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The spline-drive BC462-H as primary alternator- a success story!

Hartstoc

Well Known Member
Many hundreds of experimental and certified aircraft sport B&C Specialty Product’s various spline-driven alternators as backups, and by all accounts they have an exemplary record for service and reliability over the past 20+ years. With the recent introduction of the more powerful BC462-H, rated at 60 Amps output in the belt driven version, I began thinking about using one as sole alternator for my “electron-dependent” RV-7A.

The idea of eliminating the belt-driven unit up front along with its HEAVY steel support brackets, getting rid of the belt, and even milling the drive pulley off of the flywheel is compelling. I’d be reducing the polar moment of inertia, lowering weight on the nose wheel, improving CG, and adding the crowbar OV protection built into B&C’s external regulator in one fell swoop. The quality and reliability of B&C products is legendary.

My RV has a nominal load of about 15 Amps, occasionally 24 Amps if pitot heat is used. Because the Lycoming spline-drive rotates at just 1.3 x engine RPM, the BC462-H output is physically limited to 40-45 Amps at 14V depending upon cruise RPM. Nathan Bainbridge, son of B&C founder Bill, was very helpful when I asked about the suitability of the 462 for use as primary.

Nathan felt that it should be adequate given my load requirements, but he did point out that output performance of this (and all) alternators is inversely proportional to the operating temperature of the rectifier assembly at the rear of the unit. Heat is generated within this assembly whenever a load is placed on the alternator in amounts that are directly proportional to load and inversely proportional to alternator RPM at any given load. Removal of this heat is directly proportional to cooling air volume and inversely proportional to cooling air input temperature.

The location of the spline drive under the cowlings of most aircraft can get pretty toasty, especially after shutdown on a hot day. It can also be a fairly stagnant region as regards air circulation in cruise. After a great deal of thought, I decided that several factors, all related to heat, would have to be addressed before I could commit to using the BC462-H as primary:
1- Although the alternator has a built-in centrifugal fan designed to circulate air over the rectifiers, it would move far less air at 1.3 x RPM than at the normal belt-driven 5-7 x RPM.
2- The perforated rear cover of the alternator is designed to admit air drawn in by the fan, which is exhausted through openings around the alternator body, but in the absence of significant airflow in that region, the same, ever-hotter air could be continuously re-circulated across the rectifier assembly by the fan!
3- Battery re-charge demand upon the alternator after a hot-start involving a lot of cranking could be extremely high- just when the unit has been thoroughly heat-soaked after shutdown.
4- I like “happy” electrical components, and it can be generally stated that failure rates of all rise exponentially with stresses like heat, vibration, and inadequate or improper wiring.

My solution to all of these concerns was to build a closed shroud around the rectifier assembly, pressure fed with cold air via a 1” SKEET tube connected to the point of highest pressure recovery at the rear engine baffle.
2v2J6PwgnxBELK5.jpg

This link SHOULD take you to a number of photos with captions that you can scroll through (be sure to leave the album in “roll view”). The captions contain a lot of information, so I’d appreciate your reading them before replying with questions or comments:

https://public.fotki.com/Hartstoc/bc461-h-shroud/?view=roll

I first made the installation leaving the belt-driven alternator in place with an on-off-on alt-field switch installed so that I could select either system. Performance of both alternator and shroud have been spectacular during the 12+ flight hours of testing that I’ve completed, and I’m now confidently removing the belt driven alternator and its drive pulley from my bird. The new system including shroud and regulator added about 7.5 pounds total, and I’ll soon be able to report how much weight the items I’m removing have saved.(edit note- total weight removed at the propellor station= 10.25lb.)

In cruise, the rectifier section exit-air temperature magically stays almost exactly 100°F below oil temperature regardless of altitude or power settings. The indicated bus voltage on my EMS remains locked at 14.0V with an indicated 1-2 Amps positive at all times in normal operation, and I’m happy to report that the low-voltage light supplied with the B&C regulator stops flashing at a fast idle of just 1,000 engine RPM in normal operation.

