In article ,
Richard Harrison wrote:

Off topic, but you can`t power an antenna without power to the
transmitter.

I`m looking for a d-c to d-c converter that takes 28 volts on the input
and supplies 12 volts on the output. Up to 8 amperes may regularly be
drawn from the supply. That`s about 100 watts.

I need it now. That`s why I`m imposing on this group. There is no more
knowledgeable group to ask that I know of. I don`t have time to build
anything, though I`ve built such inverters and converters.

Check with Vicor (www.vicr.com). They make a whole range of DC-to-DC
converter modules.

Example: their V24B12C200B converter module takes 18-36 volts in, 12
volts out (programmable from 10% to 11% of this, so you could get 13.2
out), efficiency 85%, 200 watts output. Current limit is 17 amps
minimum, 19.2 amps typical.

They do have a 100-watt module, but I suspect you'd be running it
right at the ragged edge of its specs.

There are other manufacturers playing in this market space... Datel is
one.

A simple voltage divider or regulator is too lossy for high utilization.
I need lossless resistance.

You won't get 100% efficiency out of anything like this. 80-90% seems
to be achievable with commercial products.

I would like rugged, reliable, efficient, replaceable, and cheap.

I think you can get the first four if you look around.

The fifth is likely to be the hardest, if you want the first four.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!