12 to 24 volt conversion.. MORE

[J. Forster]

The problem of winding a transformer might be solved using a kludge of
three filament transformers.

First off, you'd need a pair of transformers capable of handling the
needed output power, with the 115 VAC windings connected back-to-back.
Thansformers roughly 115 VAC input and 24 VAC CT @ 10 A would be about
right. One 24 VAC winding would be used to the collectors of the inverter
transistors,m with the CT to +12 VDC. The other 24 VAC winding would be
used w/ a FW half bridge. This isolated 12 - 15 VDC would be stacked on
top of the battery.

The trick is to use a smaller filament transformer, something like 115 VAC
to 6 VAC @ 1A as a feedback winding to ythe transistor bases. All three
115 VAC windings would be connected in parallel.

BTW, it'd likely be more efficient to build a stacking PS like this,
rather than inverting the full power for the load.

FWIW,
-John

==================



> There is quite a difference between 150 W  and 750 W class inverters. The
> former are pretty straight forward and can use cheap parts like 2N3055s,
> perhaps paralleled. The 750 W units will draw 70+ Amps @ 12 VDC and are a
> lot harder. Also, they will flatten a typical car battery in under an
> hour.
>
> As to magnetics, for silicon steel common in transformers, the rule of
> thumb is 400 W/lb at 60 Hz. so a half pound core will do. More at higher
> frequencies. It'd be easier to find an EI core in this size, rather than a
> torroid.
>
> For running mil radios, I doubt any regulation would be needed.
>
> FWIW,
> -John
>
> =============
>
>
> [snip]
>> Designing a DC-DC converter to deliver 10-30 amps at 24V is not an
>> exercise
>> for non engineers.  Hefty transistors and cores are needed, as well as
>> sophisticated regulator circuits.  Sure, you can copy something, but
>> even
>> that requires some pretty good test equipment and, of course, buying the
>> components that are modern enough to work well, like good FETs.  I have
>> a
>> little training and a lot of experience, some of which involved big
>> transistors turning red hot, and I wouldn't try doing all the magnetics
>> necessary to do this thing right! [snip]
>
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