I conducted the “acid test” during a long cross country, cruising at 9,500’. 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, 14.0V and +1 Amp indicated on the EMS.
Next, I turned off the alternator field, and flew with an indicated load of about minus 12Amps on battery power for about 20 minutes. My current battery is a near new Odyssey PC-680.

During 20 minute period, with a load of about 12 Amps, indicated bus voltage slowly dropped from 12.2V to 11.7V. Interestingly, the alternator temperature dropped just 3°F to 69°F, probably corresponding to ambient temperature of the pressure cowling, whose differential with the 43°F OAT of 26°F is a combination of pressure recovery elevation and radiant heating from the engine within the pressure cowl itself (which likely explains the fixed alternator temp vs. Oil temp differential). This suggests that quite a lot of air is being “stuffed” through the rectifiers and fan by my shroud. Once I have a chance to fly in hot weather, I may be able to choke down the cooling air supply a bit, but I’m in no hurry to do that.

When I first re-energized the field, the battery absorbed an indicated load of fully 32 Amps, so with the equipment load of 10 Amps the Alternator was putting out 42Amps at 2550 RPM (3315 alternator RPM). The BC462-H was able to maintain 13.6V into this load- pretty impressive. During the next 16 minutes, the alternator temperature slowly climbed from 69°F to a maximum of 79°F and returned to the original 72°F as the battery re-charged and the indicated amperage slowly dropped below +3. Pretty cool!! - Otis Holt
 
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Otis,

Great write up!

B and C make great components!

I have a friend of mine here in New Hampshire who uses the same setup on his RV-9, no belt driven alternator at all.

;) CJ
 
Otis,

Great write up!

B and C make great components!

I have a friend of mine here in New Hampshire who uses the same setup on his RV-9, no belt driven alternator at all.

;) CJ
I have the PlanePower FS14B on the vacuum pad as my only alternator. Has worked very well in the two years I've been flying.
 
A recommendation foryour friend-

Otis,

Great write up!

B and C make great components!

I have a friend of mine here in New Hampshire who uses the same setup on his RV-9, no belt driven alternator at all.

;) CJ

John- Thanks for the kind words- I?m glad to see you are still racking up the hours! I?ve put about 60 on mine since last October.

The ?hostility factor? of the region around the spline drive varies quite a bit from airplane to airplane. I?d recommend that your friend and anyone else flying with a full-time alternator there find a way, at least temporarily, to install a strategically located thermocouple of some sort on the alternator rigged so they can see operating temps in flight, and monitor this under various conditions. Most EFIS/EMS units out there have inputs for additional probes, but temporarily borrowing a carb temp probe or even a CHT probe can yield useful info. Even though the B&C can handle some abuse, you might discover that it would welcome a breath of cooling air! It is critical that mine be ?happy? because by the time I finish these mods I will have removed not only both mags but the engine driven fuel pump. I?ll have a redundant battery system by then as well, but I don?t want to ever have to use it! - Otis
 
Engine and electrical system newbie here. I'm intrigued by this. Are there any negatives using only a great driven alternator? On the surface it seems like a good idea getting rid of the front mounted one with the belt and brackets.
 
Engine and electrical system newbie here. I'm intrigued by this. Are there any negatives using only a great driven alternator? On the surface it seems like a good idea getting rid of the front mounted one with the belt and brackets.

The main negative is that alternators need to spin at 6-10K RPM to generate full rated power. The spline mount will only give you about 3K RPM in cruise. This is why I’m using a 60Amp unit for my 40Amp need. These days, with LED’s and efficient avionics that have low power requirements, use of spline drive alternators becomes attractive for the reasons you state and others.

My writeup is intended have people consider this option, but to be careful. The most important point in my post is that when you demand a given load from an alternator spinning at a lower RPM, much more heat is generated in the rectifier section than would be for the same alternator were it belt-driven. If the alternator also lives in a hot environment, and a means of extracting heat isnot provided, you may really be torturing it and will not enjoy the level of reliability that we need in aircraft. I’m convinced that my installation will keep my alternator very, very happy.- OH
 
Terrific write up Otis. I have always loved B&C starters. Do you think you could get away with just a blast tube vs a shroud?

