In-Flight charging

[rjfon1]

Would it be possible to recharge batteries in flight using for instance, a bicycle dynamo and onboard voltage regulator?
I remember as a kid we used to have bicycles with the ?Dynamo that you pushed against a tyre and it would light the head and tail lamps. This could be used to charge a secondary battery, or suppliment onboard power if required. There would certainly be enough RPM.
You don't see them too often anymore as these days everyone has the LED versions, with rechargable batteries.
Just a thought.
Thanks in advance.
Rob
Australia.

[typicalaimster]

I think something like this is what you're looking for?

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFV20&P=0

[kd7ost]

I suppose it depends on what you're driving the unit with as far as engines go.
Here's a unit that has a ring of rare earth magnets that pass across a coil. It provides up to 5 watts but needs to go on a 2 cycle glow engine.

http://www2.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=genesys&FVPROFIL=++&search3=Go

You might also look at the Sullivan site for other special units.

http://www.sullivanproducts.com/GenesysCustomMainFrame.htm

Dan

[typicalaimster]

Hah, like minds in action! ;)

[kd7ost]

I also recall reading somewhere that a guy coupled a brushless motor to a helicopter main shaft, then built a rectifier and regulator.

Squeeked in just ahead of me Scott. :p

Dan

[kd7ost]

Hah, like minds in action! ;)


:D :D :D

[typicalaimster]

Maynard Hill set up his own version of a Generator on TAM

"Most of the electrical energy for long duration flights is produced by a three-phase alternator driven by the engine."

http://tam.plannet21.com/FAQs.htm#energy

This was done using a brushless motor driven by the IC engine onboard. He then did some electronics magic on board.

[Myron]

You can also got to Fry's electronics and pick up some small solar panels. I think the last one I looked at was good for 12 volts 250Mah.. They were pretty light and if you parallel them you could use them to power your RX or maybe some LED lighting..

Myron

[Disciple4123]

I also recall reading somewhere that a guy coupled a brushless motor to a helicopter main shaft, then built a rectifier and regulator.

I developed a helicopter start shaft alternator in 2004, works very nicely. See here for the details: www.aerialphotographyservices.com/alternator (http://www.aerialphotographyservices.com/alternator)

My current heli runs an alternator off the main gear, same concept.

Sound familiar kd7ost??

[saucerguy]

From the gis of what I'm reading, it looks like something closer to an attempt at perpetual motion, with the advent of brushless motors and their low friction ratio, I'm sure it would give the illusion of that therin. I wonder how long a flight you could achieve with it done in that manner. Also, I may do the same to one of my planes since I almost always have to add weight to the nose, enough in many cases to accomodate another brushless behind the first one.

[kd7ost]

I developed a helicopter start shaft alternator in 2004, works very nicely. See here for the details: www.aerialphotographyservices.com/alternator (http://www.aerialphotographyservices.com/alternator)

My current heli runs an alternator off the main gear, same concept.

Sound familiar kd7ost??


Hey, thats it!!!! :D

Dan

[kd7ost]

From the gis of what I'm reading, it looks like something closer to an attempt at perpetual motion,

Not at all,

This is using a wet fuel engine turning an alternator to keep batteries charged. Something like an automotive or Full scale setup. Just to keep battery weight down.

Da

[wadiprawita]

Disciple4123,

Is there any risk of current flow from battery to the duralite regulator, when the RPM is low?

-doni-

[kd7ost]

I hope he jumps in and answers but I would say there would be no problems. The AC voltage being generated by the turning motor goes through a rectifier. Rectifiers are made up of diodes configured to convert the AC from the motor to pulsating DC. The pulsating DC is then smoothed by filtering with storage capacitors. The current can flow one way but not the other.

Dan

[Unterhausen]

a brushless motor seems like it would be perfect for this, although you'd have to pick one with a Kv that was appropriate. If you were charging lipos, the whole circuit might have to be fairly complex.

[kd7ost]

a brushless motor seems like it would be perfect for this, although you'd have to pick one with a Kv that was appropriate. If you were charging lipos, the whole circuit might have to be fairly complex.

Agreed,

My thoughts for future projects call for keeping it simple by charging NiMh cells to avoid the potential problems. The power density would be fine if your recharging on board anyway. You could use smaller cells.

