SOC ( state of charge)

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SOC ( state of charge)

Postby Crabapple » Mon Sep 05, 2016 2:44 pm

I have a Renogy 100W portable solar panel that does a nice job of keeping my camper battery charged. It has a View Star PWM Solar Charge Controller and one of the menu readouts is SOC ( state of charge) which I thought indicates the state of charge of the battery. This obviously can't be the case since the numbers jump all over the place. It might be reading 86% one minute, a few minutes later 39% or 67% ...basically all over the map. No load on the battery. The owner's manual description of SOC didn't help me much either. Can someone who knows specifically what this refers to please enlighten me??
Thanks!
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Re: SOC ( state of charge)

Postby Shadow Catcher » Mon Sep 05, 2016 6:27 pm

I would say it is somewhat less than accurate, are you getting fluctuations in voltage?
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Re: SOC ( state of charge)

Postby Crabapple » Tue Sep 06, 2016 6:46 am

Shadow Catcher wrote:I would say it is somewhat less than accurate, are you getting fluctuations in voltage?

I get a panel voltage reading and I get a battery voltage reading. In full sun the panel voltage can be quite high like 19 - 20 V while battery might be 13-14V. Which makes me think SOC could be what percent of available panel energy is being fed to the battery, the balance being dumped??
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Re: SOC ( state of charge)

Postby Dale M. » Tue Sep 06, 2016 8:27 am

For me I would interpret "state of charge" as condition of battery..... Generally state of charge is derived by reading battery voltage and converting (a little black box electronic magic) it to a percentage number.... As battery charge decreases the state of charger should drop proportionally...On flip side as battery takes on charge voltage increases proportionally and state of charge should show higher percentage... Its been discusses some time back on this forum about how much charge is in battery by reading its voltage and deriving state of charge... IT should not be jumping all around, it should show slow steady ramp up or ramp down as condition of battery changes due to charge or discharge... I would not trust unit, there is to much technology out there that senses battery condition and translates it to percentage numbers very accurately and I have yet to see a proper unit give unstable readings... To me, unit is either defective and I would immediately contact manufacturer and as to what is going on, or it indicate to me unit is of poor design...

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Re: SOC ( state of charge)

Postby noseoil » Tue Sep 06, 2016 8:38 am

A volt meter tells you the battery charge, basically. Just have one you can read when everything is shut down & the battery is resting. 12.7 is a full charge & roughly for every 0.1 volt drop, you're down 10% in storage capacity. This is crude, but it's pretty reliable & works well enough for a quick & dirty read of the state of charge.
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Re: SOC ( state of charge)

Postby MtnDon » Tue Sep 06, 2016 1:24 pm

SOC refers to the battery. With a lead-acid battery SOC can NOT be determined solely by a voltmeter as there are other variables that can affect the voltage reading.

If the pv panels are exposed to sunlight the voltage measured at the batteries can move up/down with changes inclouds, etc. That voltage reading canalso fluctuate if electrical loads turn on/off.
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Re: SOC ( state of charge)

Postby Shadow Catcher » Tue Sep 06, 2016 7:02 pm

The only way to accurately gauge state of charge is with a battery monitor that measures all of the current going into and coming out of the battery. The two most used are the Trimetric and Victron. I chose the Victron https://www.victronenergy.com/battery-monitors/bmv-700
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Re: SOC vs. SOW (state of wallet)

Postby noseoil » Thu Sep 08, 2016 8:55 am

Perhaps I should have been more clear in my statement about the use of a simple volt meter for SOC. If the battery is at rest, has no loads or charge happening (PV panels in the dark, no lights are turned on, radios playing, etc.) & hasn't been used for anything for a few hours, a volt meter is a very accurate measure of state of charge.

I do understand that temperature, recent loads, charging, PV panels, a full moon or fondling your crystals can affect battery voltage, but if you want to spend more than $100 instead of $5 to find out that your battery is charged or not, be my guest. Basically, you need to have enough charging capacity to keep up with your loads in any given scenario where the battery is being used. If the voltage is down, you need a charge. If the voltage is up, you are fully charged. There are too many factors involved here to list, but a simple voltage meter or a good hydrometer will both tell you the same thing about the state of charge of your battery, as well as your charging system.

Again, I apologize for my gross oversimplification of this whole process & any misunderstanding I may have caused, but a lot of this stuff is over-thought, over-engineered & just too complex for most people. Knowing down to the mili-volt the loads & charging uses of a system will only tell you that you have more or less power than you need. I don't like to spend money if I don't have to, so for me a $5 voltmeter tells me all I need to know about my system & battery.
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Re: SOC vs. SOW (state of wallet)

Postby Dale M. » Thu Sep 08, 2016 10:33 am

noseoil wrote:Perhaps I should have been more clear in my statement about the use of a simple volt meter for SOC. If the battery is at rest, has no loads or charge happening (PV panels in the dark, no lights are turned on, radios playing, etc.) & hasn't been used for anything for a few hours, a volt meter is a very accurate measure of state of charge.

I do understand that temperature, recent loads, charging, PV panels, a full moon or fondling your crystals can affect battery voltage, but if you want to spend more than $100 instead of $5 to find out that your battery is charged or not, be my guest. Basically, you need to have enough charging capacity to keep up with your loads in any given scenario where the battery is being used. If the voltage is down, you need a charge. If the voltage is up, you are fully charged. There are too many factors involved here to list, but a simple voltage meter or a good hydrometer will both tell you the same thing about the state of charge of your battery, as well as your charging system.

Again, I apologize for my gross oversimplification of this whole process & any misunderstanding I may have caused, but a lot of this stuff is over-thought, over-engineered & just too complex for most people. Knowing down to the mili-volt the loads & charging uses of a system will only tell you that you have more or less power than you need. I don't like to spend money if I don't have to, so for me a $5 voltmeter tells me all I need to know about my system & battery.


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Re: SOC vs. SOW (state of wallet)

Postby Crabapple » Thu Sep 08, 2016 11:41 am

noseoil wrote:Perhaps I should have been more clear in my statement about the use of a simple volt meter for SOC. If the battery is at rest, has no loads or charge happening (PV panels in the dark, no lights are turned on, radios playing, etc.) & hasn't been used for anything for a few hours, a volt meter is a very accurate measure of state of charge.

I do understand that temperature, recent loads, charging, PV panels, a full moon or fondling your crystals can affect battery voltage, but if you want to spend more than $100 instead of $5 to find out that your battery is charged or not, be my guest. Basically, you need to have enough charging capacity to keep up with your loads in any given scenario where the battery is being used. If the voltage is down, you need a charge. If the voltage is up, you are fully charged. There are too many factors involved here to list, but a simple voltage meter or a good hydrometer will both tell you the same thing about the state of charge of your battery, as well as your charging system.

Again, I apologize for my gross oversimplification of this whole process & any misunderstanding I may have caused, but a lot of this stuff is over-thought, over-engineered & just too complex for most people. Knowing down to the mili-volt the loads & charging uses of a system will only tell you that you have more or less power than you need. I don't like to spend money if I don't have to, so for me a $5 voltmeter tells me all I need to know about my system & battery.


Which probably explains the variations in the SOC readout and why they don't always make sense! Thanks to all for your inputs!
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