Building a poor boy generator! Part 1

When asked (do tell), I tried to figure the best way to approach the topic of building a one off 12 or 24 volt DC generator. I could just show detailed plans, but alas, I don't work that way.

So settle in for a very short mini series, with enough information to understand why I went the route I did.

A little history!

The auto industry introduced alternators in 1960, Chrysler to be specific. Like all manufacturers of the day voltage was controlled using a mechanical regulator. This regulator was a simple chopper circuit using one or more relays.
Though it worked, the generator output was very noisy.

Within a few years of that time transistors became large enough that the auto industry introduced solid state regulators. That was a tremendous leap forward for reliability, however to maintain reliability, the chopper circuit was still the method of choice.

It has been 60 plus years, and still no move has been made to change this method of control. This is important in this discussion because dirty power supplies destroy electronics!!!

 

[Kevin D Pem]

Part 2

The auto industry alternator!
Is a high frequency 3 phase alternator. This offers a lightweight unit using less materials to produce high output! The downside is that it is harder to keep it cool when heavily loaded.

Before inverters became widely used, you could switch off the regulator, and disconnect the car from the output and run many AC/DC tools by bringing the output up to 115 volts by increasing RPM.
Many people used them that way. Although we don't know the voltage limits of the diodes in modern alternators, people have used them with oem diodes to charge 48volt off grid systems.

For this discussion, armed with the knowledge the diode will handle 48volts, I built my poor boy to charge a 24volt system(it is more common to find diodes with ratings in the 200 volt range and above than on the lower ranges)!

The numbers:

60 amp alternator at 24volts is 1440 watts a little over 2 hp. My predator 3.5 hp engine is under utilized! This is not of concern as my 8000btu ac claims 500 watts. Even at 12vdc it will service the ac.

On to the regulator!

Armed with the above information, a larger motor, simply wastes fuel.

This system will not offer 3 stage charging! It will allow hours of ac operation without deleting the battery's stored power, at a gas sipping rate.

 

[Kevin D Pem]

Part 3.

As stated in the introduction! The regulator scheme introduce spikes and pulses that are hard to filter out, not impossible just hard.
A three phase machine offers radiused peaks that after the rectifier are quite easily smoothed with a simple capacitor. Make it high frequency and it becomes a cake walk.

So where is the problem then? Switching the field transfer the pattern to the output of the generator. The dilemma is one must still control the magnetic force of the field, to control the voltage output on a variable rpm machine!

The secret is in modern electronics! This device will not control or correct for change in demand but that was taken care of by the engine! By installing a DC to DC converter as the regulator and adjusting to obtain the desired system voltage, we get a very clean output!!!

DROK DC Buck Converter CNC, 10V-100V to 0V-60V, DC to DC 12V 24V 36V 48V 12A 720W Adjustable Power Supply Voltage Regulator Module Amazon.com

The load on the engine is controlled via the built-in governor!!!

On to the wrap!

 

[Kevin D Pem]

Part 4

The wrap

I have installed two DC converters, one for 12v the other for 24volts. A dpdt center off switch gives me the option of what system I use the generator with. I still plan on an arduino project with proximity detector to turn the field power off when the fuel runs out. That will under utilize the arduino nano I plan on using, but it's easier than building a dedicated circuit, unless someone has a better solution.

 

[Rollin Ollen]

Part 4

The wrap

I have installed two DC converters, one for 12v the other for 24volts. A dpdt center off switch gives me the option of what system I use the generator with. I still plan on an arduino project with proximity detector to turn the field power off when the fuel runs out. That will under utilize the arduino nano I plan on using, but it's easier than building a dedicated circuit, unless someone has a better solution.


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Well done....I think. Some of this info went over my head but if it works for you. Awesome!! I might look you up this winter to see how it works. I hate using my noisy Cummins Onan 4000 when I need to use AC. For almost everything else my little solar plant works well.

Darrell

 

[TheLooks]

Great tutorial Kevin! This type of seat of the pants engineering is so underrated and a lost art to many. I was able to follow what you have done, but I cant do arduino. But my brother codes in 32 languages and fills in the gaps where I an weak. You exceed me easily in circuitry . I have no classic training in that area and have just dabbled at the edges. Now that I am over 60 and looking back I realize my calling was in electrical theory or engineering....to late!

 

[Kevin D Pem]

Great tutorial Kevin! This type of seat of the pants engineering is so underrated and a lost art to many. I was able to follow what you have done, but I cant do arduino. But my brother codes in 32 languages and fills in the gaps where I an weak. You exceed me easily in circuitry . I have no classic training in that area and have just dabbled at the edges. Now that I am over 60 and looking back I realize my calling was in electrical theory or engineering....to late!

So the arduino IDE has a dumbed down "C" language. All the declarations are done for you, kind of like basic. Because it is open source, many post programs they have done online. I simply find something that I think will work and modify to fit. Sparks has add ons for arduino, so It is mostly plug and play! A wonderful opportunity, I must say!!!


As I recall, I was pushing 60 when I got my first arduino. I was 45 when I started using the internet. And formal education? What is that? does it really work??? Over 70 and still learning!!! No formal education along the way!!!

My brother thinks if I ask him for help I am just picking his brain!

All in all, this project has developed over the years. And though I have been in many circumstances where I had opportunity to expand, many of my projects are an exercise of on the job training. I spend more hours learning than I spend on the project, and encourage the people I know to do the same! I may settle for it works, but I keep looking for a solution.

 

[TheLooks]

We are very similar, but I am less cryptic....lol.