PMG Help please!

[windyknight]

Having built my pmg (350mm od, 24 neos, 9coils on massey fergy corn drill stub axle ) constructed blades (3x1.1m) and tail I decided simplest way to utilise power was to preheat house water.

I was getting 10v no load on each phase at 60 rpm  on bench and this has transferred to 60-70v before furling kicks in with a steady(ish) 30v at about 10m/s wind.

I ran a 4core 10mm cable 50mts to house and then ran each phase to a 240v 2kW immersion element.

The water would then flow `in series' past each element before arriving at mains hot tank.

My thinking (flawed as it turns out!) was that high resistance would help the starting in low wind - in that at low start speeds the low volts equals low current (ohms law) but as speed increases so do volts and hence current; so it would self regulate and never burn out elements.

Having spent my first gale with head in the airing cupboard I was gutted to find my temperature went up more than the water!

I decided that obviously resistance was too high and not taking enough power from wind so Plan B was to increase voltage (yes I know you can get 110v elements but they cost!) and as I already had some stepdown 240/110v transformers I decided to wire them `backwards', one per phase at base of tower thinking this would also minimise line losses. Hand spinning of rotor (which seemed easy with no cogging) gave me 40v so thought 150-180v quite possible....... but all that's happened is rotor now spins slower still giving 60v tops and most of the time is stalling and not even doing that!

Any suggestions for (cheap) solutions? Or must I make bigger blades or maybe put more blades on rotor.  

I have lots of 2mt lengths of 6x2 (150x50mm)- is there a NACA profile which would suit say a 4 or 5 bladed design using this wood without gluing bits together?

keith

[veewee77]

If you have that genny connected directly to the element, then it probably wo't start very well because it it loaded from the get-go.

It is harder to turn when it is loaded and if you put a resistive load across the unit,  it is loaded when it first starts.

That may be why it won't spin up like you think it should.  If you put it to charging a battery, the genny-produced voltage weould have to be as high as the battery before it starts to get loaded, meaning it will spin up to a "cut-in voltage".  There is no "cut-in" voltage on an resistive load.

Doug

[Flux]

If I have understood your blade size correctly, you are only going to get a few hundred watts in a gale and that is not going to do a lot of heating.

Heat is low grade energy, to make use of a small mill you need to use the limited power for high grade uses. If you want heat, think about 15ft dia or larger.

You will not get useful heat from a small machine in low winds, you might as well match it for high winds and switch the load on when the wind is great enough and perhaps charge batteries or something in the lower winds.

flux

[domwild]

As has been answered before, it won't start with the load on. One suggestion is to use a switch, which is constructed from a mercury or reed switch. This mercury switch is attached to a swinging piece of flat metal sitting at right angles to the wind. Once there is a strong wind, the flap will lift, the mercury will flow to connect the two leads and you can then switch all three phases at once to the load via a relay.

Gusts can be a problem. Imagine a dead prop and a gust, which does not last. The flap lifts and the load is on, dead prop again!

There are relays which take high AC voltage for the coil, so use one phase for the coil and let it switch all three phases. Hopefully the cut-in voltage of the relay is not too high, otherwise you miss out on heating while the prop spins without load.

Hope it helps.