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: Sat, 14 Sep 2002 03:40:58 GMT
NNTP-Posting-Date: Fri, 13 Sep 2002 23:40:58 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.
Oops. Better include a bypass capacitor across the 12 volt source to
reduce spikes generated by the switching. Wouldn't want to blow a