I recently upgraded to a Victron MPPT 75/15 solar charge controller. My solar panel is 20 watts, 12 volts. I have a 12 volt, 80ah AGM battery for my sailboat (to power accessories) and I’m just using the solar panel to keep the battery fully charged over the winter. The accessories are all turned off at the circuit breaker so there should be zero load on the battery. However, the controller can’t seem to keep the battery fully charged. I’ve posted screen shots of the Victron app showing the charging state over the past 13 days. Prior to hooking up the solar panel (13 days ago) I had fully charged the battery using an AC trickle charger up to about 13.8 volts. You can see from the screen shots that the battery voltage has been steadily dropping, as low as 11.93 volts today. Have I got a bad battery? Any ideas?? Thanks!!
My guess would be the charge controller is using more power than the panel can supply. Mppt 75/15 has a 25ma self comsumption, which works out to 0.3w / 7.2wh per day.
Some days the panel produced zero wh.
Bigger panel required.
Also pv voltage some days didn’t reach the required +5v above battery voltage to commence charging.
Bigger panel with higher output voltage required or another same as panel in series required.
Thanks! Before buying a bigger panel and after thinking more on the matter, can you tell from the app screens whether there’s a chance that a phantom load on the battery is causing the problem? I’m wondering if it’s worth crawling into the boat and disconnecting everything from the battery except the solar charger leads and see if it makes a difference.
Yes there could be a phantom load, always worth investigation.
But going by screenshots, the self consumption of the mppt is more than the panel can supply.