How difficult is it to remove/re install your oil filter?
 
Terrific write up Otis. I have always loved B&C starters. Do you think you could get away with just a blast tube vs a shroud?

How difficult is it to remove/re install your oil filter?

Thanks for the compliment!

Well, a carefully installed blast tube would certainly be better than nothing, but it would be impossible to get full coverage of the entire rectifier installation without some sort of a shroud. I?d probably make sure that the supply end was tapping an area of good pressure recover, and take care to secure the output end such that it blasted the heat sink shown in on of my photos, possibly cutting away a bit of the rear cover to fully reveal the heat sink fins to the blast tub outlet. I?ve seen a lot of blast tubes that are just dangling in space and relly do nothing more than waste valuable plennum pressure. Note that with a fully sealed shroud, the alternator?s internal fan can also draw air though the scat tube from the pressure plennum, so there is an advantage evn slow-taxiing downwind. The stock back-cover is designed assuming that the entire rear region of the alternator lives in air cool enough to satisfy the unit?s needs.

The oil filter on mine is very easy to change. My trick, before and now, is to slip a 1-gallon zip-lock bag over the filter and zip as much as I can shut around the spin-on flange(after loosening the filter so it can be rotated by hand). The Zip-lock catches the mess, and it can be done without losing more that a few drops of the oil.
 
Alt

I have the Planepower on the back only.Going on 5 years 400 plus hours with no problems
 
Otis,

Great write up.

I'm considering the BC462-H option to replace my belt driven PP 60A alternator.

Did you conduct any test using the BC462-H as your only altenator without the cooling shroud? If so, how does the data compare operating the alt with the shroud vs operating it without the shroud?

Thank you,
 
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Otis,

Great write up.

I'm considering the BC462-H option to replace my belt driven PP 60A alternator.

Did you conduct any test using the BC462-H as your only altenator without the cooling shroud? If so, how does the data compare operating the alt with the shroud vs operating it without the shroud?

Thank you,

Charlie- Thank you for this excellent question! The answer is that I did not attempt to collect temperature data on the installation without the cooling shroud. A meaningful treatise about that would require a lot of rigorously controlled study in a variety of OAT conditions spanning several seasons, and even then it would only really apply to my airplane.

On the face of it, an alternator istalled on the spline drive of most conventionally baffled tractor aircraft is going to see some elevated stress due to several factors- A far less effective built-in cooling fan and much higher internal heat generation under load due to the very low operating RPM- Installation in an area that routinely sees elevated ambient temperatures that can often go to extreme levels at exactly the time you are demanding the highest output- All in a region that has no active mechanism for circulating replacement air whatever.

My objective was to create a happy micro- environment for the rectifier assembly and provide myself with evidence that it works, and I’ve satisfied myself that it has been successful, with an overkill factor that should serve me well in more extreme conditions than we see at this time of year. I MAY eventually even choke down the inflow a bit. It is lightweight and fairly easy to fabricate. Nathan Bainbridge, Head of B&C, has applauded my efforts, followed them with interest, and asked for permission to publish it on the new company website soon to be activated.

Well made alternators ARE fairly robust, but few people realize the extent of the demands that we routinely place upon them. Examples of installations as primary that have not failed may atest to this robustness, but it does not prove that they are not living in torturous conditions that could greatly reduce statistical reliability, and they are probably not producing their full output potential because actual output is diminished by elevated temperature. Successful field experience with spline drive emergency backup alternators is not relevant, as they sit there doing nothing and the only test they have passed it that the components can tolerate ambient temperatures in no-load conditions. - OH
 
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I have had the SD8 as the only alternator on my Bucker for over 20 years. I sent it to B&C a couple years ago to have it looked at, just because, and it was just fine and happy. 8A is all I need for this machine.
You can probably get by with a lot less amperage than you think. Add up the loads that are always on (operating input watts) and see what you get. The battery is there to handle temporary loads (landing lights, radio carrier, fuel pump, etc....)
I think this is a great way to go.

