and back up in November
FOR CONSTRUCTION CLICK HERE
BLADE DIAMETER 5 metres / 16 feet
POWER 4000 watts at 220 rpm
28 magnets per rotor 46x30x10 mm ND40
(later rebuilt using 70x30x10 mm ND40)
Here we use a steel plate that bolts onto the end of the wheel hub where the half shaft flange would normally bolt to. (You can see this better in pictures down below.) Alan is positioning the blades above the spike so we can balance them. A chainhoist is ideal because even if he could stand up (which he can't do much of due to his multiple sclerosis) he would not easily be able to hold it comfortably. The steel plate bolted to the blades is 1/2" thick. Alan likes thick plates.
The spike is a broken drill bit ,tapered to a point with a grinder, and fitted into a chuck. The chuck sits through a hole in the bench.
We drilled a small hole at the exact centre of the ring of mounting holes in the steel plate and we rest the spike in the centre of the hole so as to make a pivot.
THIS IS A NEW FORMAT I AM TRYING OUT.
|Jonah and Rissa arrive to join the fun.|
|Here you can see the spirit level we used. We hold it so that the bubble sits in the middle and then let go and see which way it falls. On the left you can see some sheet lead (flashing) that I screwed on to balance the blades. In the end it would poise level without any tendency to fall one way rather than another.|
|Fitting the front rotor. Notice how Alan and Jonah hold the rotor by the jacking screws and keep their fingers out of the gap. If it tilts sideways and the rotor bangs onto the stator you don't want your fingers in there. If you are careful you can keep it straight.|
|Ready to roll. Notice the small balancing weight on the magnet rotor (and the ten o'clock position).|
|Using the chain hoist to transfer the alternator onto the frame of the windmill.|
|You can see Alan's windmill in the background. This one is for his son Martin. When one is out of action they can charge the batteries in both houses off the other one, because the electrical systems are the same.|
|This windmill now has a disk brake. It's a lot more
the band brake we used on the truck wheel alternators. Look at
the levers and adjusters.
It's a great feature to have a mechanical brake. We could probably use a short circuit, but these blades have a huge torque. And we want to be able to stop it even if the wires come disconnected.
|We had to beef up the main brake lever to 1/2" plate after
trials bent the first one. Jonah had to make the hole in the backplate
bigger to fit the new lever.
The Danish guy in the background was very puzzled. He told me later "What you were doing today was engineering - but you are not engineers!"
He just could not get it.
|An end-view of the big blades. They are not solid wood. That would weigh a ton. They are made from plywood with a central spar.|
|On its way up...
The chain is the low end stop for the tail. It all works with heavy chains and pieces of steel plate.
|Jonah cranks the hoist. It's hard work. My turn next.|
|Up and running at last.
See below for further comments.
HERE IS THE ORIGINAL ALTERNATOR WE BUILT FOR THE MACHINE
BUT IT GOT DESTROYED WHEN A BLADE CAME OFF EARLY ON.
I WON'T SAY WHO MADE THAT BLADE :-)
NOTICE THE BAND BRAKE ON THE OUTSIDE OF THE WHEEL. VERY
AND HERE IS A DIAGRAM OF THE ELECTRICAL SYSTEM THAT CONVERTS THE OUTPUT INTO HEAT AND BATTERY POWER.
MCB MEANS 'MINIATURE CIRCUIT BREAKER' RYVITA MEANS CONTROL CIRCUIT.
THE BATTERY CHARGER IS CONTROLLED BY A BATTERY VOLTAGE SENSOR THAT TURNS IT ON OR DIVERTS TO ANOTHER HEATER IF IT GETS TOO HIGH.
The stator puts out about 1 volt rms for each rpm of speed. this translates into about 1.4 volts DC. So at 200 rpm you can get about 280 volts DC open circuit.
In reality it is loaded so the voltage is lower. The battery charging transformers are set up so that it starts to charge batteries at about 70 rpm. The first ryvita heater cuts in soon after but the others wait until the DC voltage is up a bit higher. By this time the battery charger is going strong and the 24 volt heater in series with the battery is hot.
Frequency is related to rpm, so I measure the blade speed using Hz. 60 rpm is one rev per second is 14 Hz (28 magnet poles give 14 cycles every revolution). At 63 Hz or 270 rpm I read 16.9 amps rms which translates into 21 amps DC at 280 volts or 5,900 watts. My wattmeter reached 7 kW at one point. But I prefer if the average power is more like 4kW. I don't want to melt the stator.
Next alternator we build will be the same size but we'll use slightly larger magnets 70 x 30 x 10 mm, and this will greatly improve the efficiency and allow us to run slower (nice) and also get more power.
THE CONTROL SYSTEM HAD JUST BEEN ADJUSTED TO BRING THE SPEED DOWN AND AND CURRENT UP.
WE NEED TO REVERSE THIS AND MAKE THE TAIL FURL SOONER - BOTH EASY TO DO.
IN THE LONGER TERM WE SHALL ADD MORE MAGNETS. I AM CONSIDERING
DOING A DOUBLE DECKER ARRANGEMENT ON ONE ROTOR TO GET A BIT MORE
BUT THE LONGER MAGNETS WILL BE A BETTER SOLUTION IN FUTURE.
We have to make this alternator more efficient.