[aprssig] GPS/Puck or Other Wise

Ron Stordahl ron.stordahl at digikey.com
Sun Jul 10 09:29:28 CDT 2005


Thanks for the information on your battery protector product.  Had I 
known about it a couple of months ago I would bought one!  I had the 
same problem, the load of my radio, tinytrack plus gps would draw down 
my battery during cold weather in a couple of days.  I bought a device 
similar to yours from a two way radio shop (they use them to turn off 
all the radio equipment in squad cars which can draw down the battery 
overnight).  It works well, but costs twice as much.  I am saving a link 
to your product for the time when I equip my second vehicle with APRS.

Ron, N5IN

James Jefferson Jarvis wrote:
>> On Jul 9, 2005, at 4:14 PM, Stephen H. Smith wrote:
>>  4)  Why worry about switching the GPS on and off at all?   A device
>> like the Garmin GPS-18 powered by a decent switching mode regulator
>> (not a 7805 linear device) only draws 50-60 mA at 12VDC which
>> translates to about 1 Amp-Hour a day.   You can leave this device on
>> for a week or more without affecting the car battery significantly. 
>> The advantage is that the  GPS is always locked  and has a currrent
>> ephemeris and almanac ready-to-go.
> It's doesn't work quite so well in cold climates. Here is the midwest it gets 
> to -20 degrees F for a week at a time and that will kill your battery if it 
> has any loads on it. 
> "The standard rating for batteries is at room temperature - 25 degrees C 
> (about 77 F). At approximately -22 degrees F (-27 C), battery AH capacity 
> drops to 50%."
> The above information is from "The Deep Cycle Battery FAQ" found at:
> http://www.solar-electric.com/deep_cycle_batteries/deep_cycle_battery_faq.htm
> Besides the decreased capacity the fluids in the engine are more viscous at 
> lower temperatures which requires the starter to work longer and harder to 
> get the engine started.
> Two winters ago the GPS (7805 powered Garmin 25) on my truck would kill the 
> battery if left for more then a few days without driving. Even in winter time 
> in Iowa I still do most of my traveling on bicycle, so when ever I would go 
> to use my truck the battery would be dead. I thought the problem was a weak 
> battery, so I replaced the battery with a bigger battery. Still had the same 
> problem. As an experiment, I disconnected the GPS and after a week the truck 
> started up fine in sub-zero temperatures. 
> Blatant plug: From that experience I developed my APO circuit which turns off 
> a GPS or other load when the vehicle battery voltage drops below a a 
> threshold. After installing the first APO prototype two winters ago I've 
> never had my vehicle not start. You can read about the new APO circuit at:
> http://www.windmonitor.net/apo/
> There's another possibility for people using the TM-D700 and a GPS. When the 
> radio is one there is 8 volts going to the microphone. Put a reed relay in 
> parallel with this line. Use the contacts on the reed relay to turn the GPS 
> on and off. Now whenever the radio is on the GPS is on. I can draw up a 
> schematic if anybody is interested in this.
> 73's
> -Jim KB0THN
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