Is it possible to add an additional generator/alternator on a Rotax 503 DCDI install?

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Cass256

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Before you ask, yes, I am planning on putting a different engine on the nose at some point. I haven't found a suitable replacement yet for the 503 (The Phazer comes close, but the current gearbox options aren't for me until more testing has been done), & I'm sure it'll be easier to sell the engine as a running package rather than a pile of parts, so I'm going ahead with the install for now.

The problem comes with my electrical load - I'm only using about 6 or 7 amps passively, & as long as I'm aware of when the landing light's on, the integral generator is sufficient, but not perfect.
I was recently gifted a dual USB charging port for my panel, which is something I hadn't budgeted electrical load for; Now that I have one though, the only reason to not put it in is the generator capacity.

I know most of these external generators are belt driven, & the 503 has a belt driven fan; Would it be possible to attach the generator to this belt system somehow? Has anyone already done this?
The external generators I've seen for sale all produce 40+ amps, is there any generator out there in the 20A range? I really don't need anything more powerful.

IIRC, the belt on the fan side is a direct drive to the crank; If this spins too fast for the generator, would it be possible to add the generator to the prop shaft on the gearbox? Or would the additional load damage the engine?

Also, if there's an easier solution I'm missing entirely, please let me know - I'm open to any suggestions at this point. Thanks in advance!
 

Cass256

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Kubota PM alternator, 14 amp. 20 amp version?
That looks like it'll fit the bill, looks like they're meant to spin around 2-3k RPM so I'd have to mount it to the propeller flange. I'm pretty confident I could make that work, but I'm worried it will stress the gearbox it ways it wasn't designed for - I'm not an expert on belt/chain drives or gearboxes, though.

Maybe there's a high output internal Stator you could swap in?
My search didn't come up with the standard factory equipment.
My search turned up a bunch of OEM ones for sale, but none of them are higher output. I'm also concerned changing the stator would alter the ignition timing, though I guess I could re-time it if I need to.

Would it be too unorthodox to mount a second stator behind the first one, strictly for charging?
 

Daleandee

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Minimal output at that rpm; look at the pulley size on the engine ( bigger than the alt pulley). The alt typically runs around 2-3 times engine rpm.
Correct. Dan Weseman designed a direct drive application for the Corvair engine so the dynamo is turned at crankshaft speeds. Here's the output numbers from his testing:

Engine / RPM / AMP output

850(idle) - 1~2 (erratic output)

1200 - 3

1800 - 10

2850 - 20

That information was found here:

 

rollerball

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If all you're adding is a twin USB port why do you need more generator capacity? I've had 503s and one of my current aircraft is a 582 X-Air which has the same stator as the 503. I run a radio, a twin USB for my GPS and can also plug my phone in at the same time and the ammeter still shows a good charge. I'd be happy to add LED strobes and a LED landing light as I've got in my Savannah. What more do you want to run? IMO all you would be doing is adding weight and creating potential failure points in what is a very simple and effective electrical system.
 

starrtit

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Alternators and generators should be headed to the museums now that we have flexible solar panels and LIFE-PO batteries.
No more bolts, brackets , belts, regulators , adjustment arms that are always cracked.
 

Cass256

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If all you're adding is a twin USB port why do you need more generator capacity? I've had 503s and one of my current aircraft is a 582 X-Air which has the same stator as the 503. I run a radio, a twin USB for my GPS and can also plug my phone in at the same time and the ammeter still shows a good charge. I'd be happy to add LED strobes and a LED landing light as I've got in my Savannah. What more do you want to run? IMO all you would be doing is adding weight and creating potential failure points in what is a very simple and effective electrical system.
I am planning to fly this plane to Valdez in the future, & it has a basic IFR panel with a GPS175 & dual G5s for basic RNAV capability - I don't plan on flying in any IMC until the new engine is on the nose since you're legally not supposed to according to Rotax's operating manual, however the whole system already pulls too many amps with the landing light on & without the USB ports charging, and there really isn't anything unnecessary on the panel electrical wise.

It'll run & charge fine as long as I remember when the light is on, but charging any device pulls (up to) 5A which puts me way above a safe constant load unfortunately, even with the landing light off.

Yes, all my lights are low-power LEDs already & they only make up about 1/3rd of the constant load. The GPH sensor, pitot heat, engine monitor, & G5 sensors haven't been added to the constant load estimate yet either, which makes me inclined to put a higher output generator in just for a buffer if nothing else.
 
