Electric fans burning out the fuses
 

Last year I changed both fuse holders for the electric fans, installed brand new ones with the 30 amp fuses, worked fine until yesterday. I noticed the fans did not go on at the temp they were supposed to go on. Checked it and both fuses were blown.

I have used the car maybe 3 times so far this year, I am trying to figure out the cause to prevent this from happening again. I am questioning the relays maybe?

I have not noticed a broken wire that can cause a short and the fans when working, are flawless (BOSCH fans). Any thoughts anyone please?
Tks in advance

Lou,

This could be caused by a few things. You don't have to have a broken wire to have a short and if they worked for a while before blowing the fuses it may be intermittent and difficult to find. Take an ohm meter and first measure the resistance of your fan motors to be sure they haven't gone up. Then hook it to your lead to the fans and open the fuse so you will only be checking that lead or leads if you have two of them. There should be no reading. If you get one you have a short somewhere in the lead. If you don't get one start following the lead and moving it and watch the meter and see if you see it suddenly read and drop or the reading stays steady. If you get this then you are close to the place the short is.

Ron

Tks Ron I will do that and get back to you.
Stay safe
Lou

Ron: Update tested both fuse holders for ohms, no reading, tested the fuse holders for amperage, car was off fans off no reading. Turned the car on repeated above same results. Another friend retired automotive teacher feels that is either heat or slow high amperage. No breaks on any of the lines, checked all connections ok, this is a mystery. Fans run fine at the right temp what else could cause this???? See the pictures of the two fuses burnt.

No, it's not a mystery. It is either an intermittent fault to ground along the circuit, or the increased heat on the air and the fans themselves results in current above the fuse level. Invest in an inductive ammeter and compare your amp readings at the fan when the engine compartment is nice and hot and see what sort of amps the motors are drawing. If that doesn't tip you off as to the problem, then run a temporary new circuit from the fans themselves directly to the battery and fuse the line at the same amp level. That will eliminate a funky intermittent ground out along the existing line. If the new line blows its fuses as well then there is a problem with the fans, if it doesn't then there's a flaky short on the existing lines to the fan. But remember, when an electric motor starts up you get a huge start-up surge of amperage because of the field that is created. If the fan has trouble getting going, then that can blow the fuse. Anyway, that's how I'd diagnose it. Any electrical problem that happens consistently is easy to find. It's the ones that only occur randomly that are the hardest.

Yes, all motors tend to require a surge of amperage at startup. Higher draw with heat. The older style glass fuses are available in “slo-blo” version to compensate for that. I’ve not found the blade type fuses in slo blo but they may be available. Or switch your fuse holders?

I might suggest you do a major cleanup on your chassis ground connection for the fans. (All grounds On the car would be time well spent - battery too!) Going to a slow-blow fuse for the system that has operated properly for many years as designed is really not the way to go. Your just popping fuses now, you could be roasting wires and replacing fan motors with slow blow fuses because you have not fixed the root problem. Sounds like high amperage draw due to a poor connection to me.
Just a suggestion.
Blas

As a general rule, a loose or crappy connection reduces current, because it's an increase of resistance. But that rule doesn't apply to electric motors because they're not completely a resistive load. I can see how a voltage drop across a bad connection would cause the motor to lag and, in turn, pull even more current. That, in turn, heats up the bad connection and adds more resistance, which results in higher amperage. That cycle continues until you blow the fuse. If clamping an ammeter around the feed to the fan, when it's really hot under the hood, shows an unusually high current (like high 20's) then a voltage drop test will spot the resistance point in a jiffy.

I got the induction amp meter, I will check that out today before I venture out. Don't want to overheat a brand new engine! Tks gentlemen!!

OK, don't be fooled by cold air fan amperage readings taken in your garage. Look at this typical fan graph from SPAL. Note that the difference in amperage draw goes from around 16 to 27 (it's the red dotted line). That's a pretty big difference. Throw in a crappy connection and you can easily go past 30 on even a regular day if the under hood temperatures climb up on you.

http://38.134.118.239/spal_current.jpg

All of the above is good, but you may want to trash the whole concept of fuses and go with circuit breakers. IMO circuit breakers can better handle the brief startup surge current.

