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  #31  
Old 05-20-2018, 03:07 PM
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cdeerinck cdeerinck is offline
 
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Question

Quote:
Originally Posted by Hartstoc View Post
to delete the belt driven alternator compleletly, so I needed the comfort of a broader margin, especially since my bird will soon be “electron dependent”.
Otis - Sorry to ask what appears to be an obvious question: Does this mean you intend to only run a single alternator on an electrically dependent engine?

If something happens to that alternator, what is the plan?
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  #32  
Old 05-26-2018, 08:53 AM
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Originally Posted by cdeerinck View Post
Otis - Sorry to ask what appears to be an obvious question: Does this mean you intend to only run a single alternator on an electrically dependent engine?

If something happens to that alternator, what is the plan?
Thanks for the Question- you really have two choices for electron dependent aircraft, dual alternators or a well designed dual battery system. Most go with the dual batteries, but with the second being just a 4 amp-hour or so backup that can be called upon to operate one ignition long enough to safely land after an electrical failure.

I’m going electron dependent in three stages:

1- install and test the spline-drive alternator and, if successful, remove the belt driven unit including removing the pulley fron the flywheel. This phase is now complete.
2- install one lightspeed ignition and a constant speed prop, leaving one magneto in place. I’m about ready to flight-test this phase.
3- the big one- install the second lightspeed ignition, create and install a fully redundant twin-battery system, replacing the PC680 with a pair of EarthX EXT900-VNT lithium batteries set up so that the main bus can be powered connected to either/or, with the remaining battery being charged via diodes. This setup will have so much ampacity and redundancy that it could power the aircraft through an entire tank of fuel- EVEN WITH AN ELECTRIC FUEL PUMP OPERATING, without reliance upon the alternator at all. This phase will happen next Winter, and I’ll be document all of this on VAF.

I did just post this thread on the above mentioned batteries:

http://www.vansairforce.com/communit...ght=EXT900-VNT
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  #33  
Old 05-26-2018, 09:17 AM
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Originally Posted by DanH View Post
Can you offer a reference to support the claim? It's a curiosity question. I suspect the answer require math, and the difference is tiny.

Moving to the practical, everything I find says rectifier power loss (heating) = forward voltage drop x current. Overall, total loss from all factors rises with RPM. Most of those losses also take the form of heat.

Good paper on alternator efficiency here; see pages 16 through 28:

http://www.delcoremy.com/documents/h...ite-paper.aspx

Take particular note of Fig 28.

The Bosch Automotive Handbook also offers guidance.



B&C's datasheet puts 14V output for the 462-H at 41.3 amps at 2450 engine RPM, so 15-25A is not pushing it hard. Did Nathan recommend the cooling shroud? No mention of it in the B&C literature.

The shroud appears to be a personal preference, not a requirement to make the installation a success.
Dan- thanks for this- good stuff that I will study in detail. In response to the your last sentence, the shroud IS a personal preference that has given me the confidence to make the spline drive my primary alternator. Could it survive reliably without the shroud? Maybe, but I can say with confidence that it will have a much happier life with the shroud. Nathan reviewed and approved of my initial thread before I posted it and has been highly supportive. In fact, he requested my permission to add it to his new website. He did not specifically suggest the shroud, but I designed it in response to his concerns about the impact of heat on the alternator’s output and potentially on its reliability if used as full-time primary. This is a quote from his response to the draft of my thread:

“The article is excellent. It provides very good technical detail without sounding like a textbook. Thank you so much for your effort on this. Usually, I can find at least one thing I would change, but not with this article. Again, excellent work.”
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  #34  
Old 05-26-2018, 12:15 PM
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Originally Posted by Hartstoc View Post
Could it survive reliably without the shroud? Maybe, but I can say with confidence that it will have a much happier life with the shroud.
Yes, I know, cooler is better, but without a shroud, does this rear mounted alternator actually run any hotter than the common front mount? The recent alternator poll says a front mounted B&C is very dependable.

I'm sure Nathan likes the write up. Did he recommend the cooling shroud? We already know the literature doesn't require it.
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Last edited by DanH : 05-26-2018 at 12:24 PM.
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  #35  
Old 05-26-2018, 02:47 PM
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Quote:
Originally Posted by DanH View Post
Yes, I know, cooler is better, but without a shroud, does this rear mounted alternator actually run any hotter than the common front mount? The recent alternator poll says a front mounted B&C is very dependable.

I'm sure Nathan likes the write up. Did he recommend the cooling shroud? We already know the literature doesn't require it.
Well, the answer to first question is going to be installation specific, a little different for each aircraft, but I’ll go out on a limb and guess that the answer is, to some degree, yes for nearly all aircraft. I tried to make the case in my original post that air circulation in that neighborhood of the cowl is an unknown and often pretty stagnant. Definitely yes in terms of post-shutdown heat soaking, but even that is going to be diminished by an effective shroud due to the lower-temp starting point.

I think you said it, “cooler is better”. Add that to “making an active cooling shroud is not terribly difficult”, and also that I’ve established that, for my installation, alternator temp runs fully 100°F cooler than oil temperature, and I think you have pretty good incentive to at least consider a shroud. At the very least strategically mounting a thermocouple and observing temp behavior in your own installation if you are planning to rely on it as primary. I probably would not go to the trouble for a spline-mounted backup alternator, as thesejust sit there free-spinning under no load for their entire lives.

Your question brings up another interesting subject- just how cool do belt driven alternators run? I’ve observed that many are “cooled” by a blast tube, but that often this blast tube terminates very near and at 90° to the cowl inlet flow, a region of exceedingly high velocity air. I’d be willing to bet at least a little money that most of these are producing reverse flow or no flow. Careful testing with multi-port manometers would be required to know for each installation. (Hey, and ditto for some of those Superior forward-induction setups that tap that same region!) you reallycannot know without careful testing.

