I have some old solar panels on Nautilus that I suspect aren't pulling their weight anymore. I checked the voltage and they have slightly less than the new one but does anyone now how I check the Amps they are putting out?
I have about 400w of solar but never get more than 8a coming in through the regulator.

Any ideas much appreciated.

The suns radiance is measure in Kw/m2. and solar panels performance is rated at 1000 kw/m2. This would be a nice sunny day in summer.

Now the label on the back of the panel should have a Voc (voltage open circuit) which could be about 18.5 Volts. This is what your panel should read when it still cold and getting 1000 kw/m2 of sunlight and not connected to anything except your volt meter.

The next is to short the output of the panel and check the current. The label should have these reading as well "Isc". Theoretically, the panel current should match the current stated on the label. You will need an amp clamp to do this test as some multimeter don't like this sort of current going through them.. The guys in the solar industry have a Seaward meter for doing the same test, but it costs about $2000 or more.

Things to remember. The panels work best when clean, no shade, facing directly at the sun and cool (good ventilation around them). This is how it should be when doing your test.

Cheers

As per what others have said. But be aware the maximum power is what you want out of the panel which depends totally on the load, and the voltage and current to get that will be different from panel to panel. ie. A panel producing 15V at 2A into a load is 30W (15x2) and a panel producing 30V at 1A is also 30W (30X1).

If the load is extremely light (like 1000 ohms) the power out of the panel will be lower than what it can do. If you short circuit the panel the power out will also be lower than what it can do.

The load needs to be adjusted up and down to the right value to get the maximum power out. Thats what MPPT regulators do. They (invisilbly to you) increase the load on the panel (taking more and more current) until the volts start dropping and thats the maximum power point. The then have a tricky switching power supply inside to convert the maximum power it can get from the panel by adjusting its load (it might be 28V at 3.2A for example) into around 14V to charge your battery.

If the panel is producing 28V at 3.2A (28x3.2 is 89.6) at its maximum power point thats 89.6W. (My 80W panel on Trek does that when sunny). But 28V is NG to charge a 12V battery so my MPPT solar regulator transforms that into 6.4A at 14V if its needed (6.4X14 is 89.6). Theres no free power, we are just changing its volt/current ratio.

So after all that waffle to do the perfect test you need to check the maximum power point on the panels label and put a load on to make that happen (on a sunny day). if with the correct load you get the right volts and amps the panels good to go.

Any one who doesnt believe the voltage solar panels put out can check the one on my boat Trek anytime. Just SMS the word "status" to 0431935720 (thats my Trek Transponder boat monitors number) and wait a few seconds. You will see that in the morning after the batteries have been run down by the fridge overnight and are being charged the panel is putting out somewhere around 30V!