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Author Topic: Simple generator  (Read 27533 times)

Offline broli

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Re: Simple generator
« Reply #15 on: April 28, 2014, 09:10:51 PM »
kEhYo77, that's really cool are you planning on building one too?

gyulasun, thanks for the suggestions. Currenlty I have settled with a silicon steel transformer, to be more precise this one:

http://www.conrad.be/ce/nl/product/514276/Universele-nettransformator----15-V----15-A----225-VA----elma-TT/SHOP_AREA_17430?

The holes make it easier to mount and allign in some sort of fixture. When I have the time I'll try to design a stator to hold 8-10 of these transformers and 3d print it :). The real challenge is building the rotor to be sturdy to avoid having the magnets bend the whole rotor and stick to the transformer when the airgap is small. Any collaboration is welcome :).

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Re: Simple generator
« Reply #15 on: April 28, 2014, 09:10:51 PM »

Offline kEhYo77

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Re: Simple generator
« Reply #16 on: April 28, 2014, 10:23:42 PM »
I have got enough transformers and a prime mover DC motor with the shaft extending from both ends so maybe I'll build one :)
Two rotors might be made from small weight lifting iron discs, They would serve as a flywheel and as magnetic flux linkage for those not used sides of the magnets.
I don't know when it is going to happen but the urge is there  8)

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Offline gyulasun

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Re: Simple generator
« Reply #17 on: May 02, 2014, 06:20:50 PM »
Hi Broli,

I had a look at the transformer you linked to at Conrad, it seems also okay to me (like the ferrite current transformers I proposed), the difference being in size and price.  Regarding the coils on the trafos, the only requirement may be to have as small copper DC resistance as possible, this calls for having coils of thick wire. 

I agree that there is a mechanical challenge in building robust rotor discs which are able to withstand any bending force coming from attraction. What kEhYo77 suggested (weight lifting iron discs) sounds good to me because those types of discs can be rigid enough indeed. When making such discs, radial ribs on their outside could enhance their rigidness. Perhaps making the discs with a bit higher OD than the stator would have with the transformers, you could place a few supports (distance keepers) between the discs at symmetrically opposite places.
First I thought that eddy currents in the iron discs could cause an unwanted loss but then I figured that the actual flux change via the iron discs must be small by default because the transformer cores insure a continuous quasi-closed magnetic circuit between the discs and their magnets all the way within the full circle. So the magnetic properties of iron material for the discs are not demanding, it seems.   

Gyula

Offline broli

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Re: Simple generator
« Reply #18 on: May 02, 2014, 08:07:47 PM »
The transformers arrived today. They have very flat sides which is a good thing when wanting the airgap to be as small as possible. They are rated at primary:230V, secondary:15V. This has the advantage to quickly swap between winding ratio and study the difference. In the pictures below you can see the orientation variants I'm thinking of.

Now for the more difficult job, designing the bracket to hold these in place. My new DLP 3d printer will arrive soon, so that will also help.
« Last Edit: May 03, 2014, 12:40:08 AM by broli »


Offline gotoluc

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Re: Simple generator
« Reply #19 on: May 03, 2014, 03:29:26 AM »
Thanks for your update broli

I'm very interested in your idea and still trying to understand why Lenz won't come into play in your generator design.

Looking forward to your tests and wishing you success.

Luc

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Re: Simple generator
« Reply #19 on: May 03, 2014, 03:29:26 AM »
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Offline broli

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Re: Simple generator
« Reply #20 on: May 03, 2014, 10:06:04 AM »
Thanks for the feedback Luc.

I did a resistance test across the thickness of these transformers and they all seem to be uninsulated across layers?
Resistance values are mostly low 0.6-5.0 ohm and show no indication of lamination coating. I'm kind of starting to get worried about eddy currents when the magnets start moving close to them.

Perhaps I should have went with ferrite cores from the start: http://www.ebay.com/itm/E71-Transformer-Core-Low-Loss-500mT-Power-Ferrite-x4-/181226270348

Offline gotoluc

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Re: Simple generator
« Reply #21 on: May 03, 2014, 05:10:01 PM »
Thanks for the feedback Luc.

I did a resistance test across the thickness of these transformers and they all seem to be uninsulated across layers?
Resistance values are mostly low 0.6-5.0 ohm and show no indication of lamination coating. I'm kind of starting to get worried about eddy currents when the magnets start moving close to them.

Perhaps I should have went with ferrite cores from the start: http://www.ebay.com/itm/E71-Transformer-Core-Low-Loss-500mT-Power-Ferrite-x4-/181226270348

Hi broli,

I think eddy currents will be less with ferrite. However, start with your steel lamination transformers since you have them as it should be good enough for proof of concept. If it works (no Lenz) and losses are mostly eddies, then you know what to do next.

Don't strive for perfection on the first test model as you'll never get it done. Proof of concept is all you need for now and those transformer should be fine.

All the best and looking forward to your results

Luc

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Re: Simple generator
« Reply #21 on: May 03, 2014, 05:10:01 PM »
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Offline gotoluc

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Re: Simple generator
« Reply #22 on: May 03, 2014, 08:16:26 PM »
Hi Broli,

I forgot to mention, it's normal to get conductivity between transformer lamination as some edges touch together. Many transformer laminations are even welded on the outside edges and between the I and E core to hold them together but that doesn't cause too much of eddy losses since the greatest area of a transformer surface is between lamination layers which represents probably more than 95% of the steel surface area and where the insulation is and effective.

Hope this makes sense?

Luc

Offline kEhYo77

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Re: Simple generator
« Reply #23 on: May 03, 2014, 09:28:02 PM »
Good point, Luc, about eddies.
You just want to keep the speed below 400Hz for a single transformer's core, Broli, and it should provide enough data.

Offline gyulasun

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Re: Simple generator
« Reply #24 on: May 03, 2014, 11:05:36 PM »
Hi Broli,

A simple test would be to run some of the transformers from the mains for a certain time with unloaded secondary coils and check the core temperature. Also, the idle current of the primary coil from the mains may also be relevant for the eddy loss (besides the DC coil resistance of course, you can measure the latter). I believe that these transformers would operate normally in this respect. Sometimes the through-hole bolts that fix the L brackets to the core can cause electric short between the laminations as they go through the lamination holes, a thin plastic sleeve (a tape layer) to cover the bolts remedies this if needed.

But perhaps swinging strong magnets above and below the cores in the directions as shown in your proposed generator setup may also be justified to check eddy losses, maybe this would cause a bit more eddy because the close and direct flux from the magnets would act stronger on the laminations than that of coming from the normal 230V excitation.  I believe that this would still remain reasonable, "bearable".      I agree with Luc's reasonings on the eddy issue.

However, I think Luc was curious to know the normal Lenz effect in such generator design :  when you load the output coils then how the load current may affect the prime mover of the rotor.

By the way, your arrangement shown in the second picture would be the preferred one I think because it insures a more continuous flux-closing for the rotor magnets (vs the setup with wider air gaps between the neighboring cores as shown in the 1st picture), this would result in a smaller overall flux change occuring in the rotor plates that hold the magnets. Small overall flux change in the rotor plates is desirable I think because it helps minimize eddy loss in the rotor iron material that hold the permanent magnets (especially if it is indeed made of weight-lifting iron discs hence they have a certain thickness).

Gyula

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Re: Simple generator
« Reply #24 on: May 03, 2014, 11:05:36 PM »
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Offline broli

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Re: Simple generator
« Reply #25 on: May 03, 2014, 11:20:44 PM »
I think that would be the case that makes most sense, that is to the transformer being conductive around its outside surfaces. However I'm still concerned about eddy currents as even being one laminate deep they can have a significant effect on the rotating magnets. However as Luc said, it's best to move on with these cores before considering another material/design.

Today I finished designing the rim that will hold these cores, I'm not fully sure on the specs of the 3d printer but if I'm lucky I can print it out in one piece.

Offline gyulasun

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Re: Simple generator
« Reply #26 on: May 03, 2014, 11:54:24 PM »
Hi Broli, 

Seems to me a good design!


Offline gotoluc

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Re: Simple generator
« Reply #27 on: May 04, 2014, 06:47:49 AM »
Wow broli!... excellent design

Looking forward to see this one

Luc



Offline gotoluc

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Re: Simple generator
« Reply #28 on: May 04, 2014, 06:50:53 AM »
I think Luc was curious to know the normal Lenz effect in such generator design :  when you load the output coils then how the load current may affect the prime mover of the rotor.

Gyula

Exactly... looking forward in seeing that result

Luc

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Offline broli

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Re: Simple generator
« Reply #29 on: May 04, 2014, 01:58:34 PM »
I would like to say that one of the Chinese suppliers gave me a quotation price today of 1318$ for the custom round stator core. This is a bit more reasonable than the 3500$ price from the other supplier. But in both cases the actual core is not that expensive, it's the stamping mold that jacks up the price, for instance the core alone costs 98$ while the mold is 1220$. So it's reasonable if you're looking into mass production but for prototyping it's a bit pricey. For now I'll leave the quote open untill I finish atleast one prototype based on the transformers.

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Re: Simple generator
« Reply #29 on: May 04, 2014, 01:58:34 PM »

 

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