question

ewoktech avatar image
ewoktech asked

two mppt's in paraels or serires

Hi guys


If I have the following panel set up..

2 x 250 watt in series

2 x 250 watt in series

2 x 300 watt in series

2 x 300 watt in series.

4 x strings in palarel connected to a MPPT 150/70.


We have been having trouble with wattage from the panels been al over the place and but getting enough to the batteires.

Was getting 1400wat to 1600watt from the panels, now getting 733watt to 120watt…

Out batteries were cooked and because they didn’t get enough charge current, been lead acid, they have died..

We have 4 x 6volt lead carb batteries that we are going to put on but want to sort this problem first.

We think the 250watt panels may be poly and the 300watt mono’s, plus the voltages are all different.

Victron here said we could put the 300watts in one string i.e series them all up and then do the same to the poly.

Then install another MPPT but SmartSolar MPPT 250/70-Tr VE.CAN (12/24/48V-70A) that could run in parallel with our 150/70…

But they aren’t sure what this will do to the batteries or if we would need to link a coms between the MPPTs’ so they know what each other are doing..

Has any seen or done this?


I am a sparky but I have a better handle on PLC’s and VSD’s then these things…untitle-2d.png

MPPT Controllers
untitle-2d.png (66.9 KiB)
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kevgermany avatar image kevgermany ♦♦ commented ·
To give an answer we need to know more info

Are all the 250W panels same make model?

Are all the 300W panels same make model?

If not how many of each type?

Vmp for each panel type

Imp for each panel type.


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ewoktech avatar image ewoktech kevgermany ♦♦ commented ·
in the picture on the post mate



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2 Answers
seb71 avatar image
seb71 answered ·

It's not a good idea to make a PV array from different panels.

You could go for 2s2p PV array configuration for both chargers and get a cheaper charger than 250/70.

Regarding this:

if we would need to link a coms between the MPPTs’ so they know what each other are doing..

If both MPPTs are SmartSolar you can use VE.Smart Networking for synchronized charging.

The better and more expensive way is to add a Cerbo GX.

In both cases a SmartShunt would be a good addition.

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JohnC avatar image
JohnC answered ·

Hi @ewoktech

I wouldn't change your panel setup. It's not perfect with the mismatched string V's, so you'll take an efficiency hit, but it won't be that much in the washup.

Your real issue is that your batteries are a bit small. 130Ah (24V) of batts can't probably handle (safely) more than 0.2C charge, so 26A. That's just 700W or so. Plus loads if you're drawing at the same time. And if the charge V is reached it will throttle back even more. This is actually apparent in the panel readings you've shown in your pic, the higher readings than Vmp suggest the charger throttling.

Getting good life from your batts means understanding how to treat them and having good monitoring/control. Money spent there is better value than replacing mistreated batts.

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ewoktech avatar image ewoktech commented ·
Ok totaly confused. Now....

Two different answers and two different views.

We had the same thing happen when we hooked the new battery bank up(4 x 6volt remco lead carb 200ah in series for 24volt).

They started to bubble start away and the wattage was all over the place again.

The guys that bring victron into nz said it was the panels confusing the software and change all to the same type.

So would other gear should i be hooking in?


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JohnC avatar image JohnC ♦ ewoktech commented ·

@ewoktech

Sorry to confuse you. I actually agree with Sebastian, but you'd see no improvement in the issues you report by restringing the pv and adding another mppt. I use mismatched panels myself, cos they were cheap. And I may soon add more, accepting that each 250W panel I add may only produce (say) 200W. Still cheaper doing this than adding another mppt, and I have plenty available capacity in the existing 150/100 (48V). 'Return-on-investment', hey. Not technical perfection.

A CerboGX and a Smartshunt (like Seb again) would be my first choices. Seeing what's actually happening and having easy access to your settings are great assets. Guesswork is for bunnies.

And just for fun I'll throw in a VictronConnect (Smartshunt) graph of my system right now to show you Watt variation in testing conditions of flat panels, low winter sun, and passing cloud. This is battery-only, loads I can see on different (VRM) graph(s), but right now loads are only ~200W.

1657688483132.png This is 2500W of panel into 225Ah of batt (48V). The batts at 97% SOC, and a good winter result for me. The Wattage variations I understand and accept as normal - nothing whatsoever to do with mismatched panels. If you look closely you can see 3 short periods of Absorb voltage, and the Watts gradually tapering. At about 400W the mppt will drop to Float stage, and my batts will be 99% done. Thank you GX for that capability.




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