Need More Batteries?

pabloesguapo

I currently have 16 lead acid 6v batteries (210Ah), in two series strings of 8, paralleled together for a 48v system, 420Ah.  Installed 9/4/2020.

I knew before I started that this might not be enough Ah for us, but it's what we can afford right now.  I'd like to add a third string of batteries, but won't be able to until next month, when the "original" batteries are almost 2 months old. 

As I understand it, the new batteries need to be as close as possible in voltage as the originals before integrating them, and that new batteries usually only come half charged.  I have a 6v 12v "trickle" type charger, I could charge each up individually, but that'll take a week.  Could I series 2 together at a time and cut that time in half?

I'm looking for ideas and guidance.  

TYIA

pabloesguapo

Idea:  instead of working so hard to bring the new batteries' charges up, why not just wait until the original batteries have come DOWN to a matching level, like where they would be in the morning? 

BB.

I would not worry too much about FLA batteries with different state of charge... Ideally, if all the batteries were >~80% state of charge, then the low batteries should "self regulate" current flow... That should be good enough.

The batteries should all be above ~75% state of charge if they are sitting around waiting to be installed. Below ~75% SoC, they tend to sulfate faster. I would not expect you to have some near 100% and others at 40% SoC.

And you are correct--Having batteries at similar state of charge is fine too.

-Bill

Photowhit

pabloesguapo said:

"... and that new batteries usually only come half charged. 

Simply not true, Batteries would sulfate and be destroyed quickly if stored at 50% or even 75% state of charge.

pabloesguapo said:

"... I have a 6v 12v "trickle" type charger, " 

That is not likely to be a charger that would charge a deep cycle battery, but rather a 'maintainer for a car battery.

pabloesguapo

The first batch, the starting voltage from the store ranged from 6.17—6.21v, that's somewhere in the 67-70% range, according to their woefully broad brushed spec sheet.  I would not want to keep the new ones lying around, but would want to install them asap.

  Near as I can tell so far, an average overnight leaves the bayteries' charge at 48.v for the battery bank, 6.05% each on average, for a SOC of 50%. (Hence my desire to install another string, to get the at-dawn average up closer to 70%). Maybe I can wait til about 9:30am-ish, to get the originals up to the level the new ones would be, and install them quickly?

Photowhit

pabloesguapo said:

The first batch, the starting voltage from the store ranged from 6.17—6.21v, that's somewhere in the 67-70% range, according to their woefully broad brushed spec sheet.  I would not want to keep the new ones lying around, but would want to install them asap.

I wouldn't accept that, was there a manufacture date on them?

I actually drove 100 miles round trip, because the local Sam's club had batteries that were 4 months old.  Common labeling will have a date code with month and year. 


I think you said you got Intersate batteries from Costco?

They may have a date code on the post or in the plastic. From a quick search;

"A 4 or 5-digit shipping date code is engraved into the cover of each Interstate battery at the time the battery is shipped from the manufacturing plant. This code can only be seen when looking down on the top of the battery. The code is not on the label on the battery and it is not on the rim around the cover. The code is usually near one of the corners of the battery. This code tells when the battery was shipped from the factory to the local Interstate Battery wholesale distributor. The additional digits tell where the battery was made."

www.ibslhc.com/battery-care/battery-age

It would be good to check the Specific Gravity (SG) of you batteries cells and record them for future use.

MichaelK

I just installed a new battery system with Rolls batteries (premium brand I think) this last spring.  I recorded 6.1 kWh for the commissioning charge on the day the system was hooked up.  For a 568AH battery, with a total stored wattage of 568AH X 24V = 13,632WH, that 6100W amounts to a battery starting at 55% charged.  So no, even the premium brands bought from a battery dealer don't come fully charged!

BB.

Or at least >~75% state of charge...

If you did extended Equalization Charging, is certainly possible to push more current trough the battery at (very roughly) 2.5% to 5% rate of charge If you push 25% in EQ charging...

568 AH capacity (20 hour rate) * 2.5% rate of charge = 14.2 Amps typical minimum EQ charging current for flooded cell batteries.

That is roughly:

• 25% / 2.5% EQ charge = 10 hours
• 25% / 5.0% EQ charge rate = ~5 hours (batteries may overheat if truly EQ Charging (and bubbling--EQ generates lots of heat and gassing).

The problem with Lead Acid batteries that have not been kept charged is tha they tend to start sulfating after 1-2 months of "sitting" uncharged at room temperatures (~75F or ~25C). Batteries stored cool (-18F or -10C less than room temperature), tend to have 1/2 the self discharge rate (conversely, batteries stored "hot" self discharge).

-Bill

Photowhit

MichaelK said:

I just installed a new battery system with Rolls batteries (premium brand I think) this last spring.  I recorded 6.1 kWh for the commissioning charge on the day the system was hooked up.  For a 568AH battery, with a total stored wattage of 568AH X 24V = 13,632WH, that 6100W amounts to a battery starting at 55% charged.  So no, even the premium brands bought from a battery dealer don't come fully charged!

Perhaps there is a math problem...

