Great to talk with Mary today......new power on its way :)

I fell asleep on the couch last night, with a 'working with your DVM and diagnosing voltage drops' video.

Was good to learn how to do it right.

Silly question...

Is a voltage drop always the same across a bad connection, regardless of the voltage being fed to it and load behind it?

I want to say "yes".

Hi Greg,
Does your alternator require a separate ground cable from the alternator to the body like other high output offerings?
Nice as always.
Roger

I thought that additional ground was just to allow a direct grounding port from the alternator to the chassis, not actually required since alternators ground themselves through the block via the installation brackets.

Yea, I was sorta chuckling about the idea of a separate ground strap. Very odd set up.

Truthfully, I don't see any need for that.....just seems like unnecessary stuff. Perhaps it is needed because of the funky adapter brackets that are required on that other offering, which look like they are powder coated black (which is not conductive.) I have no idea.

The bare aluminum body of my alternator bolts solidly to the huge aluminum bracket for the power steering with 10mm bolts, making contact with that bracket in three separate places. (Just like the stock alternator.) That bracket bolts directly to the engine block with two 8mm bolts and one 10mm bolt. Again, with three separate points of contact. (Completely stock.) No cheesy adapters required....this alternator bolts directly to all the original mounting pieces with all the original hardware.(*)

If anyone needs more grounding than that, they have worse problems than needing a high output alternator, right?

Also, there is no separate "lug" on the Bosch alternator for grounding....so they obviously feel it is not necessary, either.

(*) I do include a shorter bolt for the upper pivot. The rear threaded portion of my alternator has a more modern captive nut. This allows the use of a 110mm long bolt, instead of the stock 130mm bolt. While the stock 130 bolt works perfectly, getting a 20mm shorter bolt past the fan housing is a real blessing. (Anyone that has pulled that bolt out and has had to reinstall it knows what I'm talking about.)

Another side result of circuit resistance is the heat create by the power loss.

For example if a piece of wire with a resistance of 0.01 ohms will drop 0.25v at a 40A load current, then it gets 10watts of heat dissipated in it.

Greg,
Put me down for one and I guess I'll need a supplementary wire on my original harness that is on my 91 S4.
Thanks

Careful with what you discredit. The accessory ground wire on Carl's alternator is a Good Thing. Every load except the starter, temp sensors, injectors, plus a couple other small things, grounds through the chassis rather than the engine. Any resistance between alternator/engine block and the chassis risks havoc with injectors, temp sensors and the like. A direct ground from alternator to chassis removes alternator electrical noise from those systems.

Look at how later cars have a separate ground braid from coil brackets to the engine at the heads. One might presume that the heads are very securely grounded through the block. But -any- corrosion on the head bolts and mounting surfaces offers chance to leave some ignition voltage in the heads. Can you say "galvanic corrosion" three times fast?

So a direct ground from alternator to the chassis adds protection from injection and sensor errors, avoids possible galvanic corrosion issues across the mostly aluminum ground path to the other side of the block, and also electrical noise issues that might show up in audio components. What's not to like?

Further, the original ground point positioning under the coolant reservoir overflow is less than ideal. I get that the other side is clogged with steering gear and all on LHD cars. Still, from a functionality point of view, having individual connections from starter to frame, alternator to frame, and coils to heads makes much better electrical sense than what they came up with. It was good enough while the copper braid was new, and relatively easy to assemble on the car.

---

If you haven't done so already, REPLACE the copper ground braid between chassis and engine block under the right side of the engine (on LHD cars anyway). It will do charging and engine sensors nothing but good. This piece is one of only several very reasonably priced pieces left on the car. Grab an extra for later, when copper prices approach gold standards.

Bob:

If you read my original post, you will see that I put emphasis on making sure all the grounds are in perfect condition. I also offer a complete ground kit and an additional power wire between the alternator and the starter, if there is any doubt.

BTW....the starter does ground through the engine and then into the chassis. Goes through the stock ground strap.

Realistically, if the engine ground wire is good enough for the starter to turn the engine over (250 amps minimum load), an alternator that puts out 150 amps (maximum) isn't going to have any issue getting the power back to the battery....through the exact same ground strap.

That being said, when changing the alternator, it is a great time to review and refresh (if needed) any ground connections/cables. I've already emphasized this.

The large majority of my clients are trying to keep these cars as original as possible....or as close to original looking as possible. Hanging an alternator with cobbled up mounts which needs an extra ground cable run which is secured into the chassis by drilling a hole and adding a screw isn't going to fly, with almost all of these people.

Like I've also hinted at, these Bosch people have a pretty good handle on what is needed for electrical pieces.....and I'm using the same alternator to engine block attachments that they do, in the original application of this alternator. And....the engine grounding strap and chassis to battery ground are actually smaller, in the original application.

I didn't have to re-invent the wheel. My alternator mounts from the same locations, ends up with bigger ground straps, has the same size power wire (as in my looms), spins at a lower rpm, now operates in a lower heat environment, virtually jumps into the car with all the original hardware, weighs less, and looks so similar to the original that no concours judge is ever going to know it is there.

It just produces more amperage, which almost all 928s, with just the addition of a modern stereo with an amp and a subwoofer need.

In summary:

No "extra" ground wire hanging under the alternator, randomly drilled into the chassis and secured with a screw required in my application.

Just make sure what is there is good.

Thank you for your order. While I appreciate it, Mary really appreciates it....she had to write the check for this crazy project!

How are your engine and battery grounds? I'm asking every single person who is buying one of my alternators this question.

I made a complete "kit", with the original engine block to chassis ground strap, a significantly better battery ground strap, and the supplemental wire that goes from the alternator to the chassis for an additional $75, when purchased with the alternator upgrade.

Please call Mary at 714 879 9072, so she get this order going. Don't forget to tell her your tee shirt size, so we can send you a complementary shirt.

XXL

XL

Ill take that kit as well.

Any chance to visit and knock out some of our issues over holiday??