Measuring solar panel's charging ?

8 amps at 12volt equals 96 Watts. Might be a little small for 120 Watt panels??

I thought the wattage was rated at the open circuit voltage, If the OCV is 20V and the power output is rated at 120W then this would be 120/20 = 6A.
not accounting for losses of course. not sure if it can be a straight extrapulation if you reduce the voltage to 13 odd volts via the regulator and therefore be 120/13.6= 8.8A

Sirgalli
Here is a web site that gives an explanation of MPPT. Who ever wrote it seems to have made it fairly simple to grasp. (but I am an electrical)

www.solar-electric.com/learning-center/mppt-solar-charge-controllers.html/

Also be very careful if you are using a multimeter to read current by connecting it in to the circuit. It may be better to get a clamp-on meter that is capable or reading DC current (some clamp on-meter only can do AC Current, like in the house power). Something like this from Ebay for $50. (I have one of these) You can also check charge current from alternators plus the rest of the things a meter can be used for.



I also purchased some digital Ammeters for my solar panels from J/Car and they don't operate as specified. I went back to J/Car and got F/all help. Its a pity because I had already cut the holes in my switchboard panel. They were Digital Readouts with a remote shunt. The shunt is like a high current, low resistance block of metal that the meter measures the voltage drop across. It allows you to check the current at the batteries or some other location where you mount the shunt and have the readout some where easy to see.

But you may like to invest in one of these from Jaycar for $150 for monitoring current in and out of your batteries. There are numerous other more expensive ones on the market. I have a Victron (brand) on my boat which seems to be okay. (the thing beside the meter is a shunt). Bit of trivia - they actually calibrate the shunt by cutting through the thin metal strips with a hacksaw until the correct resistance is achieved. (less metal left, higher resistance) (But don't you try it).

sirgallivant, enough confused
Am I wrong, second on top left is nice voltmeter build in..?
If yes, is it working?
Learn to use it, it simple
In the evening, running light & no charge what voltage you see..
for instance just a notch under 12 Volts. 50% capacity left
what else you need to know.
this is most important info what condition is your system
switch the batteries over unles you run them in parallel

for the others ..solar panels are not typical power supply
...you can measure current without any load
and not blowing or shutting down protection
you see .3 volts on 8A, how is V * A = W apply ?

voltage available drops to nothing with the load comprende

Gentlemen, l got a meter, volt amp whatever, l bought it ages ago and because l could not use it l gave it to my dad. He loved it, measured everything with it. Rebuilt bikes, fixed cars, houses etc. Well, he died in '94.
Pic 1.


I would not spend a brass razoo on another one as l am a total incompetent as far as electronics are concerned.
The switch board, like everything else, is working faultlessly, the wiring behind it is pristine.
Pic 2.


On the four way switch one can turn electricity on and off, select no1, both, or no2 battery.
On the toggle switch, (gee l am improving, l picked this one up on googly today) and the display shows no1 or no2 accordingly.
Also, it shows on my Navman,
Pic3.


and also on my chart plotter. It is alarmed, set to 11.5 volts.

If a generous soul would have the patience to tell me what adjustment on the volt meter l have to set, and on the regulator or controller,
Pic4.


which two of the three points l have to connect with the volt meter's pencil without blowing myself to kingdom come, to see how much is the new panel charges, would make me the happiest person on the boat. I know the Sun should blast like a furnace.

Thanks for everybody who tried to explain to or reason with me, unfortunately most of your words were like throwing pearls at swine.

sirgallivant, your multimeter is one of better ones / mirror in the scale for precise reading /
Not suitable for current you wont to measure. / max. current range is 0.25 A / only.

so Sir Vigillant, if you want an observers summary, your multimeter hasn't got the capacity to read how much energy if being put back into the batteries from the solar panel. If you prefer not to buy another one, then you'll be only looking at how much voltage the batteries have got left in them.

Your meter will read this for you, the red and black leads are in the correct spot, turn the dial to 50 on the lhs (DC volts), then black lead to black, red to red on the battery, and you'll get a reading of how charged the battery is. Do it for either battery, and out of interest, use you battery selector in your main panel to do the same thing, select the battery on the isolation, and choose battery test, either for one or 2. It sounds like your familiar with this.

From Charriots chart, you will get an idea of how much juice is theoretically left in each battery.

Maybe then run your radio for 1/2 hour when the solar panel is doing its stuff, test it again, and see how much it goes down, or if the panel keeps up.
To me, this is the usable thing to know, how much 'capacity' you have before your batteries are flat.

One tip for later, if you did end up getting a multimeter later on $15 ebay digital pocket one is fine, most have a 'buzzer' setting that measures continuity.
It can be useful for finding out if a simple switch is buggered, or where a break in a cable may be, and once you've got he hang of it, it's good to know.

Having boats means you end up being a plumber, electrician, rigger, painter, meteorologist etc. to some degree in the end whether you wanted to or not

This is a BEP (NZ) marine version that basically does what you were trying to measure, showing the input the solar panel is giving to the house battery.

I purchased a larger switchboard with one built in from BEP when I rewired the boat, they can monitor more than one battery, but it does start to get a little complicated, as you need to add separate shunts like in Crusoes message above.

why not use your old 40 watter