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Flyinglion2000

Rotax 912ULS Rectifier/Regulator

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I have a test rig to test the CDI modules I make. It currently can only get to 2000 rpm...BUT I have a new one that is not finished yet but workable. Its driven with a large AC servo motor and it is geared 2 to 1 with a toothed belt and pulley. I can now spin the generator up to 5300 rpm. Its scarey by the way looking at the flywheel running at that speed. My mate who is a guru with electronics (he used to design and build the transmitters on the satellites that deliver your sat tv into remote areas for Optus) is designing a new regulator for the Rotax system. This will allow Lithium batteries and of course normal style etc to be used and safeguards are built into it to prevent overcharge and over current. We did some testing last week on my new test rig and its looking impressive. To get to the voltages that are produced out of the Rotax generator we had a cro on it and also a fluke. At 5300 rpm there was 28v RMS coming out and that equates to 39V peak so you better make sure your capacitor is at least 40V in spec NOT 25v

 

Dont forget the frequency is also extremely high at that RPM. Roger has gone away on a flying holiday as of saturday up to Townsville and over to Darwin in his World Aircraft "Spirit" so if any of the forumites up that way come across him and his wife say hello. Roger will continue working on it when he gets back. The best thing is we are testing in real world by using my test rig and can load and simulate all sorts of issues

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I have a test rig to test the CDI modules I make. It currently can only get to 2000 rpm...BUT I have a new one that is not finished yet but workable. Its driven with a large AC servo motor and it is geared 2 to 1 with a toothed belt and pulley. I can now spin the generator up to 5300 rpm. Its scarey by the way looking at the flywheel running at that speed. My mate who is a guru with electronics (he used to design and build the transmitters on the satellites that deliver your sat tv into remote areas for Optus) is designing a new regulator for the Rotax system. This will allow Lithium batteries and of course normal style etc to be used and safeguards are built into it to prevent overcharge and over current. We did some testing last week on my new test rig and its looking impressive. To get to the voltages that are produced out of the Rotax generator we had a cro on it and also a fluke. At 5300 rpm there was 28v RMS coming out and that equates to 39V peak so you better make sure your capacitor is at least 40V in spec NOT 25v

 

Dont forget the frequency is also extremely high at that RPM. Roger has gone away on a flying holiday as of saturday up to Townsville and over to Darwin in his World Aircraft "Spirit" so if any of the forumites up that way come across him and his wife say hello. Roger will continue working on it when he gets back. The best thing is we are testing in real world by using my test rig and can load and simulate all sorts of issues

So, how big is this AC servo motor, Mark? How many HP is it costing us to run this alternator?

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Hi Bob

 

The new AC servo is 240v and 1.8hp but because the torque can be controlled over the whole rev range it is far more efficient and powerful. As a std motor with nothing connected it runs when hooked up to the generator it hardly runs but the unit has software and a program that once hooked up to the mechanics it takes about 15 mins and does a whole heap of tests and turns that tailor the torque curve. The motor takes 9 amps from the mains supply at full grunt. I originally bought a servo that I thought would do the job but it wasnt even close. The original test rig is a 1.3kw normal AC motor and I had to gear it with a Vbelt pulley the other way as it wouldnt run the generator so this is why it only can do 2000 rpm. The AC servo is geared up the motor does 2650 rpm but upped now by gearing to 5300 and it does it easily. The generator would drag I think around 3 to 5 hp from the engine easily. The reason the servo works so well is the ability to taylor the torque and of course the servo in real terms is far more powerful. Picture of the unit as it runs now but I have to put it on a stand and also bolt it down because at 5300 rpm the gyroscopic effect the unit wants to swing around in a circle on the floor. Also picture of the original servo that I thought would drive it direct and that was hopeless. That servo would do 6000 rpm directly but wouldnt hardly even turn the generator at all. I got a second Generator and got Cz to machine out the housing and put a high end sealed bearing into the generator housing as the original only has a brass bush. I turned up a new shaft and fitted the toothed belt pully and the second bearing to ensure smooth alignment and running due to the high speed of the shaft

 

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Nice setup, Mark. Pity we can't come up with a more efficient method of generating power: 3-5HP would be 2-3.5kW and our microlights would normally be using just a fraction of that. I don't know anything about motors or generators, but I'd like to understand where all the rest goes, and why...

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The issue nowdays is all the electronics we have. For example say you have 2 dynons in the aircraft and a transponder and Ipad and maybe another GPS etc..the dynons can have batteries i them. The panels themselves will take say 2 amps each then another 2 amps each more each if they are charging their internal batteries as well while they are on..the transponder and radio is another amp or 2 at least and more when your transmit and a bit more for GPS and 2 amps while charging the Ipad ....now your really starting to get up there in current being drawn from the generator and I can tell you we loaded the test regulator up with about 8amps when running it and you could hear the sound of the servo change with the load so there was a lot more grunt required as the current went up. I hear of a lot of the generator stators being replaced now because they are burning out. One guy in WA has had 3 of them replaced in his CTLS its a full on digital setup. The old style analogue gauge setup draws very little only really a total of say 3 to 5 amps were this later stuff is drawing 10 to 15 amps

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Most dont think of these issues and it is a issue. All the electronics is nice to have but it comes at a cost that isnt seen if you are not aware of the finer details

 

My S21 will be a tail dragger but it will have a mix of electronic and analogue :)

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Posted (edited)

A local Flight Design (not a CTLS) just had it's generator changed.

And yes, it's FULL of electronics...... multiple dynons and gps etc

Not a cheap job either. I think over 4 grand.....We also put it down to simply overloading....

 

I'm surprised Rotax haven't made an upgraded generator. (Not counting the belt driven one which may not fit most cowls..and probably cost an arm and a leg)

Edge pergormance make one as an extra generator at 32 Amps, which to me seems a bit excessive but probably better than not enough.

https://shop.edgeperformance.no/no/hjem/458-ep-32a-secondary-alternator.html

Edited by Guest

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It probably can't be fitted in the space available. A drive belt may look agricultural but is the easiest on the Alternator. Solid and gear drives transmit vibrations. AnodisedSp? (as in anode) 32 amps is still only 2/3rd HP and probably needs a blast tube of air to cool it. For IFR work any aircraft has to have an electrical system capacity assessment. (Not surprisingly). If you rely on battery capacity for function a protracted engine start deprives you of that till you have charged the battery in flight.. Nev

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