Solar Noob Help

RedCon509

I recently installed a Renogy 400Watt set up with a Rover 40 MTTP with (2) 6v 370AH batteries. I've noticed that the charge capacity shown on the charge controller is constantly changing..... one minute it will read 60% then 70% then back to 60%. Has anyone else experienced this?

BB.

Welcome to the forum RedCon509,

The reported battery capacity by solar charge controllers are very rough estimates (not very accurate--Lead acid batteries not accurate--Li Ion possibly more accurate).

If you want "accurate" estimates of AH capacity/State of Charge for your batty bank... A true Battery Monitor that measures current into/out of the battery bank is a better (and more expensive) option:

https://www.solar-electric.com/search/?q=battery+monitor

There are less expensive shunt based monitors out there from Amazon/Ebay/etc... I have no knowledge of the product(s)... Just FYI:

https://www.amazon.com/AiLi-Voltmeter-Ammeter-Voltage-Motorhome/dp/B07FGFFHC6

There are also Voltage only Battery Monitors--May or may not be more accurate than your charge controller--And they start at pretty cheap prices:

https://www.amazon.com/s?k=12+VDC+battery+monitor+meter&ref=nb_sb_noss

If you have flooded cell Lead Acid batteries, a good quality Hydrometer is the "gold standard" for checking state of charge:

https://www.solar-electric.com/search/?q=hydrometer

Even the "high end" shunt based battery monitors can "drift" over time/cycling... Many of them will "reset" to 100% State of Charge under certain conditions (example: meter "sees" 14.8 volts for > 2 hours -- Absorb charging on FLA battery bank).

Just using a hydrometer and an accurate voltmeter you can get a pretty good idea of the "health"/state of charge of your battery bank... I.e., resting voltage of 12.2 volts ~ 50% state of charge... Under decent loads, you don't want to see below 11.5 volts for more than few minutes or so (discharging below 50% SoC under load)--Short term loads (motor starting surge, etc.) may take bank below 11.5 volts during surge--But that is "OK".

-Bill

johnmeyer

Hello,
I would like some information.
I have solar panels connected to the grid which reduces my electric bill from over $450/month to a $150/month lease and less than $400/year to Edison. 
My concern is blackouts.  So, I am going to build my own house battery.  I want only to power my refrigerator and kitchen lights for up to 2 days.  
My plan is to buy 8 100AH 12V batteries, a Jupiter 2000 inverter and some kind self sustaining charging system that will charge and maintain the batteries while the grid is functioning.  Any suggestions would be welcome.  But, I mostly need recommendations for the charging system.
Johnfrom SBCA

BB.

Welcome to the forum JohnMeyer,

Can you start a new discussion/thread in one of the forums (beginner, off grid/battery systems, etc.). That way we can focus on your exact Q&A's...

Knowing your location, daily loads, and how often your power goes out. In Los Angeles/San Bernardino, etc... Your power may go out only a few days a year (at most--Wild fire seasons in California--Who knows) vs a Caribbean Island where afternoon blackouts are almost every day.

Off grid solar is not cheap power. And for a few days a year, solar may not be a "competitive" answer vs a genset+backup fuel (propane, gasoline with fuel stabilizer, natural gas, etc.).

-Bill

AlexGomez7

BB. said:

Welcome to the forum RedCon509,

The reported battery capacity by solar charge controllers are very rough estimates (not very accurate--Lead acid batteries not accurate--Li Ion possibly more accurate).

If you want "accurate" estimates of AH capacity/State of Charge for your batty bank... A true Battery Monitor that measures current into/out of the battery bank is a better (and more expensive) option:

https://www.solar-electric.com/search/?q=battery+monitor

There are less expensive shunt based monitors out there from Amazon/Ebay/etc... I have no knowledge of the product(s)... Just FYI:

https://www.amazon.com/AiLi-Voltmeter-Ammeter-Voltage-Motorhome/dp/B07FGFFHC6

There are also Voltage only Battery Monitors--May or may not be more accurate than your charge controller--And they start at pretty cheap prices:

https://www.amazon.com/s?k=12+VDC+battery+monitor+meter&ref=nb_sb_noss

If you have flooded cell Lead Acid batteries, a good quality Hydrometer is the "gold standard" for checking state of charge:

https://www.solar-electric.com/search/?q=hydrometer

Even the "high end" shunt based battery monitors can "drift" over time/cycling... Many of them will "reset" to 100% State of Charge under certain conditions (example: meter "sees" 14.8 volts for > 2 hours -- Absorb charging on FLA battery bank).

Just using a hydrometer and an accurate voltmeter you can get a pretty good idea of the "health"/state of charge of your battery bank... I.e., resting voltage of 12.2 volts ~ 50% state of charge... Under decent loads, you don't want to see below 11.5 volts for more than few minutes or so (discharging below 50% SoC under load)--Short term loads (motor starting surge, etc.) may take bank below 11.5 volts during surge--But that is "OK".

-Bill

really helpful thank you!