280z fan fuse

[Dave WM]

Still getting hot, thought I had this worked out, but nearly blistered my finger on it today. the fuse box looks good on the under side, no corrosion etc... the contacts were polished with some very fine sandpaper (500grit IIRC) to make sure I had good contact there. Seems nice and tight, so think I have gotten all the heat generating resistance contact points, leaving the fuse itself and the motor. I don't have an ammeter that I can use that goes over 10 amps so a direct reading is out of the question. But if I did what should I expect? I seem to recall seeing 160watt somewhere maybe on the motor. if that is the case I would be expecting to see about 12amps max at 14v. I would think a 20amp fuse should be plenty to handle 12amps max?

[Dave WM]

checked it, at 14v I have about a .4 v drop across the fuse. I checked and had substantial drops from the connector to the fuse end, like .15 on each side.

Anyway I cleaned up the ends again, replaced the fuse (the old one was on its way out, had a nice blob forming in the middle), and used a different type of 20 amp a spiral wound vs the flat section. Will cool off a bit and test again (so hot that it hard to hold onto stuff when sweating in feels like 100f heat).

 

[chaseincats]

On 6/27/2018 at 2:34 PM, Dave WM said:

checked it, at 14v I have about a .4 v drop across the fuse. I checked and had substantial drops from the connector to the fuse end, like .15 on each side.

Anyway I cleaned up the ends again, replaced the fuse (the old one was on its way out, had a nice blob forming in the middle), and used a different type of 20 amp a spiral wound vs the flat section. Will cool off a bit and test again (so hot that it hard to hold onto stuff when sweating in feels like 100f heat).

 

Sorry to bring this back up but did you ever find out what was causing this Dave?  My fuse is getting pretty toasty too.

[Dave WM]

its prob just the design, the owners manual calls the fastest setting "emergency cooling" IIRC, as if they wanted it used for a limited time. Add to that ANY resistance in the wiring at the fuse box (its just crimp connected to the spring clamps that hold the fuse), the spring clamps are old and prob lost some tension, and maybe even the quality of the glass fuses sold today (imagine that), and you have a recipe for for failure. Not sure of a long term solution other than try different fuses, and deoxit and limit the time at full power.

[chaseincats]

3 minutes ago, Dave WM said:

its prob just the design, the owners manual calls the fastest setting "emergency cooling" IIRC, as if they wanted it used for a limited time. Add to that ANY resistance in the wiring at the fuse box (its just crimp connected to the spring clamps that hold the fuse), the spring clamps are old and prob lost some tension, and maybe even the quality of the glass fuses sold today (imagine that), and you have a recipe for for failure. Not sure of a long term solution other than try different fuses, and deoxit and limit the time at full power.

I was under the impression that the fastest fan speed setting was the best for the car since it wouldn't be using the resistor in the big fan case under the dash (I dont remember what its called).

[Dave WM]

Just now, chaseincats said:

I was under the impression that the fastest fan speed setting was the best for the car since it wouldn't be using the resistor in the big fan case under the dash (I dont remember what its called).

its all about power thru the fuse box, measure the voltage drop across the fuse and you will see the diff in fan speeds. more drop across fuse more heat on fuse element. You are correct about the resistor pack for speed control, it will run cooler, but I doubt they burn out, pretty stout design. The Motor and the fuse however will heat up as more power is being used, and some of that has to go to heat, both the motor and the fuse.

[Dave WM]

The only real way I think if its a chronic issue and you want more airflow would be to devise a relay scheme that bypasses the fuse box completely and runs a separate power line (and fuse that will hold up). I have thought of this but decided against it, rather I just monitor the fuse now and then and see if its running hot. IIRC i did attempt to retension the clips by using some very small o rings around the end of the clamps adding tension. I have not had issues with it and the fuse cover has not melted again.

[chaseincats]

So the resistance created by the resistor in the fan case does not move backwards into the fuse?

[Dave WM]

5 minutes ago, chaseincats said:

So the resistance created by the resistor in the fan case does not move backwards into the fuse?

correct, more resistance lowers the current I=E/R, so lower current will result it less overall power (resulting in slower fan speed), less current in circuit will result is less voltage drop across the fuse. less voltage drop across fuse less heat, lower possible blowing of fuse. 

prob should clarify I=current, E=voltage, R=resistance. 

Edited July 18, 2022 by Dave WM

[Dave WM]

something that "may" be contributing to the issue is the condition of the fan motor. Old sticky oil bushings may create some unwanted drag, adding the it over all power consumption issue. IIRC the motor was rated at 100 watts at 12v, that's around 8-9 amps at reg battery voltages (full power setting). I think actually measured this back when I was fussing with it. Prob a good idea to check the total draw at full power to make sure you are in that 8-9 amp range. You can do this removing the fuse and subbing in a ammeter. I would do this with the car running so you have full battery voltage. 

I would def check this a different "upgrade" fan and motor were installed. No such thing as a free lunch, yes more air but what about the amps (Apollo 13)

Edited July 18, 2022 by Dave WM

[chaseincats]

I changed my motor to the kia one a few years ago and immediately noticed a difference in terms of fuse consumption.  I went from changing them every couple weeks to every couple of months.

[Dave WM]

the kia may have a lower amp draw. Before doing anything I would check that at the fuse just to base line where you are. Generally speaking if you are moving more air the amp draw would be higher BUT maybe the kia is more efficent a motor, losing less power to heat and more toward useful work.