From: John Popelish
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Subject: Re: 12 vdc to 6vdc @ 30amps
References: <firstname.lastname@example.org> <3D8295F3.6B10E9CB@rica.net> <3D82A7ED.DDEE6E7C@rica.net>
Date: Sun, 15 Sep 2002 01:19:05 GMT
NNTP-Posting-Date: Sat, 14 Sep 2002 21:19:05 EDT
John Popelish wrote:
> Winfield Hill wrote:
> > John Popelish wrote...
> > >
> > > "Michael B. Williams" wrote:
> > >> I have a need to convert 12vdc to 6vdc from a motorcycle battery
> > >> to drive a electric motor which could pull up to 30 amps.
> > >
> > > I once made a very compact 12 to 6 volt converter to run a 6 volt
> > > trolling motor at half speed. I think it drew something like 10
> > > amps. The converter fit in a match box and consisted of 7 parts.
> > > It doesn't regulate, but it is very simple and rugged. I think a
> > > 30 amp version would fit in a 4 cubic inch volume. Interested?
> > That's simply a 50% PWM switch, right? perhaps with an LC filter?
> > Hmm, what about short-circuit protection, voltage soar policy, etc,
> > Thanks,
> > - Win
> No, it is just a self oscillating autotransformer DC to DC converter.
> It has no short circuit protection. A fuse should work, though.
> Here is what I had in mind. I switched from junction transistors to
> fets and reduced the parts count a bit.
> | | |
> A M A
> |. |. |
> | |
> +-\ /-+
> |D \ / |D
> -| / |-
> |-/ \-|
> -| |-
> |S |S
> (I picked parts from Digikey catalog)
> Where A is one of two schottky diodes in an I.R. 47CTQ020 (40 amp 20
> volt dual),
> M is the motor load,
> mmm+mmm is a toroidal core with a bifilar 14 ga. winding (as many
> turns as will fit) on a shield bead like a Panasonic KR16TT281815 28
> mm O.D., 18 mm I.D, 15 mm height,
> And the two Mosfets are IRF1010E, 60 volt, 0.012 ohm,
> The one I made with junction transistors was well over 90% efficient,
> and I think this might beat it.
> John Popelish
P.S. that twinned black and red speaker wire is pretty good for the
bifilar winding for this tapped saturating inductor. The insulation
takes up some room, but the wire is flexible and tough. You can also
take two large shield beads, side by side, and loop the wire through
the two holes to get more core cross section and protect the winding.