me towards a dieing alternator or simply too much current being drawn while under power?

[bansheebuzz]

checking voltage through a cig socket is a waste of time, you will always have a lower voltage at the socket.

chris - if your voltage drops under hard accel, your belts might be slipping

[Ribfeast]

Why would it be lower? Where should I tap it from, directly off the alternator?
Do the 1JZ alternators usually only supply 13 volts or more when above 1500-2000RPM?

[sideshow]

all big thermos will drop voltage for abit
is it droppin more than a voilt or are u just worried for nothing

leave the multimeter on battery and see what voltage drops when fan turns on

then maybe check the battery into the ign switch as thats the most important power feed
see if that drops

alt should chagre 13,5 to 14.5

battery when running should be over 12.5 thats ok

maybe there is not problem and yr just worried for nothing

and who gives a rats ass bout the cig lighter

its yr battery that needs the voltage not yr cig lighter

another thing to check is ign wire on ign switch make sure there is no more than .5 volt difference between batery and it

id hate for u to rewire yr whole car just because yr cig lighter is fuct heheheeheh

[Ribfeast]

Starts off around the high 13s when I start the car in the morning. When the idle drops to a normal level and the car is at operating temp, it drops into the low 12s. Then if I sit at the lights for more than 30 secs it drops into the mid to low 11s. Goes back up to the 13s depending on revs, but whenever I sit still it is in the 11s after that. Car starts first go every time, and everything runs fine, just wondering if I should be worried about the alt or batt etc.
I might rewire my gauge to measure off the batt directly

[deekay]

do not under any circumstances wire a thermo fan to the alternator unless you want to cook any voltage sensitive device. a fan will work just as happily as a generator when air flows over it but does not have the advantage of being regulated so you will feed random voltages into your wiring system. Manufacturers go to extreme lengths to stop this using zenner deiodes and more commonly relays with internal diodes. ask anyone who has had the problem of their aircon clutch energising intermittently due to welded relay contacts. this is not a good idea, den.