Sizing a mppt controller

[Willbiker]

Hi!

I am new to the hobby and after finding out today that my cheap Chinese mppt controllers are actually a scam and aren't actually mppt, I've decided to invest in a decent controller...however on a reasonable budget.

From all the reviews I have spent HOURS watching today, the Epever Tracer controllers look the best value for money but before I purchase, please could you confirm my calculations.

I have 2x 200w panels each putting out a max open circuit voltage of 45.4V and 5.4a short circuit current . As I understand, the Epever controllers amp rating refers to the output current from the controller to the batteries?. I calculate I will produce a maximum of 33.4 amps going to the batteries regardless of if I configure the panels in series or parallel. I watched a review of this controller where it was stated that it doesn't matter too much if the rated output amps exceed the rating of the controller, it just means the full benefit of the energy capturing will be hindered at peak sun exposure....so I believe I will be ok with 30a controller.


Am I right??

Thanks

 

[gnubie]

Yes, 30A controller will be OK since you understand the limitations there. Since you have a 12V battery you can use those panels in parallel without any concern when it comes to panel voltage vs battery voltage.

For lower power controllers the amp rating typically applies to the PV input and the battery output. Which ever hits the limit first is the one that will limit the power production.

If you series them check the voltage input limit for the particular model controller. It's probably going to be around 100V. If you have low temperatures there you could run into voltage problems with the array's Voc exceeding the controller's rating.

 

[Willbiker]

Thank you for the advice. I went with a 40a Epever tracer and its working well!

Can you answer a question I have which I cant get my head around. I read in some places that a fully charged battery should read 12.7v. I then read somewhere else that a fully charged battery should read 14.6v. Which one is it?

My batteries are currently at 12.9v after a full days charge from the tracer (its been cloudy). My tracer controller shows 3 our of 5 charge bars but my other battery monitor registers 100% charged.

When I am out in my caravan for 10 days ....I'm idealy aiming for my solar setup to restore my batteries back to 100% at the end of eaxh day...should I be aiming for 14.6v or 12.7v?

Thanks

 

[Liam M]

Depends on battery chemistry, but for lead acid ~12.7 - 13.1 is a fully charged battery at rest.
14.6 would be about peak charging voltage, see link.

Charging Information For Lead Acid Batteries – Battery University

Review various Lead Acid charging methods and examine why some systems work better than others. Find also simple guidelines for charging Lead Acid batteries.

batteryuniversity.com