Seeking Advice: Solar Panel Setup - Understanding Voltage Fluctuations

[Rutem]

Hello everyone,

I'm seeking some advice and insights regarding my solar panel setup. Here's what I've got:

• Solar panel: 200W
• Inverter: 350W
• PWM regulator: 40A
• Gel battery: 12V 100AH

I've been noticing some fluctuations in voltage readings at different stages of operation. Particularly, when the battery is charging through the inverter connected to the house electricity, the voltage spikes up to 14.5V. Is this voltage level normal for a Gel battery during charging?

Additionally, once I disconnect the inverter, the voltage drops to 13.1V before stabilizing at 12.9V. Is this fluctuation after charging typically?

I'm keen to hear your experiences and advice on managing voltage fluctuations and ensuring the longevity of my setup. Any tips or insights would be greatly appreciated.

Thank you all for your help and expertise!

 

[JBertok]

First, for your observed 12.9V after sitting for a bit:
All battery chemistries at rest have a relationship between "voltage" and "state of charge".
Given your AGM chemistry and nominal voltage of 12, you can Google a Volts vs SoC chart.

Next, recharging batteries of any chemistry is most optimally done in stages, the voltage ranges of which are tweaked specific to the type of battery in use. Chargers with 3 stages will recharge the battery bank in voltage and current steps over a specific timeframes that limit power flow. Controlling these parameters prevents overheating and prolongs the lifespan of the cells.
The stages are Bulk, Absorption, and Float. In the diagram below borrowed from a Google search, You'll see that after the absorption stage the voltage is intentionally lowered to a point where the charger is just maintaining the battery at 100% state of charge. Most chargers have presets for the common battery types, and many allow custom values for each stage that provides compatibility even with types not specifically supported. Your observations of fluctuating recharge voltages is consistent with the behavior to expect from a multistage charger.