Sharing ideas on how to make a more efficent motor using Flyback (MODERATED)

[gyulasun]

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Any suggestions on how or what type of coil that might be (which core)?

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Hi itsu,

I think we need to think of coils which are mainly used in audio crossover circuits. However, the usual inductance involved is not higher than 5-10 mH and you need 38 mH. Here is a link to an air core inductor calculator designed mainly for crossover coils: http://www.colomar.com/Shavano/inductor_info.html 

And my suggestion to reduce a little the received mechanical sizes for a 38 mH coil is as follows: measure your present L1 coil without the core you have in it now and enter the air core mH value into the above link. From the results you can choose between some wire gauge and/or mechanical sizes.

Of course, there are other multilayer air cored coil calculators on the web like http://coil32.net/multi-layer-coil.html  and use your thick wire size you may have in the 0.9 to 1.3 mm gauge range to get the air core inductance referred to above, then you insert a  core to increase it to 38 mH or so.

All in all, your new coil will still have a little higher size (volume) than the present L1 coil has, preferably with a DC resistance of indeed around 1 Ohm.  For a core you could use the one from the 10 Ohm L1 coil or similar like there is in the choke coil, or lamination core of  I  shape.

Gyula

[itsu]

Gyula,

i have some  audio crossover air coils, but they are specified as 0.39mH, so i will see what happens if i put a core inside, else i have to try on somewhat lower inductance.

Itsu

[gyulasun]

Yes, there are as low value crossover coils as you wrote, and no amount of a rod type core would increase it up the 38 mH I am afraid.   
Even such coils like this would probably be too small initial values to insert a core:
http://www.ebay.com/itm/Air-Core-Cross-over-Inductor-1-5-mH-1-5-ohms-/381517136716?hash=item58d431834c:g:FOIAAOSwJkJWhrDU 

Well, perhaps with such bobbins http://tinyurl.com/gp7hhjg  you could make a suitable coil, depending on what wire size you happen to have and insert a core.
I know a low DC resistance high mH coil needs thick copper wire hence large size.

Gyula

[verpies]

I think we need to think of coils which are mainly used in audio crossover circuits. However, the usual inductance involved is not higher than 5-10 mH and you need 38 mH. Here is a link to an air core inductor calculator designed mainly for crossover coils: http://www.colomar.com/Shavano/inductor_info.html 

I like air coils, too, because they are devoid of hysteresis loss and are linear.
However, their small inductance would force pulse widths to be very short and consequently, the RPM of the rotor - very high.

I have a 840mH air coil with less than 0.001Ω resistance, but it requires LH & LN

To get this kind of of L/R ratio in a home-made coil, a thick wire and a high-perm core must be used, e.g. Nanoperm or Metglas.
Also, keeping the air gap to the minimum, helps a lot.  Using a silver wire allows to lower the DC resistance by 4% and a square wire allows to lower the DC resistance by additional 27%, but at higher frequencies, the Skin Effect and Proximity Effect do much much more damage to the effective resistance....so the Litz wire comes to the rescue.

It is important to remember, that when all things are being equal, doubling the number of turns, doubles the resistance but quadruples the inductance.

[gotoluc]

I have a 840mH air coil with less than 0.001Ω resistance, but it requires LH & LN

840mH on a air core of 0.001Ω    how is that acheived?  and what is LH & LN?

Thanks

Luc