Monday, May 16, 2011

Solar Power for Ham Radio, Continued...

After the success of using solar power on the Death Valley trip last month (and indeed, using solar power for all my portable operations!), I've updated the solar system.

Solar Panels
I added another 20 Watt foldable solar panel (model F15-1200), so that brings the total panel capacity to 5+5+10+20 = 40 watts. Unfolded, the panels cover an area of about 6' by 3', and generate a nice amount of power in full sun.

LFP Battery
I also upgraded the battery from a 7 amp-hour Sealed Lead Acid (SLA) to a 6.4 amp-hour Lithium Iron Phosphate (LeFePO4) battery (model K2B12V7EB from K2 Energy). LFP batteries are very lightweight, have a high power capacity, and are very tolerant to high charge and discharge rates over many cycles. Tolerating a high charge rate is useful because it allows me to rapidly recharge the battery from the solar panels. In addition, LFP batteries are inherently very safe, and aren't prone to the thermal runaway of lithium-iron batteries. The "EB" version of this battery has a built-in battery management system (BMS) that prevents overcharge and overdischarge.

Charge Controller
Since the voltage specs on the LFP battery are similar to the SLA for max charge, I can use my exisiting SunForce 7-amp charge controller to prevent overvoltage conditions when using the solar array unattended. The controller cuts power from the solar panels when the system voltage reaches 14.2 volts. This is very important when running with a radio connected to the battery and solar panels -- without a charge controller, when the battery's BMS disconnects the battery at full charge, the full 18-21V from the panels could go direct to the radio! Using a charge controller makes sure the panels are disconnected at anything more than 14.2V.

As usual, I put Anderson PowerPole connectors on everything (solar panels and battery). The connectors on the battery are fused with a 10A mini automotive fuse.

Weight and Portability
I'm especially happy with the weight of the system! The original SLA weighed almost 6 pounds alone. Since the new SLA weighs 2 pounds, and all four solar panels 3 pounds, the entire solar power system weighs less than the SLA alone. Plus, it has the clear benefit of rapidly recharging anywhere/anytime there's sunlight! Having ample power at reduced weight will be important when taking the radios hiking (as in terrestrial VHF/UHF contests from hilltops, etc).

In Use
Initial charging tests indicate that the LFP battery charges fully in just a few hours of bright sun. I measured the charge current at just over 2 amps, so in theory that should charge an empty batt in around three hours. Initial discharge tests indicate that the LFP will power a 60-watt light bulb through a 120V inverter for 1 hour -- the system draws around 6 amps in this test so that indicates at least 6 amp-hours of useable capacity. Since the FT-817ND radios draw 500mA on receive and 2.5A on transmit, 6 Ah actually translates to quite a bit of operating time! For satellite use, my 7 Ah battery will last for around a week of causual operating with the twin FT-817ND setup.

Monday, May 2, 2011

Sat Portable Death Valley

In late April 2011 we took a camping trip to the backcountry of northwestern Death Valley National Park. I brought along the portable satellite station using the twin Yaesu FT-817ND radios and Elk antenna.

Most of the travelling in the park was via remote 4WD roads. Here's a photo of the road through Steele Pass, which connects the Eureka Valley with Saline Valley:

And Lippincott Mine Road, which connects the Saline Valley to the Racetrack Valley:

And here's the portable satellite station, including the solar array:

Again I used the twin FT817ND radios. They hang by their straps from the tripod that holds the antenna.

The solar array. I use two 5-watt and one 10-watt PowerFilm flexible solar panels. The array seems to be able to charge the battery drain from working 2 or 3 satellite passes in about 30 minutes:

The solar array feeds a simple charge controller, which then charges the 7-Ah sealed lead-acid battery:

KB5WIA talking to KC0BMF, KN6ZA, and others via the AO-51 satellite at the Eureka Dunes in grid square DM17. The remote Eureka valley to the north is in the background:

A photo of Dave KB5WIA hiking on the Eureka Dunes. These dunes are reportedly the second-tallest in North America:

More satellite QSO's from the Eureka Dunes in DM17. I was able to work two FO-29 passes, two AO-51 passes, SO-50, and VO-51 from this location. Shortly after this photo, a sandstorm came up which made operation very difficult!!

When no picnic table is conveniently available, I simply set up the station in the back of the pickup truck. Here is the station at the remote Lippincott Mine in north central Death Valley Park, grid square DM16. The photo was taken just after I had worked AA5PK on an AO-07 pass:

This is a photo of the track leading to the mine, where the previous photo was taken:

KB5WIA talking to Leo W7JPI and others on a nice early-morning Oscar-7 round-table chat. Location is the south end of the Racetrack Playa in grid DM16:

And here are the "moving rocks" of the Racetrack Playa -- the rocks were a few hundred yards from the AO-07 QSO, it was quite a scenic location to be on the radio!

All in all it was a great trip. Three days of backroads driving and two nights of camping, coupled with a day on either end travel time from CM88. In all I was able to work fourteen satellite passes, and have QSO's with around 40 stations.