Quick rundown of my setup. I have 800 watts of solar on my motorhome via 8 100 watt panels. They are in series sets of 2 producing about 44 volts together in each set and the 4 sets in parallel. I have the 250/85 Victron MPPT solar controller. I pull a box trailer with the RV sometimes. I have 4 residential panels each at 350 watts and 44 volts each all wired in parallel as well. When I have the trailer hooked up, the power from the trailer panels goes through a DC breaker into a bus bar. The 800 watts of RV panels go through a separate DC breaker into the same bus bar. But turning on or off the breakers I can use either of the panels, or both of the panels. Iāve just got everything setup and wired, and began testing to see the results. However, Iām not seeing a jump in watts or amperage in the VictronConnect or VRM app when I flip on the breaker for the additional panels on the trailer. Iām limited on my knowledge, but it seems like this setup should work? Is there any reason it shouldnāt work? Do I need to change anything in the setup to allow, or reset up the victron equipment?
Iāve also got the MultiPlus-II inverter, 500A smart shunt and the Cerbo GX and display. Everything is running to 2 400 ah lithium batteries.
A little more info about the panels:
On the RV (8 total count)
Open Circuit Voltage: 22.79V
Short Circuit Current: 5.31A
Optimum Operating Voltage: 19.97V
Optimum Operating Current: 5.01A
On the trailer (4 total count)
Open Circuit Voltage: 46.8V
Short Circuit Current: 9.59A
Optimum Operating Voltage: 39.4V
Optimum Operating Current: 9.02A
You should not mix different panels onto the same MPPT. Although the voltages are close, they are not the same. You will loose some efficiency due to the overall MPP being between the two individual ones.
The MPPT has a ten minute cycle on doing a broader check for a new optimal MPP. Give it that time after switching configuration. I expect it to ramp up the power once it registers the newly added panels.
Whats the reason to use a 250V MPPT to then only feed it 44V? You could very likely put all eight 100W panels in series and feed the MPPT with that (i guesstimated the temperature coefficients, so better check again with the full specs). Higher PV voltage will generally yield more energy.
Same for the trailer, you could run all four in series on that as well. This would also avoid the need for inline fuses, which you should use when running three or more strings in parallel.
The total series voltages are again very close, so you could run the two series strings in parallel, with same suboptimal MPP caveat. But the 85A charge current of the 250/85 would limit the power on good days to about 1kW. You should consider using a seperate MPPT for the trailer, a 250/100 for example
The arrays are producing less than they should probably because of a couple reasons. Itās winter mainly and these screen shots were taken at 10 am. As the day goes on the rv rooftop gets up to around 550 watts.
However, in the combined screen shot, wouldnāt we expect to see combined amperage? Why has the amperage not increased. At all?
The batteries for this test were sitting at about 80% capacity. I actually have 2 Mppt controllers in the trailer that can take the input from the trailer panels if it is separated from the rv. Here you can see their performance alone:
The reason for the 250/85 was simply that I wasnāt sure what the panel makeup on the trailer was going to be. And wasnāt sure if I was using one or two Mppt controllers.
The trailer, as you might has just seen in another response, has 2 Mppt controllers for when itās alone. Those mppt controllers dictated how I setup the panels individually like I did. And it matched the rv setup for voltage, so I assumed that was best.
I may have to get a second Mppt controller for the rv, but didnāt want to jump right at that answer without digging in more as to why the current setup didnāt work. I figured the voltages were similar enough to work.
Thanks for the continued input. I have the bare minimum knowledge and am working with āI think this worksā lol.
Further question for you lol.
You said: You could very likely put all eight 100W panels in series and feed the MPPT with that (i guesstimated the temperature coefficients, so better check again with the full specs). Higher PV voltage will generally yield more energy.
Would I actually be able to do this with cables coming off those 100w panels? I assume they are 10awg and therefore limited to about 30 amps (without looking at 2:00 am). With 8 in series Iād be up around 40 amps.
