Dramatic alternator failure, or how my 1987 300D left me stranded.. - Page 4 - PeachParts Mercedes-Benz Forum

renaissanceman · #46 06-22-2017, 04:20 PM

Quote:

Originally Posted by funola

That'd do it. Did you over tighten the nut on the stud? That stud is on an insulator and the torque should be just tight enough so the nut will not undo itself. Probably not more than 1 to 2 ft/lb.

I put a wavy lock washer on it and bottomed out the lock washer with a 1/4 inch ratchet. I generally don't have issues with breaking things as I'm very slight (135lb soaking wet).

Could have been that, though, hard to say. Either way it's gotta come out and get replaced.

Mxfrank · #47 06-22-2017, 08:35 PM

Quote:

Originally Posted by Diseasel300

Coming from someone involved in the power generation industry, that is utter nonsense. This harkens back to the old myth that a generator running unloaded will build up a dangerous discharge of voltage and explode.

A self-excited alternator can run a vehicle without a battery connected with no ill effect provided that the load doesn't exceed its production capacity. I have personally started several cars without batteries using only jumper cables, then disconnecting and insulating the leads to move the vehicle and never had an alternator fail from that.

If the alternator packed up from a loose connection it was due to arcing at the battery lead causing EMF spikes flashing back at the alternator, or it was a POS alternator to begin with. I'd strongly lean towards the latter.

Nonsense to nonsense. This alternator is very far from unloaded. An alternator that's busy charging a run down battery will generate a huge inductive spike if the battery cable is suddenly removed. Without the battery to absorb the spike, something nasty can happen to the alternator (and/or the OVP if so equipped). Since you were probably jumping from a fully charged battery or a running car, the jumped circuit didn't present much of a load. But in this case, the battery is obviously run down. It would be a shame to go through a couple of alternators before a loose or dirty ground strap was identified and repaired. One useful precaution would be to charge the battery off the car before installing the new alternator.

Diseasel300 · #48 06-22-2017, 09:51 PM

Quote:

Originally Posted by Mxfrank

Nonsense to nonsense. This alternator is very far from unloaded. An alternator that's busy charging a run down battery will generate a huge inductive spike if the battery cable is suddenly removed. Without the battery to absorb the spike, something nasty can happen to the alternator (and/or the OVP if so equipped). Since you were probably jumping from a fully charged battery or a running car, the jumped circuit didn't present much of a load. But in this case, the battery is obviously run down. It would be a shame to go through a couple of alternators before a loose or dirty ground strap was identified and repaired. One useful precaution would be to charge the battery off the car before installing the new alternator.

You need a much better understanding of how an alternator works and how the voltage regulator reacts to loads before making claims that you know nothing about. The alternator can be fully loaded at once (block loaded) and fully unloaded (load dumped) in one single step and still survive without any damage. It is designed to operate this way. Even if the regulator is slow to react, the worst that can happen is an instantaneous voltage spike, which if a load is present will absorb it. If no load is present, it will dissipate in the windings and iron of the alternator.

The alternator isn't magic, nor is it something that's sensitive. They can take an enormous amount of abuse and still come running back for plenty more.

renaissanceman · #49 06-23-2017, 03:51 PM

Hmm.

Regardless of whether the alternator can be damaged this way, I will avoid running the new alternator in without proper connections. I'll also be wary of tightening the bolt.

The alternator came with zero instructions. I follow torque specs to the letter, but in the absence of this information, all bets are off...