A few more questions about solar panels...

This may help. Solar panel cells are not batteries and are electrically diodes and hence the higher voltage panel cannot backfeed the lower panel. Hence no heating occurs in the lower voltage panel and blocking diodes are not needed. Most modern controller prevent the function of isolating the panels from controller and hence the battery is not discharged at night. Ie Blocking diodes are not needed.

Scroll down the the 4 parallel panel diagram with different amps and voltage for an example. https://solarpanelsvenue.com/mixing-solar-panels/

Qwazert wrote:
Does the controller sense that less is required because the batteries are fully charged (still connected to shore power)?

You have these panels hooked up AND connected to shore? I guess the simplest answer would be your 2-3 amps is all the batteries are asking for, and adding another panel doesn't make any difference.

Turn shore off, put some load on the batteries, drain them a bit, then try again.

Assuming controller is PWM the panels will operate just above battery voltage and provide Isc in the bulk phase of charging.

Panels in parallel need to be the same voltage (within 1 volt or less).

CA Traveler wrote:

time2roll wrote:
Put a 20 amp load on the battery and test again.

X2 Your 2 parallel panels can deliver 5.4A+5.17A = 10.57A at 17.6V (the lower voltage panel). This power loss from the higher voltage panel will not be a factor for a PWM controller as long as your wiring losses do not limit the maximum charge rate the battery will accept, ie the absorb voltage for flooded batteries.

:h

Hmm, not so sure about that.

In parallel the combined voltage will result in a lower voltage than the highest panel voltage rating which does affect PWM output. Some of the voltage (hence some of the wattage) developed is wasted (IE is lost) as heat in the lower voltage panel.. The lower voltage panel due to additional heat may result in a further reduction of harvest.

This is the same thing as paralleling old wornout battery(ies) with new batteries.. The old batteries will draw down the voltage of newer batteries until they reach equilibrium in voltage..

Mismatched voltage panels for maximum harvest are better suited to be combined in series and use a MPPT controller.

There is a considerable 5.2V difference between the two panels open voltage rating, that is about 11 - 12 cells difference (each individual solar cell in a panel develops about .5V).. My guess is the max harvest might be in the range of 7A-8A at best, not 10.57 as it isn't going to be a linear addition of current.

This is why adding isolation diodes might prove beneficial since Schottky diodes only drop .3V and would help maximize the harvest in parallel with mismatched panel voltages with PWM controller.

I would agree that if the OPs batteries are already charged and topped off, they will not see more than a couple of amps.. In this case for testing purposes they need to turn on at least a 10A "load" then check the current being harvested from the panels.

You can also test each individual panel separately two different ways....

One way is with a volt meter / amp meter. In sunlight, connecting the meter to the MC connectors of the solar panel you should be able to read the Voltage and then the amps. This way you know your panels are both good.

Another way is to hook them up to your controller by themselves (one at a time). Do each of them work (according to your solar charge controller)?

If your batteries are fully charged, you will not see a difference if you hook up 100w, 200w, 1000w....your battery can only accept a certain amount of amps and when fully charged that amount is quite low (usually .3 to 2 amps). Are your batteries also hooked up in your rig? If so, you can turn on a bunch of lights/etc to create a load (draw) on your batteries. This will allow more current to flow from your solar panels.

Keep us posted and good luck!
Chris

time2roll wrote:
Put a 20 amp load on the battery and test again.

X2 Your 2 parallel panels can deliver 5.4A+5.17A = 10.57A at 17.6V (the lower voltage panel). This power loss from the higher voltage panel will not be a factor for a PWM controller as long as your wiring losses do not limit the maximum charge rate the battery will accept, ie the absorb voltage for flooded batteries.

Put a 20 amp load on the battery and test again.

One has open circuit voltage of 22.60V and the other has open circuit voltage of 20.8V

Most likely neither panel has a isolating diode which prevents battery from discharge at night. So, basically the panel with lower open circuit voltage is now drawing power from the panel with the higher voltage until both panels are the the same voltage..

Basically one panel canceling the other panel due to a mismatch in voltage.

Ideally paralleling panels without a isolation diode they should be "matched" in voltage..

You can correct that, but that requires adding a isolation diode to output of each panel and then connecting in parallel..

The drawback of diodes is they drop about .7V for standard diodes and .3V for Schottky diodes.

Otherwise, you could of coarse you can run a dedicated controller on each panel..