I did address the other question about Nathan in my previous answer. Given the unique nature of each installation, I don’t think there is any point in B&C declaring that any particular shroud or cooling strategy be manditory. My only hope here is that my experience here be food for thought, perhaps at least spurring those considering spline-mount primary alternators to at least dedicate some effort to do a bit of testing and insure themselves that they have a happy component.

Btw- I just completed removal of the flywheel pulley, belt, alternator and brackets from my bird so now there is just the spline mount. I also installed mini-sensors for dual lightspeeds, which are a critical component of that system. Not only are the sensors fully accessible with the pulley gone, but the possibility that a broken belt could easily wipe out the sensors has been eliminated. - Otis
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  #36  
Old 05-27-2018, 06:40 AM
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Quote:
Originally Posted by Hartstoc View Post
.....I’ve established that, for my installation, alternator temp runs fully 100°F cooler than oil temperature...
No, you didn't. That's the point. You measured exit air temperature, not alternator case or rectifier temperature. Ouote:

Quote:
Originally Posted by Hartstoc View Post
In cruise, the rectifier section exit-air temperature magically stays almost exactly 100°F below oil temperature regardless of altitude or power settings....
and

Quote:
First, I allowed plenty of time for everything to stabilize, with OAT at 43°F, oil temp at 173°F, and alternator exit air temp at 72°F....
It's like claiming low CHT based on low cowling exit air temperature.

Allow me to be clear. I cheerfully accept "cooler is better". That said, how much better is an unquantified belief system. No evidence presented here says the additional cooling is necessary to make the installation a success, the focus of your original post.
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  #37  
Old 05-28-2018, 02:20 PM
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Quote:
Originally Posted by DanH View Post
No, you didn't. That's the point. You measured exit air temperature, not alternator case or rectifier temperature. Ouote:



and



It's like claiming low CHT based on low cowling exit air temperature.

Allow me to be clear. I cheerfully accept "cooler is better". That said, how much better is an unquantified belief system. No evidence presented here says the additional cooling is necessary to make the installation a success, the focus of your original post.
OK, touché’- you make a completely valid point- and I thank you for that- but the rectifier assembly is not provided with a thermocouple well like the cylinders are. I selected the location for mine to be at what I thought would be the best location to serve as an indicator of what is going on in the rectifier assembly. It would be ideal to simultaneously monitor a number of locations for a more rigorous assessment, measuring inlet temp, a couple bonded to surfaces inside the assembly itself, etc. A control study of several installations working under various loads in various conditions without any supplemental cooling would also be part of a scientifically valid study. That was outside the scope of my personal objective. I will look at going back making a few edits clarifying that stated temps are exit air temps and not core temperatures.

I do think I can claim that the temperature behavior I’ve observed, particularly observing the exit air temperature’s rise and recovery behavior during the “acid test” phase, strongly indicates that the shroud provides the alternator with a very healthy flow of very cool air(possibly more than needed, and I may throttle back the inlet a bit after observing temps in more severe Summer conditions.) This provided the confirmation I needed to confidently cut the drive pulley off of my flywheel.- Otis
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Last edited by Hartstoc : 05-28-2018 at 02:23 PM.
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  #38  
Old 05-30-2018, 08:48 AM
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Default Further thoughts

Quote:
Originally Posted by DanH View Post
No, you didn't. That's the point. You measured exit air temperature, not alternator case or rectifier temperature.

Allow me to be clear. I cheerfully accept "cooler is better". That said, how much better is an unquantified belief system. No evidence presented here says the additional cooling is necessary to make the installation a success, the focus of your original post.
Dan- I may have been a bit too conciliatory in my previous response. Rereading my original post, it clearly references all temperatures as exit air temperatures, and it nowhere suggests that supplemental cooling is essential to a successful installation. Its premis is that using a spline-drive alternator as primary is very different than using one as backup in that potentially hot, stagnant, and hostile environment and worthy of special care.

Also, I question your statement that my inferences based upon exit air temperature are analogous to inferring CHT from cowl exit temps. The rectifier assembly is a thin, pancake-shaped body weighing no more than 8 ounces, and includes a heat sink and a number of openings through which cooling air can flow. My thermocouple is continually bathed in air 100% of which has passed through my shroud, across the rectifier assembly, and through the fan, all withing a depth of about 1.5”. Behavior of these temperatures during the limited testing that I documented clearly indicates that significant heat proportional to load is being generated within the rectifier assembly, and that exit air temperature responds quickly and directly to changes in rectifier temperature.

A more definitive, better quantified study using more sensors and proper controls is certainly possible but beyond the scope of my objective, and I stand behind what I have offered here.- Otis
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RV-7A (bought)
Built Monnett Moni
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RV-8A, S-7C, Europa, Glastar.
-2018 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
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  #39  
Old 05-30-2018, 08:58 AM
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Keep up the good work Otis. I think you have done a prudent job in testing, prudent enough to make your assumptions. This is way more than most do. I look forward to seeing how things pan out.
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  #40  
Old 05-30-2018, 09:51 AM
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Default Further Thoughts

Otis,

I whole heartedly agree with JonJay on this issue. You conducted testing that was rational and met your needs to confirm results. It may not be the way others would have done it but it gave you (and many of us) the indications necessary to feel comfortable with the configuration. I commend you on the extent of the testing, the clarity of your explanations, and the willingness to document this for VAF. I look forward to your longer term results. And yes, you were too concilliatory--there comes a point in a "discussion" where you simply say--"Well, maybe so" (W-ms), which, in my family, is code for "I have explained the basis for my position, I am comfortable with this position, and I will not give you any more of my time!" And we say it with a smile!

Best wishes and of course,

Cheers,

db
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