[Geza-aka-Zombo]

You may have noticed that over at the other place, Brown introduced and is peddling a “new and improved” alternator forward housing for the custom alternators he sells. Reading the thread and reviewing the pictures threw out a few red flags that I’ll describe here.

I’m not familiar with the history of his product, but what I’ve gleaned is he takes a more modern design 996 (120A) or 997 (150A) Bosch alternator and replaces the forward housing with a custom design, which has mounting features enabling it to mount to a 928 engine. I think this is a great idea. The original custom housing (left) looks to be a beefy sand cast aluminum part machined where required. The new part (right) appears to me to be machined from a solid billet of aluminum vs. machined from the casting. This would be an improvement because billet aluminum has better structural properties than cast aluminum. Now to the red flags:



Red Flag 1: Weight reduction of 1.25 lbs
Though sounding great, reducing weight isn’t always desirable, particularly for thermal design. An aluminum bar 1” X 1” X 12” weights ~1.25 lb. Removing this much aluminum from the forward housing has a negative impact on its heat capacity (amount of heat it can absorb with a given temperature rise). Remove material, and it’s going to heat up more and faster, cooking the insides you’re trying to keep cool, because, in addition to being structural, the forward housing is a thermal component which absorbs heat generated inside the alternator, and helps transfer this heat to the cooling air. The walls between the cooling slots around the perimeter actually act as fins – heat is absorbed into the cooling air as it flows out the unit.

At a given engine speed, the alternator is turning at a constant speed, thus the flow of air in and out is constant. However, electrical load can vary significantly (turning components on/off) which also varies the amount of heat generated (it’s basically proportional, load to heat generated). So, to handle these surges in heat generation, you need that thermal mass to absorb this transient heat. I’d be interested in how the new design housing weight compares with the 996 or 997 housing it replaces – if it is about the same, this is probably not an issue.

Red Flag 2: Reduced cooling air effectiveness
By extending the cooling air exit slots all the way to the top of the housing, the cooling air, driven radially into the centrifugal fan appears to flow straight in the slots near the fan, which reduces the amount of air drawn thru the alternator from the back. Ideally, the cooling air would flow in from the rear (to cool the rear mounted diodes in the rectifier), and also be drawn in over the coils from the sides ultimately exiting at the front. In this design, it looks to me like it’s going to flow in at the front sides and immediately flow out – path of least resistance.



Red Flag 3: Apparent structural weakness
As the electrical load varies, so does the force on the alternator mounting. The alternator requires more torque from the engine, via the belt drive as electrical load increases. This belt force gets ultimately transferred to the mounting feet, so they are constantly exposed to differing forces – this causes fatigue. I would be concerned about a failure at the mounting feet (at least this one – don’t know what the other looks like).



The 997 front alternator housing is shown here. I think keeping the design as close the Bosch’s would be the lowest risk solution. Without extensive testing, both thermally and structurally, I’d be skeptical, though I applaud the effort to come up with a product for the community.

[Stepson]

Geza,

I posted on the other forum about the testing and warranty on the alteration of the alternator. I am not an engineer (and I don't believe any of those guys are either), but I also wonder what effect the larger air ports are going to have on the amount and size of additional debris that is sucked into the altered alternator. It appears that some pretty good sized pebbles oculd be sucked into the fray.

I hope that folks who buy this product have great luck with it.

[Geza-aka-Zombo]

That's a good point about debris ingestion. As a design engineer, I'm usually skeptical about changes made to product, unless proven with extensive testing. Not that the engineers are perfect and the original design can't be flawed.

[Zirconocene]

It's an interesting question, not least because compared to where the original alternators are installed (at the rear on the 996/997, or right in the middle of the car on the 986/987), Porsche/Bosch already (presumably) determined that the airflow in those positions was adequate with respect to warranty with the original openings. As pointed out, the balance between flow through and conductive (heat sink) cooling of the alternator must have been part of the production choice. Of course, no engineering effort will get things right 100% of the time, but it's also hard to imagine that something as simple as providing larger openings was left on the design table.

