[Mobile-Portable] 500 Watt Mobil Amp

[paul goble]

One should seldomly (if ever) transmit without the engine running.  Many
of the modern radios sound like manure or are virtually unintelligible
at "battery-only" voltages.  The spector of running the batteries down
so far that one couldn't start one's engine after long periods of
engine-off operation, therefore, shold be minimal at most. 
Additionally, power out of many solid state PAs also drops off
significantly from 13.8 Volts to 12.6 (at best, engine-off) Volts.

If you're THAT worried about drawing your batteries down, carry one of
those "cold start" emergency portable batteries which are self-contained
in a carrying case complete with handle and battery clip leads, etc. 
Many wrecker trucks use them in their daily operations, as do auto
repair shops - they are not that expensive, especially in comparison to
installiing separate batteries, isolators, etc., in one's vehicle.

Additionally, separate batteries installed with isolators, with voltage
sensing so the alternator puts out more to compensate for the isolator
keeping the separate battery at proper voltage levels, CAN cause
problems with one's normal auto electrical system, because everything on
the auto side of the isolator gets a tad more voltage than it's designed
for - I've seen it happen (to others - HI!).

For over a decade I have been using 400W 2m PAs while mobile. 
Efficiencies being what they are versus frequency of operation, I've
been drawing as much current as a 500W HF PA.  Based on my trouble-free
operation for this time, I make the following recommendation:

KISS (keep it simple) - DO NOT modify your vehicle DC system.  At most,
if you REALLY want to, change out the stock alternator for one which can
handle more current.  My '92 Plymouth Acclaim, with it's stock 90A
alternator, did just fine for 6 years (40K miles per year, every inch
doing mobile ops, even to and from work, with 400W PA in operation - I
make more contacts on 2m SSB than all the other bands combined, HF
through 23cm, except no 902MHz - yet!) until I changed vehicles.  Now
I'm doing just fine in my F-350 pickup truck with it's 130A stock
alternator.

Be glad to entertain questions on the subject, but this is like
everything else:  You pays yer money and you takes your choice.  As for
me and my vehicles, we're gonna keep it as simple (and, therefore, as
inexpensive) as possible!  I run #1 AWG wire from both positive and
negative battery terminals to the radio/PA stack, and I have a battery
shut-off switch in the positive side ("master battery switch" available
at myriad auto parts stores - mine is rated 175A - overkill is cheap
insurance - and cost $23), and I fuse the positive side for 100A.

"complicated" is expensive and unecessary.  If it can be screwed up,
I'll find the most ways to do same in the shortest amount of time
(you've heard of the "midas touch" which turns everything to gold? 
Well, I've got the "shidas touch" which turns everything to manure! -
HIHI!), but I haven't had any trouble at all keeping it simple as
described above.  

Good luck to all, and to all, good mobiling!

73, Paul ND2X/5
99.9999% mobile except working on a 5M dish for 23cm EME from home!