Building your own generator

[jimmyhorns]

once i have mocked something up, if wood isnt up to the job, and you can work out how to isolate the two , you are on



;0

[PorscheBoy]

Ok, when you're ready.

Wood won't last unless you have some pressure treated timber. I am sure I can come up with some kind of non-porous isolation material.

Anyway, once your sorted we can discuss.

[jimmyhorns]

Measuring RPM

Well im now onto this conundrum....

I had thought about sensing the HT to the spark, but this is littered with noise, and not that straightforward for the arduino to sort out..

So, lying about after converting from nitro are a couple of crank rpm sensors... these are hall effect and give a logic 1 or 0 (albeit at 3V) with a state change....

Off comes the cover, and fortunately there are gaps in the flywheel at 12 and 6 o'clock, so this should be an easy way to sense

[PorscheBoy]

I think there is more science here than NASA used to launch the Apollo missions.......

[jimmyhorns]

I think there is more science here than NASA used to launch the Apollo missions.......

Yep, the arduino has about 10,000 times the processing power...

[cjcj1949]

The arduino is a development board/system. The chip that does the work is an ATMega 328. It's a microcontroller with analogue to digital convertors, counters, a comparator, voltage reference and digital input output. You can program it when it's in circuit as well. The arduino software and the extra interface boards (called shields) make it easy to interface with the real world. The BBCB used to do that but that was a few hundred pounds a long time ago. A working Atmega in one off costs under £4. Less if you go for the smaller chips and use its internal clock. It's all a bit frightening really, as the newer stuff is even better, not that most applications need anything better.

[Gixxer]

Why do you need to isolate the alternators? There should be no problem with them both using a common earth.

[jimmyhorns]

Why do you need to isolate the alternators? There should be no problem with them both using a common earth.

To get your 24V, using two 12V alternators and batteries, you need to connect the positive of one to the chassis or earth of the other. If you use a common earth as well you end up with a direct short across one of the batteries and alternators.

[Gixxer]

To get your 24V, using two 12V alternators and batteries, you need to connect the positive of one to the chassis or earth of the other. If you use a common earth as well you end up with a direct short across one of the batteries and alternators.

Ah, right, I thought you were just charging two 12V batteries. Why not just use a 24V alternator, surely it would be more efficient?

[jimmyhorns]

Ah, right, I thought you were just charging two 12V batteries. Why not just use a 24V alternator, surely it would be more efficient?

They are more difficult to get hold of, and generally more expensive.

They are also harder to turn, so if I have to bail out and go for a less powerful generator I have that option..


Plus..... the 'interesting' latvian car breaker did me a deal for the two alternators (matching pair) and car batteries for £40

[jimmyhorns]

Progress

Well, I managed to get a bit of a move on today and fitted the crank sensor to measure rpm via the arduino...

photo(48).JPGimage(7).jpg
image(5).jpgimage(6).jpg

Because there are what I assume to be holes drilled to balance the flywheel, im getting 12 changes in signal per revolution. I think the arduino can keep up with this, but im going to change the interupt programming so that it triggers on a rising pulse, rather than a change, which should cut me down to 6 triggers of the interupt on the arduino.

For those who are interested, but dont know about programming the arduino, its a pretty simple language to learn/write.

There is a main loop of program that runs over and over, but you can interrupt this and perform other tasks using interrupts, basically in this case, a logic 1 (high) applied to one of the interrupt pins. This allows it to work out rpm in the background without it having to 'wait' to receive a signal from the cranksensor, which would slow things down.

[jimmyhorns]

Well.... that didnt work.... initially....

The output from the sensor isnt anywhere near enough to trigger the interrupt on its own..... I tested the output voltage when it was hooked up to my AR7100R, and it was 3.5 which should have been plenty, but im only seeing 0.3V now... which must be something to do with the circuitry in the AR7100R..


So, back to my old friend the LM741 OP AMP. The plan being to saturate the output whenever anything more than 0V is present... my initial circuit didnt work, but a solution was found when testing outputs.... perhap xygax will be able to help here.... Anyway, end result, I now have 4.5V when not triggered, and 0V when triggered feeding into the arduino interrupt pin....

[jimmyhorns]

So here is the code for this program as an arduino sketch. It outputs the pulses it sees through the serial port back to the computer. Nothing fancy and no real rpm calculations yet, just a test of the sensor functioning reliably:

// sketch to test the function of the hall effect crank sensor
// reads crank sensor output as an interupt, adds this to a counter and then outputs it to the serial port


volatile unsigned long count = 0;
int lastcount = 0;




void setup()
{
Serial.begin(9600);
attachInterrupt(0, addcount, CHANGE);
}


void loop()
{
if (count != lastcount)
{
Serial.print(count);
Serial.println();
lastcount = count;
}

}


void addcount()
{
count++;
}

[jimmyhorns]

And here it is working

[cjcj1949]

The output from the sensor isnt anywhere near enough to trigger the interrupt on its own..... I tested the output voltage when it was hooked up to my AR7100R, and it was 3.5 which should have been plenty, but im only seeing 0.3V now... which must be something to do with the circuitry in the AR7100R..

It might be worth looking into this. Perhaps you have an open collector output that needs a resistor to 3.3V or 5V. There are resistors you can enable on the arduino, but they are too large. Some hysteresis on the op amp and a capacitor to 0V will help with noise immunity.