That said, I am happy to have a way to use a spare 987 alternator that I have, and the machining is very pretty.

Cheers

[maddog2020]

Despite extensive testing he still sold a defective part. so either he didn't test and is lying or he tested and wont share the data. either way it's a waste of money.

[worf]

Despite extensive testing he still sold a defective part. so either he didn't test and is lying or he tested and wont share the data. either way it's a waste of money.

Wait. What did I miss?

[Stepson]

Worf,

Re: https://rennlist.com/forums/928-forum/1 ... nator.html

Basically GB is selling a repurposed and altered high output alternator that he can' t quite figure out if he tested it (Post 29: One sentence he says as with all his products he did extensive testing, and another sentence, he basically said it MIGHT work) or if he didn't test it. In Post 31, It also appears that he is going to try to use the original manufacturer warranty for a part that was disassembled, and reassembled with altered parts. I'd love to know what Bosch thinks of that. Post 34, His words: " I'm hopeful that this slight change in the front housing, makes some difference" How about that extensive testing?? And finally in Post 37 under "what does this mean/" "3. The "new version" MIGHT run cooler, due to higher air flow potential" Buyers beware

[SeanR]

I can attest that the one Roger got from GB never worked well when the car got up to temperature. Didn't even need to be 100f outside. If I recall correctly GB even sent him a 2nd one and it was no better. I know this because I was the one who installed it both times. Which was why I never jumped and got one for myself and am in need o f a more powerful alternator. I just don't want to spend $1000.00 to get one.

[worf]

Worf,

Re: https://rennlist.com/forums/928-forum/1 ... nator.html

Basically GB is selling a repurposed and altered high output alternator that he can' t quite figure out if he tested it (Post 29: One sentence he says as with all his products he did extensive testing, and another sentence, he basically said it MIGHT work) or if he didn't test it. In Post 31, It also appears that he is going to try to use the original manufacturer warranty for a part that was disassembled, and reassembled with altered parts. I'd love to know what Bosch thinks of that. Post 34, His words: " I'm hopeful that this slight change in the front housing, makes some difference" How about that extensive testing?? And finally in Post 37 under "what does this mean/" "3. The "new version" MIGHT run cooler, due to higher air flow potential" Buyers beware

Thanks for that summary and pointing me to the relevant posts.

I read them and come away with a different perspective.

Nevertheless, I still don’t know why Sterling @maddog2020 hates the alternators specifically. Oh I *know* why he hates GB and I understand. But, I don’t know if he has direct experience with the alternator.

I have always wondered if deleting the cooling shroud and attached fresh(-ish) air hose was a good idea in a 928 with/without belly pans. I haven’t taken the time to ponder the ‘new’ one and my original side-by-side so as to form the beginning of my own opinion.

*I* have one of his first-gen alternators on my Supercharged ‘91. My experience with it, despite ~8k miles of use (mostly two trips to SITM), isn’t sufficient for me to weigh-in with comparative observations against my ~110k-mile original alternator.

Both alternators suffer from voltage drop when heat soaked. That’s just physics. I have no data on if one or the other is worse. It’s not easy or quick to gather that data in contexts which allow conclusions to be formulated(*). My twin-screwed ‘91 is not a candidate for that kind of data gathering in any case for obvious reasons.

(*) On the flip side, I also haven’t given much thought to test protocols.

[worf]

I can attest that the one Roger got from GB never worked well when the car got up to temperature. Didn't even need to be 100f outside.

The question is: did it work better or worse than a stock alternator in Roger’s 928 under the same conditions? Any conclusion would be best presented with data and a description of the test protocol.

One could also ponder the setting of expectations with how ‘new’ products are marketed. One could argue that based upon the presentation the advantages of the new one should have been so obvious that no need to ‘dicker’ about data and test protocols should have been required.

For the peanut gallery: don’t construe my posts as either defense or offense of the alternator.

[Crumpler]

For my part, my only observation is that I’m surprised the thread in question has not yet imploded.
I see that GB is going to “reconnect “ with Roger and send him an improved version. Which made me guffaw.

