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Old 29-08-2016, 04:27   #1
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Battery Voltage in the Morning

The other morning my solar panel was supplying about 2 amps into the system, the battery was discharging about 1 amp, the batteries were 30 AH out of a 460 AH bank, the voltage was reading 12.6V.

Can the voltage be believed?
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Old 29-08-2016, 04:33   #2
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Re: Battery Voltage in the Morning

What was the panel voltage?


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Old 29-08-2016, 05:07   #3
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Re: Battery Voltage in the Morning

... if there was around 430Ah left in the (lead-acid) battery the reading looks ok.

State of Charge - 12 Volt battery - Volts per Cell
100% - 12.72
90% - 12.52
80% - 12.42

Measuring State-of-charge - Battery University

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Old 29-08-2016, 05:24   #4
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Re: Battery Voltage in the Morning

Quote:
Originally Posted by CarstenWL View Post
... if there was around 430Ah left in the (lead-acid) battery the reading looks ok.

State of Charge - 12 Volt battery - Volts per Cell
100% - 12.72
90% - 12.52
80% - 12.42

Measuring State-of-charge - Battery University

Regards,

Carsten
Those voltages should only be used as a VERY ROUGH guestimate of SOC when you are cruising. Since you cannot disconnect your battery and let it rest 4 hours, you can't completely rely on voltage. As per the linked article
"To get accurate readings, the battery needs to rest in the open circuit state for at least four hours"

However.. A battery voltage of 12.6V in the morning is very good.. We are usually 12.3-12.4 in the morning!
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Old 29-08-2016, 05:25   #5
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Re: Battery Voltage in the Morning

The meat of the question revolves around whether the solar charge that was being supplied to the system results in a higher voltage reading ever though the batteries were slightly discharging.
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Old 29-08-2016, 05:45   #6
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Re: Battery Voltage in the Morning

Quote:
Originally Posted by sailorboy1 View Post
The meat of the question revolves around whether the solar charge that was being supplied to the system results in a higher voltage reading ever though the batteries were slightly discharging.

Yes it does. If the solar panel was not raising the system voltage then the batteries would not be charging.


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Old 29-08-2016, 05:46   #7
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Re: Battery Voltage in the Morning

Quote:
Originally Posted by sailorboy1 View Post
The meat of the question revolves around whether the solar charge that was being supplied to the system results in a higher voltage reading ever though the batteries were slightly discharging.
No, if for example your were putting 10 in but drawing 20 out, in reality you were drawing 10 out, battery does not see the coming in if the outgoing is larger.
Voltage I believe trumps all except maybe specific gravity as the indicator for battery charge, so yes they can be believed.
Ideal world of course resting voltage is best, but if your only in a slight discharge then using the voltage as if it were resting voltage will be a little conservative, giving you a little cushion.
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Old 29-08-2016, 05:47   #8
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Re: Battery Voltage in the Morning

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No, if for example your were putting 10 in but drawing 20 out, in reality you were drawing 10 out, battery does not see the coming in if the outgoing is larger.

Voltage I believe trumps all except maybe specific gravity as the indicator for battery charge, so yes they can be believed.

Ideal world of course resting voltage is best, but if your only in a slight discharge then using the voltage as if it were resting voltage will be a little conservative, giving you a little cushion.

Except he's putting 2 in and taking 1 out.


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Old 29-08-2016, 05:47   #9
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Re: Battery Voltage in the Morning

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Yes it does. If the solar panel was not raising the system voltage then the batteries would not be charging.


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They were not charging, but if there was even the slightest bit of positive charge, you would be correct.
Electricity is like water, it only runs downhill, you need a higher voltage than the battery or no charge will occur, you need a hill.
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Old 29-08-2016, 05:49   #10
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Re: Battery Voltage in the Morning

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Except he's putting 2 in and taking 1 out.


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I thought the opposite, your correct, the panels did raise bank voltage by a small amount or there would be no charge
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Old 29-08-2016, 05:50   #11
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Re: Battery Voltage in the Morning

I was using using 3 amps, 2 amps were being supplied by the solar and 1 amp was being supplied by the battery. In other words the battery monitor said it was discharging 1 amp.

The solar panel supply voltage, battery monitor and panel voltage all read 12.6V as expected since they were all connected.

In theory since the battery was discharging the solar panel shouldn't really effect the battery voltage, but is that really true?
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Old 29-08-2016, 05:54   #12
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Re: Battery Voltage in the Morning

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Originally Posted by sailorboy1 View Post
I was using using 3 amps, 2 amps were being supplied by the solar and 1 amp was being supplied by the battery. In other words the battery monitor said it was discharging 1 amp.

That's a different story. But the voltage can still be that high while discharging. The panels will raise system voltage some in order to output any power at all.


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Old 29-08-2016, 06:06   #13
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Re: Battery Voltage in the Morning

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Originally Posted by Sailmonkey View Post
That's a different story. But the voltage can still be that high while discharging. The panels will raise system voltage some in order to output any power at all.


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Not a different story, just different wording as I can see how post 1 could be misread.

The 12.6V to me seems to match close enough for me for a 460 AH (rated) battery bank that has 30 AH out (from overnight use), with a 1 amp discharge.
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Old 29-08-2016, 06:27   #14
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Re: Battery Voltage in the Morning

As someone who has become far more aquainted with batteries and charging than I ever expected to be, I'd say you are correct. A 12.6v measure is showing close to full, which is what you're at if only down 30 amp-hrs. A 1 amp net discharge will lower the battery voltage a little, but not much.

Even if your voltage is closer to 12.5v that's still within the error bars of your system: (30/460 = .07 or 7%). At 12.5v a 12v battery system is said to be about 10% discharged.
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Old 29-08-2016, 06:36   #15
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Re: Battery Voltage in the Morning

The thing is that I've seen the same AH out in the morning with 3 amps discharge before with the solar snoozing, and the voltage reading 12.4-12.5.

So the question is whether the supplied solar is raising the voltage even though it isn't meeting the demand. Or whether an extra couple amps discharge really effect the voltage reading that much (.1-.2).
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