Normal Voltage For A 12 Volt AGM Battery?

[Arlou52]

My grandson was given a solar panel, a charge controller and a 50 amp agm battery to experiment with solar power. He noticed that the battery usually sits at 13.2 volts at night when there is no load on it. Is that the common normal voltage when a 12 volt battery is resting and fully charged? He was running the charge controller at a max limit of 13.6 from the solar panel because he was told 13.6 was supposed to be normal. Even if he changes the charging controls where the battery reads 14.5 volts when the panel is in full sunlight it always settles back down to 13.2 after dark, maybe dropping a little more the next day. I'm trying to help him but I'm not very smart in this area. Should he leave it at 13.6 or is it safe to run it at 14.5 volts which I assume charges the battery quicker?

[littleharbor]

12v_Battery_SoC_Table.jpg

Lead acid, 12 volt, batteries will settle to 12.7 - 12.8 when fully charged with no loads and no charging source. All is well with the voltage you're seeing. 13.6 ish is the float voltage the controller holds the battery at when done charging. Of course after dark there is no voltage coming from the controller so the battery settles to the numbers seen in the chart.
The bulk/absorb viltage point should be 14.4 to 14,8 for AGM batteries. If you can find the recommended charging voltages online you should set the charge controller to their recommended numbers.

[inetdog]

The voltages in the chart are for a typical lead acid battery which has not been either charging or discharging for at least 4 hours.

[Mike90250]

And the other variable is the accuracy of the volt meter being used.

[Arlou52]

Thanks for the information but I'm a little puzzled. The chart shows 12.7 volts as 100% charged. This battery levels out at 13.2 volts after 5 hours and stays there. Is it over charged? It's an AGM if that makes any difference. Is he hurting the battery if he let's it charge at 14.5 volts when the sun is shining? He has checked the voltage with 3 different meters and all are within 0.1 volts of each other.

[littleharbor]

Probably fine at those charging points. Some AGM batteries recommend up to 15 volts for cyclic use. Which is scary due to the fact that AGM batteries are very susceptible to high voltages causing excess gassing that they cant recombine fast enough.
If you were to let the battery sit long enough to let the surface charge dissipate it will settle down to the high 12's voltage wise.

[Arlou52]

I have another related question. Is it safe to run an old CB radio and a 100 watt linear amplifier on this solar equipment? When the battery is fully charged it registers 13.2 volts, but when the radio is keyed up with the amplifier on it immediately drops to 11.7 volts and stays there. When the radio is unkeyed it jumps back up to 13.2. According to the chart LittleHarbor posted above 11.7 volts would be about 30% state of charge and below the 50% safe level as I understand it. Is the battery being damaged by using that amplifier this way? Thanks

[inetdog]

I have another related question. Is it safe to run an old CB radio and a 100 watt linear amplifier on this solar equipment? When the battery is fully charged it registers 13.2 volts, but when the radio is keyed up with the amplifier on it immediately drops to 11.7 volts and stays there. When the radio is unkeyed it jumps back up to 13.2. According to the chart LittleHarbor posted above 11.7 volts would be about 30% state of charge and below the 50% safe level as I understand it. Is the battery being damaged by using that amplifier this way? Thanks

Every battery has an effective internal series resistance which reduces the output voltage by an amount proportional to the current being drawn. The 11.7 volt figure for 30% SOC is only when measured not only when no current is being drawn, nor charging current flowing, but that the zero current condition has been in effect for four or more hours.
As to whether the battery is being damaged, probably not, but look at the actual depth of discharge (DoD) and determine how many cycles you are removing from the useful life of the battery.
In addition, the immediate return to 13.2 volts strongly suggests that the battery is being actively charged at the same time the full power load is being drawn, and the battery voltage of 13.2 volts represents the absorb or float value setting of the Charge Controller (CC).

[earthrealm]

I have another related question. Is it safe to run an old CB radio and a 100 watt linear amplifier on this solar equipment? When the battery is fully charged it registers 13.2 volts, but when the radio is keyed up with the amplifier on it immediately drops to 11.7 volts and stays there. When the radio is unkeyed it jumps back up to 13.2. According to the chart LittleHarbor posted above 11.7 volts would be about 30% state of charge and below the 50% safe level as I understand it. Is the battery being damaged by using that amplifier this way? Thanks

Confirm how many batteries are hooked up, also what are the voltage setpoints on your charger/charge controller,??
you should have them on 14.4 to 15v for boost and 13.4 - 13.8v for float. its best you go with the battery specs as written on the battery

[Mike90250]

I have another related question. Is it safe to run an old CB radio and a 100 watt linear amplifier on this solar equipment? When the battery is fully charged it registers 13.2 volts, but when the radio is keyed up with the amplifier on it immediately drops to 11.7 volts and stays there. When the radio is unkeyed it jumps back up to 13.2. According to the chart LittleHarbor posted above 11.7 volts would be about 30% state of charge and below the 50% safe level as I understand it. Is the battery being damaged by using that amplifier this way? Thanks

Where are you measuring this voltage? Battery? Charge controller? Linear Amp ?
This could also be too small of wire for the amp. 100w RF, likely 200w consumed from battery, that's about 16 amps, so the amp should have at least 10 ga wire, even for short runs.

[Arlou52]

Voltage is being measured at the linear amp. Would a wire too small over too long of a run be the cause of these weird voltage variations?

[Tecnodave]

Yes, too small of wire or a too long run will cause excessive voltage drop.

[HansWT]

What is the best way to measure "settled" battery voltage if one is cycling daily; charging and discharging? How does one go about doing so, if one immediately puts batteries into service? Is/does a shunt at the battery (neg terminal) the best, most reliable reading? Or would a simple voltmeter wired to the 2 battery/bank terminals without any load an option? I have several LED voltmeters at switched load panels (USB/Outlets), plus on the Charge Controller and the Inverter Display. Rarely do any match... so at best I'm guestimating SoC via various volt meter readings.

FYI... 4 12volt AGM/SLA 35 Amp-hour batteries in parallel.

[Mike90250]

I've found best is early AM, before anyone starts using power, or solar charging starts.