Small alternator

A general question for the electrical folks on here. I notice that I'm using somewhere around 5-7A of power (avionics, lights) on a regular basis just flying around. Obviously larger power draw when using the flap motor or starter or such, but those aren't used very much or very long. So, I've been wondering whether a small alternator would be sufficient to keep the battery charged for a modest panel and other electrical needs. I'm thinking here of the vacuum-pad-mounted B&C 20A model or something similar. Seems it would allow for some weight savings compared to the larger 50- or 60A belt-driven models that are more typical. I'm not going to be changing things out any time soon, but just idly wondering about weight savings on a potential future project.

So, any reasons why this wouldn't work reasonably well, if the power draw is not too much?

Greg

I've been thinking along the same lines for our new RV8 project.
With LED strobes and lights the power demand should be much less.
It would be great to reduce weight and maintenance. Seems crazy that the prop has to come off to change a belt.
Must confess I don't know much about the various pad mounted offerings though.

Back up B and C Dynamo

Have you looked at the SD-8? Meets my needs for a backup power supply to keep the battery charged while making it to destination after main alternator failure. Since I have built in backups on the Skyviews, All I need is a little extra for communications and some lighting. Lots of excess amps available, if used judiciously.
It is very lightweight and has a proven reliability.
http://www.bandc.biz/alternator8ampshomebuilt.aspx

I installed the PlanePower FS-14B as my primary alternator on the vacuum pad. Rated output is 30A at 6 Lbs, with no bracket or belts to adjust.

My power needs are limited to a single SkyView and VHF for now. LED nav & landing lights will come eventually with a GTN650, but even that won't be taxing things too much.

Be aware that these alternators tend not to produce much (if any) usable current at typical ground-idle speeds, so you're drawing off the battery from start until takeoff, and from landing until shutdown.

B&C L-40 is what you need.

No reason at all not to swap to a vac pad mounted alternator if you need only 20 to 30 amps. B&C and Plane Power both make something suitable. If you are pulling 7A normally I would steer clear of the SD8 as your battery will never charge - it does only put out 8A and you don't really want to be hammering it all the time. Weight savings will be around 4lb, cg will shift aft as the alternator moves back around 18".

Pete

Plane power

I'm going to use a plane power vac pad altenator on my 6. Have a friend with one on an IO550 and it keeps up nicely. I'm just wondering about what spin on filter I can use with it

alt

I have the plane power 35 amp alt as my only alternator. Works fine. Spin on filter is close but does clear. O-360 and have 280 plus hours.

Plane power

Do you have a straight filter or 90 degree, and which spacer?

My son has an older SD-8 on his Pitts S1. It's a 2 pole single phase permanent magnet alternator, so it requires a fairly large filter capacitor, carefully mounted. It has not been playing nice with his com radio, although it's useable now after several reconfigurations. Peter theorizes that LiFePO4 batteries might not be as good of a natural noise filter as a lead acid battery? (that will stir up some debate, I bet!) It's a nice set up for a daytime VFR ship. The weight savings is noticeable in a competition aerobatic ship.
I tried a belt driven PM alternator off a John Deere garden tractor in my RV-8, but the pulley ratio ran the alternator RPM too high, and the voltage regulator could not prevent voltage run away. Too bad, it was a slick 20 amp solution.

filter

Straight filter mount with what I assume is standard mount. engine type is A1A

Sd-20 pad mount

Greg,
I went with the SD-20 B&C pad mounted alt and their LR3C-14 regulator mounted behind instrument panel. Those folks are great to work with.
Cj