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Need to power 1.5W 5V load with a battery /recharge off solar.

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oriddlero

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Hi everyone, sorry for the noobish questions but I’ve been trying to figure this out all day and I need help.
I have a 1.5W 5V (USB) load I want to power with a battery and have the battery recharge off of solar power.
Requirements:

• 2 x Solar panels (aesthetics) ,
• Ideally enough lipol battery to last for 24 hours of contant operation (in the event there is no sun)
• I need to keep the parts as cheap as possible. As this will be produced in high quantities.

Parts I have laying around thank might be useful (ignore if this is the wrong starting voltage:

• Already have 2x 12v 1.5w panels
• 12V 3000mah lipol battery
• 2V - 24V To 5V 9V 12V 28V MT3608 DC-DC Boost Module 2A Adjustable Step Up Module Boost Converter Power Supply Module

I’ve never really worked with solar and battery recharging It seems like every part I find outputs the wrong voltages for my application.
There has got to be a simple solution here without having to throw step up and step-down modules in the loop.
Questions:

• If I’m using two solar panels in parallel do I need to add some sort of diodes to stop them from back feeding each other?
• I was looking at this part https://www.banggood.com/5V-2A-Solar-Panel-Power-Bank-USB-Charge-Voltage-Controller-Regulator-Module-6V-20V-Input-p-1099540.html?gmcCountry=US&currency=USD&createTmp=1&utm_source=googleshopping&utm_medium=cpc_bgs&utm_content=frank&utm_campaign=pla-all2-us-pc&gclid=Cj0KCQiAtP_iBRDGARIsAEWJA8gv7jFdlLQEhNNZQ3IlqADMzDZ4vgypSrIBJpDkoaahc6PeP27bi3saAjmqEALw_wcB&cur_warehouse=CN
o (can take 6-20v IN and turn its into 5v) what battery to use?



Anyone who could help point me in the right direction and maybe provide some part numbers would be greatly appreciated!
 

KlausST

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Hi,

You may use this configuration:
Solar panel --> charging circuit --> battery --> SMPS --> load.

It seems you know the specifications of your load, then go step by step back from load to solar panel.

Klaus
 

BradtheRad

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1.5W 5V (USB) load
...
Ideally enough lipol battery to last for 24 hours of contant operation (in the event there is no sun)
In terms of raw calculations you need 36 Watt-hours of power.

12V 3000mah lipol battery
This is sufficient to provide 36 W-Hrs of power. On average you expect to draw .125 Ampere continually.

You need to examine charging instructions for your battery. It may advise charging at a maximum Ampere level based on its capacity in Amp-hrs. What is safe range of voltage for it? When discharging? When charging? Etc.

have 2x 12v 1.5w panels
Total 3 watts. Is this correct? Suppose your charging session lasts 12 hours (typical summer day). Then they yield 36 W-hrs of power for charging your battery. From these calculations you can discharge the battery and charge it in a 24-hour period.

However in winter the sun shines for fewer hours and is not so high in the sky. You may find you get only 2W from your panels for a 6 hour session. This makes 12 W-hrs. Therefore your battery receives less juice. Later it may power the USB device for just a few hours and then it is drained.

These are questions which may be answered by doing many trial runs, on long sunny days and short cloudy days. One consideration you must decide is whether your PV panels shall do both jobs simultaneously, or only one job at a time, namely: (a) charge the battery, and/or (b) power the USB device.
 

KlausST

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Hi,

Total 3 watts. Is this correct? Suppose your charging session lasts 12 hours (typical summer day).
This calculation is true when your application is switched OFF during charging.

When your application is running, then there is only 1.5W available to charge the batteries.
Then the charging time is 24h.

--> You need a lot more peak solar power.

Klaus
 

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