You may be considering using a 12V, 7Ah battery in your DIY project – Note that it is common to find it used in several appliances such as alarm panels, UPSes, power wheels, and others.
While there’re countless project ideas, one such project, you may be interested in, at least one I have considered is running a 12V camera off solar.
This then poses these questions and probably many more:
Can you keep the camera running reliably with solar? And how much solar do you need?
In this post, you’ll learn how much solar you need, and what other components to consider to reliably use solar to keep a 7Ah, 12V battery charged.
How Many Watts of Solar for a 7 Ah Battery?
To ensure that the 12V, 7 Ah is reliably topped up, use at least 30 watts of solar for a 7Ah AGM and 40 watts of solar with a LiFeP04 battery.
Or, to keep it simple, you could go for a 40-watt solar panel to cover you with whichever battery type you use.
Note, this assumes that your location receives a minimum of 4 hours of sunshine.
The calculation
AGM Battery
First, find out how much energy in Wh is stored in the battery – 42Wh from available capacity to use with 7Ah, 12V battery capacity:
Recommended depth of discharge – 50% x 7Ah =3.5 Ah. Converting into Wh, 3.5Ah x 12V (battery voltage) = 42Wh.
To replenish this capacity (theoretically), you’ll need, 10.5 watts of solar using the calculation:
Recommended battery capacity – 42Wh / sunshine hours at your location / 4 hours.
To allow for overcast days, you should oversize and at least double this to 21 watts of solar.
I would personally go with at least a 30-watt, 12V solar panel to keep a 7Ah, 12V AGM battery topped up.
LiFeP04 Battery
Find out how much energy in Wh is stored in the battery – 67.2Wh from available capacity to use with 7Ah, 12V battery capacity:
Recommended depth of discharge – 80% x 7Ah =5.6Ah. Converting into Wh, 5.6Ah x 12V (battery voltage) = 67.2Wh.
To replenish this capacity (theoretically), you’ll need, 16.8 watts of solar using the calculation:
Recommended battery capacity – 67.2Wh / sunshine hours at your location / 4 hours.
To allow for overcast days, you should oversize and at least double this to 34 watts of solar. I would personally go with at least a 40-watt, 12V solar panel.
Can you Use a Lower-capacity Solar panel?
You could use a smaller capacity solar panel if your location consistently receives more than 4 hours of sunshine or your appliance does not discharge the battery up to 50% of its capacity (AGM) and 80% LiFePo4.
I’d recommend to error on the side of oversizing the solar panel to guard against the risk of damage to the battery from being over-discharged or kept in particularly drained condition for a long period!
What Size of Charge Controller (Amps) to Use?
To guard against overcharging the battery, you’ll need to include a charge controller.
Use at least a 6 amp charge controller or larger. This can adequately handle the estimated maximum current output of 3 amps!
How Many Solar Panels?
A single 40-watt solar panel will work fine. For such a small system, it’s convenient to have the solar panel in one package!
The 40-watt solar panels are available on Amazon.com.
How Long to Charge 12v 7Ah Battery with Solar?
It’ll take an estimated 4-6 hours to fully charge the 7Ah, 12V battery assuming it has been discharged to its recommended depth of discharge.
Charging time can be less if the battery is only partially discharged.
Closing Thoughts
Consider using a 40-watt, 12V solar panel to keep a 12V, 7Ah AGM, or LiFeP04 battery charged. The expected charging time for the batteries is about 4-6 hours.
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