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Cass256

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Any chance that an air-driven generator/alternator might provide what you need and perhaps be simpler to install?

Just a thought.
You're right, & I am going to investigate this; I'm a little worried about extra drag considering I'll only cruise around 70-80mph, I don't really want to go slower :p

How much power do you need ? I would invest into more efficient aka mosfet voltage regulator.
Really, an additional usable 3-5A (so really like 7-9A) would be enough, I don't know if it's possible to get that from the stator though.

When you say a more efficient voltage regulator, is that the same regulator/rectifier used for AC->DC conversion? I have a Key West rectifier, which as far as I understand is the preferred regulator/rectifier because it doesn't require the constant 1A load like the Rotax OEM one - Is there a different one which might make a difference?
 

stanislavz

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When you say a more efficient voltage regulator, is that the same regulator/rectifier used for AC->DC conversion?
Yes. Just that standart regulator uses triacs and shunts alternator when voltage on battery reach 14.4 volts. Mosfet one uses pwm to convert rising voltage with rpm after rectifier to make more amps and same 14.4 volts.

In another words. We can wind alternator with thicker wire and less turns to provide more amps at higher rpm, but it wont charge at lower rpm. And pwm thing makes it from standard one with still charging at low rpm.

 
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Lucky Dog

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Unless you already use LED landing lights, switching from incandescent to LED will dramatically reduce the draw on your electrical system and provide a simpler solution.
 

Cass256

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Unless you already use LED landing lights, switching from incandescent to LED will dramatically reduce the draw on your electrical system and provide a simpler solution.
I'm already using LEDs for every light, the landing light still draws about 3A, though - I think there are some incandescent bulbs out there that would exceed the max amp budget by themselves! The 503 only produces about 12A at cruise rpm; I think the rule of thumb is to not use more than 80% of the charging output, which means I can only use about 9-9.5A continuously.

Yes. Just that standart regulator uses triacs and shunts alternator when voltage on battery reach 14.4 volts. Mosfet one uses pwm to convert rising voltage with rpm after rectifier to make more amps and same 14.4 volts.

In another words. We can wind alternator with thicker wire and less turns to provide more amps at higher rpm, but it wont charge at lower rpm. And pwm thing makes it from standard one with still charging at low rpm.

Thank you very much for this info, I had no clue you could get rectifiers with mosfets so easily! I ordered one rated for up to 30A single phase, hopefully it'll give me the few extra amps I need to make this work. I'm working on overhauling the engine soon, once it's running I'll do a comparison of the amperage output with the Key West rectifier & the mosfet one.
 

rv7charlie

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As someone who cannot bring himself to fly a 2 stroke above a tree, I'd just like to say that I'm very impressed with anyone who has gonads large enough to fly a 2 stroke powered 80 mph aircraft in IFR conditions.

;-)
 

Armilite

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AMES, IA USA
Before you ask, yes, I am planning on putting a different engine on the nose at some point. I haven't found a suitable replacement yet for the 503 (The Phazer comes close, but the current gearbox options aren't for me until more testing has been done), & I'm sure it'll be easier to sell the engine as a running package rather than a pile of parts, so I'm going ahead with the install for now.

The problem comes with my electrical load - I'm only using about 6 or 7 amps passively, & as long as I'm aware of when the landing light's on, the integral generator is sufficient, but not perfect.
I was recently gifted a dual USB charging port for my panel, which is something I hadn't budgeted electrical load for; Now that I have one though, the only reason to not put it in is the generator capacity.

I know most of these external generators are belt driven, & the 503 has a belt driven fan; Would it be possible to attach the generator to this belt system somehow? Has anyone already done this?
The external generators I've seen for sale all produce 40+ amps, is there any generator out there in the 20A range? I really don't need anything more powerful.

IIRC, the belt on the fan side is a direct drive to the crank; If this spins too fast for the generator, would it be possible to add the generator to the prop shaft on the gearbox? Or would the additional load damage the engine?

Also, if there's an easier solution I'm missing entirely, please let me know - I'm open to any suggestions at this point. Thanks in advance!
==============================

I see a few options. Why not just add a 2nd Litium Battery 2.4 lbs if you need extra Juice?

Rotax did make at one time a 2nd Stator Power Soruce that went between the C & E Gear Drive!

With all the Low Power Gauges out today, I don't see why your 503UL shouldn't be able to Power them all.

They also make flexible Solar Panels today that you could Glue about anywhere on the Airplane Skin.
 

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