Anybody done the math to see what minimum continuous operating amps are for their system excluding temporary loads? I should do my RV to see. I bet a 20A unit would be more than adequate for many unless you hop a lot of short rides.
 
I have had the SD8 as the only alternator on my Bucker for over 20 years. I sent it to B&C a couple years ago to have it looked at, just because, and it was just fine and happy. 8A is all I need for this machine.
You can probably get by with a lot less amperage than you think. Add up the loads that are always on (operating input watts) and see what you get. The battery is there to handle temporary loads (landing lights, radio carrier, fuel pump, etc....)
I think this is a great way to go.

Anybody done the math to see what minimum continuous operating amps are for their system excluding temporary loads? I should do my RV to see. I bet a 20A unit would be more than adequate for many unless you hop a lot of short rides.

Yes- this legendary permanent-magnet unit is indeed nearly bullet-proof and immune to most of the concerns I?ve mentioned. Unfortunately, it would not serve my needs, as I?ll end up needing reliable power to feed 4.5 Amps continuously to an electric fuel pump for the Airflow Performance FI system I?m installing, 2 Amps driving dual Lightspeed Plasma III?s with over-rev protection, 4 Amps for full time LED Strobes, nav, and dual wingtip wig-wags, 5 Amps to drive avionice, and a couple more to charge my 10.4? iPad running Foreflight Pro. Not long ago, an equivalent suite of devices would have drawn 2-3 times that, but now I CAN consider a spline-drive alternator! You really do need significant surplus output to cover those situations where the battery is demanding a re-charge, or there is a danger of drawing down Voltage to a level that could be harmful. It is astonishing how much a battery in good condition will demand with a 3V differential between bus and battery. 2X operating Amperage is a reasonable number. I?m now at about 2.5.- OH
 
I really like the B&C alternators on the vacuum pump pad, but fwiw, I have had to replace a number of shear couplings over the years. If you are depending on that as your only alternator source, I would recommend keeping an extra shear coupling in your plane as well as the tools to change it and a new gasket if it?s needed.
 
Increasing the speed of gear driven alternator

Has anyone thought about putting a gearbox between the accessory pad and the alternator to increase the rotation speed?
 
Engine and electrical system newbie here. I'm intrigued by this. Are there any negatives using only a great driven alternator? On the surface it seems like a good idea getting rid of the front mounted one with the belt and brackets.

For some of us, there are potential CG issues. Use of a lightweight composite prop on my -7A has put me near the limit of the CG range for some circumstances (nose is on the light end). Would be nice to switch to an EarthX battery but that would only exacerbate the situation. Eliminating the nose-mounted alternator would do the same.

Erich
 
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For some of us, there are potential CG issues. Use of a lightweight composite prop on my -7A has put me near the limit of the CG range for some circumstances. Would be nice to switch to an EarthX battery but that would only exacerbate the situation. Eliminating the nose-mounted alternator would do the same.

Erich

I'm putting an IO360 on my 9A so along with a Catto prop I should be good. Trying to keep as much weight as I can off the nose wheel though. If I could save a pound or two using that alternator and if it was a reliable thing to do then I may consider it.
 
For some of us, there are potential CG issues. Use of a lightweight composite prop on my -7A has put me near the limit of the CG range for some circumstances (nose is on the light end). Would be nice to switch to an EarthX battery but that would only exacerbate the situation. Eliminating the nose-mounted alternator would do the same.

Erich

Oops see next post down
 
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For some of us, there are potential CG issues. Use of a lightweight composite prop on my -7A has put me near the limit of the CG range for some circumstances (nose is on the light end). Would be nice to switch to an EarthX battery but that would only exacerbate the situation. Eliminating the nose-mounted alternator would do the same.

