Solar Design

GOALS

1. Operate through a week of rain (battery life of 10 days).
2. One day of sun provides 2 days of operation (operate unit 1 day and charge batteries 1 days worth) so need an average of 50% sunny days.
3. Low profile (solar array fits on the top of a 10 frame Langstrough hive.)
4. Affordable. Readily available parts.
5. Simple. Easy to build and maintain.

Disabling the LAN9512

On the Model B, the Ethernet and USB ports are provided by the LAN9512. This chip consumes almost 200mA. The File:9512.pdf explains some of its power saving modes: SUSPEND2, SUSPEND1 and SUSPEND0.

echo 0x0 > /sys/devices/platform/bcm2708_usb/buspower will effectively disable the device

echo 0x1 to the same file to wake up it.

See this StackExchange post for details.

Note that this technique reduces the Model A current draw from 200 ma to 120 ma even though it doesn't have the LAN9512.

GPIO serial port

USB to TTL Serial Cable

USB to TTL Serial Cable

When using the Model A (or turning off the ethernet/USB ports on the Model B), this USB to TTL Serial Cable will allow connection to the console.

http://elinux.org/RPi_Serial_Connection

From AdaFruit:

USB to TTL Serial Cable - Debug / Console Cable for Raspberry Pi $9.95

From Amazon:

Elesonic Vomaxtech Pl2303hx USB to TTL to Uart Rs232 COM Cable Module Converter $5.99

Kootek PL2303HX USB to TTL to UART RS232 COM Cable module Converter $2.65

DESIGN

Power calculations

Average power consumption

Pi A: 200 ma @ 5V = 1 W
Scale: 50 ma @ 12V = .6 W
(The actual measured Pi power consumption is 120 Ma.)
Assume PS efficiency is 85% 2 watts/.85 = 2.4 watts
2.4 watts / 6 VDC = .4 amps
.4 amp x 24 hours = 9.6 AHr
derate 200 AHr battery to 100 AHr
100 AHr / 9.6 AHr/day = 10.4 days

Charge rate

Goal: 4.8 watts (2x consumption)
5 watts x 24 hours = 120 watt hours
120 watt hours / 20 watt = 6 hours at maximum output (12 hours at 50% output
Derate panel to 15 watts = 7.6 hours
(note: 20 watts is maximum output and that probably won't ever happen - especially if the panel is flat on the top of the hive. I would feel more comfortable using a 40 watt solar panel 2.3 amps max output.)

NOTES

1. Battery Amp Hour ratings are theoretical. A 200 AHr battery in theory would supply 200 amps for 1 hour or 1 A for 200 hours. In practice this is far from true - there is a better chance of getting closer to 1 A for 200 hours than 200 amps for 1 hour. The point is, the AHr rating of the battery must be derated (depends on the rate of discharge and temperature).
2. 6 V golf cart batteries are better deep cycle batteries (thicker plates) than 12 V marine deep cycle which are a compromise. Battery life depends mostly on Depth of Discharge (DOD) - the bigger DOD, the shorter the battery life.
3. A solar "Charge Controller" probably won't work - DO NOT USE THIS: http://www.amazon.com/Sunforce-7-Amp-Charge-Controller/dp/B0006JO0XI/ref...
Hardware:
40 Watt solar array:
http://www.ebay.com/itm/40w-New-40-watt-Module-Sun-Solar-Panel-PV-Poly-c...
$54 on ebay
Battery:
http://www.ebay.com/itm/Trojan-Black-Box-6-Volt-210-Amp-Hour-Deep-Cycle-...
$95 on ebay, probably find locally (Sam's Club)
Solar Charger/PS:
http://www.prodctodc.com/dc-auto-boost-buck-converter-25w-315v-to-0530v-...
$7 WiFi Adapter: http://www.amazon.com/Importer520-Wireless-Adapter-Antenna-54Mbps/dp/B00... $10
(This is about $170 not counting shipping/taxes.) May need gain antenna: http://www.mfjenterprises.com/Product.php?productid=MFJ-1800 $30

Raspberry Pi Model A vs Model B

The SMSC LAN9512 USB Hub and Ethernet Controller.

LAN9512 Data Sheet

Misc Info on power reduction

http://www.daveakerman.com/?page_id=1294 http://www.bitwizard.nl/wiki/index.php?title=Reducing_power_consumption_of_a_raspberry_Pi http://www.youtube.com/watch?v=L1EihTxIdnQ http://traffic.integreen-life.bz.it/default/wiki/power-consumption http://raspberrypi.stackexchange.com/questions/8498/disable-lan9512