Model generator build from scratch

[darwenguy]

Next to copper, aluminum is about the worst stuff that you can use for efficiency. Just consider that magnetic brakes are, essentially, magnets held up to a good conductor that's moving. Back irons behind the magnets and the coils will significantly increase efficiency, and far more so if you use laminations that are electrically isolated from one another (the traditional thing to do is use varnish -- just about any paint-like material will work).

Personally, if I could find a sheet of magnet iron and I had a laser printer (or a friend with one) I'd cut out a stack of laminations from that, varnish them, and stack them.

Alternately, I've always wanted to try getting hunks of ferrite, and having them laser- or water-cut to shape.

If you don't want to mess with back iron, consider making the whole thing out of bakelite, or some other non-conductive material.

Thanks i understand the need for iron cores and stator housing to make an efficient generator. Im not worried about efficency at all i just want it to look nice and make a few volts from a little steam engine. I mentiond it will be more like the diy wind generator type that use no iron at all if possible. If its usless then il add iron coil cores then iron rotor and and so on untill i get somthing working
Il have to find a link to a thread on here to explain what im aiming for. Again if the alloy housing causes that much loss il cast it in iron also.
First thing i need to do is make the coils and figure out the wiring setup that is the biggest task in my view the rest is all casting and maching the fun bit.

 

[darwenguy]

This is the sort of thing im aiming for but a little smaller. see this thread by Manfred, i love the look of his model
https://www.homemodelenginemachinist.com/threads/dynamo-build-by-castings.17756/

 

[Tim Wescott]

With 12 coils and 16 magnetic poles, what frequency would result by spinning it at 1000 RPM?

You should get one cycle per pair of magnetic poles per revolution. So, (16 / 2) * 1000 RPM * / (RPM / 60Hz) = 133Hz. More faster is more better, though.

 

[Tim Wescott]

If you don't want to mess with back iron, consider making the whole thing out of bakelite, or some other non-conductive material.

I know you're probably not going to go there, but I had a thought.

I just realized that if you wrap some varnished iron wire around a form and bake it into shape somehow, you'll get the magnetic conductivity you need while breaking up the available path for eddy currents.

Assuming I could find really soft iron wire (physically soft usually means magnetically soft) I'd even try varnishing it myself, then wet it with epoxy and wind it up.

Alternatively, get the highest permeability iron-powder toroid cores you can find (amateur radio folks use them). I know from experience that these will machine, although they're probably abrasive as all get out. Use these for your back iron.

Or a ferrite core, if you can find a pair with pleasing shapes. It looks like there's some sorta-OK ones from Fair-Rite (Amidon site shown, but they just resell Fair-Rite stuff. This one's too small by a mile, but you could dredge through all that's available: FT-114A-67).

 

[Chiptosser]

Tim
What is magnet Iron?? Bakelite, don't know of anybody making that.
Are you talking abut phenolic material?

 

[Tim Wescott]

I should have said phenolic. You can get rods of bakelite, from artsy types if nothing else, but phenolic-linen would have better mechanical properties. (It's actually a fun web search -- there's a lot of interesting phenolic plastics out there. If I had a project that needed artsy knobs & levers, I'd have a collection of Bakelite rods to make them from).

Magnet iron is steel that's alloyed with silicon instead of carbon.

Steel that's hardened with carbon is both mechanically and magnetically hard. Magnetic hardness means that the steel will become a permanent magnet. It takes energy to coerce a hunk of steel into a magnet, so a magnetically hard steel causes loss each time the field reverses. This causes drag (there's actually a kind of motor that uses this to good effect -- do a search on "hysteresis motor").

Steel that's hardened with silicon gets mechanically hardened but it's hardened magnetically to a much lower degree. It's on the market as "magnet steel" or "transformer steel". It's also hard to get in less than industrial quantities; you'd basically have to luck into it. Unlike carbon steel, silicon actually lowers the ultimate strength of the steel, so it's not nearly as good a structural material as carbon steel -- but it's a worthwhile trade for a transformer or a motor.

 

[jkimberln]

I have non-grain oriented electrical steel available. This is good for generators not for transformers. What I have is 0.014" thick and coated both sides for electrical insulation. I had to get this stuff for a small turbogenerator I am still in the process of building. This type of steel is hard to work with, machines like a pig and is better punched than processed any other way. I'm using a 1" x 1" diametrically magnetized rare earth magnet. The field coil is 4 pole and at 2600 rpm I'm getting 4.4 volts (I think) but have not measured the amps/watts.

