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  #1  
Old 04-06-2018, 01:05 PM
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Hartstoc Hartstoc is offline
 
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Default The spline-drive BC462-H as primary alternator- a success story!

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. 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/bc...oud/?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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Last edited by Hartstoc : 04-07-2018 at 09:14 AM.
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  #2  
Old 04-07-2018, 05:45 AM
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Captain_John Captain_John is offline
 
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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
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  #3  
Old 04-07-2018, 08:09 AM
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KRviator KRviator is offline
 
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Quote:
Originally Posted by Captain_John View Post
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.
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  #4  
Old 04-07-2018, 08:51 AM
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Hartstoc Hartstoc is offline
 
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Default A recommendation foryour friend-

Quote:
Originally Posted by Captain_John View Post
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
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RV-7A (bought)
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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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  #5  
Old 04-07-2018, 09:09 AM
dwranda dwranda is offline
 
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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.
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  #6  
Old 04-07-2018, 11:13 AM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by dwranda View Post
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
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RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2018 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
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  #7  
Old 04-07-2018, 02:07 PM
springer springer is offline
 
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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?
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  #8  
Old 04-07-2018, 03:43 PM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by springer View Post
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.
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RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2018 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
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  #9  
Old 04-07-2018, 04:51 PM
868RM 868RM is offline
 
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Default Alt

I have the Planepower on the back only.Going on 5 years 400 plus hours with no problems
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  #10  
Old 04-07-2018, 09:14 PM
Chkaharyer99 Chkaharyer99 is offline
 
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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,
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Last edited by Chkaharyer99 : 04-07-2018 at 09:19 PM.
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