Sizing question - charge controller max wattage etc

[pseudo]

Hey

So I currently have a Renogy Rover 40a MPPT charge controller, 3x 100W 12V panels in series, and 2x 6V golf cart batteries wired for 12V.

I'd like to upgrade to bigger panels and possibly add 2 more batteries for more Ah, and stay with a 12V system.

The Renogy controller says it can take up to 100V max and up to 500W of panels at 12V or 1000W at 24V.

I have found some cheap used panels on eBay from a seller with good reviews (SantanSolar). They are 245W each with the following specs:

• Open circuit voltage (VOC): 37.5 V
  
• Max power voltage (VMP): 30.2 V
  
• Short circuit current (ISC): 8.68 A
  
• Max power current:  8.13 A
  
• Power Tolerance 0/+3%
  
• Maximum system voltage: 600V (UL)

If I get 4 of those and make two parallel pairs and wire those in series, I would be at 75V and 17.4amps which is still within the charge controller's voltage and amperage specs, but over the stated max 500W at 12V. 

Would this work?

Thanks!

 

[Cajunwolf]

@pseudo
You need a charge controller that will handle the amperage. To me, for your description, the best setup would be a total of 980 watts of solar, and 980 divided by 12 volts gives you 81.3 amps. You already have one 40 amp controller, right? An 80 amp is expensive, so get another 40 amp and your good. I don't see the parallel/series setup up as a solution because your charge controller isn't going to handle it. Now, this is just my 2CentsWorth base on the limited description you've given. Maybe some more details or a diagram might help, but I see what you're trying to do.

 

[B and C]

Your 6 volt batteries are wired for 12 volts so the controller will take 500 watts.

If your 6 volt batteries were wired for 24 volts, the controller would handle a 1000 watts.

It will be a lot cheaper to add another controller (so they are set the same) than to try to down convert 24 volts to 12 volts.

 

[Elbear1]

I already proved this...the 500w max listed is just an generic number that assumes 500w = 40A.

It does not in reality. Im almost double the max listed input wattage as my controller. IOW You can input any amount you just arent going to get more out than the controller is rated for.

To make it simple each of those panels are gonna be 18-20A real world. 4 = 75-80A. So....2 40A controllers would be perfect.

 

[Elbear1]

FYI - Calculate vmp/imp not open circuit voltage/current

 

[pseudo]

Ok, thanks! The two controller setup sounds like the way to go.

I just saw santansolar also have 280W panels for just $10 more, 72 vs 60 cell, also poly.
Specs for those are:
Open circuit voltage (VOC): 44.4 V
Max power voltage (VMP): 36.7 V
Short circuit current (ISC): 8.45 A
Max power current: 7.78 A

Would those work with two of the 40a controllers or would that be pushing it?

 

[Elbear1]

You know those are pickup only in phoenix, right? Or pay $300+ for freight.

 

[pseudo]

You know those are pickup only in phoenix, right? Or pay $300+ for freight.

Yup, I'm just a couple of hours away.

 

[brahmon]

i checked out your beautiful photos. really awesome but desolate. how remote?

 

[wayne49]

"IOW You can input any amount you just arent going to get more out than the controller is rated for."

No, you should not input an amount exceeding the specifications. The controller will self destruct to some degree. Or blow an appropriately sized fuse on the 12V charge to battery bank wiring.

 

[pseudo]

i checked out your beautiful photos.  really awesome but desolate.  how remote?

Thanks

 

[pseudo]

Any input on whether two of those 280W ones could work?