New to the Group, Need recommendation on suppressing arcing at the relay and fuse for radiator fan

Thread Starter

MB107

Joined Jul 24, 2016
345
This car uses a capacitor that I have not seen before used in any other car. Its 4700 Mfd and connects to a terminal where battery voltage splits to many different circuits. I would assume it has something to do with protecting the computers.

Could it be possible that this capacitor is bad.DSCF0007.JPG
 

Thread Starter

MB107

Joined Jul 24, 2016
345
Yes.
Did you read my "note:" in post #18?
I was referring to the note in #18. Shoulden't the fuse take care of the direct short as you refereed to in your note.

New twist on the situation.
The fuse holder was not found because I was looking to fix my fan. At the time I had no idea the fan was not functioning and for all I know maybe it was. I was fixing something else and found the melted fuse holder. I broke it open and poured the powder out and just assumed that the fan was not working. But maybe it was. Maybe

My new theory is that the fuse sort of half blew 6 years ago and somehow caused the relay to blow. I replaced the relay and every thing was fine until I looked at the fuse. For all I know the fuse was melted like that for 6 years. I just put an ohm meter across the fuse holder, and this is after cracking it open and dumping the powdered guts out. I got 0.7 Ohms across that powdered mess. It may have been even better than that if I didn't jack with it. So now I'm thinking that maybe there was only on event. Weather it was the fuse or the relay that started it I will never know.
 

crutschow

Joined Mar 14, 2008
34,285
I was referring to the note in #18. Shoulden't the fuse take care of the direct short as you refereed to in your note.
.................
A proper fuse should, but it sounds like a direct short may have created such a large arc when the fuse blew that the arc went between the fuse terminals. The current would then continue to flow until the terminals disintegrated from the heat of the arc.
 
In an Early AC system that was installed in 1968 by me and my father liked to destroy fuse holders until I stopped it. An ant-short cycle timer was added and the problem went away. Before power glitches or rapidly moving the setpoint back an forth would cause the AC to start on a huge load. The 2-3 minute delay provided by the timer fixed that problem for good.

So, did buying a new AC where anti-short cycles is incorporated in the thermostat.

Did you happen to turn the fan on a cat or bird nest? Don't laugh - I removed a bird nest from my car last week.
 

Thread Starter

MB107

Joined Jul 24, 2016
345

Thread Starter

MB107

Joined Jul 24, 2016
345
A proper fuse should, but it sounds like a direct short may have created such a large arc when the fuse blew that the arc went between the fuse terminals. The current would then continue to flow until the terminals disintegrated from the heat of the arc.
I'm thinking of going from a standard ATC size fuse holder to a maxi size fuse holder. Standard ATC only goes up to 30 amps. Maxi starts at 20 and goes to 80. I think when a maxi blows the likelihood of holding an arc will be reduced. I will have to find a fuse block to mount to the fender wall because the in line ones come with 6 or 8 gauge wire. Difficult to splice to my fan wiring.
 

xray_man

Joined Jul 22, 2016
1
Hi, I just retired from over 40 years working in the medical electronics field. I have seen very heavy duty contactors destroyed like this before. Most of the time the problem is caused by a rapid reoccurring signal voltage to the contactor coil. Some refer to it as machine gunning. Back in the 70s some TTL chips would go bad and send out oscillating signals. Also I have seen defect power supply capacitors let bad AC ripple into relay circuits that would destroy contactors.
Is the relay controlled by an engine management computer of directly by a thermostat switch? I have seen a defective thermostat switch destroy fan relays in cars.
 

bwilliams60

Joined Nov 18, 2012
1,442
The fuse holder in the picture is the only thing that melted suggesting that there was a large amount of heat created by excessive resistance. The green powder is oxidation created by water and the metal from the fuse terminals. There could have been a loose connection between the terminals and fuse but I don't think the fan motor is involved in this problem. I do not see the fuse suggesting that it melted (???) but still due to heat over time.
As for the relay, most automotive relays have a suppression diode placed across the coil to suppress voltage spikes from the magnetic field collapsing. Generally if there is not a suppressor, something up the line will take the hit in the form of a large voltage, low current spike. The motor is generally cut off from the circuit and should not be able to backfeed any voltage or current through the relay.
As for the original relay, I would have liked to seen pictures of that. Almost 40 years of working on Motive Power Electrical and I have never witnessed a relay exploding. Too cool!
 

Thread Starter

MB107

Joined Jul 24, 2016
345
Well today I tried the 5 amp diode suggested. I took the cover off the old relay and actuated it manually both with and without the diode. There did seam to be a slight decrease in the arcing across the contacts but nothing impressive.
 
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