Simple generator

[broli]

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

[gotoluc]

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

[gotoluc]

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

[kEhYo77]

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.

[gyulasun]

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