Charge controller sizing

[DonQuix9810]

We are interested in getting (4) 445 w panels = 1780 total watts. We read it will require 178 amps at 12v. We haven’t found a charge controller that big. Is the information we read true? If so, would it be better to lower our solar panel watts or use 24v? Are there other options? Thanks!

[rffffffff]

Originally Posted by DonQuix9810

We are interested in getting (4) 445 w panels = 1780 total watts. We read it will require 178 amps at 12v. We haven’t found a charge controller that big. Is the information we read true? If so, would it be better to lower our solar panel watts or use 24v? Are there other options? Thanks!

If you get max output from 1780w at 12v you are at 148 amps. 445 watts at 12v is 37amps.

Half those numbers for 24v.

There are very few compelling reasons to go with 12v systems once you get into numbers like this, so absolutely go with 24v if you don’t have any real reason not to. It’ll save you half on charge controllers, even if you have to rebuy a pump or lights or something it’s still likely worth it.

That being said, you can pair two 100a charge controllers or four 40a charge controllers if you want to stay at 12v, or my vote would be to look into 24v and two 40a charge controllers. I would consider a 48v system too, but you have to look at components too, as 48v parts are not as plentiful as 24v or 12v.

[Bert06840]

Agree 100%.

24V.

[john61ct]

Best efficiency is one MPPT SC per panel.

Victron SmartSolar line is excellent, very flexible.

100/30 model should be fine for a 12V bank

75/15 for 24V

[rffffffff]

Originally Posted by john61ct

Best efficiency is one MPPT SC per panel.

Victron SmartSolar line is excellent, very flexible.

100/30 model should be fine for a 12V bank

75/15 for 24V

If I did the math right (question everything!) 30a and 15a may not be enough. Not sure that you’ll practically hit full power but in theory a 30 amp charge controller should be limited to 360w, same for the 15a@24v, so you should likely step up to the next level for 445w panels.

[Bert06840]

For a 100/30, it is 100V on the input, 30A on the output. I’m sure you knew that already but just in case.

If you are hell bent on a 12V system, you’ll occasionally max out a 100/30 converter with those panels, but it’ll happen rarely. Bulk absorption by LFP batteries happens around 13-13.5V, so with 30A you’ll be able to touch 400W.

It is not uncommon to oversize panels and undersize microinverters in modern residential installations, because that - if dimensioned right - can give you peak efficiency.

The Victron controllers are indeed great, I love their stuff too.

But as it has been said before. 12V is too low at those power levels. You will lose efficiency in the cabling, internal resistance of batteries and BMSes. It is not worth chasing the last couple procent by spending $500 extra charge controllers.

[rffffffff]

Originally Posted by Bert06840

For a 100/30, it is 100V on the input, 30A on the output. I’m sure you knew that already but just in case.

If you are hell bent on a 12V system, you’ll occasionally max out a 100/30 converter with those panels, but it’ll happen rarely. Bulk absorption by LFP batteries happens around 13-13.5V, so with 30A you’ll be able to touch 400W.

It is not uncommon to oversize panels and undersize microinverters in modern residential installations, because that - if dimensioned right - can give you peak efficiency.

The Victron controllers are indeed great, I love their stuff too.

But as it has been said before. 12V is too low at those power levels. You will lose efficiency in the cabling, internal resistance of batteries and BMSes. It is not worth chasing the last couple procent by spending $500 extra charge controllers.

I just read up on this a bit, John and Bert are indeed correct. I'm very literal with specs much of the time but going over wattage a bit on the charge controllers is fine, just not over voltage. I was afraid it might heat things up in there but it seems to be able to just ignore the extra watts somehow.

[john61ct]

Originally Posted by rffffffff

If I did the math right

Nope.

Amps rating times your charging voltage, not nominal.

[john61ct]

And your **input** side can go way over the amps spec no worries

but you should stay well below the voltage spec.

Note you will **very** rarely get anywhere close to the rated Watts output, like freezing bright days with reflections off snowy mountains

At 12V figure 150Ah per day per panel actually into your depleted bank, in ideal insolation conditions

half that at 24V