I have a MPPT 100/30 Smart Solar charge controller. I tested the panel and connected it and it worked fine. I then disconnected it so I could mount it on the vehicle roof. After mounting it and reconnecting the panel to the charge controller, it only shows low voltage varying between 2-13v no higher I have tested all the wiring and connections the whole way from the panel through and it’s always showing 16v or greater depending on where the sun is. But as soon as I screw into the terminals in the controller the voltage drops back below 13v.
Picture of the solar display when I tested the panel before mounting and now currently.
Straight line from the 250w panel on roof to anderson plug connection on back of 12v system box, straight from that anderson into the solar controller. Have taken readings at solar panel,anderson connection and wire ends before going into controller all well above 18v but as soon as connected to controller terminals, shows a massive drop.
It looks like a metal frame, the devices are mounted to, right?
What is the voltage reading when u use a voltmeter on the screw terminals?
Does the readings of the mppt and voltmeter correspond?
Just unscrew/isolate the mppt from the mounting surface and check whats happens.
BTW: 16V is not enough, the voltage of the panels must be at least 5V above Battery voltage for the MPPT to start.
In general a significant voltage drop of the panels is to be expected, because that‘s the way MPPTs are working. They are shifting voltage/current to the point where the power is maxed out.
What are the specs of your panel? Do you have two identical panels to use them in series to double the voltage?
Hi there. I have an identical problem to Jason. Jason, did you find a solution? I have a domestic roof 36V panel that I’ve modified to give 24V. I have a van with a Victron 75 I 15 controller. I am not using the load terminals. I simply have the battery and the panel connected to the controller and then the switchable van load connected in parallel with the battery. Again, I normally get 22V from the panels but this drops to 12 as soon as I connect the panel to the controller. Could this be because I have nothing connected to the load?
Thanks for any advice. I am a commercial LV electrician but little experience with DC or solar.
This has nothing to do with the load output if nothing is connected to it. The normal reasons for the PV voltage dropping to the battery voltage are
Poor connection in the cabling between panels and controller including poorly crimped MC4 connectors, loose connectors, cheap resettable breakers etc. Look for voltage drop.
Panel fault.
Low light on the panel.
Panel poorly specified so the maximum power voltage is at or below the battery voltage.
It is interesting that you say you have modded the panel from 36V to 24V. One has to ask why.
Hi there. Thanks for getting back. Yes, an odd decision to modify the panel. I did it before I had a controller. It still doesn’t explain why the input voltage drops from 22V to 12V when I connect the controller. Do you think I should revert to 36V?
Check your panel wiring first. Do a short circuit current measurement on the panel using a DC ammeter setting on multimeter usually up to 10A or a DC clampmeter. This will tell if you have a wiring / panel fault.
Re the mod, I was more wondering if the mod had damaged the panel rather than affected its maximum power point. Swap it back if you can.
Do you have cheap resettable breakers in the panel supply like the ones below. These are not very good and often have high resistance.