Regardless of which you choose, you obviously need to find the root cause and solve the problem that caused your fuses to blow.

Are these mini fuses?
I would be using a maxi fuses, and measuring the startup current.

ALL electric motors draw more current at startup, especially in a switched on/off scenario.

Resistance anywhere else in a motor circuit will LOWER overall current, and fan speed.
That's how we alter interior fan speed.
You can locate poor connections as a voltage drop test across each connection, and can be felt as heat in extreme cases.

On your DC motor, as the voltage drops (because of a bad connection) the motor current will increase (but the speed and torque will decrease). ;) Now, I know you're going to look that up, and when you do, you have to come back and write "well, ok Pat you were right.":)

When the voltage drops the current flow (amperage), goes up so does the heat generated. Ever watch a cordless drill when the battery gets low that's when they will burn up and smoke is bad. It's time to swap batteries or take a break and charge that battery.
I have my 4 fans ( two sets of two fans , 2-upper and 2- lower that cover the radiator) supplied by Bosch relays, battery current supplied to relays and control from adjustable thermostats and dash bypass switches to get ahead of the thermostats if anticipated.

Posible internal short on motor windings cheap chinesse motor

BAsque1 you said "fans" which I assume is two. Have you checked the amp load of the fans?
Is there a label on the fan or model number where you can see what the fans amp load is suppose to be?

The best way to check is with an amp meter. I bought a industrial 50 amp DC meter and wired it so I can pull a fuse then plug in the meter to read the amp load. Some Multi meter will check a 30 amp load but mine with not. That's way I bought one.

Check a fan last fall that was labeled at 7 amps but when we check it over 15.

Oh, another thing to check is wire size.

4 fans? That a lot of fans. I would guess you are over taxing the electrical system and alternator when the all fire up. You might want to look into a couple high quality puller fans and be sure to have the radiator shrouded around the fans.
4 fans eh?.... that’s like a hovercraft.
Blas

The fans are not really large and all 4 together cover the copper radiator. I bought a rebuilt alternator that was rated at 74 amps . The normal single belt alternator that would be used on a FE engine in that era. I used to have problems with the heated water rising to the top of the radiator and draining the batteries when parking and not turning off the master battery switch, I installed a Flaming River push in to kill master switch, It is convenient now, twist to engage and bump to off. I installed a yellow top Optima battery. My car came with the smallest 12V battery he could use. I'd forget to turn off the master switch under the dash on the firewall, Not convenient while belted in. expecting to be there only a moment. The hot coolant would rise to the top and turn on the fans which didn't make that much noise and given a little time I would be left with not enough battery to restart the engine also back then with the way the carbs were set up foe Reno it didn't take much to start just the incline of a gas station drive way was enough to roll a little and pop the clutch it would fire and off I'd go. Now it takes a lot more cranking to get it lit now and the weather here is cooler than Reno during Hot August Nights 1999. I usually start with a full battery, I have left home almost out of gas.

Yes I do have 2 13" Bosch fans that came with the car. Last year I changed the fuse holders for each fan because they were deteriorated with age etc. I have to brand new mini fuse holders properly installed. Yesterday I tested the amp draw the second the fans go on at 205 degrees with an induction amp meter. One was 45 amps and the other was close to 100 amps, the one with the 100 amps was closer to the alternator so I attributed the spike to the EMF generated by the nearby alternator. THat been said both fans run freely there is no apparent hesitation or binding that would draw more startup amperage.
I changes the mini-fuses for 30 amp circuit breakers, tested them and they work as they supposed at 205 degrees. However, I will need to use the amp meter that you talk about so that I can accurately test how much start up amperage is being drawn. No the fans only show the model # voltage the amps is 15 according to the manual I have for them. Here is a picture of the info on the fans.

And we have found start up current as the cause, as it nearly always is with electric motor faults.

I would swap your fans over, to prove the the fault to a fan motor or EMF from the alternator. I will say the fan motor.

I don't think you have any other "resistances", otherwise they would be glowing with 100 amp spikes, so your wiring is good.