 

[darwenguy]

I have non-grain oriented electrical steel available. This is good for generators not for transformers. What I have is 0.014" thick and coated both sides for electrical insulation. I had to get this stuff for a small turbogenerator I am still in the process of building. This type of steel is hard to work with, machines like a pig and is better punched than processed any other way. I'm using a 1" x 1" diametrically magnetized rare earth magnet. The field coil is 4 pole and at 2600 rpm I'm getting 4.4 volts (I think) but have not measured the amps/watts.

Im very interested to hear more about your turbo generator!
This is exactly somthing im also planning to make myself. I was just researching diametrical magnets last night and was looking at the same size magnets.
I have already made a small turbine running a small dc motor as dynamo and creates around 6v max. But i want to make a direct drive type to add onto my turbine and brushless is the way to go i think. Il add pic of my current little turbo gen set.
Regards luke.

 

[darwenguy]

Today i made a simple winding bobbin that splits and mounted on a shaft to hold in the lathe. The other parts are formers to press the coils into the correct radius for the housing.
The plan was to glue the coil a little while winding and then remove it from the bobbin. This didnt work out very well and without a counter i guess far too much wire was required to fill the coil.
Ive already designed and will print some permenant bobbins to wind the coils onto tomorow. Im still waiting on a counter to come so will make a more permenant coil winding rig in the mean time.

 

[Tim Wescott]

I'm trying to remember how I did this -- I think I put epoxy in the groove in my bobbin and then just wound the coil -- enough epoxy got squeezed out at each step that it glued the next layer down.

Obviously it was very messy, but it worked.

If you want to buy wire by the pound, you can get magnet wire that's coated with heat-sensitive glue. Wind your coil, bake at the right temperature, and the glue melts. Then you have a permanent coil that is, if you want, free-standing.

(Bobbins are easier).

Model airplane motors of the approximate size you're working with generate up to 20V at 10000 RPM with just ten or so turns of wire. But -- 10000 RPM.

 

[darwenguy]

I'm trying to remember how I did this -- I think I put epoxy in the groove in my bobbin and then just wound the coil -- enough epoxy got squeezed out at each step that it glued the next layer down.

Obviously it was very messy, but it worked.

If you want to buy wire by the pound, you can get magnet wire that's coated with heat-sensitive glue. Wind your coil, bake at the right temperature, and the glue melts. Then you have a permanent coil that is, if you want, free-standing.

(Bobbins are easier).

Model airplane motors of the approximate size you're working with generate up to 20V at 10000 RPM with just ten or so turns of wire. But -- 10000 RPM.

Thanks yes i think permenant bobins in the coils is the way i will go now. I thought about epoxy but doing one at a time or making lots of formers isnt viable i would like to eventualy make more than one of these so il spend time making the coiling setup.

 

[Richard Hed]

Im very interested to hear more about your turbo generator!
This is exactly somthing im also planning to make myself. I was just researching diametrical magnets last night and was looking at the same size magnets.
I have already made a small turbine running a small dc motor as dynamo and creates around 6v max. But i want to make a direct drive type to add onto my turbine and brushless is the way to go i think. Il add pic of my current little turbo gen set.
Regards luke.

That's totally beautiful. Can we see it run?

 

[darwenguy]

That's totally beautiful. Can we see it run?

Thanks i cant find any videos of mine, but if you search youtube for 'cringle turbine' you will see some made by some customers.

 

[SailplaneDriver]

With 12 coils and 16 magnetic poles, what frequency would result by spinning it at 1000 RPM?

Output frequency will be Number of Magnetic poles times RPM divided by 120. For a 16 pole machine running at 1000 RPM you will get 133 Hertz output.

 

[BaronJ]

Output frequency will be Number of Magnetic poles times RPM divided by 120. For a 16 pole machine running at 1000 RPM you will get 133 Hertz output.

I think you have a zero too many or you have missed a zero out !