[SeanR]

For my part, my only observation is that I’m surprised the thread in question has not yet imploded.
I see that GB is going to “reconnect “ with Roger and send him an improved version. Which made me guffaw.

The two of them should never have let it get as far as it did, but both are stubborn guys with a temper.

Worf, it's been a while since he's driven the GTS with me around. I know on first installing them the output was fantastic and I was getting excited to get them for myself and my customers. Just when hot at idle the stereo would die due to low output (less than 12v) which was exactly what the original was doing. (new harness, all grounds etc cleaned) I've had an original on my car for 10+ years (rebuilt unit) and it started to do the exact same thing this past summer, which is annoying, and have been looking at options.

A buddy of mine had a company build a one off for him and I should have the information on them and the specs on the alternator some place. It was $800 at the time, put out 13.5 hot at idle and the amps were north of 270 at 2krpm. He ran stereo competitions with it. Installed that thing about the same time as I did my rebuilt unit. The buddy since totaled his car out and we put it on Milrads (now gretches) GT and it was as strong as day one last fall with stereo pumping, ac on, all fans running. He had posted a thread about it on Rennlist when we did it and was told by a few of the "smart" guys on R-list that it would overload the car, things would burn, etc. So he stopped posting about it.

If I quit being lazy I'll find the specs, contact the company and see what they would charge for a run of 10 of them and either sell them through Rog or just use in house.

[maddog2020]

the problem is that he makes educated guesses as to what should work and then professes it is fact and sells parts with very little testing. based on the latest posts its just a cover and the new one is only for cosmetic's and may have better flow. It may also ingest bigger rocks and debris too. he's selling them and doesn't even have a finished part from the machine shop. That is where he is just like Carl.

[worf]

The new part (right) appears to me to be machined from a solid billet of aluminum vs. machined from the casting. This would be an improvement because billet aluminum has better structural properties than cast aluminum.

Taking the above as a very general example I have a question for those (you presumably) who are less than a decade behind the start of the art in structural modeling.

For purposes of my question let's set aside electrical, thermodynamic (cooling, both passive and active), along with any other properties except structural (e.g. stress, strain, etc.)

Fundamentally, the question is "did the removal of material compromise the structural properties of the component?"

And what's the easiest most cost-effective way to objectively answer the question?

Let's assume that we have
- a good solid model of both the original component and the new "material removed" component,
- knowledge of the material(s) used in both
- knowledge of the manufacturing (e.g. cast vs. forged, etc.)
- a general idea of the forces the component will see in use

I would assume that it is now possible for a "desktop computer" to run a FEA of both components and spit out data that could be used to answer the fundamental question.

Is that assumption correct?

[worf]

Worf, it's been a while since he's driven the GTS with me around. I know on first installing them the output was fantastic and I was getting excited to get them for myself and my customers. Just when hot at idle the stereo would die due to low output (less than 12v) which was exactly what the original was doing. (new harness, all grounds etc cleaned) I've had an original on my car for 10+ years (rebuilt unit) and it started to do the exact same thing this past summer, which is annoying, and have been looking at options.

Fair'enough. Thanks for the answer.

[worf]

the problem is that he makes educated guesses as to what should work and then professes it is fact and sells parts with very little testing. based on the latest posts its just a cover and the new one is only for cosmetic's and may have better flow. It may also ingest bigger rocks and debris too. he's selling them and doesn't even have a finished part from the machine shop. That is where he is just like Carl.

Thanks for the answer to my question.

I have a suspicion that more of the general ire has its basis in the way GB presents his products and, of course, the perceptions he creates through his posts. (Obviously, the "big" issue you had doesn't fall into this category. In your case it wasn't "presentation" but, indeed, effect that drives your ire. And this is very understandable.)

[Zirconocene]

@worf : I think that your assumption about modelling is correct and that a program like Fusion360 would be able to model the forces quite accurately. The version that does that is not free, however. I don't know of a low cost way to get that analysis, separate from someone that has access to those tools from their job (or serious hobby).

