Chevy454 wrote:
This item prevents your thermoelectric cooer from draining your car
battery to the point where you can not start your car:
http://koolatrononline.stores.yahoo....ery-saver.html

Can something like this be easily homebrewed from a couple of 30/40
amp horn relays and a couple of pots? That would permit its use for
the same purpose in mobile QRO radio.

I tested one and it open the circuit at 11.5V and closes it again at
12.8V. The dead zone is needed to prevent cycling.

Ken KC2JDY
Ken:

If your relay "reliably" will not actuate, or will drop out at 11.5
volts, then you may wish to trust it to keep from depeting the battery
so far you can't start the vehicle. However, having tried similar
methods (including a variable settable sensor that then controlled a
relay to allow use of "accessories" such as ham radio xciever, I found
the best solution for me was to have a separate battery that powered the
radio equipment (charged via a battery isolator diode) from the
alternator, so the starting battery wasn't affected at all. This worked
for both a tow vehicle (89 chevy silverado pickup) and a marine
installation (19ft ski boat with entertainment electronics, marine and
and ham radios) such that I could be on the water all day without the
engine running, end up with the radios and cd player inoperable and
still start the engine to return to the marina (of course, everything
worked as soon as the engine started, and I had a bypass switch so I
could run the marine radio from the starter battery if there was an
emergency...)

Though you may want to do with only a single battery, after several
different configurations, I really prefer a second battery for
entertainment and radios. Thus I knew that when the radios crapped out,
I still had a FULLY CHARGED battery to start and run the engine, whether
on the water in the land based tow vehicle. It's been more than a few
years since I ran that configuration, but would do it again in a minute
if I even thought about "long term operation" without the engine
running. In the truck I currently have mobile ham radio, I don't have
the second battery, but am careful to start and at least idle the engine
if I run the radio for more than an hour, just to keep the battery up to
normal levels... I probably helps that the radio isn't spec'd to run
below 12.0 volts, so I tend to watch the voltage that shows on the radio
display and any time it looks like it's dropping, I get the engine
running. Of course, as I age, I find my operating time between moves
has been decreasing, so the actual times I have to remember to start the
engine are pretty rare... [sigh]

--Rick AH7H