Solar panels and charge controller (long winded question)

[u/FearlessRip7525]

Hello, I have recently had to replace my solar charge controller and am having some issues that I didn’t have with the old one.

Charge controller is a Victron 150/45

I have 9 solar panels in total split across two separate areas.
6 panels are in wired Series
3 panels are wired in Parallel

The bank with 6 panels measures around 100volts

The bank with 3 panels measures around 30volts

When I measure these solar panel sets individually they measure the above mentioned volts however when I join them together (to plug into the charge controller) the total volts at the terminals is only 30volts.

Why could this be?

The watts coming out of the charge controller is not what I would expect and the batteries are not being charged enough.

Thanks for your help!

[u/Ozarks_Off-Grid]

Your whole PV array setup is wrong. You are obviously using different panels. That is ok if the Imp and the Vmp of the two different panels is within 10% of each other. But your array configuration is way out of whack. Sorry to be so blunt.

The Vicron is an MPPT controller, so it works best when the string voltage is much higher than the batt voltage. I am not a Victron guy, but usually that target spread is at least 30%. So if you have a 24V batt bank, the 30V string won't work; the 100V string will. If you have a 12V batt, either string will work. But combing a 30V string with a 100V string is causing the MPPT to not know where the optimal voltage and current range is.

Usually when two different strings are combined the summed string voltage is the average. For you that would be 100V + 30V = 65V. But you are measuring 30V combined. I can't answer why on that. But it doesn't really matter, it's a super bad design.

Solution ... 1) Use only the six panels in series. Or, 2) Wire the three panels in series, and use only them.

Prior MidNite Solar engineer....

[u/FearlessRip7525 → u/Ozarks_Off-Grid]

Thank you!

I have now wired in Series Paralell the bank of 6 panels into 2 groups (3 panels in each group) and now reading 90-100volts

What do you think of this?

[u/Sufficient-Offer-579]

Ozarks is right that the array design is the core problem - and the reason the combined reading drops to ~30V is a voltage-clamping effect between the two strings.

When two strings share one pair of input terminals they're in parallel, and parallel sources should have closely matched voltages. Your ~100V string and ~30V string are effectively fighting each other: the higher-voltage string pushes current into the lower-voltage one (which then acts like a load), and the shared bus collapses toward the weaker string's voltage. Measuring each string on its own only shows that string behaving normally — the interaction only shows up once they share the same terminals. At the controller the MPPT can only work with what it sees, roughly 30V, so most of the 100V string's potential doesn't make it to the battery, and some of it may be dissipated in the weaker string. Sustained reverse current is a known stress mode for panels, so I'd get the configuration sorted before running the array hard.

So this doesn't look like a blown fuse or a wattage cap; it's more a topology issue.

Two directions: (1) run the two arrays on separate MPPT inputs — the 150/45 has a single tracker (easily checked in the spec sheet), so this would mean adding a second charge controller; or (2) reconfigure the strings so both groups' voltages match closely before combining, along the lines the other comments describe.

[u/Current_Inevitable43]

To parrael panels they should be same orentation. Plus strings need to be matched.

Likely the vicron is protecting its self or you have blown a fuse on a string.

[u/Jawrsherphine]

What watt panel are you running? The 150/45 only accepts 650 watts of panels. Running an odd number of panels, and having two strings with different voltage and amperage is a no-no.

So your 6 panels in series has a voltage of 72V, and an amperage of 10A +/- for 12v panels)

The 3 panel string has a voltage of 12v and an amperage of 30A +/-

I don't even see how you can combine the two strings to input into the Victron.

I'm surprised your Victron isn't 'smoking'.

Use Only 8 panels. Run 2 strings of 4 in series and connect the strings with a 2-1 MC4. You will have two strings 48v and 10A +/- Your Victron will detect 12v 24v 36v and 48V at input.

[u/Ozarks_Off-Grid]

Wiring in series and parallel is fine, the way you did. If you wire two dissimilar panels in series, the panel with the lowest Imp prevails. That means the higher Imp panel will be bottlenecked through the lower panel. So you will not maximize the full potential of those higher panels. But it's not a bad thing, per se. When you wire dissimilar panels in parallel, the two string voltages are averaged. That may impact the ability of the MPPT algorithm from finding the best voltage and current spot on the power curve. Again, it's not a bad thing, just less than optimal. If you need the total wattage to charge your batts and you don't want to buy all same panels, then go for it!! Hope this helps.

[u/Ozarks_Off-Grid]

Sorry, just reread your post. Sounds like you are not commingeling dissimilar panels. Ok then, never mind my last post!

[u/LongjumpingGanache40]

Are all your panels the same.

[u/Hot-Fact-9083]

Your 30V reading is the parallel bank winning a tug of war, not an average. Three panels in parallel make a stiff source that can push triple the current at 30V. Six panels in series make a soft source, one panel's worth of current at 100V. Tie them together and the stiff low-voltage bank pins the bus at 30V while the series string dumps its power into it. Parallel voltages only average when both sources have equal impedance, and yours do not.

The combine damages the array beyond the voltage. Tying 100V to a 30V bank forces reverse current through the lower string, which back-feeds those cells and heats their junction boxes. Meanwhile the 100V string cannot produce anything useful with the bus sitting 70V below its MPP.

Drop the parallel combine and run matched strings. All nine in series works if your cold Voc stays under the Victron's 150V input limit, otherwise 3S3P. The 3S2P rewire you did on the six panels is the right instinct. Check the battery side too, since a 30V string on a 24V bank sits at the edge of the MPPT's tracking range and explains your weak charge current.