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Primary/Only Alternator on the Vacuum Pad?

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.
 
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
 
Alternator on Vacuum Pad

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.
 
This is what I did

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.
 

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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.
 
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.
 
And I should clarify: never heard of a RV breaking a belt that a result of age or natural wear. :)
 
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.
 
Monkworkz will give you 15 amps at 1000 RPM

The Monkworkz MZ-30L will give you 15 amps at 1000 crank RPM, 2.6lbs all up weight, and the shear coupling is completely redesigned. Above 1800 RPM it will give you 30 amps.

Yes you do have to provide cooling to it but from the testing I have done it's barely measurable.

I do have people running it as the sole means of power but it also has several features that allow it work very well as a back up.

Most of the guys at Reno run their electrics off the vacuum pad so they can save the weight of the belt, mount and groove in the flywheel(spinner bulkhead if you like).
 
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Yes

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.

This is what I am doing.
At what RPM do you start seeing charge current flowing to the battery when first starting up?
 
Why not? No belt to worry about.

I think there is little doubt that this is the future, but it will take a few years before everyone does it, similar to EFIS, electronic ignitions, and other technological advances in aviation - it will take time.

There are three good competitors on the market that I'm aware of, all of whom make what looks like a good product. I would have gone this way but when I got my engine the only pad mounted alternator was the SD-8 which I felt was a bit tight for my power needs.
 
pad mount

This is what I am doing.
At what RPM do you start seeing charge current flowing to the battery when first starting up?

I have a pad mount backup bc410 rated for 20-40 amps. After start, it comes online at about 950 rpm, any less than that and the battery is discharging. My idle is set at about 750-800, so after start I increase to 1000 and watch the engine page to see that alternator pick up the load...
 
RE: Primary/Only Alternator on the Vacuum Pad

The Monkworkz MZ-30L has been working great as a primary/only alternator source for me. It's more compact size wise than the equivalent B&C backup alternator and the controller is mounted firewall fwd. At 1100 engine Tach RPM it produces 14.4 VDC. Like the B&C that lower left mounting nut is difficult to get at. No external excitation required just an enable/disable switch on the instrument panel that I just leave in the enable position during all operations from start up to shutdown.
 
Ok, so forgive me, because once again, the answers I get here are WAY smarter than the questions I ask. I'm going to restate what I think I've heard to make sure I'm keeping up with you guys.
1. The Vac Pad, since it works off the direct engine RPM may be running at an speed too low to power the systems at idle. Also, the tight space makes mounting a larger alternator challenging.
2. As a result, the battery may be discharging initially to provide what power the under-speed alternator cannot.
3. Question: If I have a system back up battery, for the EFIS for example, then that battery would be initlally discharging too. If all goes well (always something to depend on in airplanes) BOTH the aircraft battery and system back up battery would recharge once the engine comes up to the speed required for the alternator.
4. Is the inability of Vac Pad alternators to provide sufficient power at idle an insurmountable challenge, or is it simply something that has never been needed before, and so it may well be possible once it's attempted?

That's enough for now, as Monty Python used to say, "My brain hurts!"
 
Just me

OK to answer your questions, I think we need to seperate out the behaviors of the two types of pad mounted alternators:
1) the B&C pad mounted alternators like the 410, are standard type of alternators just running off the pad instead of the pulley up front. Yes they are smaller in physical and electrical output too. These types suffer because the pad drive RPM is 1.3 less than the crank shaft RPM (please check my math, but that is what I recall). Whereas the pulley alternators are running at faster than cranks shaft speed. Some say the pulley alternators are actually turning too fast due to the size of the pulley on the crank. (another topic altogether)
2) There are also the permanent magnet type of pad mounted alternators. These may produce sufficient power to charge the battery at idle. These are new to me, so I don't have the details.