Erich

For me, getting rid of the belt drive alternator has several advantages. One is that I am installing dual Lightspeed ignitions so that I can take advantage of the rev-limiting option, which could save my behind if I ever experience a runaway prop situation(not as uncommon as you might think). Being able to mill the big drive pulley off of the flywheel makes the region around the magnetic triggering sensors easy to inspect and adjust any time the upper cowl is removed. Of course, RV?s with constant speed props are less likely to have the CG issues that your airplane does.
 
Otis, please accept my compliments. The shroud itself is pretty work, and your report is well written.

In the spirit of peer review, I would note that...

(1) the reported values are measurements of exit air temperature, rather than the actual temperature of the rectifier or other alternator components. Component temperature would indicate if the shroud is necessary, or overkill. Air temperature tells nothing about component temperature.

(2) there is no measurement made with the shroud removed for comparison, i.e. no determination of its actual effectiveness. Does it in fact lower component temperature significantly?

(3) the initial assumption appears to be that the rear mounted alternator operates in a hotter space than a front mounted alternator. However, there is no measurement of cowl space air temperature, or comparison with the temperature of an ordinary front mounted alternator, which operates in the same cowl space. If the cowl is well sealed, similar front and rear alternators at the same output would operate at about the same temperature.
 
Nice setup. I'm glad it's working out well.

I previously had a Socata TB-9 Tampico that had a similar--though much less elaborate--SCAT-tube-fed shroud around the alternator, and it'd burn one out about every 300 hours. Not well-implemented--but, again, it wasn't nearly so elaborate. Yours appears to be fully enclosed to positively put the cooling air where it needs to be, then extract it effectively. I like it!
 
...snip ...

The most important point in my post is that when you demand a given load from an alternator spinning at a lower RPM, much more heat is generated in the rectifier section than would be for the same alternator were it belt-driven.

...snip..
- OH

Other than from less cooling air from the built in fan, why would the rectifier section run any hotter at lower RPM?
 
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Alternator

Does the alternator work at idle RPM?

If you have a long ground taxi time before takeoff, will the battery be depleted and all radios go dark?
 
Some testing I've done...

I have tested the B&C 40 amp vaccum pad alternator on my RV-10 this way to see if it would handle a realistic failure of the main alternator:

Assuming a belt breakage in flight on the main alternator, I turned off the main alternator 20 minutes from landing and turned on the standby. (yes, you can wire the regulators such that the backup alternator will come on automatically, but I have a field switch for each of them). I then landed and taxied in for fuel. After that, I restarted the engine and took off only using the backup alternator. The battery appeared to be back up to a full charge in about 20 minutes of flight. This was with the Earthx 1200 battery.

I haven't added any cooling shrouds, and I have tested this multiple times. So far, I am pretty comfortable that it will work if/when needed, and I could come home on the standby, without having to pull the prop to change a belt out in the field.

I do change the prop belt every 500 hours.

I used to have the SD-8 as a backup, but as everyone knows, it was just barely adequate and one had to carefully manage electrical loads after a primary alternator failure. Not so anymore with the 40 amp backup. It caries a full-up flight load of avionics, lights, and pitot heat.

Just my experience.

Vic
 
Does the alternator work at idle RPM?

If you have a long ground taxi time before takeoff, will the battery be depleted and all radios go dark?

Sorry for the delayed response- I was pleasantly surprised that amps went positive and the low voltage indicator off at around 1,000 RPM, so once you are taxiing or in the runup area no problem.

Since starting this thread, I have completely removed the belt driven alternator and cut the pulley off of my flywheel- now installing dual lightspeed ignition and the mini-sensors, magnet ring, and all adjustment svrews are FULLY accessible with the top cowl removed. Also installing Hartzell composite CS prop, will report back on all soon.
 
Another delayed reply:

Other than from less cooling air from the built in fan, why would the rectifier section run any hotter at lower RPM?

A partially depleted battery ?demands? a certain load at any given voltage . The regulator is ?demanding? that the alternator maintain a certain voltage. The alternator tries really hard to satisfy these demands, but at low rpm it just cannot. Attempt to satisfy these demands at low rpms results in the generation of a lot of heat in the rectifier section, because the total work required is divided between fewer cycles. At high RPM the alternator has no problem satisfying this load demand, and the work required is divided over many more cycles. It is a little bit like an engine being ?lugged? under a great load at low RPM. Things heat up quickly.

