newbie needs second opinion

[big-pete-007]

Hello everyone.. newbie here.. Just need someone to check my work and tell me that I'm not crazy.

I have 3 - 100Ah 12v lifep04 batteries in parallel.. 12v - 300Ah total.
I have victron SmartSolar Charge Controller MPPT 100/50
I have 2 solar panels set up in series
panel voltage (voc): 46
panel wattage (w): 325
panel short circuit current (isc): 9.1
panel max series fuse rating : 15
panel temp coefficient : -.398c
I have 3000w 12v inverter

I want to hook the 2 panels up in series to the charge controller and then connect charge controller directly to the 3 batteries in parallel for charging.

the online calculator (see attached images) show the 2 panels in series would deliver max of 100v to the charge controller at 35F.. I live in Phoenix, AZ so that's about our lowest daytime temp.

thanks soo much in advance.. its easy to become overwhelmed with all these numbers but I think I'm on the right track..

 

[WrenchLight]

Did you use degrees C or F when you calculated the max voltage at 30F? I still wouldn't want to exceed the max voltage rating of the MPPT.

 

[littleharbor2]

If you're going with a 12 Volt system, I would recommend running these two panels in parallel So you do not risk burning out your charge controller The voltage is just too high and close to the maximum voltage limit of that controller to series wire. Besides, the voltage of those panels is plenty sufficient to get MPPT benefits from the controller to your 12 Volt system

 

[Brucey]

Connect them in parallel. Too much of a risk of exceeding 100V during early morning cold temps. Magic smoke will be released.

Amazon.com

 

[big-pete-007]

If you're going with a 12 Volt system, I would recommend running these two panels in parallel So you do not risk burning out your charge controller The voltage is just too high and close to the maximum voltage limit of that controller Besides, the voltage of those panels is plenty sufficient to get MPPT benefits from the controller to your 12 Volt system

appreciate the response.. do I lose potential charging speed/power when connecting in parallel? if I were to keep them in series could I just put an inline DC 100v breaker with the panels so it doesn't ever go over 100v which is seemingly unlikely? thanks.

 

[Brucey]

appreciate the response.. do I lose potential charging speed/power when connecting in parallel? if I were to keep them in series could I just put an inline DC 100v breaker with the panels so it doesn't ever go over 100v which is seemingly unlikely? thanks.

In a 12V system your voltage will be above the Victron sccs minimum charge voltage requirements, so parallel will be fine.

You cannot use a 100V dc breaker (which trips on overcurrent - amps) to protect from over voltage.

 

[littleharbor2]

What Brucey said.

 

[big-pete-007]

In a 12V system your voltage will be above the Victron sccs minimum charge voltage requirements, so parallel will be fine.

You cannot use a 100V dc breaker (which trips on overcurrent - amps) to protect from over voltage.

Very good info. I really appreciate it. One last question. If I connect panels in parallel would it allow me to connect more than 2 panels in the parallel configuration without blowing anything up and getting higher amp charging?

 

[MichaelK]

Very good info. I really appreciate it. One last question. If I connect panels in parallel would it allow me to connect more than 2 panels in the parallel configuration without blowing anything up and getting higher amp charging?

Yes and no. You have a 50A controller. That means that anything above 50 amps passing through the controller is wasted. It might not blow up, but running that many amps through your controller is just a waste of resources.

To get an honest estimate of what your real-world output will be, I like to divide the wattage by the lowest voltage your controller is likely to put out, and also include an 85% de-rating to account for heat, consumption by the electronics themselvs, and less than optimal sun. So what you are likely to actually see is.....


[(325W X 2 panels)/12.5V charging] X 85% = 44.2A

So, adding another set of panels facing the same direction would mean 88A. The controller will still only output 50A, so the other 38A just is unused.

What you can do though that works very well is virtual tracking. That is having different strings facing different directions. If you end up with four panels, facing one set of two SE, while the other two faces SW, would insure that you more or less double the wattage produced over the course of the whole day, without exceeding the amp limit of your controller.

 

[mikefitz]

If I connect panels in parallel would it allow me to connect more than 2 panels in the parallel configuration

Yes, your two 325 watt panels will produce a maximum current of 18 amps, well below the 50 amp limit. In theory with ideal solar conditions the 650 watts of panel charging at 13.5 volts givs 48 amps In to the battery.
Adding more panels in parallel is possible if the voltage is similar to the 325 watt panels ( Voc 46v). The controller may be overpaneled but this is allowed, the output current will be limited at 50 amps.
Your three 100 watt panels could be used with an additional controller, 3 in series and a 100/20 controller, or use two in series and add in parallel with the two 325 watt into the 100/50.