Every time I think I have somewhat of an idea of what is going on, I seem to get completely puzzled again!We have 1 AGM battery in our trailer. While boondocking in full sun, our 100W solar panel shows the battery is almost full and the following: 14.4V, 2.8 Amps, 10.9 AHThen, I plug in a small inverter in the trailer (one of those small inverters to use in a car and I plug it into the 12V cigarette lighter port in the trailer) and connect the laptop to the inverter's 110V port for charging. The laptop is a regular Dell laptop and the laptop AC adapter shows on the label:- input 100-240V, 3.2 A- output 19.5 V, 10.8 AAfter a few minutes of having the inverter and laptop plugged in, I check the solar panel controller and it is rapidly going down. When it is down to 13.2V and the battery level indicator (on the controller) shows as 50%, I call it a day and unplug the inverter in the trailer, worried that the inverter/laptop charging will drain (& kill) the AGM battery if the solar panel can't keep up.What's going on? For someone who knows what those numbers mean... :-)Thanks!

Nothing wrong. As power is being taken from the battery, the controller is reverting to bulk charging voltage. What you should be concerned with is the amperage going in vs going out.

So it appears to me that the solar is providing 2.8 Amps while the laptop is taking 10.8 A? Or is it taking 3.2 A?

your charging power in watts 14.4v*2.8amps= 40.32 wattsyour PC use ? 19.5v*10.8amps= 195watts this is probably max power use (not counting conversion losses) Not avg PC power useany way, these numbers say you are using almost 5 times the power, than the solar panel is providinglaptop power use is probably about 1/2but even 100w of use is 2.5 times the solar supplyso yes you are using mainly battery power, with solar just pinch hitting a little bitmy laptop avg about 50watts of power useyou did not say HOW long this use cycle isminutes? hours?

You are just burning down the surface charge that accumulates while charging. The controller indication is not designed to be accurate with a load on the battery while charging. Your battery will continue to drop until you are down to 12.7 volts that represents full charge. At that point it should hold much more steady down to 12.2 volts representing 50% under modest load.The 12 Volt Side of Life

Newbie question about solar charging | Good Sam Community

2oldman
Explorer II
Mar 26, 2019
That seems like a huge amount of battery charger for a laptop. Your solar won't handle it.
time2roll
Nomad
Mar 26, 2019
You are just burning down the surface charge that accumulates while charging. The controller indication is not designed to be accurate with a load on the battery while charging. Your battery will continue to drop until you are down to 12.7 volts that represents full charge. At that point it should hold much more steady down to 12.2 volts representing 50% under modest load.

The 12 Volt Side of Life
2oldman
Explorer II
Mar 26, 2019
..
MrWizard
Moderator
Mar 26, 2019
your charging power in watts 14.4v*2.8amps= 40.32 watts

your PC use ? 19.5v*10.8amps= 195watts this is probably max power use (not counting conversion losses) Not avg PC power use

any way, these numbers say you are using almost 5 times the power, than the solar panel is providing

laptop power use is probably about 1/2
but even 100w of use is 2.5 times the solar supply
so yes you are using mainly battery power, with solar just pinch hitting a little bit

my laptop avg about 50watts of power use

you did not say HOW long this use cycle is
minutes? hours?
jornvango
Explorer II
Mar 26, 2019
So it appears to me that the solar is providing 2.8 Amps while the laptop is taking 10.8 A? Or is it taking 3.2 A?
2oldman
Explorer II
Mar 26, 2019
Nothing wrong. As power is being taken from the battery, the controller is reverting to bulk charging voltage. What you should be concerned with is the amperage going in vs going out.

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