Generally speaking, the spline drive alternator turning at 1.3 x engine RPM is requiring the same total work from each revolution as the belt driven version gets to spread over 3 or 4 revolutions, so heat becomes a more critical issue. I?m very confident that my installation addresses this issue adequately, and there is no longer a pulley on MY flywheel!- Otis
 
I have tested the B&C 40 amp vaccum pad alternator on my RV-10 this way to see if it would handle a realistic failure of the main alternator:

Assuming a belt breakage in flight on the main alternator, I turned off the main alternator 20 minutes from landing and turned on the standby. (yes, you can wire the regulators such that the backup alternator will come on automatically, but I have a field switch for each of them). I then landed and taxied in for fuel. After that, I restarted the engine and took off only using the backup alternator. The battery appeared to be back up to a full charge in about 20 minutes of flight. This was with the Earthx 1200 battery.

I haven't added any cooling shrouds, and I have tested this multiple times. So far, I am pretty comfortable that it will work if/when needed, and I could come home on the standby, without having to pull the prop to change a belt out in the field.

I do change the prop belt every 500 hours.

I used to have the SD-8 as a backup, but as everyone knows, it was just barely adequate and one had to carefully manage electrical loads after a primary alternator failure. Not so anymore with the 40 amp backup. It caries a full-up flight load of avionics, lights, and pitot heat.

Just my experience.

Vic

Vic- Yes, I?d feel comfortable with your setup as a backup(though I think the actual max output of that unit on the spline drive is well below 30Amps). My goal was a bit different- 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?. The BC462, capable of an honest 40+ amps true output on the spline drive, my nominal 23Amp max continuous operating load, and the positive cooling I?ve provided, all coupled with B&C?s legendary reliability, together provide me with that margin of comfort.- Otis
 
Great

Otis,
Great write up and photos....
Nice craftsmanship as well.
Well thought out and follow thru.
This is what experimental is all about.
Thinking this might make a good article in Kitplanes....
Thanks for sharing.
 
Otis, what engine is this alternator mounted on? I am also considering going all electric and using a B&C spline drive alternator on my IO-360-B1E.
Concerned about overcrowding with mags and spin on oil filter.

George
 
Attempt to satisfy these demands at low rpms results in the generation of a lot of heat in the rectifier section, because the total work required is divided between fewer cycles.

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/high-efficiency-white-paper.aspx

Take particular note of Fig 28.

The Bosch Automotive Handbook also offers guidance.

2mh63ja.jpg


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.
 
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?
 
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/community/showthread.php?t=160727&highlight=EXT900-VNT
 
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/high-efficiency-white-paper.aspx

Take particular note of Fig 28.

The Bosch Automotive Handbook also offers guidance.

2mh63ja.jpg


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.?
 
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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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
 
.....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:

In cruise, the rectifier section exit-air temperature magically stays almost exactly 100?F below oil temperature regardless of altitude or power settings....

and

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.
 
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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Further thoughts

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
 
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.
 
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
 
Otis, please accept my compliments. The shroud itself is pretty work, and your report is well written.

In the spirit of peer review, I would note that...

(1) the reported values are measurements of exit air temperature, rather than the actual temperature of the rectifier or other alternator components. Component temperature would indicate if the shroud is necessary, or overkill. Air temperature tells nothing about component temperature.

(2) there is no measurement made with the shroud removed for comparison, i.e. no determination of its actual effectiveness. Does it in fact lower component temperature significantly?

(3) the initial assumption appears to be that the rear mounted alternator operates in a hotter space than a front mounted alternator. However, there is no measurement of cowl space air temperature, or comparison with the temperature of an ordinary front mounted alternator, which operates in the same cowl space. If the cowl is well sealed, similar front and rear alternators at the same output would operate at about the same temperature.

