Charging voltages

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cptdondo
cptdondo Solar Expert Posts: 103 ✭✭✭
in Solar Beginners Corner #1
I've been watching my new solar system. It consists of 2 Kyocera 135 panels and a Morningstar Duo controller charging two 6V Trojan T145 batteries in series. The system is mounted on an RV.

Trojan says on their website:


System Voltage 12V
Daily Charge 14.8
Float 13.2
Equalize 15.5

The controller never records voltages above 14.5, and that's only when being charged with the vehicle alternator. The controller can't seem to get voltages above 14.1 or so..... It's never hit above 15 at all.

Is this normal? Should I be worried?

At the end of the day the batteries are at 13.7V, which I'm assuming is surface charge.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #2
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    Re: Charging voltages

    Make sure the DVM you are using is accurate.

    A vehicle will regulate voltage. Shortly after starting it will limit to about 14.3 vdc then drop back to about 13.5 vdc.

    You should have enough panel power to fully charge batteries. It will depend on how much you have discharged them. You should charge at 25 to 35 amps.

    The Morningstar duo is PWM charger limited to 25 amps. A PWM charger means it just connects or disconnects from panel to regulate battery voltage. This means the battery current at max will be what panel illumination current is producing.

    The Kyocera 135 panels at maximum sunlight direct facing will produce about 8 amps maximum for each panel. Assuming you have the two tied in parallel you should get something less then 16 amps maximum charging at full sun. This will drop off based on sun angle to panels.

    If you batteries are half way discharged it would take about a day and a half of full sun to charge them back up.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: Charging voltages

    Charge Voltage is limited by the controller. The Morningstar Dual can be set for an Absorb charge at 14.1 (for sealed batteries) or 14.4 (for non-sealed). It does not have the ability to regulate to Trojan's preferred 14.8 Volts. Its equalization point is 14.8 These settings are a tad low but over-all it won't matter much.
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  • cptdondo
    cptdondo Solar Expert Posts: 103 ✭✭✭
    #4
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    Re: Charging voltages

    Interesting... I have a Bank-1 Bank-2 Off switch. I turned it off this morning, to eliminate any parasitic draws on the system. This completely isolates the batteries while leaving them connected to the solar controller. Now I'm seeing 14.5V in morning light. Maybe that controller (or all controllers?) is sensitive to draw? The parasitic draws are well under 1A; maybe 300 mA (mostly propane and CO alarms and some electronics.) We'll see what happens during the day.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: Charging voltages

    There's many things that can vary Voltage by a few tenths, including the quality and calibration of the meter doing the reading as RC mentioned. The length and size of wires and the amount of load will also have an effect. That is why Voltage isn't a good indicator of SOC. Even a battery "at rest" and measured with a "perfect" meter may not read to specifications. On a 12 Volt system, 0.12 Volts is only 1%. Don't worry about it.
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