[aprssig] Tesla Field Day mode

[Stephen H. Smith]

On 2/20/2019 2:23 PM, Greg D wrote:
>   
>
> Just putting a ham radio in my EV was a challenge, since one can't pull
> much power from the "accessory" outlet.  Mine is only rated to 8 amps,
> and most mobile rigs can pull up to 13 amps.  In some cars, going direct
> to the relatively small 12v battery isn't much better unless the car is
> on or actively charging.

This was the issue I had with my 2006 Prius, where the 12 VDC battery is about 
the size of a motorcycle battery.     The tiny battery was primarily to boot 
the electronics that control the hybrid power system.   I discovered that the 
240 VDC-to-12 VDC switching down-converter, used to recharge the small 12 VDC 
battery and power the 12 VDC lighting & accessories was capable of several 
hundred watts at 12 VDC when running.

I connected a 55 AH Optima Yellowtop AGM deep-cycle battery through a 
Hellroaring isolator across the small Prius 12 VDC battery.   This battery was 
just narrow enough to lie on it's side in the hidden lower trunk of the Prius.  
When the hybrid power system comes on and starts producing 12VDC, the FET 
switch would close and charge the added battery.   The Hellroaring device is 
not the run-of-the-mill diode RV battery isolator.   It uses a power-FET switch 
that has less than .05 VDC drop at 75-150 amps when on.    This was critical in 
the Prius -- the DC-DC converter only produces about 12.8 VDC, instead of the 
typical 13.8 V or more, when on.  (Apparently, Toyota was trying to maximize 
the life of the small 12 VDC battery by not charging it as highly as car 
batteries usually are.)  The Optima would never have recharged fully with the 
usual .4-.7 VDC drop through a typical diode isolator.

-------------------------------------------------------------------------------

Another trick I have done with the Optima is to power high-current loads off 
the lighter jack (a.k.a. "DC power outlet.    Connect a short heavy (12-14 GA) 
red-black zipcord DC cable between the battery and a PowerPole DC distributer 
panel.    Then connect about 20 feet of 18-20 GA red-black zip cord between the 
battery and a lighter plug connector.

Normally, engine-on a moderate current will flow from the car's power system 
through the lighter socket to the added battery. When you key up a full-power 
HF rig  with a 25 A TX draw, most of the current comes from the added battery; 
not the lighter connection.   When the terminal voltage of the added battery 
drops a few tenths of a volt below the car's charging system voltage, a larger 
charging current will try to flow through the lighter socket to the second 
battery.      But as the current tries to increase, the voltage drop across the 
18-GA zip cord increases, limiting the inrush current to something the lighter 
socket can handle (8-10 A).  As the second battery reaches full charge, the 
voltage drop across the zip cord decreases, allowing the second battery to 
ultimately reach the same voltage (+/- millivolts) as the car's battery and 
charging system.  It's basically an el-cheapo semi-constant-current charging 
system.

This works like a charm to throw high-power HF rigs, 300-watt inverters, 
100-watt-out VHF/UHF Micors, etc into a vehicle with just a lighter jack, on 
short notice.

-------------------------------------------------------------------------------
Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

Live Off-The-Air APRS Activity Maps
    <http://wa8lmf.net/map>

Long-Range APRS on 30 Meters HF
    <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>





-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.tapr.org/pipermail/aprssig_lists.tapr.org/attachments/20190220/f683b974/attachment.html>