Diode Pump

[tanner0441]

Hi

I have a 6ft system that sits for hours at 7 to 8 volts. In fact I don't think it has ever hit 12v let alone enough to charge.

I have some big diodes, and I remember some years ago building a unit on a 6V ex gov  genset it did 6V AC at 10A I think it was a GPO bell ringing current generator. It fed a transformer that stepped it up to 50 V. Didn't manage to get the transformer so with the help of a couple of friends and a few diodes and capacitors we got it to just over 12V at about 3 or 4A. enough to charge a 12V battery for portable HAM Radio equipment.

I have the diodes but can't remember the formular for calculating the caps. can anyone help?

(Don't sugest building a low RPM unit can't justify the expense of that)

Brian

[vawtman]

Hi Brian

 Do you have any pics of the construction?Always a good thing.Are you still trying to run a car alternator from a 6ft turbine(system?)?If so maybe the expense would be justified. Just my opinion.

Mark

[tanner0441]

Hi Mark

Car alternators...... First after reading lots of postings on this site, and having had a few ideas shot down in flames, also on this site. I realised early on I was never going to produce enough power from wind, especialy after watching a fluffy dandilion seed drift through the blades of my mill then reverse and drift back through them the other way while they were still turning.

So I decided to just experiment with what I had, I tried several unmodified alternators and generators, waste of time, then I re-wound a couple and the one I am using at the moment will produce over 100 watts at 700 RPM. 3Ph Star. All my testing is done into resistive loads. Batteries change their conditions as they charge. Bulbs and heating elements are fairly stable.  I have a shed load of different blades 2 and 3 blade sets, plastic pipe and wood.

I have 6 curved magnets out of a Mercury Marine starter when I get another 6 I will make a PM rotor. I have a large south facing roof area so as funds allow I will go down the solar way, it is easier to upgrade than wind, but meanwhile I get a lot of pleasure out of playing around with wind devices, for a start you can see it doing something, (or not in my case).

So that is why I come up with some daft ideas, I think 10% of the power for 100% of the time is better than 100% of the power 10% of the time.

Brian.

[Flux]

If you have gone as far as converting and rewinding these car alternators I don't see why you are trying to play with a voltage doubler that is not going anywhere.

I suspect your basic problem is no wind and there is no cure for that.

I also have doubts about your interpretation of measuring power into resistive loads.

If you have an alternator that will produce 100W into a battery at 700 rpm you should be close to managing something. If you had rewound it with more turns then it would have started producing at a lower speed. Not sure of blade sizes you are using or what cut in speed you actually have into a battery.

If your trouble is lack of wind then boosting your 6v to 12v will bring you to cut in but you may still not have sufficient power to do any useful charging. If the only trouble is low volts then rewinding with more turns of thinner wire is the way to go.

Try charging a 6 v battery and if you can get several amps then you will do some good if you rewind. If the thing just brings the speed down and the current is tiny then you have no wind or unsuitable blades.

You can easily get up to about 500rpm with fast well built 5ft blades in less than 10 mph. If your alternator genuinely produces 100W into a battery ( not a resistive load) at 700 rpm. with it's inherent low efficiency it ought to be cutting in at 12v at 500 rpm or below. I suppose there comes a time when small fast blades will not start a pm converted car alternator against eddy drag in a sensible wind but I would have expected a 5ft prop to start in speeds where you are producing enough to supply the iron loss.

For a very low wind area rewinding for a lower cut in of about 350 rpm and using a fast 6ft prop  you should be able to get something useful in winds over 10 mph.

If you want to try boosting the present alternator then I think you need to go to electronics rather than voltage doublers. They need monster capacitors and with 3 phase you are struggling to do anything better than half wave.

A mixed bridge boost converter would be infinitely better but is not likely to be an option without some electronic skills.

Flux

[Bruce S]

Brian;

   The math for this can get complicated quickly.

Reason being is that the Cap size needs to be determined for both voltage and Frequency.

For a simple voltage doubler that uses diodes, then the simple circuit found in some of the diaries will work, merely use diodes that are rated for the current you're working with.

The caps that are normally used in things like diode charge pumps and such, you'll need to select them according to both frequency and voltage, BUT the voltage after each doubled stage is not linear.

Going from 6Vac to 12Vac would need to use probably a Cap rated for 25V just to be safe.

Since you have the Diodes, why not go with the simpler diode voltage doubler? will make life easier and much easier for each phase.

Cheers

Bruce S

Also, since you have 6Vac you could wind a stepup transformer.:-)

[tanner0441]

Hi

I don't fancy winding a 3 phase transformer to handle the frequency range that would be covered.  As Flux said I don't have the wind, I just enjoy fidling with things mechanical.  I have however learned a lot about blades, and the outcome is not always what you expect. I have sets in wood and plastic pipe, that will spin up in less than 2MPH and with sufficient torque to overcome the cogging on an Amtek motor. I have a 3ft set on the Amtek that works fine when I have wind but that is not too often.

Thanks for the sugestion though.

Brian