Same with the residential panels. At 10 amps each Iād but up around 40 amps total as well if the were series. Not sure what size cables are on those panels though.
So it has its own 12V system then. Presumably with its own LiFePo battery?
Then you could simply use a Cyrix combiner between the two. You leave the RV panels connected to the RV MPPT, and the Trailer panels connected to the Trailer MPPTs, then join the two systems with the Cyrix (you need matching battery chemistry on both systems)
No switching around. As soon as the two are combined, and at least one of them receives a charge, the Cyrix will share that.
Alternatively you could use an Orion Smart/XS, but that would only allow for one-way charging (until the XS receives its long awaited update). However works with dissimilar chemistries.
In series you add up the voltages, so about 200V in total, the current stays the same, 5A. Your parallel system currently adds the current, to about 20A at 40V. The parallel setup produces the higher current, so you are loading the cables more at the moment.
Did you use inline fuses in your parallel setup? If not, thats a risk. Reverse current could flow through one of the series strings. A single series string, all eight panels in series, completely avoids that.
Correct me if Iām wrong, but you have one array at 800w and another at approx 1400W?
If correct, and both arrays individually were producing essentially the same output, then something is limiting the output of the MPPTs, regardless of the winter conditions. The 1400W array should output more than the 800W array under the same conditions.
Could be 1 or more settings, in the MPPTs, cerbo, or BMS, or otherā¦ total charge current limit, or battery charge profile, etcā¦
I just noticed you said lithium batteries, and its winter. Their BMS will slow or completely stop charging if their temp is too cold, especially below freezing.
I agree with you. Their output should have been different and should have shown an increase when all were working together. (At least in the limited theory in my head).
Winter has been weak here. While Iād normally see 5-10 degrees Fahrenheit around this time, it was about 50 degrees at the time of those readings.
Iāve not heard of the Cyrix combinerā¦. Iāll read about that. We (my dad and I) did a system using relays to switch between the two systems. Yes they are both lithium.
I used dc breakers instead of inline fuses. Does that cause any issues?
I was speaking about the limitation of the cables on the panels. 8 of them at 5a each is 40a. The cables built in the panels I believe are 10 awg, so they should be limited to about 30a.
If you rewire them all in series, in series voltages add up, not currents. Your total current will be up to 5A, anywhere in the PV system, on the positive cable, on the negative cable, on all cables between the panels.
You currently use a single breaker for all eight 100W panels? Like this (symbol shows a fuse, but ignore, should be a breaker)
Iām using 1 breaker like your 1st image. Fuses are easy to do in your 2nd picture but breakers arenāt lol. And fuses are a pain to get to on the roof when Iām not at home.
Sorry. My brain wasnāt thinking straight on series voltage increasing .
May give an indication of potential system lossās due to panel voltage / current differences.
Why do you have a 250v capable mppt , but only have panels configured to 49v ish pv?
Higher voltage configuration would reduce cable size / number of cables and connectors.
I have this controller, as I said earlier, because I wasnāt sure what configuration was going to do with panels. Thereās definitely no issue with over sizing the controller and allowing for different panel installation options or growth.
However, the reason for the post is that there is something definitely off. Inefficiency caused by different panels on the same Mppt shouldnāt cause a 50% reduction in current. And I should see some increase in current when I combine the existing roof panels with additional panels. This is the issue Iām trying to resolve. Which size mppt controller and how I wire the panels will just provide me with potential efficiency gains. Iāll go down that path as well - but not until the basic question of why itās handling the power itās getting now isnāt correct.
Have you tried the above link i posted.
You may be surprised at the lossās with mismatched panels.
Ps to use the calculator simply work out the series strings first, then use the result as a panel and put that in paralell with other serirs panels.
You have proved each array supplies power.
Yet when combined the combined power is not the sum of the two.
Reasons
Wiring is incorrect / breaker is off.
Something is limiting charge - check mppt settings / check battery bms settings / is mppt controled by inverter or bms?. If being controlled what is the actual current the mppt is being set to by inverter/bms?
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