Cheers

[worf]

I think that your assumption about modelling is correct and that a program like Fusion360 would be able to model the forces quite accurately. The version that does that is not free, however. I don't know of a low cost way to get that analysis, separate from someone that has access to those tools from their job (or serious hobby).

It is my suspicion that Fusion360 and SolidWorks (or whatever it’s called now that’s it’s owned by Dassault Systems) can do this. Free isn’t an issue.

[Geza-aka-Zombo]

The new part (right) appears to me to be machined from a solid billet of aluminum vs. machined from the casting. This would be an improvement because billet aluminum has better structural properties than cast aluminum.

Taking the above as a very general example I have a question for those (you presumably) who are less than a decade behind the start of the art in structural modeling.

For purposes of my question let's set aside electrical, thermodynamic (cooling, both passive and active), along with any other properties except structural (e.g. stress, strain, etc.)

Fundamentally, the question is "did the removal of material compromise the structural properties of the component?"

And what's the easiest most cost-effective way to objectively answer the question?

Let's assume that we have
- a good solid model of both the original component and the new "material removed" component,
- knowledge of the material(s) used in both
- knowledge of the manufacturing (e.g. cast vs. forged, etc.)
- a general idea of the forces the component will see in use

I would assume that it is now possible for a "desktop computer" to run a FEA of both components and spit out data that could be used to answer the fundamental question.

Is that assumption correct?

I don't do this type of analysis myself, but work closely with folks in our analysis groups who do. You are correct, using a high end PC is all that is required these days. Using software such as ANSYS, you can import the solid model geometry directly from the design software (CREO or Solidworks, etc.), and the FEA software will create the mesh automatically, after which an analysis can be run using the assigned material properties.

[worf]

I don't do this type of analysis myself, but work closely with folks in our analysis groups who do. You are correct, using a high end PC is all that is required these days. Using software such as ANSYS, you can import the solid model geometry directly from the design software (CREO or Solidworks, etc.), and the FEA software will create the mesh automatically, after which an analysis can be run using the assigned material properties.

Excellent. Thanks.

[maddog2020]

I think keeping the front of the alternator as close to the original one is a safer bet. I do have data logging on my ecu and when it is hot enough again, I can dump out the logs for voltage and ambient air temps. I agree that voltage is going to drop as temps go up and the 928 is somewhat unique from a lot of modern cars. I'm not an engineer but the new case looks to have several physical weak points. Personally I would prefer a larger case with more surface area on the fins. everyone seems to think lighter is better and it's not always the case. I do worry about catching road debris in the larger front holes.

[Alan]

I'm sure Greg's alternator is better than the stock version since it uses a much more modern alternator, but there are fundamental limitations in the packaging (size) & location (hot) that mean the benefits are going to always have upper limits. I believe if you live somewhere with really hot long summers (I do) then only a more radical solution will get you much better performance. There is actually little in the physics that dictates much lower output at high ambient temps - its really just a deliberate protection mechanism built into the regulator to protect against the alternator overheating - in order to maintain reliability. The alternator overheating really has much more to do with generic alternator design and placement in a 928 than the ambient temps IMO.

Note I have not implemented this yet, but I think a deconstructed modularized alternator is best. Remove the rectifiers and regulator and open up the shell/rear for better cooling and relocate those items remotely onto much larger heatsinks with active fan cooling. You are then left with a much simplified alternator: body/frame, stator windings, bearings, rotor windings & brush pack but then also some new connectors for the high current stator phases and the rotor slip ring connection (4 or perhaps 7 total connections, assuming a case ground). The rectifiers dissipate by far most of the power in the alternator (well over 200W max) followed distantly by the regulator, stator winding self-heating, rotor winding self-heating, then bearing & slip ring friction. A lot of complexity remains in making a reliable/robust remote rectifier/regulator - but relocating most of the power dissipation away (say to the driver front fender area [LHD]) buys you lots of additional temperature margin in the alternator body. You do need a more advanced regulator with remote temperature & voltage sensing and there are other considerations: better generation at idle may also need an alternator with a higher max RPM and a better pulley ratio for higher alt RPM at idle - this likely also requires a better belt arrangement with a wrapping tensioner. Many considerations but I think this is the best path to MUCH better high temp alt performance on a 928.

