How long to charge a battery???

[cobra1]

I am working on a project and trying to find out how long it takes to charge a battery using a given source. The source is a solar array, problem is i dont know how big to build it.

The battery would be a 12v,90Ah deep cycle battery,

Connected to 12v is some low power electronics (5v microcontroller) circuitry,and led lighting also there is a inverter to give 240v AC

The following equipment is connected to the system:

Air Pump, 240v, 30w, 0.125A ..Runs 24/7

Lighting, 12v, 36w, 3A.. Runs 24/4

Water Pump, 240v, 36w, 0.15A.. Runs for around 30 mins total per day.

I need to build an array big enough tho power this during the day, and also charge the battery from the night before, ready for the following night.

I guess i need an array that can put out like just over 100w but i dont know what extra is needed to charge the battery in a quick enough time scale.

 

[Dragon Tamer]

What kind of battery are you trying to charge, and what is the total current draw of all of these accessories?

 

[ronv]

If your inverter is about 75% efficent you will need about 74 watt hours or 6.2 amps at 12 volts. It looks like your battery may be a little undersized as just 10 hours would use up 62 Amp Hours. Keep in mind the ratings are ususally in "full sun light". So lets say you have 8 good hours of sun and 16 of dark. You would take out 99 amp hours and need to put it back and still power the stuff. That would take 12.4 amp hours for the charge plus 6.2 amp hours to run everything. 18.6 total at 12 volts = 223 watts. It really adds up quick when you only have 12 volts to work with. I think I would shoot for 300 watts so you have a bit for clouds and charger.

 

[cobra1]

will a bigger battery pack help me?? For instance if i went to 24v, 90Ah pack

 

[ronv]

I think I would stick with 12 volts just because it is easier to find 12 volt solar panels and inverters -- but yes it would give you twice as long before the batteries went dead, but you still need about 300 watts of solar to recharge them.

 

[crutschow]

I calculate at total energy draw of (30W *24 / .75) + (36W * 24) + (36W x 0.5 / .75) = 1848WHrs per day including a 75% efficiency for the inverter. Thus the panel must deliver an average of 231W for 8 hours. To allow for cloudy days and low winter sun, I would double that to a minimum of 462W.

You may want to also consider a battery large enough to supply the power for several cloudy days in a row.

 

[cobra1]

400w would be doable, think i might go for that,
any idea what size pack would let this run for say 7 days, 12v @ ???Amps

if my maths is correct,going by the numbers above, one day will drain 20amps and take 8 hours to recharge,

so for a week of cloudy days etc, that means i need 140Amps, so 3 batteries will allow for 270Amps. this should be more than enough i guess.

with the solar panels aswell this should never really go down that much.

 

[crutschow]

Don't confuse amps with ampere-hours. Amps is current and ampere-hours is related to battery energy capacity. You divide the ampere-hours by the current to determine how long a given battery will last.

One day without any charging would require 1848Whrs/12V = 154Ahrs of energy from the battery. Thus for each day of no charging, you need at least 154Ah of battery capacity. One of your 90Ah batteries would power the system for, at most, 14 hours (at which point the battery is completely discharged).

 

[bryan1]

Gday Cobra,
With using solar it is best to use a factor of atleast 5:1 for solar panels, and don't forget living in pommie land that factor might rise to 10:1. so for a 100 watt constant load thats 1kw of solar, the far best way will be going for a 24 volt array so the current draw is 1/2 that of 12 volts and just put the 12 volt panels OF THE SAME SIZE in series to get the 24 volt charging array. Also a separate means of charging the batteries will be needed to cover for those cloudy/ rainy days so a smart mains battery charger will be the go or a homebrew generator that can be easily kicked in where needed. There are many ways to homebrew a generator for a battery charger which can be easily made.

Cheers Bryan