Solar Power Design Ver 1



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.
5. Simple.


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.)


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:


40 Watt solar array:

$54 on ebay


$95 on ebay, probably find locally (Sam's Club)

Solar Charger/PS:


WiFi Adapter:


(This is about $170 not counting shipping/taxes.)

May need gain antenna:


I have testet the first HAT board, with a 12 to 5V adapter and the HX711 onboard
Have done several test with different connections
I'm using a Raspberry Pi 2 model B

Pi + HAT , LAN, Scale
Idle: 0,10 A
running 0,13 A

Pi + HAT , LAN, Scale, 1 x DHT22
Idle: 0,13 A
running 0,14 A

Pi + HAT , LAN, Scale, 2 x DHT22
Idle: 0,13 A
running 0,15 A

Pi + HAT , LAN, Scale, 2 x DHT22, 1 x TSL2591
Idle: 0,13 A
running 0,16 A

Pi + HAT , LAN, Scale, 2 x DHT22, 1 x TSL2591, Huawei E180 3G USB modem
Idle: 0,16 A
Connected to internet: 0,20 A
When running traffic on the adapter is sometimes comes up in 0,30 A

Pi + HAT , WLAN adapter, Scale, 2 x DHT22, 1 x TSL2591, Huawei E180 3G USB modem
Idle: 0,19 A
Connected to internet and WLAN: 0,27 A

The power consumption on 3G/4G and WLAN will vary a lot on the different signal strenght from the senders

I see a problem on the internet connection that the NTP protocol sends a lot of packages to keep the time correct. I have tried to change the poll time for this but with no good success, maybe the NTP protocol needs to check when the connection is up, and then stop until next time to save a lot of power

0.16A Eth + 3G modem + HDMI on
0.16A Eth + 3G modem + HDMI Off
0.14A 3G modem + HDMI Off
0.10A USB power off + ethernet cable in + HDMI Off
0.08A USB power off + ethernet cable out + HDMI Off