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I have a 12V battery linked to my solar panels.

In the middle I have a PWM charge controller, that is configured by default to charge the battery if Voltage if lower than 14.8.

At night, battery goes down to ~13.8V. (Which I think is the voltage of the full battery) - with no added voltage from solar panels.

Is it safe ? Does it reduce battery life ? (I have a deep cycle lead battery 80Ah.)

Should I change the PWM default configuration to put 13.8V instead ? Why isn't it 13.8V by default ? Is there some advantages I don't understand when set to 14.8V ?

EDIT : I have a battery Hankook DC24MF and a cheap 15$ PWM 20A.

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  • \$\begingroup\$ Given the values you give here, I'm assuming this is a lead-acid battery. That would be helpful to mention. \$\endgroup\$
    – Hearth
    Jul 1, 2019 at 13:14
  • \$\begingroup\$ Look at www.batteryuniversity.com for comprehensive lead acid battery management information. For maximu lifetime and charge acquisition lead acid batteries need to be boost charged for a defined period based on prioe depth of discharge (and other factors with less impact) BU covers all this. Also search this site for lead acid charging. \$\endgroup\$
    – Russell McMahon ♦
    Jul 1, 2019 at 13:32
  • \$\begingroup\$ @Hearth Isn't it already mentioned ? (I have a deep cycle lead battery 80Ah.) \$\endgroup\$
    – bob dylan
    Jul 1, 2019 at 13:35
  • \$\begingroup\$ Ah, you did mention it, but it's a little buried in there. \$\endgroup\$
    – Hearth
    Jul 1, 2019 at 13:56

2 Answers 2

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Check the battery datasheet for proper voltages that are exactly correct for your battery. Otherwise use safe values.

I have a commercial solar battery charger that by default overcharges the battery once per month to 15 volts to equalize the cells. Otherwise it charges it to 14 volts. These voltages can be changed from the user interface.

If you use too high battery voltage, it will cause gas formation in the cells. Traditional wet batteries will dry, gel batteries not so much as they contain chemistry to minimize it. But they will suffer and the end result is diminished battery life.

The most important thing for me has been to learn that it's not a good idea to overcharge the batteries. While it "feels" like you have more charge in your batteries when they say 15.0 volts than 13.5 volts, the difference is quite small in reality, as the last couple of percents of charge raise the voltage very quickly compared to the normal operating conditions.

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  • \$\begingroup\$ Thanks, but is there a point of all of this ? I'm confused seeing 14.8V on the PWM lcd screen (and slight buzzing sound.) because it will drop down to 13.8V anyway when sun goes down. (Without using the battery at all of course.) What is the point of this ? I have an Hankook DC24MF and a cheap 15$ PWM 20A. \$\endgroup\$
    – bob dylan
    Jul 1, 2019 at 9:31
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    \$\begingroup\$ That's because the battery is full. A small amount of current will quickly raise the voltage to 14.8 volts, at which point the PWM charger quickly stops charging. Then the voltage of the battery drops immediately to 14.x volts and the PWM charges again to 14.8. This happens a few dozen times per second, hence the buzzing sound. That's just the way the ultrasimple PWM chargers work. When sun goes down, and there's no more amps going to the battery, the voltage drops to the cell full resting voltage, 13.8 volts. \$\endgroup\$
    – PkP
    Jul 1, 2019 at 9:39
  • \$\begingroup\$ "PWM" is a buzz word in the el cheapo controllers. So it must buzz. :) \$\endgroup\$
    – PkP
    Jul 1, 2019 at 9:42
  • \$\begingroup\$ Sorry not everything is clear for me, if I use the settings of the PWM to 13.8V instead of 14.8V it would charge exactly the same amount ? (except not equalizing the cells if I understand correctly.) \$\endgroup\$
    – bob dylan
    Jul 1, 2019 at 9:51
  • \$\begingroup\$ @bobdylan, that's basically true. You charge to 97% instead of 103% and your batteries last longer. \$\endgroup\$
    – PkP
    Jul 9, 2019 at 19:51
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Wet cell batteries can be overcharged, and benefit from it. Maintenance involves adding distilled/de-ionized water to the cells.

Sealed cells, including gel cells, have a way of recycling water that is lost, and don't need maintenance as long as the charge voltage is not "too high". But they don't have a way of adding distilled/de-ionized water lost if the charge voltage IS "too high".

14.8V is quite high for a sealed cell. It will probably reduce the life of the battery. Boost max is typically around 14.2 and absorption around 14. You should check your battery specification.

14.8 - 15.0 is quite reasonable for a wet-cell battery, but maintenance will be required if it is held at that voltage for long: absorption around 14.0 will reduce water loss.

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