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I have a small 12V solar system. The reported charge voltage to battery frequently exceeds 15V, reading ~15.5V as I write this.

I read 14.7V is the most one should charge these batteries at. Should I be concerned?

Details: 12V 20Ah LifePO4 hooked up to a BSC3048 charge controller and one 100W panel. Frequently the USB charge port is used for phones, tablets, etc. Aside from the voltage reading, the system otherwise performs admirably.

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This sounds somewhat high for any battery, either lithium iron phosphate or lead acid (exception: maybe below 10 degrees Celsius it could make sense for lead acid, but only for absorption charge though -- 15.5 V is too high for float in any reasonable temperature).

From Amazon: "The default battery type is sealed valve-regulated lead-acid, also suitable for gel batteries, liquid lead-acid, lithium iron phosphate and ternary lithium batteries;"

Have you selected lithium iron phosphate as the battery type? If yes, then you should maybe consider customizing the parameters (Amazon says this controller supports it).

Generally, you have two voltages of interest:

  • Absorption charge voltage
  • Float charge voltage

Ideally, you could customize these currents too but sadly this is rare:

  • Bulk charge current
  • Current when to end absorption charge

Look at your battery specs and set the absorption and float charge voltages from it to the controller. If float charging isn't specified, then just put some very low voltage so that practically no current flows.

If you can't find specs for your specific battery, find specs for some other lithium iron phosphate battery and use its specs.

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  • The BSC3048 indicates it does have LiFePO4 direct support and I doublechecked it was configured for that. I'll triple check and experiment with manual settings and check against this particular battery specs as you suggest. I'm told that when the battery is at near-full conditions, one might see very high voltages from time to time
    – Malachi
    Sep 16, 2022 at 22:59

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