Do I need a 30A or 40A SCC? Calculators disagree....

[SolarQueen]

This is a different issue than this discussion. This is about the ARRAY'S CURRENT INPUT INTO THE CONTROLLER, NOT THE BATTERY CHARGING CURRENT.

Since his TriStar is PWM, the input and output charging current is the same. The OP was talking about MPPT, which is different (as you well know).

 

[ianganderton]

I think there could also be 2 very different types of install being discussed

grid connected where code is king

off grid where optimal performance is king

SSC manufacturers are going to make devices differently for these different use cases

 

[Zil]

Oh I'm such an ass. I thought the original question related to selecting a CC . Beside which, I was just quoting some thing from a manual that I thought would be of some interest to folks that do not know every thing. no longer matters. NLM

 

[Forbisher]

System is 12v, 4 Panel 100W
18v-21.6v,
5.5A-6.11A.
2 Series, 2 Parallel.

Apparently rule of thumb is to size it to be 2/3 max output. 400W / 14.4 Volts = 27.8A. If it's sized at 2/3, that would require a 41A output. I think 40 would be close enough.

However, Victron's calculator says to use a 30A controller.

I would think that Victron knows what they're doing. Are their controllers that more efficient?

So, do I go with a 100/30 or do I go higher? There doesn't seem to be a 40A, so 100/50 is the next step. Any thoughts would be appreciated...

Yes Victron knows what they are doing and I would think they are better than an Epever.

Epever Trace AN 50A at 12V is 600 watts
Reading the Manual.
50A Rated Charge Power 12V is 625 watts.
50A Max PV Power 12V is 937 watts.

So Epever says you can overpanel their 50A scc by about a third.
937 watts ÷ 12V is 78A

You have your 2/3rds rule of thumb backwards.
Buy a 100/50 if it makes you sleep better at night but Victron controllers are robust.
There was a guy on here over volting his Victron and it kept working but melted the plastic. Lolz

 

[zipsonic]

You have your 2/3rds rule of thumb backwards.

I didn't have the 2/3 rule backwards. I posted where I found that rule. It's also apparently from a reputable source. There are companies and installers recommending this. This is directly from the link I posted:



What Size Controller to Get
Add up the total watts of solar panels and divide by either 14.4 for 12-volt systems 28.8 for 24 volts or 58.8 for 48-volt battery banks. This will give you maximum output amps from the controller. If you don’t want to waste output in heat, size the controller at around two-thirds the rated output of the controller.

• 20 amps is good for a 30-amp controller​
• 45 amps is perfect for a 60-amp controller​
• 65 amps is about right for an 80-amp controller​

Using these guidelines, the system won't run hot or waste precious energy. In addition, the fan won’t fail prematurely, which is important because if that happens, the controller could release smoke that will be very tough to get back in.



There is a bunch of conflicting information out there.

 

[gnubie]

From what I've seen of the market decent solar charge controllers intended for installation in an open environment ie not in a box, until you get up into the really big end of things far greater than 80A, are passively cooled. Only the elcheapo units with poor thermal designs use fans.

Plus you seem to be entirely ignoring what I said about efficiency curves that blows the entire argument of using an over spec'd controller to reduce power loss clear out of the water.

 

[Forbisher]

However, Victron's calculator says to use a 30A controller.

I would think that Victron knows what they're doing. Are their controllers that more efficient

That's funny that you as a new to solar guy are doubting Victron's calculator which always seemed conservative to me.

That inaccurate sales pitch you posted sounds like they want you to buy a more expensive controller so they make more money.
Good point by Grubie that there is no fan on a Victron 100/ 30
If you are never going to add to your array then why buy a 50A instead of the 30A?

 

[snoobler]

Good point by Grubie that there is no fan on a Victron 100/ 30
If you are never going to add to your array then why buy a 50A instead of the 30A?

No Victron SCC has a fan, including the 250/100 unit. MASSIVE cooling fins.

IMHO, the "derating" is a hold over from typical electronics guidelines. For resistors, shunts and other electronic components, it is commonplace to recommend a 2/3 to 80% maximum continuous use vs. "rated." This is likely imposed by "conservative" installers that also benefit from promoting higher priced/higher rated components.

Duty cycle is also at play. A SCC may only see the maximum current for a few hours a day. The other 7-8 hours will be at progressively lower currents as you approach beginning and end of solar day.

I don't see manufacturers recommending reduced utilization. In fact many recommend the exact opposite.

Pick a SCC based on the current you want or need. Make sure you comply with the input voltage and current limits. Done.

 

[ianganderton]

From what I’ve read there is no rule of thumb that covers all devices, the manual needs to be read

some manuals have recommended under panelling the specific device by 20 to 30% others over panelling by 20 to 30%

plus if standards/codes apply you need to stick to those to get required certification.

 

[digit]

i may be in a position to test this. currently have 4x 320w panels, had planned to do 2s2p on a victron 100/50.
i scared myself off when i watched output amps reach 50 and invested in another victron 100/50.
this was before i had any understanding of overpanelling.
currently running one set in series and one set in parallel on seperate controllers.
seems that the parallel setup has a better yield.
i could reconfigure back to 2s2p setup and track output but i dont know how to account for variables