Mark Fellhauer KC7BXS writes...
Just a reminder as the winter weather really sets in (we got to -3 degrees fahrenheit last night here in Sioux Falls), that as the temperature drops, so does your battery efficiency.
A battery is rated by the manufacturer at 70 to 80 degrees F in it's full
capacity, and if you look at battery peformance tables you'll find that
this can drop by as much as 60% when the temperature drops to zero. This
is compounded by the fact that an intenal combustion engine is much harder
to start (due to the high viscosity of oil and coolant) at this
temperature. Car manufacturers rate cranking amps required also at room
temperatures. At zero degrees F it can take twice as much energy to turn
an engine over.
Another factor to consider is that a wet battery with a voltage of 12 or
less (or a specific gravity of 1.14 or less) can FREEZE when the
temperature drops below 10 degrees. If your battery actually freezes this
can lead to all sorts of problems, including plate damage and even battery
wall bursting. Most battery manufacturers warn that trying to charge or
jump-start a frozen battery can be dangerous. If your battery freezes take
it indoors, if at all possible, and let it thaw out gradually.
As a funny aside - Specific gravity of acid is a goofy thing - I once left
a 4000 gallon tanker-trailer of 85% phosphoric acid in a parking lot (a
locked guarded yard, actually), as we did not have time to pump it into an
indoor tank - during the night we had a sudden cold snap and the
temperature dipped to 60 degrees (A cold snap in Phoenix) and when I came
back in the morning the acid solution had frozen solid (!). We had to wait
several hours for it to warm up before we could pump the trailer out.
My advice: If the temperature drops below 20 degrees it's time to turn off
the APRS tracker if you normally leave it on all night. If you must leave
it on, invest in some kind of underhood heater, either engine block,
battery wrap, or external hydronic. If you have the room under the hood,
an Espar hydronic heater looks to be the way to go. These are powered by
the vehicle's liquid fuel system and can sip as little as a cup of fuel
(diesel or gasoline) an hour to keep your engine compartment (and cockpit)
toasty warm. Espar also makes liquid fueled air heaters, and were/are the
OEM for the "infamous" BN4 heater (if you've ever owned an older VW
microbus) I'm not too young to remember the "whump" and whine of our 1960
Corvair's auxillary gas heater - not to mention the flames that shot out of
it's tiny exhaust pipe when you first started it up. 40 years ago my
father had a car with instant (dry) heat in the winter, why can't car
makers provide that today?
In conjuction with an hydronic heater, it might be wise to invest in a
system that will start your vehicle automatically and run it for a preset
amount of time when the battery drops below a certain voltage or the
temperature of the engine compartment drops below a certain value.
I know, liquid fuel heaters and autostart systems are expensive and "waste"
fuel. Some people even think they're dangerous. But 120 volt engine block
and battery heaters (beside being inexpensive) require an outlet to
work. And I bet I can find as many instances of an electric engine block
heater burning up a car...
I use the $35 Wal-mart solution: A 1.5 amp underhood battery charger and a
cheap metal drop light with a 60 watt bulb. A piece of carboard in front
of the radiator rounds out my winterizing. I'm very happy with the $25
underhood battery charger they sell (model WM-1-12A). I've monitored it
with a multimeter and it properly charges and maintains a battery. Even in
the very tight confines of my Geo's engine compartment I found a high dry
spot to mount the charger, actually on top of the battery itself, and an
added bonus is that it's trapped there without the aid of any mechanical
fasteners - although the 120 volt cord is secured by cable ties. I ran a
short appliance extension cord out through an under bumper vent so I can
plug in the charger without opening the hood. I carefully routed it to
avoid any hot or moving engine parts or sharp metal edges.
73 and keep your stick on the ice - and don't forget to wear your choppers
and your chooks, eh? I'm off to run the snowblower...there's too much snow
on the roof.