This page must be accessed by typing in www.aerialphotographyservices.com/alternator , it does not link from the main business site, but will link to the main site with the buttons above.  It is a work in progress, actually info from a compilation of emails I have sent out to individuals asking me how to build an alternator, I will update it periodically, last update 09,2007. Another unlinked page concerning camera mount design is available at www.aerialphotographyservices.com/mount.

Below you will find a parts list and modification instructions to particular components. There are two ways to go about regulating the voltage from the motor.  First, if a brushless three phase motor is used (and that is the preferred power source), you will have to make or use a three bridge rectifier to convert that to DC voltage. I recommend the 26MT20 unit from Digikey, it is $16, one inch square, and both mechanically and electrically very robust.  After that conversion you will have unregulated +-13volt DC power.  The power must be cleaned up with capacitors and regulated to be useable.  My initial alternators used a variable resistance board regulator Kit #85 from Electrokits, and some heavy wiring leading to an external LM 338 voltage regulator chip.  This setup was acceptable, electrically it was an overkill and mechanically it was somewhat susceptible to broken wires.  Then I spent about a year using a regulator from Duralite that was all inclusive, and smaller, it is available as a custom item from Duralite batteries,.  This had been used in the Predator and was OK, but ran temperatures of about 110 deg. F. in 70 degree weather. I was not comfortable with it's heating in the hotter weather.  I had melted one down, and they were kind enough to replace it, the replacement looked a little different when I disassembled it, but was still too hot.  In 06-2006 I went back to my homemade regulator arrangement. This version was only twice the size of the Duralite, previous ones I made turned out to be about 5 times larger comparatively.  This unit uses JR type 20 gauge connectors rather than the molex's, and it uses the LM338 chip in the board with angle aluminum as a heat sink rather than externally with a production heat sink.  I have bench tested it with 13v coming in and constant servo movement and it reached about 95deg. in the hot areas, after flights it is cooler than that, so consider this to be the best choice. I also feel that JR type wire connectors and servo wire is less likely to break than larger wire.

I have gotten good service out of my homemade alternator systems and have had one occasion where a battery was ejected and a proper landing was made due to alternator support only.  They have been subjected to a lot of vibration and some unexpected landings since the first one was put in service in 11-2004.

Parts:
1) The power supply can be bought from Electrokits, part number 85, listed as an LM317 power supply. Modifications will have to be made, below are additional parts for it...

Parts from Digikey:
 

1) Scottky diode, 3 amp rating.
8)LM338T-ND - LM338 volt reg. 5 Amp rating (replaces 317 in kit)
9)26MT20-ND - encapsulated 25 amp 3 phase bridge
10)CT20P102-ND 1k ohm variable trimmer resistor. Alternate part # is Radioshack # 271-342.
11) get hex standoffs, usually 10mm threaded ones with M3 threads to mount the circuit board to whatever box you are using.
12) get an Axi 2212 brushless motor or equivalent with about 740-1100 RPM/V.
13) I currently use an MXL belt drive to drive the motor, see www.aerialphotographyservices.com/alternatormount for further (I no longer sell these mounts by the way)

The power supply board requires some modification to function and be robust in this application;

1) remove the LM317 power supply (3 leg module) from the kit and replace it with an LM338. The LM338 is a five amp equivalent and looks identical. It costs $2 from Digikey.

2) Remove the potentiometer from the kit and replace it with item #4 above, the 1k trimmer resistor. Trim one leg off and it will fit in the stock holes, after assembly power it up, put a small load and tune to about 5.3V.

4) Use the three phase encapsulated rectifier to allow your three phase motor to power the two phase voltage regulator created above.

5) remove the 4 pole 2 bridge rectifier that is included in the board, it will overheat and throw the solder off. You can replace it with wire to bridge the gap in the correct polarity, or a couple of higher rated diodes. I recommend two wire bridges since diode protection will take place externally at both ends of the reg.

6) Solder in JR type leads to the board directly, do not use their input-output hookup choices, they are inadequate.
 

Below is a schematic of the layout with an old Duralite regulator setup, using my currently recommended Kit #85 regulator does not change the layout much.

OLD, 2004--Below are thumbnails of the Bergen Intrepid EB with an alternator that delivers 5.3vdc regulated and 14vdc unregulated, inside the box is the rectifier in black (barely visible in last photo) and the modified circuit board to the left of it.  The box is a Radio shack plastic one, bolted to a u-channel in the frontend with some very firm rubber under the box for vibe isolation. This was one of the first alternator setups.

OLD, 2005--Below are some pictures of an alternator I have installed in a Century Predator, it operates on similar principles; except the regulator I used for a while was a Duralite model that is a lot smaller. I just recently put a kit #85 regulator in as the Duralite is not able to dissipate enough heat.  The generator shown is capable of delivering 500w, suitable for searchlights, etc.  The rightmost picture has a rectifier shown, that is the same model I have used since the beginning, it is far preferred over using six diodes and a board to make a rectifier.

OLD, 2005--Below are some pictures of the completed Predator in 11-2005, with the exception of the mounting of the alternator, voltage regulator is hidden under the battery tray near the front.  The rectifier is above the elevator servo.  The last photo shows a spare alternator installed.

Below are some pictures of the Predator in 06-2006, changes include: Belt driven large capacity alternator, homemade regulator instead of the Duralite.

OLD,2006--Below are pictures of an alternator mounted on a Venture 50 off the main gear.  The heli did not last long due to engine issues, but the alternator was fine, the mount is angle aluminum precisely drilled and cut.

Similar to current--Below are photos for the Vario Acrobatic alternator mount, belt driven inside the frames to the intermediate shaft. This item will be produced and sold as a kit, designed to fit Raja Bort's production alternator system.

Current setup 09, 2007--

Vario Acrobatic, using two regulators, left one powers 12v to the downlink (and navigation lights if I ever get to them), right puts out 5.3v to the rest of the electronics. 

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