>Hi Bob
>Thx. for the reply.
>">>Curiosity question, according to B+C a SD20S alternator turning when
> >>hot at 2500RPM it will produce 24 amps at 14V, how much approximate
> >>loss will there be using a LR3C regulator? How much approx. loss
> >>using a switcher?
> >>
> >>Same question for SD20S at 2000RPM, 15 amp output at 14V?"
>
>" "> No difference. The regulator's influence on max current
> > available is minimal. The alternators driven from a
> > vacuum pump pad are RPM limited. > " "
>
>I may not understand what you said, or I find what I think you said
>hard to believe. Are you saying that a LR3C creates no loss what so
>ever off the listed output of a SD20S on B+Cs spec sheet? Are you
>saying that a switcher is not more efficient than a linear
>regulator? I was hoping perhaps someone had actual measured losses.
>B+C never measured a switcher, but thinks perhaps LR3C will incur a
>1.5 amp loss (the more amps, the more loss) not more than 2 amps in
>my scenario.
Not sure what you're calling "losses". The controlling
device in a plain-vanilla duty-cycle controlled regulator does
not get as hot as the linear device. However, just because a
linear tosses off heat (maximum when the field voltage is
1/2 of bus voltage) doesn't mean that there's more energy
available from the alternator.
Minimum speed for regulation, minimum speed for full output
and maximum output are measured under conditions that the
regulator is turned on max-hard. In both styles this is
100% duty cycle output with the field voltage being only
a tad below bus voltage.
The drop in a max-on linear vs. a max-on switching
regulators might be a bit different . . . but both
are on the order of 1 volt. In a belt driven alternator
running nearly 10,000 rpm, this is an insignificant
drop that does not limit the alternator's ability
to deliver max rated power.
When you're RPM limited, then it MAY be that one
regulator may produce a tad more output. You'd
have to do a side-by-side bench test or have
access to the alternator's transfer function curves
for the RPM of interest.
In any case, the differences are small and mostly
academic . . . if ones successful termination of
flight in the endurance mode hinges on the availability
of just a tad more alternator output, the load
analysis for that condition needs to be re-evaluated.
Keep in mind too that field current supplied through
the regulator comes from the bus and is probably
on the order of 2.5 amps. This is PART of your running
load. So energy available to run the elecro-whizzies
is taxed by the value of field supply current.
For internally regulated alternators, rated output
is over and above field supply requirements. But
for the SD-20 in an RPM limited mode, the field
current comes off the top of what ever the total
output of the alternator happens to be. A switching
regulator of any style cannot improve upon that.