Low voltage from rooftop panels

[wareaglewalt]

I have 4 panels (2-90 watt and 2-100 watt) on the roof that all feed into a Victron controller. These have worked flawlessly and in tandem with my 200 watts of portable (on a separate Victron controller) until now. The Victron app is showing the charger for the rooftop panels is off even when in full sun and not even close to a full charge. The solar voltage displayed is around 13.4 volts. It appears from all this that I might have a connection problem somewhere along the line. Each pair of panels feed into a single connector to the box on the roof of the Airstream and each panel has its own pair of MC4 connectors between the panels and that junction box. I want to start narrowing down where the voltage issue is coming from. Can I safely check voltage on each of those connectors going into the junction box with a voltmeter and sun shining on them? In other words can I disconnect the cable from the junction box and put the voltmeter leads on the end of that cable with sun on the panels?

[kb0zke]

Yes, you can. A better question is should you? My suggestion is that you physically check each connection. Since the system was working until recently, something happened to mess it up. Maybe a connection came loose, maybe a wire broke. If everything looks and feels right, then start checking the volts.


Remember that you are working on metal, which conducts electricity, and you are on a ladder. A shock can startle you enough that you can fall. The fall doesn't hurt, but the landing does. Also, you are working with voltages and currents that can electrocute you. That said, people safely do this every day, so it can be done. Just think about the hazards and how to avoid them and you will be fine.

[waninae39]

if you get a clamp style meter, you can measure the currents on each line

I use a klein CL390 meter and it works very well
https://www.amazon.com/Klein-Tools-C...s%2C192&sr=8-1

[vanderwielen]

Yes, you can safely do this. But you might disconnect one panel at a time and interrogate the Victron App to see if a difference is detected. It would appear that your battery voltage is being reflected back to the MPPT controller, which might mean its failure. So, before getting not the roof, you might disconnect in input to the MPPT controller and measure the panel voltage. BTW, down the road, a simply way to test each panel is throw a towel over each one individually and watch the result on your app. Good luck

[vanderwielen]

[QUOTE=waninae39;2769595]if you get a clamp style meter, you can measure the currents on each line

I use a klein CL390 meter and it works very well

If he gets no current, an ammeter is worthless. Additionally, this would require he slice the cable for each to expose the + wire since you can't clamp both the + and - at the same time.

[Redbarron55]

I bought a cheap AC/DC clamp on meter on Amazon that works pretty well for me.
Here is a link to the $30 thing.

https://www.amazon.com/dp/B0CVXCFMLY...sin_title&th=1

It works pretty well, but the test leads are not the best.
Being able to make measurements from an amp or so to 400 amps could be useful for lots of things.

[Rolind]

Others certainly may have more info than I do on this subject. I seem to recall that white zamp rooftop combiner boxes were subject to internal fuse failure. If you have a white rooftop combiner box, this might be a good place to start.
I would also consider disconnecting all ac and dc power to the TT and see if charging resumes when you turn everything back on.
Good Luck

[OrangeCrush]

We had similar issue and it turned out to be a bad Shortsop breaker in the Zamp rooftop port. This device is only rated for 14V and it is not clear in your post but it sounds like your are running 2 series and 2 parallel. If so that puts you in the 40-50 volt range and based on communication I had with the manufacturere this device is likely to fail at those voltages. Your plan to start by testing the panels is good but make sure you turn off your Victron controller before doing any hot plugging of the pnaels. To do this properly you need a multimeter and if you don't have one I suggest getting one and make sure it has at least 10A current test capability (<$35 Amazon). There are many online videos that can walk you through testing the Voc and Isc of the panels. Bottom line is you should be within a volt of the Voc even in marginal sun (~22-25V) and you should be getting decent current depending on sun (50+% Isc). If the panels test good then your issue is from the Zamp port down.

[JeffKim]

Our connections in the combiner tend to come loose as others have indicated, but I just notice the output is much lower than I expect in full sun, not zero. I need to figure out something to keep them from working their way out.

Originally Posted by kb0zke

Remember that you are working on metal, which conducts electricity, and you are on a ladder. A shock can startle you enough that you can fall. The fall doesn't hurt, but the landing does. Also, you are working with voltages and currents that can electrocute you. That said, people safely do this every day, so it can be done. Just think about the hazards and how to avoid them and you will be fine.

Wondering about this. I agree it's good to be cautious and safe, but if 2s2p, that's 48V or so at 5A on each set of panels. The safe DC limit is set by OSHA at 50V (not sure about current), so it might be felt but not life-threatening I'd guess.

[Redbarron55]

I Think that I was not as clear as I could have been about the AC/DC clamp on ammeter and testing solar panels.
To see the actual current from and single panel in parallel or any string of series you just have to clamp the meter around the wire going to or from the panel(s). You clamp only one of the wires as if you measure the input and output at the same time you will read zero.
If you have four panels in parallel then all of the negative leads come together and all of the positive leads also come together. Clamp around each in its turn and read it's contribution to the total. A bad connection on any one of the two leads of the panel will be detected.
If you have series or parallel then clamping around any one of the leads in the string will read the current of that string, Of course the voltage will be higher than a single panel.
There is not really a problem with electrical shock in the above case as the panel wires are insulated to the 1000 volt range and the meter is also insulated.
As an aside I had 4 panels in parallel, but I am currently getting more charging with two in series paralleled with another series pair.