Commissioning charges are usually equalizing charges, but even without an equalizing charge you recorded 6.1 kWh mostly at absorb rates. So you are charging according to Rolls 568 ah battery bank. While charging you are losing 20% at normal charging parameters and 25 at equalizing. In addition the cells are forming and will increase in capacity over the first few cycles. The loss is easy to see when you are sending voltage of 29.5-30 volts and the resting voltage is 25.3.

So what was running, was your inverter on? Was this measured across a shunt at the battery?

MichaelK

Commissioning charges are usually equalizing charges, but even without an equalizing charge you recorded 6.1 kWh mostly at absorb rates. So you are charging according to Rolls 568 ah battery bank. While charging you are losing 20% at normal charging parameters and 25 at equalizing. In addition the cells are forming and will increase in capacity over the first few cycles. The loss is easy to see when you are sending voltage of 29.5-30 volts and the resting voltage is 25.3.

So what was running, was your inverter on? Was this measured across a shunt at the battery?

I follow the rule of never performing equilization unless the battery is fully charged first.  I first got the bank hooked up on a Saturday morning (2/8/20), and charged it at about 30amps the whole day till the sun went down. I continued charging till full starting Sunday morning.  Sometime before noon or so it reached full charge, then I performed equilization.  Nothing was on the whole time, not even the inverter.

BTW, I am extremely happy with my Rolls batteries, and plan on replacing my cabin batteries with the same model in the future, maybe next year.  I recommend them to everyone.

My charging amperage was a bit low at first because I only had the first of my two arrays (4-250Wpanels) connected and producing power.  When I do this again, I'll be able to charge them at 60amps or so.

wellbuilt

I bought 16 gc215s for my system but set it up one string of 8 first , I needed to finish off the battery box and some other nicknacks  but needed some lights and radio . 

  When it came time to add the second string to the system I place the battery’s in the battery box and when the first string was full I did a eq charge then disconnected them from the system in the morning I charged  my second string and eq it  the parallel to two 

SethandBecca

I have noticed several people talking about Golf Cart batteries from Sam's Club. Do they work for a whole house off-grid system? 

Photowhit

SethandBecca said:

I have noticed several people talking about Golf Cart batteries from Sam's Club. Do they work for a whole house off-grid system? 

You should start a thread/discussion. It appears you are just starting out with a new system.

In general Golf cart batteries are a good learning tool. From your other post, it looks like you are at 48 volts. The problem with golf cart batteries is they only store about 1.25 kWhs each. For a large home a single string of 8 - 6 volt batteries would only represent about 10 kWhs of storage. That would be pretty minimal for a off-grid home. 2 strings would likely be minimal depending on where you live. It ends up being a lot of cells to check, and 2 strings is as many as I would suggest. I really only like to use one if possible.

For cost effect alternative a forklift battery might work out for you, particularly if your system is outside. Half the number of cells to check and longer battery life. I tend to expect 4-5 years out of golfcart batteries, I'm in my 11th year with my forklift battery. 

BB.

SethandBecca,

You really need to figure out your loads (peak Watts and total energy per day in Watt*Hours) and location (hours of sun per day by season).

For a "medium sized" cabin / very efficient home system--You can have a "near normal" electrical life aiming at 3,300 Watt*hours per day (3.3 kWH) or ~100 kWH per month (energy star rated fridge/freezer, LED lighting, laptop computer, "solar friendly" water pumping, clothes washer). If it is just for lights, laptop, cell phone charging, and RV water pump--You could look at 500-1,000 WH per day.

For a "starter" bank of batteries on a small to medium sized system, "Golf Cart" batteries can be a cheap way to start--And if you "murder" your first bank, you have not tossed 1,000's of dollars down the drain.

I suggest doing your own thread and we can discuss the details... But to give you an idea of (sort of suggested maximum size GC battery bank) on 3.3 kWH per day (1,000-1,500 WH per day for 120 VAC full size energy star fridge, LED lighting, laptop computer, RV/DC well pump, using a clothes washing machine on sunny days, etc.--Propane/other fuels for heating/cooking/hot water):

• 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage/no sun * 1/0.50 max planned discharge * 1/24 VDC battery bank = 647 AH @ 24 VDC battery bank

In golf cart batteries:

• 4 * 6 volt batteries in series = 24 VDC
• 3 * parallel 24 VDC strings of 220 AH GC batteries = 660 AH @ 24 volt battery bank
• 4 batteries in series * 3 parallel strings = 12 "GC" batteries (6 volt @ 220 AH each)

Plan on such a bank lasting 3-5 hours in "normal usage"... "better batteries" can last 5-7 years--"Forklift/traction batteries" 10-15+ years (again, assuming "no major mistakes" in bank operation).

Personally, I suggest your bank should be 1-2 parallel strings, and try to avoid more than 3 parallel strings of lead acid batteries. More parallel strings--More wiring costs--More maintenance--More "things" to fail (checking SG, adding water, more electrical connections to make/keep clean, etc.).

-Bill

SethandBecca

Okay I do have my own thread over at CO Solar. Sorry to muddy the waters here. 

BB.

No problem--Just trying to keep stuff relating to your Q&A in your thread.

-Bill