Hello again Dan- my review of the thread also made me realize that I never properly addressed your points quoted above- sorry about that. I really do appreciate everyone’s questions, comments, and criticisms.

The first point has, I think, been addressed pretty well by now.

As to the second, True. Unfortunately, I no longer have a stock rear cover, which would be required for a meaningful comparison, and removal of the shroud would be pretty difficult. Besides, I’m really happy with it. I WOULD argue, though, that if you look very carefully at the data I did collect, you can infer that my shroud is indeed very effective. There was a drop of several degrees when the alternator was turned off after being stabilized at an output of about 15 Amps, a gradual rise of about 10 degrees during the time the alternator was forced to operate at max output, and a speedy return to the operational ambient level at the previous load as the battery became fully charged. That ambient condition is fully 100°F below oil temperature. It would be great if someone else rigorously tested these parameters with no supplemental cooling in a typical RV closed cowl, but can YOU imagine that they would even be in the same realm? I can’t!

Your third point is well taken, along with the question I posed a few entries back questioning the effectiveness of most blast tubes we see on forward-mounted alternators. Personally, I regard most simple blast tubes as being ineffective, pointless wastes of valuable plenum pressure recovery unless very carefully aimed and secured in place, and would bet that if you do want one on a forward mounted alternator, it would be much better to route it forward from the rear baffle area than to install it close to the cowl inlet. In short, many of the questions about suitability of the pad-mount region’s environment apply equally to the forward belt-drive area! The more significant difference, of course, is that the pad-mount unit works harder at reduced RPM’s and moves far less air with its cooling fans than does the front-mount. I’ve witnessed many alternator failures during my 38 years in aviation, and even experienced two of my own. I wonder if at least some of these might have been prevented by better cooling strategies. - Otis
 
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I would wager that the highest alternator temperatures will be soak back heat after shutdown. with no airflow the shroud will not be effective and may be detrimental. the shroud adds some weight that may affect the vibratory response from the baseline. what about just using the alternator as is, no shroud, for your primary and have a battery backup?
 
I would wager that the highest alternator temperatures will be soak back heat after shutdown. with no airflow the shroud will not be effective and may be detrimental. the shroud adds some weight that may affect the vibratory response from the baseline. what about just using the alternator as is, no shroud, for your primary and have a battery backup?

Actually, because the built in fan can ONLY draw air that has passed through the scat tube and shroud, cool-down is very rapid after a heat-soaked startup, even while taxiing on the ramp. In flight, the tube is fed by the most highly pressure-recovered air in the entire cooling plenum, so cold air is literally being STUFFED Through the rectifier section. The entire shroud, supply tube, and related parts total less than six ounces. The alternator is bolted directly to the engine at a location very near the center of radial motion, and I built the shroud, so it could handle vibration several orders of magnetude greater than it will ever see.

I’ll ask that you go back and read my original post in this thread for about a half-dozen really good answers to your final question. And by the way, as previously mentioned I will have a twin, fully redundant pair of EarthX ETX900-VNT lithium batteries in the final installation, set up in such a way that one of those will at all times be immune to discharge due to an undetected alternator failure or other electrical failure.

Have a great day - Otis
 
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<snip>

My writeup is intended have people consider this option, but to be careful. The most important point in my post is that when you demand a given load from an alternator spinning at a lower RPM, much more heat is generated in the rectifier section than would be for the same alternator were it belt-driven. <snip>

Actually, the rectifier section is not generating more heat. It's the field coil that is generating more heat at low RPMs. The rectifier gets hotter because the field coil is hotter and the alternator fan is not cooling as efficiently at low RPMs.

Nevertheless, cooling the rectifier is a very good thing. Keeping the RPM up after at hot engine start will help too.

I really like your write-up. If the major engine manufacturers are monitoring this thread it would be nice for them to offer the rear alternator as a build option with a modified flywheel. Perhaps SDS can offer their lightweight flywheel with this mod for even lighter weight.
 
