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ATPhillips

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Posts: 1
Reply with quote  #1 
Hello, this is my first thread...

I am a PhD researcher working in the area of acoustic ecology and am looking to deploy sensors to collect data from the treetops in a remote region of South America, two components of which will require solar power.

One is a Verizon Jetpack, which has its own lithium ion battery -- which, clearly, will need to be recharged at regular intervals (claims to be able to hold 20 hours of power per full-charge).  The battery requires 4000mAh and 3.7Volts.

The second is a mini-processor that will require a constant energy source, and requires 700mA.  Since I need continuous power for this device, I will have to purchase a separate battery for this.  I am looking at batteries that run at 2200 and 4400 mAh and 5Volts.

(Data being collected by the mini-processor will be sent to the Jetpack via WiFi, and sent from the Jetpack via cellular.)

Ideally, I would like to be able to power both devices from one portable solar device, but the more research I do, the less possible I expect this to be -- I suspect that I will need one solar charger for each of the two devices.

Furthermore, although I understand Volt-Amperes-Watts relationships at a rudimentary level, I am not entirely clear on how to go about making these calculations when talking about using a solar charger, to power a battery, to power a device.  There are two stages of charge and discharge going on here, and the relationships seem a bit complex.  I am attaching a brief diagram that I drew up of my understanding of how the system *might* work, in a generic sense.

I am looking at several portable solar options, including:
-store-bought, 4 panel, 14W: http://www.amazon.com/gp/product/B00E3OL5U8/ref=as_li_ss_tl?ie=UTF8&tag=ianker-20&linkCode=as2&camp=217145&creative=399373&creativeASIN=B00E3OL5U8
-DIY 4 panel: http://parisnakitakejser.com/2013/04/raspberry-pi-battery-charger-from-solar-panels/
-40W???:http://www.instructables.com/id/All-Weather-Solar-Powered-Raspberry-Pi/
 
So, to recap:  I have two devices that will require solar power, both of which would ideally run day and night.  One device (Jetpack) comes with its own battery, the other (Android device) will require an external battery to run continuously.  I want a circuit that can utilize solar power by day to operate and to charge both batteries while running the devices, and then at night automatically uses the power from these respective batteries -- and this "switch" should happen automatically.
 
I apologize for any confusion, but am happy to try to answer questions to the best of my ability.  Any insights or suggestions are very welcome.

Thanks and regards,
Andrew

 
Attached Files
docx Battery_Charging.docx (188.77 KB, 5 views)

paulstef

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Posts: 98
Reply with quote  #2 
Ok, then theoretically the Jetpack consumes 200mA. 
+ the Android device 700mA.

Let's say 1A continuously at 3.7V? What voltage does the Android device require? Why a battery of 5V? If the Android device has an external DC IN port of 5V I would not use a battery of 5V but at least 6V and put an LDO (low dropout voltage regulator) in series.

Let's assume it's 3.7V at 1A, i.e. 3.7W.

Now you need to know: 
- How long does the sun shine?
- What's the power input during cloudy days? Does it need to work on cloudy days?

I somewhat have my doubts that an intelligent (uC controlled) charger like the one you posted (from amazon) will power two separate batteries with different mAh ratings. Furthermore if you have two different voltage then one charger can certainly not do this.

Does the verizon jetpack have an external DC jack?
If it does, then since you need an additional battery anyway why not use ONE battery for both devices and connect this battery to both DC inputs of the two devices?

I wouldn't worry two much about current sharing from charger and or battery etc. I would worry about a TOO intelligent charger.
Whatever charger you use you should read the manual beforehand. 

Everything put in parallel (charger output, battery and the two devices) it should actually maintain the battery charged without any problems during the day. If the current for your devices comes from the battery when the charger is off or directly from the charger is irrelevant.

For the charger the 3 loads would like a battery with increased leakage.


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