So what's all this solar battery stuff anyhow ?

[OldSmokey]

Here we are with the first of several posts concerning solar design. before I go any further, let me say that most of the information in my posts will relate to off grid stationary solar installation design best practices and will therefore differ with what an RV'er might consider good practice.

I will address RV specifics as and when needed.


So first to Batteries.

when I ask most people about lead acid batteries, they almost always think of the car battery.. it's 12 volts dude, what more do you need to know ?

well that response is just like ice cream.. it's cold right ?
like ice cream, batteries also come in assorted flavors..


The SLI or car battery..

this type is designed to deliver high amperage for a short period, cranking over that big engine for several seconds at 400 amps or more..they are designed with thin lead calcium alloy plates for low resistance and low voltage drop. they are NOT designed for deep cycle use and will fall apart internally very quickly if you treat them as such.

Pros: high current typically ( high c rating )
inexpensive due to high volume manufacture
Cons: low lifespan if cycled.



Hybrid batteries ( FLA or flooded lead acid )

The hybrid has negative plates of lead calcium alloy and positive plates of lead antimony alloy, the plates are thicker than a SLI battery to give more deep cycle capability and is a trade off between high current and deep cycle useage. these have names such as Golfcart, Trolling, RV, marine etc... note that these batteries are marked with CCA and Ah. CCA or cold cranking amps is what you would see on a SLI battery..

Pros: Good all round battery for medium cycle useage
cons: much less current rating than SLI


VLRA or AGM ( advanced glass matt )

valve regulated lead acid batteries come in several flavors.
Hybrid just as the flooded battery, these are the typical AGM sold
and have very low internal resistance and therefore high discharge and charge capability. they have the advantage of no electrolyte maintenance ( it is absorbed into a glass fiber cloth ) but cost considerably more than a FLA, also they don't have near the cycle capability of FLA.

Pros: very high c rating like SLI
No electrolyte maintenance
higher cycle capability than SLI
cons: High cost compared to SLI
lower lifespan than deep cycle


Telecom or UPS AGM

this version of AGM is designed to spend most of it's useful life on float charge much like the SLI. like the SLI it's a high current battery and has a low resistance. not recommended for solar RE applications or RV.

pros: Very high c rate
cons: very low cycle capability like SLI


Deep cycle FLA.

these are the mainstay of solar RE. very thick plates of lead antimony built for deep cycle use and long life. the trade off here is the high internal resistance. these are NOT designed for high current use, they are designed to be used down to typically 50% DOD ( depth of discharge ) at relatively low currents and will withstand this use pattern for a very long time. deep cycle batteries are not rated in CCA. capacity is rated at the 20 hour discharge rate ( c/20 )


Lithium iron phosphate ( LiFePO4 )
This is the preferred lithium chemistry for us normal folks.
it's quite stable and not prone to self ignition or combustion like other lithium types. they are made in numerous shapes and sizes.

two main types to consider for us..

Prismatic cells.

The popular form ( in large capacity sizes ) is the prismatic cell. the basic cell has a voltage of 3.2 volts is available in capacity from 10 Ah to 1000 Ah and needs to be assembled into strings to achieve the desired voltage.

Drop in's

these are made as a form, fit and function replacement for SLI batteries. and are targeted at people who like the idea of lithium but neither know or want to know the technology and have cash to burn.

pros: extremely high charge and discharge rates
no electrolyte issues
very light weight compared to FLA
unlike FLA and AGM, can be placed in parallel service
without adverse effects.

cons: very expensive ( 400 to 500% higher than FLA )
for most use require a monitoring system to prevent cell
imbalance. AKA a BMS or battery monitoring system.


I'll finish up with a mention of C rates.

the C rate is just the batteries capacity divided by the charge or
discharge current.

example: a T105 of 225 Ah capacity
if we charge or discharge at say c/8 then we have 225/8 = 28 Amps

for charge or discharge there are ideal rates that battery makers suggest these are not arbitrary figures but recommended values for maximum lifespan for general use. refer to manufacture data for those rates.

personally, I would not recommend a rate of anything higher than
a c/4 rate for FLA and c/2 for AGM, anything higher than this will shorten life. just like a car, the harder you drive it the quicker you wear it out. same applies to batteries.

so that's enough of batteries, next installment will a short one on solar panels and controllers. followed by a real system design and suggestions for RV use.

[Almot]

time2roll wrote:
Yes lithium chargers that plug in are programmed to turn off.

Yes. This is why it's interesting to hear that some Li batteries need to be floated - like GBS.

When I read Battle Born manual, it explicitly says "Do not need to Float". You can set solar controller Float to 13.6, and the only result will be that battery BMS will stop the charging at this point. Also, there is no Absorption or Equalize for these batteries. Manual only says that Absorption (or Bulk) should be set to 14.x because 13.x is too low for charging. To sum it up - there is only Bulk and Off for this battery, no Float or Absorb. Manual just explains how to set up a conventional charger to make it compatible with Li battery.

I was unable to find an official manual for GBS where it would mention Float as a necessary stage.

[time2roll]

If you use it, charge before next evening. If you don't use it, let it sit.
Life critical equipment should be duplicate.

[MEXICOWANDERER]

Unless
The
Partial
Charge
Leaves
You
In
The Dark
Vulnerable
To
A Fall

I use this stuff as a tool not as one of your cellular playtoys.

[OldSmokey]

red31 wrote:

OldSmokey wrote:
Here we are with the first of several posts concerning solar design.

So the dealer threw in a G24 RV battery, what's next :W

how about one of these..:B
and 10 to 15 feet of 14 AWG on the 12V side..


Kaboom!

