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40A alternator

TShort

Well Known Member
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?
 
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."
 
Yup, I have the 410-H as a backup and it works great.

Just wondering if anyone has downsized the primary to 40A. I can?t really see any negatives, but just looking for other thoughts. In terms of future-proofing I can?t really think of any high draw add ons...
 
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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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.
 
Stay with the 60 amp alternator

. 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
 
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.
 
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.
 
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.
 
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.
 
I?ve been running 1100 hours and 7 years with the B&C 40amp on one bus and the 20amp power pad unit on a 2nd bus. I have 3 power hungry GRT EFIS screens along with everything else.

My electrical system is a 2 bus, 2 battery, 2 alternator Z-14. I?ve had a voltage regulator fail and a connector failure. The former had me running everything on the 40 amp for a few legs. The latter failure had me running on the 20amp for more than a few legs before the problem could be identified and fixed.

Clearly no problem running on the 40 amp, day or night. No problem keeping both batteries fully charged.


Running on the 20 I found that there were no flight limitations - all systems could be run and the batteries would be charged except after landing. Taxi idling would not run the 20amp fast enough to keep the batteries charged with my normal daytime load. But unless stuck in a conga line at Oshkosh, it really wasn?t a problem.

The 40 will be more than fine based on my experience.
 
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