Checking Panel Voltage w/ Multimeter

Hi,
I have a 100W panel on the roof of a RV with the Wanderer 30A charge controller.
I wanted to check the panel voltage by using a multimeter on the cable screws / connectors on the charge controller. But in full sunlight, I'm getting like 12.4Volts. I am charging a couple of items (laptops, cellphones) when I took this voltage reading, but I assumed that the PV should not be affected by the load on the battery.

Do I need to completely disconnect the wires from the charge controller to get an appropriate reading of the panel voltage? Or am I supposed to get the good Panel voltage from the connector screws? Ideally I'd like to be able to get the PV without going on the roof and/or disconnecting the cables.

Also, the PV green light is very dimmed and it's pretty much always like this, normal? It's not a bright green light like the Battery (BATT) one is. But PV is slow flashing and BATT is solid, so based on the manual, it means it's charging normally.

Thanks in advance for your help!

See diagram page 6 www.renogy.com/template/files/Manuals/Renogy-Wanderer-30A-PWM-Solar-Charge-Controller-Manual.pdf

Battery and PV voltage should be the same during Bulk, the panel is directly connected to the battery thru the controller, the panel operates at battery voltage (PWM controller).

During boost the controller disconnect/reconnects the panel to battery as some high freq. to keep the battery voltage going higher than the boost voltage. The on/off times change, as the batt gets full the on time is shorter and shorter and the off time is longer and longer.

On time/connected, panel V ~ battery V.
Off time/disconnected, panel V ~ Ioc on sticker on back ~21v.

Meters measure the AVERAGE of this on/off so during boost you can measure voltage at the screws of up to 20v.

The same things happens during FLOAT.

Using stuff like charging items lights etc will draw down the batt and panel v so it reverts to BULK (always on/connected).

You 100w panel may be rated 5.5A @ 18v, charging a batt in full sun ya still get the 5.5A but lower V so @ 13.0v @ 5.5A the panel only 'makes' 72w!

Thanks a lot! That is great information and helps me better understand how this system works.
So as you said, as the batt gets full (closer to 100%), the "off time" is longer and longer, I assume this is to charge at higher voltage for the battery to get to 100%.

I always thought that if the panel is doing 5.5A @ 18V, then the charge controller would convert that voltage to 13v and amps would become something like 7.7A to maintain the 100W produced, but I guess I was wrong! So thanks for clarifying that.

MPPT controller has a buck converter, that is what you are describing. mppt controller forces the panel to operate @ max power ~18v and transforms that to battery voltage so in that case 5.5A x18v transforms to 14.1v x 7A or 8+A @ 12.0v or ...

PWM does a direct connect and panel operates @ batt V.

Look at the bottom of this doc, look at the IV Curve, The panel is a constant current source, note the current is constant from 0 volts to 18v (it does start to drop off @ 15v). Temperature and sunlight change this curve constantly!
www.renogy.com/template/files/Specifications/100-Watt-12-Volt-Monocrystalline-Solar-Panel-Specifications.pdf

Your controller tries each day to raise (bulk) batt v to 14.? and hold it there for a couple of hours  (boost) and then hold it at 13.? float. Once the batt gets to 14.?v the on/off starts to keep it @ 14.?v for the 2 hrs (this is how it tapers charge energy). If it did not taper the solar energy would continue to raise battery v well over 16v and overcharge!

The key to understand why you can measure voltage at the terminals in boost over 14.?v is that when disconnected panel voltage is ~20v.
ON/off time is called duty cycle so @ 50% duty cycle the on time = off time so a meter would read the average of 14.?v boost and Ioc of ~20v, (14.6+20)/2 = 17V, as the panel warms up in the sum, Imp goes down, Ioc goes down. DYNAMIC.

Thank you! I guess I'll be shopping for a MPPT controller now!

one of favorite explainations of how panel v matches load (no battery)!

www.youtube.com/watch?v=JZQEJ33xblE

Ya might care to read how high TEMPERTURE reduces MPPT and cold does the opposite 

www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf