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Look on the fans to find the amperage both starting and running....
... fuse as close to the battery as possible.
This is good advice. I believe factoid called this one above when he surmizes that this is a slow burn from inrush current (weren't we talking about that on a nearby thread?) which is how it looks to me. The holder melts, the connection is impared and heats up... I see no fault to ground. It is possible the motor has a problem but if so I'd think there would be more evidence. I had fuse holder after fuse holder, stock type and location on the AC fan of my 63 Impala. 30amp fuse, correct ampacity would never blow. But the damn fuse holders would melt and open up. It was the high draw reproduction fan motor causing the problem in that case.
Put an ammeter in series with the circuit and see what the fan sucks for amps, Those fans draw seriously large amounts of juice.
Dan
Last edited by dplotkin; Sep 18, 2020 at 10:03 PM.
Fuses are chosen to protect the device(s) in the circuit, not the wire. The fuse must be heavy enough to not blow upon initial motor start from locked rotor. The wire has to have a capacity greater than the fuse rating to protect the circuit. So, what size wire did you have and what load and fuse? Also you must allow for the length of the wire and temperature under the hood.
Look on the fans to find the amperage both starting and running.
The fuse doesn't protect the wire from the battery to the fuse. You should keep it at a minimum with the fuse as close to the battery as possible.
I agree with pretty much everything you say except the first sentence and that may be just a matter of semantics. Fuse size is based on the current draw of the device with the wire size being a limiting factor. If the device draws too much power, the fuse opens to protect the circuit. This prevents a fire in the wiring and/or the device. The over-current condition can be a result of a device failure or a short to ground between the fuse and the device, but in either case, it's the circuit that is protected from burning up.
Good morning! With a clear head and a few cups of caffeine, I’m back.
It is possible that fan is a “slow starter”. The initial start of a high torque DC motor is more difficult than an AC motor where a starting capacitor can be used to provide an initial boost. A stiff bearing, grit, minor blade interference or any number of things can cause the start cycle to be prolonged creating the situation you experienced. It is not a pleasant environment under the hood of a car, particularly in Texas in the summer!
This is a great example of the old TQM root cause analysis example of what is called a why-why assessment. In that example, a sensitive piece of electronic equipment overheated and burned up.
Why did it overheat? The cooling system failed
Why did the cooling system fail? The coolant pump failed
Why did the cooling pump fail? The motor seized
Why did the motor seize? The bearing burned up
Why did the bearing burn up? Lack of lubricant
Root cause: The tech never checked and maintained the proper oil level
Sometimes called 5 Whys and a How, the point of my long story is that simply replacing the fuse and wiring may not address the root cause. You stated earlier that maybe the fan motor was at fault and I think that is a real possibility as a root cause. Spin that one by hand. It should have periodic very slight resistance, almost like it is ratcheting as it passes between motor poles. Now do the same thing to the other one. Even a slight difference in resistance could be the root cause and why this one got the slow burn vs. the other one. Good luck!
General rule of fuses/CBs: size the wire to the device and the fuse to the wire and place the fuse/CB as close to the power source as possible. This is why I always caution people who have a 12 gauge wire with a 20amp fuse and then connect 3 or 4 18 gauge wires with devices on the other end of the fuse. They basically create 3 or 4 fusible links in those 18 gauge wires with a 20amp fuse that is more than happy to provide sufficient current to fry the wires in spectacular fashion. This happens regularly in the off-road world where some people think the more lights the better! Chances are, nothing ever goes wrong, but if it does it could be catastrophic.
I agree with pretty much everything you say except the first sentence and that may be just a matter of semantics. Fuse size is based on the current draw of the device with the wire size being a limiting factor. If the device draws too much power, the fuse opens to protect the circuit. This prevents a fire in the wiring and/or the device. The over-current condition can be a result of a device failure or a short to ground between the fuse and the device, but in either case, it's the circuit that is protected from burning up.
It is as you say, semantics. The wire has to be able to handle more current than the device it feeds, including locked rotor current needed to start a motor. Then the fuse has to be sized to protect the device and the wire, thus the fuse has to always be the weak link. The other variable that comes in is temperature. The wire insulation is rated at maximum temperature and must be selected to not melt when heat from maximum current is heating the wire that is already hot from the underwood heat. The fuses and holders today are made in China, may I say more?
Today I replaced the burnt fuse holder. Couldn’t find any info on the fans except they are Spal and, I assume, was together with the DeWitts radiator as Buns indicated, so pretty sure they use 30 amp fuses as Buns suggested, as that was what was in there originally.
Anyway, fired it up and drove around a little, fuse holder didn’t get warm and both fans came on and worked as they should. So, as many of you has said, I believe it was just a bad fuse holder.
Thanks to everyone for helping me resolve this.
Just for a warm and fuzzy feeling, you might want to contact SPAL and have them give you some info, like starting amperage and running amperage and discuss your wiring / fuse configuration along with the problem you experienced. I didn't spend much time on the site, but couldn't find the information. I personally have a problem with manufacturers that are not transparent in the technical information - but, maybe I missed it. I wouldn't just dismiss it as a bad fuse holder based on guesses on this forum. https://www.spalusa.com/products/fans/11/# might give you some technical help.
Not being pushy, but warm and fuzzy is something you want in bed under a comforter, not when in your car and find you have wet britches.
Well, it’s happened again after 3 years and 9 months, same fuse holder, same situation. Been fine until now. Unfortunately I had to buy the same brand fuse holder as before from O’Reilleys. Any suggestions?
"AUTO reset; check for the cause of the problem, then a quick flick gets your System back up and running"
I have a couple of those but guess I'm not familiar with what I'm using. What is the quick flick needed to reset, and if it's automatic reset, why do you need to do anything?
"AUTO reset; check for the cause of the problem, then a quick flick gets your System back up and running"
I have a couple of those but guess I'm not familiar with what I'm using. What is the quick flick needed to reset, and if it's automatic reset, why do you need to do anything?
Probably a bad Chinese translation as they are not, they reset automatically. These are even better.
4 Pieces DC 12V - 24V Automatic Reset Circuit Breaker Circuit Breaker with Cover Stud Bolt for Automotive and More (30 Amp) https://a.co/d/02SANkbO
Thats the same kind of circuit breaker I had in the 63split window its a automatic circuit braker that opens up when it gets really hot thats why i asked you what was the load
It has been my experience that if the fuse does not blow and there is smoke then there is resistance at the connection caused by corrosion, connection not tight, wire gauge to small. Most of the time it is loose fitting connectors. JP
Yes thats true thats why i asked him what load is the circuit controlling reduce load ,tighten connectoin coude be the case also Think about it this way a header is a controlled short fused the right way
It has been my experience that if the fuse does not blow and there is smoke then there is resistance at the connection caused by corrosion, connection not tight, wire gauge to small. Most of the time it is loose fitting connectors. JP
It has been many others experience as well. Connections must be clean and tight to pass current with minimum resistance.
Electricians will often re-torque bolted high current connections in panels for this reason. They tend to loosen with heat cycles and when they do comes heat. Many a panel has burned up from under-torqued conductors. Infra-red detectors are used by electricians and utility companies to spot these problems.
Its no different at 12 volts and thirty amps. A undersized connector or one that fits loose and is not clean will heat up. Resistance does not pull current to blow a fuse or open a breaker. Resistance is what toasts your toast. It gets hot, and it burns plastic.
Find a connector to withstand the conditions. An automotive connector may not do the job. Consult your electrical supply house.
