Newbie question about solar charging

My iPad 2 has a charger rated at 12 watts, meaning the maximum power that it can provide. The maximum would probably only be used when the device battery is very low. We routinely charge two iPads in our RV with a 100 watt solar panel. We never plug in to shore power and never take the generator with us. The battery monitor seems to always stay at 80% or more.
My laptop charger is rated at 45 watts but I haven’t used it in the RV. If I did, I would add another solar panel.

So just to verify the numbers in a new test I'm doing...

It's 11am and full sun. The portable solar panel is facing the sun and the controller reads 14.4V and 2.6A. That's 37.44W that the solar is providing.

I plugged my cell phone charger into a small car inverter that's plilugged into the 12V outlet in the camper. The cell phone charger's output reads 5V at 1.2A = 6W. So, this is much less than the 37W provided and the solar is able to charge my phone AND have 31W left over to charge the house battery. Correct?

My wife wants to charge her iPad Mini next. Her iPad charger's output reads 5V and 600mA. Is that only 3W it will use?

An AMP HOUR METER will show how full or empty the battery is without having to deduce and memorize a dozen formulas. A new sensor circuit between the pickup (shunt) at the battery, and the new meter on the wall is required.

3.2amps * 120v =384w input to the power supply
195w output from the power supply, most likely PEAK USE

whatever the real use is, you are using more watts than the solar is producing

Airdaile wrote:
Mine is 19v at 2.37 a DC. The OP must have a Mac.

It's a Dell Precision laptop which is Dell's mobile workstation laptop so it's more performant compared to 'regular' laptops.

DC output is 19.5V 10.8A 210W

Mine is 19v at 2.37 a DC. The OP must have a Mac.

2oldman wrote:
That seems like a huge amount of battery charger for a laptop. Your solar won't handle it.

I agree, just checked my lap-top and the power brick output is 3.25amps at 20volts. Call it 60 watts. I suspect the computer actually draws less than that. Something is not adding up in your figures. But even if the computer power draw is comparable to mine, it will slowly discharge your battery.

jornvango wrote:
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?

The 3.2a is at "120v" for the input spec of the charger.
The 10.8a is the "12v" output spec of the charger.

The laptop will pull about 60 watts when being used and when "off' but charging, will pull a smaller and tapering amount as it charges up. 60w is about 6 DC amps using inverter and times ten rule.

The 2.8a is what the controller is providing from the solar panel. You have no way to know where the 2.8a is going, as some will be for the battery unless it is all going to your RV "12v" loads

There is no way a controller can tell how full the battery is like 50% or whatever.

The solar (and other chargers like your RV converter) will supply the loads first, and the battery gets what is left over if any. Your laptop when on will be taking it all with your solar set-up. Might be some going to the battery when just recharging the laptop with it off.

To understand what is going on you need a battery monitor that does only battery in and out, and compare that with the solar controller's numbers.

BTW, you "100w" panel will do about 6.2 amps aimed at a high sun, but its "power" (the watts) will be less. If the controller is PWM, the solar's voltage will be battery voltage, and with MPPT, your amps to the battery will be watts out divided by battery voltage, and the watts out will be reduced by the sun heating the panel, line loss, and controller loss. So you never get that "100w".

jornvango wrote:
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?

If the charger actually drew 3.2a, then it would be 32! The rule is that for any given 120vac amperage, the 12vdc amperage is 10 times that. Why? Because 12v is 1/10 of 120v, and watts must be conserved.

Your charger's output is about 20x11 or 220 watts. Assuming about the same power goes in to it, I'll let you figure out what the amperage would be coming from the battery. This is stuff any good RV electrician should know.

To make any sense of all these voltages and amps, you must convert it all to watts first.

Nothing wrong. Those are the sort of numbers to be expected from the hardware at hand.

A 100 watt solar panel will deliver AT MOST 100 watts but only at high noon on a bright sunny summer day, and then only if oriented perfectly at the sun. Any sub-optimal conditions will yield less power, and 40 Watts is an expected output in normal use. Meanwhile, your laptop charger is pulling 195 watts, so yes, that will draw down the battery to the tune of 155 watts.

To fully power the laptop charger, under those conditions, you would need another 400 watts of solar panels. The truth of the matter is that 100 watts of solar is almost enough to keep your battery topped off if you use minimal power, a few lights and refer control board. 200 watts would be better and 400 better still. 400 is also probably too much for a single battery to handle with regard to maximum charging rate under optimal solar conditions.