Mongo

Could dying fan motors cause fuse blowing? This was the case with my 944. I blew them constantly until replacing the passenger side cooling fan.

Mrmerlin

make part of your check the fan connectors you will probably find them melted or corroded

Giovanni

That is on my checklist

Giovanni

In that case would the fan overheat too or at least the wire connectors?

mark kibort

30s dont work for very long and they still get hot. 10 amps per fan min, is tough on a fuse, and I think they both go through one fuse, so 20-25amps through a 30 amp fuse will get it very hot. simple ohms law here! I^2R.

anyway, i use 60 ampers PER fan on my racing set up and the protective tape and wires leading to the fuse holder (custom) are beginning to melt, but fuses are still intact) 30s blew all the time.

mk

DR

Gio,

Check the harness connectors on the back of each fan...they get dirty, start arcing and melting the connectors. This alone could be causing the high circuit load, seen it too many times.

DR

Duh, too much of a hurry and didn't see page 2 :-)

Happy 4th!

dr bob

Mark--

Power feeders, fuses, and fans are wired separately on S4+ cars. Failure of one side lets the other side run. There is commonality only where the circuits pass through the controller on the front apron, and there the only thing shared is the case. So each 30A fuse is for one fan.

Remember a few things when you look at these circuits. First and foremost is that the fuses and/or breakers are there to protect the wiring, not the fan motor. This means wiring from the battery all the way to the motor itself, and the return to chassis ground. If you are serious about running 60A protection per fan, that means the -all- wiring needs to be 60 amp capable. Think in the 6-gauge range for that duty, one separate conductor for each fan, from battery to relay to fan motor, from fan motor to ground. Is your fan relay rated for 60 amps? Not one of the cute little plug-ins obviously. It looks more like a Ford starter relay, copper disk between copper studs in a sealed cylinder. If your wiring and relay aren't up to the fuse rating, don't bother with the fuses at all; the wiring will fail first, protecting the fuse.

Fuses (and thermal circuit breakers such as those in the links) all depend on a certain amount of resistance, and the subsequent heat generated, to determine the amount of current flowing through them. Smaller fuses have higher resistance, so more heat is generated with less current flow. Enough heat, and the link inside melts (or the thermal element opens) to interrupt the current when it's excessive. Bottom line: Expect fuses and thermal breakers to get warm in normal service. It's what they do!

mark kibort

yep, know how fuses work, but in extreme cases, like racing, with extreme duty cycle, the fuses can blow over time, all things working fine. starting and stopping, has higher current spikes, which wears on the relay and the fuse. didnt know that the entire fan circuit on the s4 is separated, so thats fine. so is mine. one fan, 12amps or so, but peaks can be much higher. add some real hot under hood temps , increased alternator voltage , more load on the fan motors, and you get the idea. putting a 60 amp fuse in there has proven to fail first. I ran the eRAMS with 12 guage wire, because it was intermittant. 90amp peak, 60amp duration and we actually fitted the system with 30amp fuses, which blew eventually, but saved the motor for dummy installs or over use. 60s is what was called out later. there are charts and graphs of the blow cycle for all fuses. 30 amp, doesnt mean it will blow at 30amp.

anyway, Ive got 2 60s that finally did the trick. cant take a chance on a blown engine, certainly can take the chance that the wiring melts or the fan gets damaged if there was a real issue, and that might happen if we got to the true 60amp draw or higher pretty quickly. the relays were rated at 30amps continious, and 90amp intermittant. so the match of the two is pretty good.

Alan

Guys we have been through this many times now. When fuses get hot enough to melt the fuse body (not the fuse element) it really has nothing to do with circuit overloading 99.9% of the time.

The only exception is really low quality fuses that don't even approximately meet their intended specs.

So:

Buy high quality fuses ONLY.

Melted fuses are caused by fuse holder connection problems that heat the blades of the fuses (or the end caps for the cylinder style). Heat transfer melts the body.

The S4+ fuse holders are really not well designed for 30A loadings - small contact areas - once they start to deteriorate they are close to a lost cause. Crappy cheap fuses cause lots of the problems (plating material, blade dimensions...)

There are really only 2 good S4+ remedies:

1) Take out the CE panel & replace the melted fuse-holder block (from a donor) Be careful - blocks are not all configured the same by block and by year (so inspect inside - there are shorting bus bars)

2) Simply remove the fuses at the CE panel (jumper the fan in/out connections at the bottom CE panel plugs). Add in in-line fuses at the battery box where these supplies originate (the fuses should really be here anyway for the best wiring protection) - however use a high quality 30A rated fuse panel.

Adding dangling in-line fusholders on the Ce panel is not a great looking solution to me.

Typically fuse bodies melting has absolutely nothing to do with the fans or downstream wiring or anything but poor fuse holder connections. I know its hard to believe but re-read what I just said 3 times... and convince yourself that it is true...

Fan faults will cause fan non-operation or the fuse to blow cleanly, wiring faults the same, increased connection resistance anywhere else will only lower the current seen at the fuses...

So - Its just the fuse holders - don't bother looking anywhere else till you solve that issue. Once affected - cleaning the fuse holders is pretty much a lost cause... it may buy some time - but recurrence is almost guaranteed.

Alan

Example of battery box fusing

dr bob

Mark,

You continue to amaze me. I'll leave it at that.

Alan

Moi Aussi...

ROG100

Alan we have done exactly what you suggest on a number of GTS's and added a fues holder with a good quality (Porsche) fuse. Why just the GTS cars I do not know.
Never had the problem with 87 to 91 cars.

On my own GTS I just had the problem again where the new fuse holder began to melt. The fuse did break. I replace both fans with new units recently so I know the connections are good.
I also had at the same time a burning clutch on my original compressor as the compressor had started to seize. It was while checking for the AC issue that we found the melted fuse.
Any connection?

Roger

Alan

Roger - no I think not in this case.

I have seen this on S4's also. The fuseholder design is not that good unfortunately - I'm sure its fine up to 15A - but higher current especially if the panel has seen any water infiltration or in areas of high humidity is problematic. The fan feeders are strange - the wiring comes direct from the battery to the bottom of the CE panel - then to the fuses - then back out the bottom of the panel and forwards to the fan final stages. Really the fuses should be at the battery end of the feeder - and its possible to put in 30A ATX fuses there for better load capability. That may be the upgraded solution if all else is failing.

On the CE panel just connect the ins & outs directly together to bypass the fuses there.

Alan

ROG100

Alan,
I am not doubting the S4/earlier cars have the problem just never seen it.

So where do we put the fuse holder? At the connection at the battery maybe? That is where the direct feeds come from. What is this 30A ATX you speak of O wise boffin.