There are of course no off the shelf solutions for this but there are suitable components. e.g. large body 200+A 3-phase rectifiers, avalanche protection diodes and advanced marine remote sensing regulators.

[N_Jay]

You could try a water cooled alternator.

Don't laugh, used on Touareg and probably some other VW/Audis

[Hey_Allen]

BMW has been using water cooled alternators for years as well, but as always, with BMW prices as well.

[h2pmr]

would it be possible to fit a 2nd, small alternator where the air pump was mounted to help the standard alternator ?

[worf]

Does a 928 with a stock alternator, with cooling shroud and hose fitted, in a pre-‘90 “overheat?”

I do not believe that it does. At least, I have no pre-‘90 clients that have ever complained about alternator performance.

Above when I wrote “that’s just physics” that was oversimplified. It’s really thermodynamics…

… as long we are discussing apples and apples.

There’s a big “thermo” difference between’78-‘89 and ‘90-‘95 in terms ofthe environment in which the alternator lives.

Now, if you want to redesign the system (Hi @Alan ; it’s nice to “see” you over here!) and make oranges then you can change the thermodynamic parameters.

[Alan]

Well of course I'm really only thinking about my GTS - but by overheat I mean enough that it starts reducing output voltage to protect itself - in that sense I have heard almost all model year owner complain IF they live somewhere really hot.

Alan

[Alan]

would it be possible to fit a 2nd, small alternator where the air pump was mounted to help the standard alternator ?

The place where the vacuum pump lives?

Alan

[h2pmr]

would it be possible to fit a 2nd, small alternator where the air pump was mounted to help the standard alternator ?

The place where the vacuum pump lives?

Alan

the smog / air pump assembly

[hessank]

Didn't Bulvot otos moded a Ford 200 Amp alternator (Ford Motorcraft type 3G series with Heavy Duty Voltage Regulator and Heavy Duty Bridge Rectifier ) for like $400?

I am actually planning on doing this during the winter and retiring my old alternator

[Alan]

the smog / air pump assembly

On mine it actually IS a vacuum pump!

But a second alternator suffers from the same problem as as the primary one - once hot its output declines significantly - that's what needs a solution. Of course if you live somewhere hot - you will be running max cooling fans and max HVAC blower a lot of the time too - most especially at the times the alternator is struggling the most - heat soaked hot idle after a long high speed run at maybe 115F daytime or perhaps even worse 100+F at night time with all lighting on.

Alan

[worf]

Right… so the first place to look is get more cooling to the alternator.

‘90+ is more of an issue since the oil cooler does no cooling at low speeds. The oil gets super hot. The lines run right by the alternator. I believe it’s non-trivially hotter in the alternator vicinity. Sterling’s got that covered in his latest build.

For all 928s, make sure the alternator has it’s shroud and air hose.

In an alternate universe where I have some spare time, I’d instrument an alternator on a pre-‘90 and post-‘89 with and without shroud and hose and gather temperature data under specific conditions.

[Crumpler]

Didn't Bulvot otos moded a Ford 200 Amp alternator (Ford Motorcraft type 3G series with Heavy Duty Voltage Regulator and Heavy Duty Bridge Rectifier ) for like $400?

I am actually planning on doing this during the winter and retiring my old alternator

He did.
Based on recent discussions, no problems with that set up so far.

[hessank]

Didn't Bulvot otos moded a Ford 200 Amp alternator (Ford Motorcraft type 3G series with Heavy Duty Voltage Regulator and Heavy Duty Bridge Rectifier ) for like $400?

I am actually planning on doing this during the winter and retiring my old alternator

He did.
Based on recent discussions, no problems with that set up so far.

Good to know. Thanks

[Zirconocene]

@hessank : Much less than $400, in fact. I used his instructions for a 968, modified appropriately for the smaller engine. The alternator I found was less than $150, from a US based alternator supplier (no idea of the provenance of the alternator itself, but also not some random part from eBay). The additional parts were no more than $50, if I remember correctly.

Cheers