Great Work Otis

The plenum you made to cool alternator rectifier shields it from radiant and convective heat under the cowl... With the blast tube you are as cool as it can be in this configuration, from what I see. Great job. I'd might suggest you consider routing exit side of alternator plenum to low pressure area, which might help delta pressure and improve follow. However dumping exit air at the top of the cowl seems to be working for you.

The Temp numbers you provide are useful. I understand Dan H. saying your are not measuring diode Temp it self, fair enough. Who has measured the actual diode Temps? Is there any reason to think they're excessively high? No. You could try and bond a thermocouple on the rectifier. Easier temperature sensitive tape that changes color if temperature is exceeded. However based on what you stated and service history of these alternators mounted on the pad, you are good. Time will tell how reliable it is. You progressive approach is prudent.

The biggest issue to reliability I can see is sheared coupling. I know very little about it, but apparently it is a thing. We know these alternators have run for decades on the pad without extra cooling and without sheared coupling issues. They may have not been primary alternator, had less load, but the coupling is reasonably reliable. Interesting some have no issue and others sheared several? I think B&C recommends every 100 hours or annual (condition) inspection the alternator be removed and checked/tested. I could be wrong, but sounds like a good idea.

ADVANTAGE?
The front mounted alternator is path of least resistance. Belt drive is pretty reliable and somewhat isolates the power pulses from engines. With that said all the weight savings on the nose sounds good, but you are not saving that much weight. You are moving CG aft. As Otis did he carved the flywheel pulley off which is more weight savings and moves CG aft. However some Electronic Ignitions use the flywheel pulley to mount pickup magnets, so you can't cut the pulley off (that is my case). Also it seems the alternator on pad will make much less than the rated output due to low RPM, especially at idle. Belt mounted alternator will make more power at idle and all RPM's.

Either way, fwd belt drive or aft pad drive, you have the weight of the alternator. The standard belt drive BOSS mount and adjustment arm alternator installation is not that heavy. The pad mounted alternator has weight. However any weight savings/moving CG aft is attractive. B&C alternators are expensive and require an expensive external Voltage Regulator. Plane Power makes an Internally Regulated 30 Amp pad mount alternator as well. For a day VFR RV you could get away with the 8 amp permanent magnetic version (seen it done).

Just an aside, my VW has an isolation clutch/pulley on the alternator, which isolates alternator from engine power pulses, and it also allows alternator to freewheel, so if engine de-accelerates, it keeps alternator from back driving the engine. Didn't know that was an issue. I'm assuming Pad mounted Alternator on the Lycoming with the low gear ratio keeps the alternator from seeing engine power pulses or "jerk" in the drive gear. I guess the back accessory case area is busy and the front alternator is easier to access and remove. But everything is a trade off.
 
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Mine has no tube

I've been running my pad mounted primary for 150hrs through the hottest part of the summer. Only problems I've had were hot starting after a short shutdown, which had nothing to do with the alternator.

In my RV9 no blast tube was installed and had not been needed. Alternator performs fine.

Steve
 
Still okay?

I've been running my pad mounted primary for 150hrs through the hottest part of the summer. Only problems I've had were hot starting after a short shutdown, which had nothing to do with the alternator.

In my RV9 no blast tube was installed and had not been needed. Alternator performs fine.

Steve

Steve,

Are you using the BC462 and is it still performing well w/out any blast tube or specific cooling?


Brian
 
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Thread back to life

I was curious when this thread would be brought back to life.

After reading, and re-reading, this thread several times, and consulting with B&C, I have decided to use the 410 as my primary alternator. I have mags, mech fuel pump (fi), led lights and all glass.

I plan to not destroy the back cover, but will run a 1” blast tube and probably a minimalist shroud around the rectifiers. I will let you all know in a year how it worked out.
 
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I contacted B&C a couple months ago to see if they were going to run any Oshkosh specials. It took a LONG time to get an answer and to even have anybody return my emails. Finally they said they were and it would be announced on their youtube channel. Well Osh came and went and no specials. Hey B&C if you see this maybe run a belated special. I am planning on a 462 on the pad as my primary.
 
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