 

[Steamchick]

I understood Bakelite was the first "plastic" - actually a thermo-setting resin, that is plastic until set. It is derived from a waste from refining coal to make coke: Coke manufacturing By-products include fuel gas right through to all the bituminous products that cover roads and waterproof roofs, etc. (If we didn't dump it on the roads we would have huge festering mountains of "oil waste" for environmentalists to complain about). Nowadays, oil refining produces thousands of different resins and plastics - most better than Bakelite. Beware when machining "Tufnol" types of materials (fibre reinforced resin): The fluff from organic fibres, dust from glass fibres, resin dust, etc. are all TOXIC. They clog the lungs, can get into the blood stream and can (in quantity) cause anything from irritation, sore throat, coughing, to bleeding lungs and emphysema. You REALLY don't want to risk it!
Read the Safety material/data-sheet for the type of material you select. WEAR A GOOD DUST MASK! - Especially when cleaning the machine afterwards. USE A VACUUM CLEANER WITH DISPOSABLE BAG.

 

[SailplaneDriver]

I think you have a zero too many or you have missed a zero out !

My answer is correct. Here is the formula from Alternating Current Machines by Puchstein, Lloyd and Conrad first published in 1936. This is the 1954 edition.

The output frequency is inversly proportional to the number of poles in a generator or alternator. Same for the RPM.
Now think of it pragmatically by what actual motors or generators you can find. Here is a Baldor motor table showing number of poles versus RPM for a fixed frequency. As the poles go up, the RPM decreases. For 60 Hz, the RPM will be 3600 for 2 poles, 1800 for 4 poles, 1200 for 6 poles etc. Similarly for 50 Hz, 3000, 2000, 1000. For 16 poles at 50 Hz the base machine speed would be 375 RPM. We are running the machine 2.67 times as fast at 1000 rpm which means the frequency will be 375 times 2.67 or 1000 Hz.

 

[BaronJ]

My answer is correct. Here is the formula from Alternating Current Machines by Puchstein, Lloyd and Conrad first published in 1936. This is the 1954 edition.

View attachment 123541

The output frequency is inversly proportional to the number of poles in a generator or alternator. Same for the RPM.
Now think of it pragmatically by what actual motors or generators you can find. Here is a Baldor motor table showing number of poles versus RPM for a fixed frequency. As the poles go up, the RPM decreases. For 60 Hz, the RPM will be 3600 for 2 poles, 1800 for 4 poles, 1200 for 6 poles etc. Similarly for 50 Hz, 3000, 2000, 1000. For 16 poles at 50 Hz the base machine speed would be 375 RPM. We are running the machine 2.67 times as fast at 1000 rpm which means the frequency will be 375 times 2.67 or 1000 Hz.

View attachment 123542

Sorry !
Don't worry about it ! My error, I've got too many zeros, dammed fat fingers, I'll just blame the calculator...

Anyway interesting reading, thanks !

 

[darwenguy]

Today i spent more time figuring out the coil manufacturing, i think ive got a good sytem now. The coil bobbin is clamped onto the former and clear epoxy was added during the winding, clear film was used to stop it sticking to the former. I then got a neat solid coil when the epoxy set. Although this method works its very messy and time consuming. So im makeing a set of 12 formers lined with teflon tape and use maybe clear nail polish lacker then at least i can do a set of 12 in a day.
I did a quick test with a single coil and a small led, and at 500 rpm it produces 0.7v at 1000rpm it produces 1.7v.
I think il get what i need now with the voltage so im getting on with the pattern designs for the housing and will have somthing more interesting to show soon.
Some pics of carious stage of the latest coil winding and test setup.

 

[Rotormac]

My answer is correct. Here is the formula from Alternating Current Machines by Puchstein, Lloyd and Conrad first published in 1936. This is the 1954 edition.

View attachment 123541

The output frequency is inversly proportional to the number of poles in a generator or alternator. Same for the RPM.
Now think of it pragmatically by what actual motors or generators you can find. Here is a Baldor motor table showing number of poles versus RPM for a fixed frequency. As the poles go up, the RPM decreases. For 60 Hz, the RPM will be 3600 for 2 poles, 1800 for 4 poles, 1200 for 6 poles etc. Similarly for 50 Hz, 3000, 2000, 1000. For 16 poles at 50 Hz the base machine speed would be 375 RPM. We are running the machine 2.67 times as fast at 1000 rpm which means the frequency will be 375 times 2.67 or 1000 Hz.

View attachment 123542

Surely if a 16 pole motor @ 375RPM = 50Hz then the same motor @ 1000RPM = 50*1000/375 = 133.5Hz ?