🚀 go-pugleaf

In article <C1It67.5E5@world.std.com> DPierce@world.std.com (Richard D Pierce) writes:
>
>It's now a trivial excercise to design and mass produce car audio
>electronics that have output amplifiers that run of supply rails that are
>much in excess of 12 volts. Try, for example, supply rails of +- 50 volts.
>Before we see how, let's see what this gets us. Assuming a couple of volts
>drop across the output fevices when they're fully conducting (a generous
>assumption but what the hey), that gives you a peak-to-peak output
>capability of +- 48volts, which translates, by your math (which I will
>accept as essentially correct) to an output power 143.9 watts into 8 ohms.
>I would hope that you agree that this is a bit more than the couple of
>what figures you came up with.

And it will deliver 288W into 4 ohm speakers, assuming it can handle
them.

>Poof! like magic, you have a perfectly realizable 150 watt amplifier
>running off a 12 volt car battery. (The downside, of course, is that when
>you realize the the switching converter runs probably 80% efficiency, and
>the am, if biased class AB runs at best about 43%, then we have to have
>about 420 watts running into the beast, which implies an input current at
>13.8 volts of about 30 amps. And there are people who drive vehicles with
>systems having capabilities in the multi-killowatt range, implying many
>hundreds of amps of current draw. Gulp!)

This is where I have trouble accepting the amps that deliver many hundreds
of watts of power.  I have no trouble accepting that it is possible to
pump hundreds of watts into normal 4 and 8 ohm speakers by stepping the
voltage up, I don't see how the car's electrical system can supply the
necessary current for any length of time more than a couple minutes.
I have plans for a stereo 300W/channel amp, and it gets that rating by
stepping up the supply to about 50 volts, and by using 4 ohm speakers.
When tested, it actually clips at about 290 WPC.  Now, assuming that
the amp and supply are 100% efficient, that would take over 48 amps
at 12 volts.  If you consider the 80% and 43% given above, that comes
to 140 amps at 12 volts.  Now you understand why people with these
kinds of amps run power cables directly to the battery, and the cables
are the same size as the battery cables.  Well, batteries can deliver
many hundreds of amps for short periods, but they must be recharged
by the alternator.  And the alternator in my car can put out only 60
amps, and a major portion of that goes to running the cars electrical
system, especialy when the lights are on.   What I am wondering is if
people with these amps have dead batteries all the time...

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Carl D. Smith                                       Inhale to the chief!
csmith@plains.nodak.edu