I chose the pad mount as my primary (and only alternator) for weight and size. Since I am running LED lights and glass panel, I no longer have the current draw of a old school plane. That was my choice. I reserve the right to change back to a pulley alternator after flight testing.
 
questions

Ok, so forgive me, because once again, the answers I get here are WAY smarter than the questions I ask. I'm going to restate what I think I've heard to make sure I'm keeping up with you guys.
1. The Vac Pad, since it works off the direct engine RPM may be running at an speed too low to power the systems at idle. Also, the tight space makes mounting a larger alternator challenging.

Actually, B&C has the 462 which is rated at 35-60 amps. It is a bit larger than the 410. I have the Airwolf remote filter and the 462 will NOT work without some mods to the air wolf adapter or possibly a small extension drive. The 410 will fit, and works great.

2. As a result, the battery may be discharging initially to provide what power the under-speed alternator cannot.

True. Realize that as soon as the engine starts and the alternator is brought online, 1000 rpm is adequate for the alternator to produce power, and 1000rpm is not an unusual idle speed on the ground.

3. Question: If I have a system back up battery, for the EFIS for example, then that battery would be initlally discharging too. If all goes well (always something to depend on in airplanes) BOTH the aircraft battery and system back up battery would recharge once the engine comes up to the speed required for the alternator.

True.

4. Is the inability of Vac Pad alternators to provide sufficient power at idle an insurmountable challenge, or is it simply something that has never been needed before, and so it may well be possible once it's attempted?

Not sure how you would get around it. As was previously posted, the pad turns at a slower rpm than the belt drive alternator would be turning, at the same rpm.

That's enough for now, as Monty Python used to say, "My brain hurts!"

Not sure that it is actually a problem, as people seem to be doing it successfully...
 
If you use the B&C published outputs for the 410-H, at 2000 alt rpm [1540 eng] the output is 15amps, with the average glass panel drawing about 10amps that leaves a meager 5amps available for everything else including trying to recharge the battery. 1500rpm is a pretty high idle. Bottom line is voltage will be low and battery is not being charged until run up/takeoff.

Personally I would find that unacceptable unless VFR only with magnetos.
 
alt

Here is a data point.

I use the B&C 410 as a secondary alternator. It is used primarily to power the essential engine systems, which historical data shows to use between 6 and 8 amps. When the alternator is turned on after start, it picks up that load and the battery charging load. Ammeter shows between 10 and 12 amps at 1000+/- rpm idle for a short time then around 6 amps as the battery is topped off...

EarthX ETX900 battery
 
vacuum pad alternator current capability summary

Vacuum pad alternator current capability summary ref attached image.

AFAIK, wound-field alternators are normally rated at 5,000 alternator RPM so they can't reach rated output on the vacuum pad.
.
 

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B&C wound-field vacuum pad alternator current capability summary ref attached image.

Your chart matches my 475 hours of real world performance. I use the 410 as an auxiliary alternator on a bus with a second battery.

At idle and taxi RPM I get a low volts warning (which is set for 13.5v) on the auxiliary bus. Little load is on the second bus at those times as the primary alternator is picking up most of the load.

I did have an inflight primary alternator fail at about 300 hours. Engine was running at 2300 RPM and the auxiliary alternator picked up the load with no issues.

While waiting for a replacement primary alternator, I flew several flights with the auxiliary alternator only with no issues. Normal total load after batteries have recharged is about 21 amps.
 
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've only had one belt failure in several decades of flying and only heard/read of a handful of others, so I agree belt failures aren't common.

I do my best to review posts here on a daily basis, but I don't recall seeing weekly posts of failures of the B&C pad mount alternators. If there were weekly failures, it should be easy to search/find hundreds of examples. I would find that alarming.

I spent time on the phone with B&C when considering a traditional belt-driven alternator or their pad mount variant. They reported to have thousands of pad-driven alternators in the field on Beechcraft, Cessna and Piper aircraft with excellent reliability - to the point I was comfortable with this option for my flying mission.

There were a few questions about power output from others. The output rating is here in this chart from B&C. I start to get output around 800rpm, and at 2300rpm, it is capable of delivering around 30amps at 14.4V given the alternator turns at 1.3 rpm for 1 engine rpm.
 
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