Measuring amps. 120 watt panels.

Thanks Ross, another peice of the puzzle falls into place. What I am trying to do is measure the output in amps to understand the period of time an 80ah battery will last running a 40 liter fridge. I guess the answer is calculated at the rated output of the panel.

Kevin the thing you MUST understand is that there are many variables ........ a battery is not a bucket of water, a solar panel is not a tap and there will be no hard and fast simple figures.

The output capacity of the pannel will vary with the amount of sun it recieves.

The capacity of the battery will vary dependfing on how heavily it is loaded.

The charge current of the batter will vary greatly even with a constant voltage ....... beginning at a low state of charge, the battery will accept high charge currents ...... as the battery " fills with charge" the charge current will progressively drop till practically nuthin'

Oh yeh ... the average current drawn by the fridge will vary dramaticly depending on how the fridge is used and what the ambient temperature is.

Cheers

Actually your 250 puts out 20A until the battery terminal voltage rises to about 14.4V (its maximum allowed voltage) at this point it swaps to constant voltage mode, this occurs when the battery is around 80% - 90% charged dependent on the size of the battery. As the battery continues to charge the charge current will gradual reduce as the internal voltage of the battery rises. The charger will continue in this mode till the current drops top less than a amp and then switch to float charge.

Regarding alternators, most alternators have no idea when the battery is charged, they simple maintain a float voltage, the voltage may reduce overtime but this is due to temperature compensation.

ECU controlled systems are different, the ECU determines the charge state of the battery and controls the alternators output, generally the voltage will be around 14.2V@24C and then reduce to a very low level once the ECU is happy the battery has reached a "reasonable state of charge"

Pretty much what I said, without the complications. I was trying to show a bit of empathy for the original poster who did say he did find the whole thing a bit difficult to understand.