Dan

[typicalaimster]

My thoughts for future projects call for keeping it simple by charging NiMh cells to avoid the potential problems.


I agree. At this point you're generating power and don't need the lifespan of a LiPo cell. Weight can be kept low by using smaller mAh packs. The charging circuit can be fairly simple. With LiPo's a more complex circuit would have to be devised.

[kd7ost]

And not to mention they have a pretty good charge and discharge rate as well as no memory effect. If you accidentaly do deep discharge them they won't likely be ruined if you get them charged back up soon enough. And, you don't have to cycle them like a Nicd.

They have a lot of good qualities. Even though I don't recharge them onboard, thats all I use in my plane except for the video link where I use 3 surplus LiIon's.

Dan

[Unterhausen]

I like the idea of using the brushless as a starter, but that's going really crazy.

[kd7ost]

Naw, take a look at the product on the bottom of this page.

http://www.sullivanproducts.com/GenesysCustomMainFrame.htm

Dan

[Disciple4123]

Some discussion I see, haven't been on for a while. Regarding the battery draining back issue that was mentioned: There are diodes on the circuit board to prevent that, the LM338 chip I use may fail if power is let in the OUT side of the reg., diodes take care of that completely.

Regarding the battery choice and such, I have used primarily NIMH packs of 2000 to 2700 mah. They are nothing special. If you let the voltage drop very low on the batt, 4 volts or so, then fire up the heli and try to charge it with flight the charge rate will be tremendous and will shorten batt life or kill it. I did that once. My alternator plans have no charge rate control, i.e. limit voltage to permit no grater than 2 amps, etc. If the batt is off the lowest light on a voltwatch, and this alternator is set to a voltage of about 5.3 volts, then it will not fry the battery by flying to charge.


As far as my use of Duralite regulators: I started by making my own regulators with external heatsink and LM338, then I went Duralite, the Duralite was too light duty for this application and wes melting down. They make a good product for their application, just not for alternator service. I have in the past year been using my own version of the Electrokits voltage regulator kit (compact, emchanically robust version of what I started with)

Brushless motor selection: I generally try to pick a brushless motor and gearing to deliver 14 volts or so at running speed, this allows the use of 12v searchlights, which I have not gotten around to doing, but it is in the works. Heli's run a constant engine speed during most flight maneovers, however since airplanes do not and I have never had a plane, I guess I'd also stick with about a 14 volt motor output (regulator input) at max RPM Example- 800 RPM/V brushless, at 12k RPM max anticipated engine speed =15V at max engine speed. Take about 1 volt off for inefficiencies in the 3 bridge rectifier, now you have 14v coming into the regulator at 12k RPM. That is the best my 6:00AM math can do :)

This sort of resistance (non-switching type) regulator will turn excess voltage into heat, i.e. if thru improper motor selection you feed it 25 volts and expect 5.3 volts out it will convert a lot of energy into heat and be a not so fuel efficient regulation setup but it will work with light current loads. If however you pick the wrong brushless motor and set it up to deliver 9 volts at max engine RPM, at half RPM you will get 4.5 volts into the regulator, and the regulator cannot increase the voltage, only reduce it, so it will not charge or deliver power until the voltage coming into the regulator is about 2 volts over the expected 5.3 volts. So by picking a brushless motor that delivers about 14 volts at max RPM you manage heat, efficiency, and the ability to deliver electrical engergy over much of the powerband of the engine.

Hope that helps.

[Disciple4123]

One additional reference, for those who wish to purchase an alternator, I do not make them to sell, but I know a guy who does. He is Raja, a frequent poster on the Runryder forum, his site for alternators is here...

http://mysite.verizon.net/vze49gsg/index.html

They are designed for helis, but a little creativity can likely get one mounted on a plane as well if needed. I have not gotten to see his product, but all posts on Runryder seem positive about his alternators.

[Hovertime]

I developed a helicopter start shaft alternator in 2004, works very nicely. See here for the details: www.aerialphotographyservices.com/alternator (http://www.aerialphotographyservices.com/alternator)

My current heli runs an alternator off the main gear, same concept.

Sound familiar kd7ost??
Oh, this was exactly what I was looking for! A DIY guide!
Thank you for sharing :cool: