Following on from previous topic I have decided to my finger out and get on with this project.

I know what I want to do, but not shure how to do it so it will be a bit of trial and error. Please feel free to comment as we go.

Thinking about making my own generator. Not to supply a house, just to do it from bits and pieces.

So I have secured the use of an old exercise bike and this old induction motor.



As you can see the motor has received some water damage.

When meggerd two of the winding were shorting so we have cut them out and are in the process of rewinding those two by hand

What's the motive force? Windmill? Water? Surely not the exercise bike!
That's a wierd motor. 36 poles! Whats it from ?
Why not use an ordinary car alternator; readily available and (I think) fairly efficient?

I’m no expert on this subject but my old mate Tom Foster in Bordeaux is. A car alternator looks good at first thought; robust, good power output and easily got from a breaker’s yard, but in practice the machine’s design rpm is far too high. At 4000-12000 rpm useful power band, you would need a gear train for a wind or leg powered generator. The ideal rpm, [ or ‘cadence’, if you want to talk the talk ], for a trusty average hairy Scottish-type leg is around 70 rpm. A typical 3-blade prop producing 500 watts in average wind-speeds would be about 9 feet diameter and run at around 400 rpm. There is a tip-speed ratio restraint on well-designed props; a factor allowing a broad power band and low stalling risks scenario. The tip speed of this prop is nearly 130 mph [Mach 0.18 ] at 400 rpm and it does not take much imagination to realise what will be the resulting noise levels of a tip running at the speed of sound! So again, a gearbox is necessary if using a car alternator. For the DIY man, finding any sort of gearing which is within cost bounds & weight limits, yet efficient is a daunting task. Direct drive is the best option with perhaps a simple belt and pulley arrangement with a VR of 3 or 4 being tolerable for a man powered device.

Ken, your 24-pole permanent magnet generator, modified from a washing machine looks ideal. This should start pumping out volts at very low speeds. As you are rewinding it, you can arrange the generator to produce 3 [ or 6 or even 12!] phase. This will give a flatter rectified wave that 1Ø.

If your project is to be wind powered, a good starting site is Hugh Piggot-Smith’s Homepage:

http://www.scoraigwind.com

[Hugh is a Scot BTW]

Loads of stuff on prop design, tip-speed ratios, high wind mill shutdown, generator stator winding, carving your own props etc..

Bon appetit!

Geoff I just counted and there are indeed 36 poles. Wow!!! You could run 3, 6, 9, 12 or 18 phase!

Goeff
It is a strange motor. It came from an LG "Direct drive" washing machine.
There has been a bit of discussion about this item in my topic "How to sell washing machines?" and because I am just starting out in these experiments I will initially be using leg power to drive it.

Allan
I have been looking at that web site before and got some ideas from it.
You have given me something to think about. I think using that motor is a bit adventurous for our first attempt.(might try it later though) So I am going to the scrap yard at the weekend to get a car alternator, and see how that goes to start with.
I have not measured it yet but given the circumference of the flywheel of the exercise bike, and the circumference of the driveshaft on the alternator. I should get more than 4:1 ratio.

Decided on the change so the team can see some positive results and keep them motivated in case things do not work too well in the future.

PS. I have ordered lots of laminated wire.

Here are both the exercise bikes I was given to use for this project.
(I get on well with the gymnasium staff)


We stripped the black one it was in poor condition. I intend to experiment with that one and keep the red one until we know what we are doing.

The turn ration on the black bike is something like 1:21 the final drive being the silver disk at the front.

Great Kenbo !
Excellent idea to try it out with the bike.

As Alan also sais the great thing of your 36 pole machine is the low speed required to get a reasonable output, to experiment with.

Most big hydro electric powerstations run at very low speeds, 75, 100, 120 RPM with large diameter multipole alternators.

Keeping yourself fit and generating some electricity to drive your stereo or a couple of lights is more fun then putting your energy in a friction system, to dissipate the excess power, to make the bike exercise a bigger workout.

This motor is exactly the same principle as the one I have.

The hardest part is to center the rotor around the stator if you are not using the washing machine assemble i have found out.
Exact line up of all components is critical here.

Keep your project going and keep us posted mate.

Kind regards, Raymond

Ken, I may be wrong but I think you will need to exite an ex-motor car alternator's stator windings with an external 12vdc supply on startup to get an output.

Hey, that's a project I'm interested in too!
Only my idea was to build a gas powered generator that gives 220-230V AC 50Hz.
Key problems I identified: find a suitable generator, match and control the running speed of the motor and generator, voltage and frequency regulation.

Ideally the result would be mounted to a heavy steel frame, painted green and have a bakelite control panel with analog volt and ampere meters and a few old-fashioned surface-mount receptacles.

TR
As this is the first time I have tried anything like this I have not set myself too many goals. I would be happy just to light the odd light bulb at this stage.

The site that Alan listed is excellent for a jump off point for me.

If you are so worried about voltage and frequency why not generate 12v DC and put it through an inverter. I have one in my workshop rated at 300w and use it with a motor bike battery to run some 40w lamps. Which is charged from a solar pannel.

12 / 240 volt 1.5Kw invertor

Alan
Just pulled out my old "Haynes" for the old sierra I used to have. (Loved that old car) In the wiring diagrams I could not see any feed into the alternator. Only the output is marked in the diagrams, (don’t mean you are not correct) but I will nip down to the breakers yard tomorrow

Ken, the car alternator terminals won’t show any “exiter” feeds, they’re part of the wiring loom and internal alternator diode circuit. The type of alternator fitted to cars is invariably the ‘rotor field’ type, because this alternator type’s output is easily controlled by varying the field current. Voltage regulation is built into the unit and modulates the small field current required, [say 2 amps], thus varying the output, which might be 60 amps or more. The rotor field is exited initially [ before the engine is started, normally ] by operation of the ignition key and through a ‘charge lamp’. When the engine starts, the alternator diode feeds such that it equalises volts across this lamp. This then ‘goes out’, [ although it’s probably is still running at a very small voltage], indicating that the alternator is charging.
Loss or failure to supply initial exitation current to the alternator means it won’t generate.
However if you are getting the parts from a breaker, it will be a simple matter to include an ignition lamp as part of the deal. Any 12v battery can supply the initial field current, say a cordless drill 12v ni-cad.

When wiring up the unit, follow Haynes’advice about terminal attachment - the alternator’s internal diode will not tolerate wrong polarity! Connect battery +ve first, negative last. Disconnect battery negative first, +ve last.

Finally, pedalling like fury, a human being is unlikely to generate more than about 150 watts. Bon courage!

This motor will generate allright because of the strong magnets in the outer rotor which will provide all, excitation and running current.

Most car alternator can be rewired to access the 6 power diodes and 3 excitation diodes.

I have a simple but reliable 12 Volts charging regulator circuit, which works with discreet components, can be build for a couple of $$.

I have trialled it in 3 different cars for over 10 years with no problems with this circuit.
In my old Falcon XY i put in a ducellier alternator with this cct when the old Email alternator failed because of a mechanical regulator faillure. (ok i talk old cars here).
In a Rover P5b i put it in with the original lucas alternator.
In a Renault 16 it worked with the Paris Rhone alternator.

This circuit can be mounted on the firewall somewhere, in a small insulated box with the heatsink for the 2N3055 on top.

https://i123.photobucket.com/albums/o298/RODALCO/DSC01723.jpg

12 V car regulator schema.

D2, D3, D4 are the internal excitation diodes already present in the alternator.

By separating the two wires from the field brushes from the internal regulator, these wires can be taken outside to connect to this cct.
Sometimes the brush holders are part of the complete regulator assembly, and you need to try out what to disconnect to make it work.
You can even leave the old regulator in the alternator and isolate its supply.

As I understand it, the excitation current of most car alternators is a flat 5A, and it takes a pretty high RPM to get any reasonable efficiency. And yeah, the Scoraig windpower site is as good a resource as any for that.

If a 12 Volt battery is flat, the excitation current may be up to 2 Amps for a short period, in general when the battery is 80% full, the current may be 1.5 Amps, but will taper off quickly to about 500 mA's when the voltage reaches 13.7 Volts, and even less when the battery is full.

Most car alternators have excitation diodes which are rated for 1 Amps continuously.
OK i Talk 40 -60 Amps alternators here.
If you have a 100 Amp alternator the initial excitation current will be more in the range of 3 - 4 Amps.

For certain wind applications when there is no wind for certain periods the 300-500 mA excitaion current may drain the battery bank, a method used is to pulse the excitation, via the exc lamp, on and off for 1 second, every 20 seconds or so. If there is enough wind the alternator will excite itself immideately and start charging the battery.

I have built over the years various 3Ø rotary batterychargers to quickly charge heavy batteries, to start diesel engines, and have done quite a bit of testing on excitation circuits, so i have a good idea of these exc current.

Kind regards, Raymond

Well, it's not exactly a precise plan, just a vague dream... frequency and voltage should be stable enough to run light bulbs (the smallest problem), angle grinder, rotary hammer and similar tools.
Creating DC and running it through an inverter sounds nice but unfortunately contradicts the part of my dream about doing everything with technology that was readily available 50 years ago...

As I said, it's a dream thing.

Limited success.
Got everything working this afternoon and it worked, but we could only get half a volt out of the alternator. 0.78 volts with some furious peddling.
Clearly we are not getting enough revolutions at the alternator. Still reasonably happy with that.
The guys are going to try using the induction motor as a generator next

.78 Volt into what kind of load? Open circuit?

Yep open circuit. Measured with digital voltmeter

Should I have put a small load on it?
I have some 3watt varible resistors.

Kenbo, you are trying the car alternator at the moment i understand ?

You need to excite the field winding via a 12 volts supply, through a 3 watt lamp otherwise nothing will happen. ( perhaps 0.78 Volts )

The stator windings of an alternator have not got enough remanent magnetism in them to create enough flux for self excitation.

At relatively low speeds you should be able to generate a couple of Ampères.

you could switch to a generator from an old volkwasgon or a tractor.

Hi, all.

I have done a quick voltage measurement with a small 12 pole motor i have, base on similar principle, with permanent magnet in outer rotor.

By turning the shaft by hand quickly, then taking the photo, at about 100RPM it generates over 8 volts ac.

The big washing machine motor should work very well, The problem here is to get a proper bearing to center the rotor. The washing machine bearing was impossible to remove from the machine (corrosion on the drum) and was left on site.

I use this in my workshop to quicky advance low voltage steppermotors in kWh counters to check if they advance correctly.

http://farm1.static.flickr.com/181/457283590_eff2827b23.jpg Tacho gen. Open

http://farm1.static.flickr.com/202/457283588_619a490103.jpg Tacho gen. 8.24 volts ac

Regards, Raymond