Hi, I try to understand why I dont get any charging in below circumstances? Full sun but with an angle not optimal, but I should get something? I have normal lead acid batteries, appr. 400 Ah and two 50W panels. Thanks/Martin
asked
Smart Solar MPPT 75/15 not always charging?
Hi,
The PV voltage has to be 5+volts above the battery voltage before the charge controller can start charging the batteries.
What panels do you have?
Aha, I was not aware. My previous MPPT did not have that threshold. Any reason for having it? Can I change the threshold? Same for 24V or is it then 10V? It’s two Sunbeam 50W Flush.
Many thanks!
Rewire the 2 panels to be in series - this will double the voltage and avoid this issue in future.
Also, I think that you will need more than 100w of solar to keep up with a 400Ah battery bank.
Yes, I will double my solar panels to 200 W. You think a 24V system will start charging earlier?
Many thanks!
I'm not sure if you mean 24v battery or solar, but the MPPT 'wake up' logic is always consistent at battery voltage +5v, regardless of the setup. Then only +1v is required to keep it active.
With your current MPPT you can run a peak solar voltage of upto 75v.
With MPPT You should always design to have the solar voltage significantly higher than battery voltage for best results.
This also helps with power loss in the solar cables and enables smaller size cable to be used.
Regarding your proposal to upgrade to 200w. That's better but probably still not enough for a 400Ah battery bank. Roughly speaking, for a properly designed system you need about 1000w of solar & a larger charge controller.
During bulk phase it's generally recommended to charge at a current of 10% to 20% of your battery capacity - so for a 400Ah bank thats 40A to 80A, but your charger has a max charge current of 15A max... (confirm what's recommended / allowed for your particular batteries by referring to the specific data sheet).
