B+ terminal cover melted

[Peter]

Hey all,

This post is about my: 2004 dodge stratus SE, 2.4L DOHC PZEV

When I got to work today, I smelled burning plastic. I opened my hood and found that the plastic cover that protects the B+ terminal connection on my alternator had started melting into the terminal (on the alternator). The stud on the alternator was black/charred and the nut looked like it started to melt. Note, it didn’t actually catch on fire. I have my tools with me and a spare alternator at home, but I ran some tests once I got to work (I had my battery tester and DVOM with me).

The battery tested good (at 568 CCA out of 700), and the voltage was steady at 12.41 volts after getting rid of the surface charge. It’s a duralast gold that’s less than a year old.

I did a diode test on the alternator, but I don’t think there is a diode in this alternator (it’s externally regulated inside the ECU). If it matters, my dvom told me it was an open circut (on the diode test, which consisted of putting the + of my dvom onto the b+ stud while I put the – to ground on the alternator.

Also, I have a charging system circut diagram (from my FSM), and I checked all of the relevant grounds and fuses (all were fine). Here is the diagram if you care to look:

I also tested the voltage while running, and the system was charging at around 14.4V at idle (750 RPM). Is it just me, or does that seem high? The car otherwise runs fine.

I may just throw my spare alternator for now, but any idea what would cause this?

Thanks!

Attachments:

• chargingsystem.jpg

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[none]

14.4 volts is fine. Make sure that the cable is actually tight to the post on the alternator. A loose connection can cause wiring to get hot. Any significant amperage through a weak contact point is going to do it. Then voltage drop test that cable from the alternator to the battery with the engine running. I’d check for a hot battery too. If the battery itself is shorted, that might get you some heat up the cable or a problem on one end of the cable might have caused a problem at the other end.

[Peter]

I did check all the connections, the b+ terminal and wire were all snug (I actually had trouble getting the nut off because it got hot enough to start melting the nut a little).

I tested my battery again/did a parasitic draw test, and it turns out the alternator was drawing current. My battery voltage also jumped from 12.32 to 12.5V after disconnecting the alternator and re-installing my backup. Now I’m going to return this shorted duralast alternator (That’s less than a year old) and get another one. I’ll make sure to have them test the replacement before I’m out the door though (it has a lifetime warranty, so it’ll be free).

Thanks!

[george gonzalez]

The only way to get a hot nut is if the alternator is charging a lot and there is some corrosion somewhere very near the nut. All it takes is like a tenth of an ohm of resistance in the lug or the bolt connection. Power is current-squared times resistance, so 40 amps squared is 1600 times 0.1 is 160 watts, plenty enough to melt some plastic. I would swap the alternator AND put on a new connector lug, a big one, preferably soldered onto the wire, not just desultorily crimped on.

[Peter]

Yep, I had a spare terminal nut and washer to replace the somewhat melted ones. I also did a diode test on the alternator that caused the melting, and it failed badly. I’m going to the parts store now to exchange it.

[EricTheCarGuy]

Many have mentioned checking the connection but it sounds like you’ve got that covered. If a diode had failed, you’d have a lot more issues than just a burned up terminal. That would allow AC voltage to get into the electrical system and as I stated, you’d have a lot more issues than just a burned terminal. Normally what I find with what you describe is a loose or corroded connection somewhere that causes increased resistance which can equate to heat. Perhaps the connection problem is inside the alternator somewhere. Replacing it may not be out of the question at this point. More info on electrical problems here.

http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems

Good luck and keep us posted on your progress.

[Peter]

Yep, it seems a loose connection could be the easiest explanation. The alternator had to come out for my recent timing belt/component change, so it might have worked it’s way loose over the last month or two since.

Though the alternator I took back to the parts store tested good, the obvious melting of components let to them replacing it anyway. I’m going to get it into the car as soon as my new serpentine belt comes in the mail (they’re so much cheaper online, and I can’t see myself taking things apart twice when I can just do it once).

Good thing I have a spare 😉 .

Also, I’ve finally been able to source a replacement terminal cover. None of the pick and pulls around here have one, and neither do any of the local stealerships. I’ve ordered it online, so hopefully I used the right part number.

Thank you for all the replies!

[Bill]

Sounds like the wire on the alternator is oxidized or not tight causing a high resistance. I don’t like using any lock washer, just the nut.

[Peter]

Any thoughts on using dielectric grease on any of these high amperage connections?

[Mike]

Any grease on there, dielectric or otherwise, will inhibit corrosion and is good. Like most greasing of parts like that, less is more.

I also agree that your connection there had high resistance due to corrosion or being loose, causing enough heat across there to start melting things nearby. I’ve seen that effect many times.

[Author]

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