[red31]

OldSmokey wrote:
Here we are with the first of several posts concerning solar design.

So the dealer threw in a G24 RV battery, what's next :W

[time2roll]

Yes lithium chargers that plug in are programmed to turn off.
My comment was about solar aligned with the title of the thread.

[Almot]

time2roll wrote:
{Li no floating} is a bit of a conundrum for solar as I don't know of any controller that fully disconnects. Honestly I believe if the float voltage is set well below the fully charged resting voltage the typical RV will have no issues.

I would trust what particular Li manual says.

Those Li battery/charger combos that I've seen, recommended shut down. Some are automated and allow charging to either 80% or 100% or an arbitrary point in between, based on voltage (and then it shuts down). BMS would only protect from overcharging and overheating, overcharging meaning running the current past 100%.

In storage the recommendations were to top it up every 2-3 months (though it wasn't clear - with a cheesy charger that came with the battery or with one of better models that allow 80%). None of them was for 12V though. I hear that in electrical cars it does limit to 75-80%, whether BMS or the charging circuits.

Cell phone - yes, you should not keep it on charger when charging is completed. This is what it reads on the screen of my phone - "charging completed, please disconnect" 🙂 ... For protecting charger, if nothing else. Don't know how sophisticated its BMS is, and when exactly it reads "completed" - at 80, 100, or several minutes past 100%. The industry approach is to treat it as a disposable and very short-lasting item, I usually keep mine longer than they would like me to, but their thinking makes me wary as to the product features.

[time2roll]

MEXICOWANDERER wrote:
....so, if floating is not part of the program then the battery and controller has to have voltage control thresholds. Specific setpoints. I wonder what they are? I have a 7 amp hour lithium battery pack. Once the idiot light says the charge has completed, reinitiation of charge lasts under a minute until the LED changes to green. Let device sit connected for two weeks and a recharge takes 15 minutes.

That is NOT an acceptable protocol. Wait! If I charge then unplug the exact same recharge in minutes is necessary. At what point does the exercise recycle? Lithium is still being treated like a toy in consumer electronics.

plug/unplug repeatedly.... you are treating it like a toy. Just like my brother that had to bend my stuff too much or too far and it would break.

lithium will hold a charge for a year at least and probably several. No harm in leaving partial charge so no reason to top up unless you will be using the toy.

[Itinerant1]

pianotuna wrote:
Hi 2oldman,

Glad to hear that I'm wrong--at least in some cases. It would certainly be a deal breaker for small solar.

2oldman wrote:

pianotuna wrote:
Except Li doesn't want to be float charged. Not ever!

My 48v pack has a float specification. Perhaps the 12v drops ins do not.. don't know.

My 12v GBS li-ion have a float setting.

Doing a quick view from Battleborn Batteries drop ins, from thier FAQ section.
"You can use any standard charger, solar or wind charge controller to charge our LIFEPO4 deep cycle battery. There are some chargers and controllers that are programmable to get full usage out of your battery, but most will have an AGM setting which normally bulk charges about 14.4 volts and floats at 13.6 volts. These levels are great for your Battle Born battery."

Maybe you're thinking of absorb stage?

Here are the settings used by my installer.
The following parameters are for programming the ME-ARC Version 4 advanced control.

Setup 02B LBCO Setting: Volts = 12.0
Setup 03C Battery Type: = Custom
Set Absorb Volts: = 14.2
Set Float Volts: = 13.6
Set EQ Volts: = 14.2
Set EQ Done Time: = 0.1
Setup 03D Absorb Done Time: = 0.1
Setup 03E Max Charge Rate: = 100%
Setup 03G Final Charge Stage: = Float

[MEXICOWANDERER]

....so, if floating is not part of the program then the battery and controller has to have voltage control thresholds. Specific setpoints. I wonder what they are? I have a 7 amp hour lithium battery pack. Once the idiot light says the charge has completed, reinitiation of charge lasts under a minute until the LED changes to green. Let device sit connected for two weeks and a recharge takes 15 minutes.

That is NOT an acceptable protocol. Wait! If I charge then unplug the exact same recharge in minutes is necessary. At what point does the exercise recycle? Lithium is still being treated like a toy in consumer electronics.

[pianotuna]

Hi 2oldman,

Glad to hear that I'm wrong--at least in some cases. It would certainly be a deal breaker for small solar.

2oldman wrote:

pianotuna wrote:
Except Li doesn't want to be float charged. Not ever!

My 48v pack has a float specification. Perhaps the 12v drops ins do not.. don't know.

[2oldman]

pianotuna wrote:
Except Li doesn't want to be float charged. Not ever!

My 48v pack has a float specification. Perhaps the 12v drops ins do not.. don't know.

[time2roll]

pianotuna wrote:
Except LI doesn't want to be float charged. Not ever!

That is a bit of a conundrum for solar as I don't know of any controller that fully disconnects. Honestly I believe if the float voltage is set well below the fully charged resting voltage the typical RV will have no issues.

[BFL13]

pianotuna wrote:
Hi BFL13,

Yes, EXCEPT, the device may lie to you about the 100% or have circuitry to disconnect. I have seen my laptop do just that.

BFL13 wrote:

pianotuna wrote:
Hi time2roll,

Except LI doesn't want to be float charged. Not ever!

My puny solar hardly ever gets past float. I just don't have the watts.

Does that mean you shouldn't leave your cell phone or laptop plugged in?

Actually, it turns out that the software in the phone turns off the charge so it does not float as such. I don't know if this is true about laptops. Good read here about Li--BUT--do read the corrective comments at the bottom about the meaning of "cycle"

http://www.androidauthority.com/leave-phone-plugged-overnight-703078/