Primary/Only Alternator on the Vacuum Pad?

claycookiemonster · #1 01-09-2022, 03:06 PM

Why not? No belt to worry about.

RV6_flyer · #2 01-09-2022, 03:23 PM

Quote:

Originally Posted by claycookiemonster

Why not? No belt to worry about.

I like the idea and am considering it for the RV-8 project.

The CON that I am concerned with has to do with low engine RPM ground operation not reaching rated output of the alternator. It is possible that I may have enough power from the alternator to run the aircraft on the ground at idle while I taxi but have no current flow back into the battery.

Carl Froehlich · #3 01-09-2022, 04:43 PM

Sure, but consider:
- Longer recharge time after engine start. Should not be a problem if you have a healthily battery to start with.
- I have never seen a belt driven alternator with a broken belt (I assume they happen). I have seen a vacuum pad alternator with a broken shear drive.
- I’d take a close look at the standard 60amp alternator weight to compare. I’d guess the difference will be in the grass.
- Cost is about the same.

Carl

Avanza · #4 01-09-2022, 04:48 PM

If the alternator is rated for 40 Amp it should give about 10 Amp on 800 rpm.
This supports a standard equipped plane with EFIS /radios etc.
On 2100 it should carry close to full load.

If you add more load (A) than the alternator can carry at 800 rpm the battery
will supply the difference. A 20 Ah battery in god condition can supply at least
10 A for 15 min without any voltage drop.

However departing with electronic ignition/ fuel injection, I would
like to have a full battery before take off.

Northernliving · #5 01-09-2022, 05:15 PM

Quote:

Originally Posted by claycookiemonster

Why not? No belt to worry about.

I recently installed a new engine/prop and ditched my belt driven alternator in my RV8. I opted for the b&c BC410-H. It doesn’t charge at very low RPMs. That’s the only negative that I’ve experienced. I’m VFR only and don’t have high power loads. I only have around 10 hours on the engine, but so for I have no regrets and like the peace of mind with no belt up front to break. The thought of pulling the prop to change a belt wasn’t appealing. Here are a few pics.

rocketbob · #6 01-09-2022, 06:13 PM

Quote:

Originally Posted by Northernliving

I have no regrets and like the peace of mind with no belt up front to break.

I don't know if you're reading much of the alternator posts on VAF but I've never seen/heard of anyone breaking a belt and its generally once a week someone posts about issues with a pad-driven alternator.

scsmith · #7 01-09-2022, 06:45 PM

Quote:

Originally Posted by rocketbob

I don't know if you're reading much of the alternator posts on VAF but I've never seen/heard of anyone breaking a belt and its generally once a week someone posts about issues with a pad-driven alternator.

I had a broken belt on a C-152 early in my ASEL flying experience, on a night flight too.

rocketbob · #8 01-09-2022, 06:48 PM

Quote:

Originally Posted by scsmith

I had a broken belt on a C-152 early in my ASEL flying experience, on a night flight too.

What was the cause?

rocketbob · #9 01-09-2022, 06:53 PM

And I should clarify: never heard of a RV breaking a belt that a result of age or natural wear.

scsmith · #10 01-09-2022, 08:55 PM

Quote:

Originally Posted by rocketbob

What was the cause?

Unknown. It was fine on the afternoon flight - was a pre-flight item to check tension. (could barely get a finger on it through the cooling inlet IIRC. It was fine for the evening return flight departure, failed in flight about half way home.

I assume it was age. This was a Navy Flying Club airplane, and as a rule, the club planes were maintained very well. But the four C-152s did get a lot of hours on them. It was the only squawk/failure I ever had on a Navy Flying Club plane.