If you have a 110 amp hour battery that needs 45 more amp hours for full charge, you will need 30 hours of very bright sunlight falling on your panel to reach full charge, so a week to a month. The 12.9 volts will likely increase to 13.0 volts the next bright sunny day.
If all is going well, the input voltage will fall to about 12.5 volts if you connect a 700 watt load to your inverter. If it reads less, you should not leave the load connected to the inverter more than a minute. If the charge controller voltage is significantly higher than the inverter input voltage, you likely have a poor connection.
If your battery is 100 amp-hours, it generally takes about a 120-watt panel to keep up with what you can draw from the battery each day without harm. There are many assumptions embedded in that, including that you have a good location with at least 5 peak equivalent hours of sun. That is about the amount that you get in most places in California and Hawaii. Higher latitudes will be less. If you panel is a true 20 watts, that means 6 days of charging for 1 day of use.
If the battery started from flat (dead), then allow 12 days.
That could be fine, if your only purpose is to have a bit of emergency power.
Full charge for lead acid battery is ~13.2 V.
If that inverter is putting even a token load on the battery you
might already be at full open circuit voltage.
You have several good answers, but you don't mention
the battery's Ampere hour rating, or explain why you don't
use a normal charger if it's intended for emergency use.
Begining with basics, 700W-1,400W ÷ 12V = 58.33-116.66 Amps
from the battery. Does your battery have this capacity?
Second, 20 Watts ÷ 12.9V = 1.55 Amps delivered to
battery neglecting losses, and low Voltage difficulty.
If you pulled 58.33 Amperes (700 Watts) for one hour
you would need 58.33/1.55 = 37.6 hours of full sun
to recharge it.
For extended power outage your inverter is limited
(for practical purposes) to 10 Watts at 120V while the sun is
shining.
Add detail for a better answer.
12.9V terminal voltage is too weak to charge any lead acid type 12V battery. It could take weeks or month to fully charged a high AH rate battery. Either you set up the controller ( constant current source ) was wrong or your solar panel open voltage is too low.
Peak battery voltage under change is 13.6V to 14V.
Hello,
I recently purchased a 12 volt deep cycle batter to use as a charging cell for emergencies. Since I am just at the beginning stages of my setup I've only connected one 20 watt solar panel to my configuration. Connected through a charge controller the panel charges a 12 volt battery which is connected to a 1400/700 watt inverter.
When I turn the inverter on it reads zero output wattage and 12.9 input voltage. The charge control I have also reads that it is still charging the battery and should indicate a full charge once the battery has reached a charged level.
How much longer should it take this battery to charge? What should be the highest input voltage the battery reaches?
