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  #1  
Old 05-15-2019, 08:55 PM
TShort TShort is offline
 
Join Date: Jan 2005
Location: Indianapolis, IN (KUMP)
Posts: 924
Default 40A alternator

I had an alternator failure in the -10, and am replacing the primary alternator.

Anyone using a 40A alternator as primary? I have the B&C accessory pad / gear driven backup, and am thinking about the B&C 40A as a replacement for the primary.

Flying this evening, with EVERYTHING turned on (all lights, pitot heat, fuel pump, 3 EFIS screens, etc) I was at 28-29A. The only thing I wasn't doing was transmitting on the radio, but that is intermittent.

B&C recommends you not exceed 80% of rated amps with usual load, and I am not close to that.

Benefit would be weight reduction, and somewhat cheaper.

Any downside?
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KUMP - Indianapolis, IN
RV-10 N410TS bought / flying
RV-8 wings / fuse in progress ... still
1948 Cessna 170 N3949V
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  #2  
Old 05-15-2019, 09:46 PM
terrye terrye is offline
 
Join Date: Feb 2010
Location: Vancouver, BC, Canada
Posts: 772
Default 40A Alternator

I'm using the B&C pad driven alternator BC410-H as an auxiliary alternator. You should look at B&Cs website for this alternator to see the RPM vs AMPS output graph.

When I questioned B&C after I looked at the graph (and the nameplate said 40 amps), they replied: "The BC410-H has been used as the base alternator in a lot of different configurations, some of which required de-rating it to 20 amps. Additionally, some accessory pads will run faster and increase the output. You can expect about 32 amps at 3500 rpm (alternator speed at 2700 rpm engine speed). The output may vary a little depending on cooling."
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  #3  
Old 05-16-2019, 06:59 AM
TShort TShort is offline
 
Join Date: Jan 2005
Location: Indianapolis, IN (KUMP)
Posts: 924
Default

Yup, I have the 410-H as a backup and it works great.

Just wondering if anyone has downsized the primary to 40A. I canít really see any negatives, but just looking for other thoughts. In terms of future-proofing I canít really think of any high draw add ons...
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KUMP - Indianapolis, IN
RV-10 N410TS bought / flying
RV-8 wings / fuse in progress ... still
1948 Cessna 170 N3949V
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  #4  
Old 05-16-2019, 07:10 AM
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Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
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Default

Been running the BC 40A for the last 15 yrs, I see no need to carry around the extra capacity (weight) of the 60A unit if you don't need it.
I also have the BC 20A backup but have never needed it.

99% of my flying is daytime in warm weather so lights and pitot heat are seldom used. Typical current draw for my all glass IFR panel is around 10A.
With everything on I'll get to around 30A.
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Last edited by Walt : 05-16-2019 at 07:14 AM.
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  #5  
Old 05-16-2019, 07:40 AM
TShort TShort is offline
 
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Location: Indianapolis, IN (KUMP)
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Default

Thanks Walt.

That is almost exactly my situation, both in terms of panel / draw and flying.

I keep the lights on during the day for wig wag / visibility, but they are LED so not much current draw.
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KUMP - Indianapolis, IN
RV-10 N410TS bought / flying
RV-8 wings / fuse in progress ... still
1948 Cessna 170 N3949V
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  #6  
Old 05-16-2019, 08:00 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
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Default Stay with the 60 amp alternator

Quote:
Originally Posted by TShort View Post
. SNIP...

Flying this evening, with EVERYTHING turned on (all lights, pitot heat, fuel pump, 3 EFIS screens, etc) I was at 28-29A. The only thing I wasn't doing was transmitting on the radio, but that is intermittent.....SNIP
What you did not include was battery charging load. After start this could be the largest load on the alternator. This is not a trivial issue for an electrically dependent IFR plane.

The 40 amp B&C weights 6.1 pounds. The 60 amp B&C weights 7.1 pounds.

For an IFR RV-10 I consider the extra pound a non-consideration. Recommend staying with the 60 amp.

Carl
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  #7  
Old 05-16-2019, 09:56 AM
Mconner7 Mconner7 is offline
 
Join Date: Feb 2018
Location: Bradenton FL
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With a 40 amp main and a backup, I cannot see you are in any danger of running your battery dry or overworking your 40 amp main. I have a 25 amp Honda that powers my <10 amp normal load just fine. Pitot heat and landing lights are used for a brief time when needed and raise the load to just under 20 amps. It may take another 5 minutes to fully replenish my battery after start up but I always warm up for 5-7 minutes anyway. If mine dies, I will probably go with a 40 amp replacement.
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  #8  
Old 05-16-2019, 11:57 AM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
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I had a B&C 40A alternator in my dual glass, IFR plane with heated seats and never pulled enough juice that the alternator could not support. Now, I don't believe I ever head ever single electronic parts on at the same time (i.e. pitot heat, heated seat, fuel pump, etc) but in practicality, I did not encounter any issues.
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  #9  
Old 05-16-2019, 02:41 PM
TShort TShort is offline
 
Join Date: Jan 2005
Location: Indianapolis, IN (KUMP)
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Default

Quote:
Originally Posted by Carl Froehlich View Post
What you did not include was battery charging load. After start this could be the largest load on the alternator. This is not a trivial issue for an electrically dependent IFR plane.

The 40 amp B&C weights 6.1 pounds. The 60 amp B&C weights 7.1 pounds.

For an IFR RV-10 I consider the extra pound a non-consideration. Recommend staying with the 60 amp.

Carl
Yes, agree - and I considered this.
But really, the battery amp draw after a normal start diminishes quickly, and by the time you warm up, taxi, run up etc is a non issue with respect to current draw.
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KUMP - Indianapolis, IN
RV-10 N410TS bought / flying
RV-8 wings / fuse in progress ... still
1948 Cessna 170 N3949V
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  #10  
Old 05-16-2019, 02:56 PM
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MarkW MarkW is offline
 
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Location: Edgewater, FL. KSFB
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I am full glass and have wished I had done a 40 amp rather than the 60 amp B & C I installed with the build. Just don't need that much. An I don't have a back-up.
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