Brushless Alternator Regulator

[BentRods]

Hi,
I was just messing around with a spare C50 series motor from Hacker,
the plan is to use this as an Alternator, I'm looking for 13.8V @ ~100 Watts
maximum . I'll do some more tests with various loads to see how HOT this motor gets.

Obviously varying the RPM's will control the Volts but has anyone utilised a way to regulate the the Voltage output as the RPM's vary so as to obtain a stable output ?

I was thinking of 2 options, a Voltage Regulator like the kind thats in a Motorcycle (Zener Diode) or perhaps just a linear V Reg like the LM7812 with a few Pass transistors (2N3055) to carry the extra current.

any thoughts
Regards

Thomas

[TMetalMan]

I don't claim to be an expert, but my thoughts are that you would need a brushless ESC like that from a car that can use partial brake (shorting out) on the motor, and that has regenerative braking. Then from the input of the ESC (which in this case would be the output) you could use a switching buck/boost regulator to put out a steady voltage.

[XJet]

The simplest way would be to use a 3-phase rectifier setup and a switching or linear regulator to obtain a stable out put voltage.

Whether you get enough voltage depends on the RPMs and the KV rating of the motor.

If the engine is (say) 750KV, don't expect to get a volt out of it when you spin it at 750 RPMs, most will put out quite a bit less than the KV figure.

Another (more sophisticated and efficient) option is to use an SCR-based switching rectifier that not only rectifies but also regulates in one fell swoop. That'll take a bit more work though.

[Zlatko]

http://www.rcgroups.com/forums/search.php?searchid=10700248

[BentRods]

Thanks Gents
As expected the constants change for V/KRpm due to load, I knocked up a 3# Bridge Rectifier and so far it appears to be ok but 100 watts could be a little ambitious to start with for a continuous rating ..see how it goes.
The buck boost reg I was messing with are only good for around 3 amps are there any Home brew schematics lurking around for something in the order of 8 amps cont ?

Has anyone got a favorite Buck Boost Reg ?

I also think I may just stick with the linear Reg to begin with as parts are easy to get, however i do like the sound of the SCR switching reg .. I did see something a while back but kinda over looked it

appreciate the help

Thomas

[BentRods]

http://www.rcgroups.com/forums/search.php?searchid=10700248

that link not working :eek:

[Zlatko]

that link not working :eek:

Sorry,

On top right hand corner you will see a "Search" button, click on it and type
"Brushless Alternator" in Search Forums, then click on "Go" .

This subject has been discussed a few times already and the results will give you some more ideas.

Cheers

[AndyKunz]

You might also try googling for terms such as "3-Phase Rectifier" and reading app notes from TI, Microchip, IR, Micrel and others. The company I work for makes industrial size ones with efficiencies in the low 90%'s pretty easily. Of course, the best way to get efficiency is to start with a higher voltage (ie, a motor with a high KV).

Andy

[TommyBurger]

Andy, did you mean low Kv? Kv is RPM per volt so for a given rpm, lower Kv motor is higher voltage.

[AndyKunz]

Yes.

It's late here.

Andy

[BentRods]

Thanks for the replies,
I found a few good links from previous post appears to be that the good ol LM317 is popular I'm sure there are better ways.

Btw has anyone spotted a circuit for the SCR Switching Reg for this application ..still gooooogle'n .

my testing is quick and dirty and i'll need to rig it up a little better for a longer duration test... and see how warm it all gets.

Alternator RPM = 17780
13.8V@7.2A = 100watts

1288 krpm/V

gotta be happy with that

Thomas

[AndyKunz]

An SCR isn't a very efficient way to do it, but it works. Look into FET-based rectifier designs.

Andy

[BentRods]

cool, so what do you guys consider an efficient way to to regulate this, lets consider 2 options here...

1-simplicity and reliability
2-the ultimate setup when it comes to efficiency

my no 1 choice so far is the LM317 or 7812 with a pass transistor looks like a simple approach.

Thomas