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jtprouty

Brushless motor as alternator?

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Hi All,

Is it possible to use a brushless motor being turned by the aircraft's engine as an alternator? I know the alternators on jets (biz-jets anyway) are triple phase AC that is converted to DC but don't know if we could do this on our R/C stuff. Any ideas would be greatly appreciated. Would love to try it on my Telemaster with the 31cc 4-stroke and have a couple of motors to try it with.

Happy flying,

Jim

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I'll give you our results next week, we'll test a 1kW alternator that we are designing with a big brushless driven by a 10cc engine.

BTW if I remember correctly cyber-flyer is already using this on one of his helis.

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I have switched to AXI outrunner brushless motor as generator and it works great. The motor weigths couple of ounces and generates 70W of power on my heli. 6 diodes arranged in a 3-phase bridge are used to rectify the output. Only small capacitor is required due to 3-phases overlapping each other. The trick is attach the motor to the engine which is easy on X-Cell gas helicopter:

http://www.cyber-flyer.com/heli/axi_gen_s.jpg

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Cyber-flyer,

Great work! That's a beautiful install on your X-cell. I have a gas X-cell as well and will hopefully add power to it in the future. Right now I'm trying to add a generator to my Telemaster which has a 31cc gas 4-stroke on it. Luckily it has a power take-off shaft on the back of it with threads on it. :)

Is there any place I can read up on what I need to do to make a 3-phase bridge? How do you determine what diodes to use?

Happy flying,

Jim

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3-phase bridge has 3 diodes connected with common cathode and other 3 with common anode. Take regular 1-phase bridge with 4 diodes and add another pair of diodes for the 3-rd wire coming from the motor winding. I don't have any links, or drawings but I am sure you can find it on the internet.

Use shottky diodes with acceptable forward current rating. I use 20A rated diodes, but they are pretty big in size, 10A may be better.

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Thanks, Cyber-flyer.

I found the following page to be very interesting and helpful as I stumble through this project: http://www.windstuffnow.com/main/3_phase_basics.htm I assume that we're dealing with a delta configuration as show towards the bottom of the page.

I have a few different brushless motors (all Hackers) and will post any progress that I make as I make it.

Thanks again for your help! :)

Happy flying,

Jim

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Ok, hooked up a 3 phase bridge and put the Hacker B50 in the drill press to do some testing. I'm currently getting 1V per 1400 rpm. Does that seem correct? This is a no load voltage and I still need to check how many watts I can get out of the system. Looks like I'll need to gear the system to get the voltage that I need. Anyone know of a good source for gears?

Happy flying,

Jim

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I would guess that a motor with a highish number of turns would give you what you need.

Terry

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Anyone know of a good source for gears?

I whould use in-line planetary gerabox - mega makes 3:1 gearbox that will work with Hacker.

Or try to get a motor with lowest Kv possible.

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That's what I was thinking about. I'm concerned about driving the motor through the gearbox. I don't know how long the gearbox would hold up.

Jim

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1350 RPM/V

Then your drill's 1400RPM results are in perfect order. The Motor's Kv spec goes both ways. :)

BTW, you can use the Kt spec to predict the current output.

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Right now I'm trying to add a generator to my Telemaster which has a 31cc gas 4-stroke on it.  Luckily it has a power take-off shaft on the back of it with threads on it.  :)

Hey Jim,

A little off topic here, but where did you get and what is your 31cc 4 stroke gas engine with rear shaft?

Thanks

Dan

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Dan.

Carr Precision sells one that's a converted weed eater engine. http://www.carrprecision.com/Pages/prod02.htm The PTO runs right through the oil sump and is perfect for hooking up things that you want to drive. The only issue is that the shaft gets pretty hot so you have to come up with a coupling that won't tranfer the heat to the motor.

Cheers,

Jim

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Cool, Looks good. Nice and efficient. What is the size of that shaft exiting the rear? Diameter and Length wise? I have a shaft exiting my Fuji but don't have near the economy as that 4 stroker. The power to weight ratio is the trade off but on a Telemaster? You should be good. Is that Telemaster the 150 or the smaller senior?

Dan

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Shaft is reverse thread, metric. I don't remember diameter..just fair warning on backwards thread and being metric....

Matt Klarich

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