Need help with charging schedule for L16 interstate batteries

MauiSun · August 2017

First, thanks for any help, this site has been a godsend.

I just upgraded my battery bank from golf cart batteries to L16s, and I'm having trouble finding the correct charging and EQ voltages.
I read somewhere that L16s should be charged at a much higher voltage, with absorption at 61.2V and float at 54.6, both which seem a bit high.
I couldn't find anything on equalizing voltage. It also said absorption time should be at least 3 hours long.

I couldn't find any information from interstate, and trojan recommends completely different numbers for their L16s, with absorb at 57.6 and float at 52.8, and EQ at 61.92

These seems like drastically different numbers..... which ones do i go with? and how often should i schedule an equalization cycle with these batteries?

Thanks for any tips!

mcgivor · August 2017

From what I understand, therefore not 100% sure, Interstate batteries are manufactured by US Battery, perhaps someone who knows for sure can verify. Here is the pdf. for US Battery, if nothing else, it's information.
Edit. Johnson Controls may be the parent, manufacturer/owner of Interstate, or both? Who knows, major conglomerates are eating up everything, or so it seems.

Marc Kurth · August 2017

What does your battery dealer suggest?

Marc

jonr · August 2017

You might find that time constraints with solar force the use of higher voltages than normal. Check specific gravity (SG) to verify.

mcgivor · August 2017

Some interesting reading regarding L-16 batteries.

From Home Power Magazine.

Battery management and

maintenance are significant

concerns in off-grid PV systems.

Many of the user problems associated

with these systems can be traced to

improper treatment and

misunderstanding of battery

performance.

Modern battery chargers use three charging stages—

bulk, finish (absorption), and float. Bulk brings the

batteries up to the high voltage regulation point; finish

holds it at this high voltage regulation point based on

time. In the absorption stage, the voltage is constant,

and the current tapers off as the batteries are filled.

Float trickle charges the battery to a lower, userdetermined

voltage to keep it full.

From my experience, the most common battery problem

is undercharging, leading to sulfation, loss of storage

capacity, and shortened service life. Sandia National

Laboratories recently published “PV Hybrid Battery

Tests on L-16 Batteries” (see Access). Their tests

represent several years of systematic testing of a PVgenerator

(hybrid) system.

The Sandia report is very thorough. Four different

brands of batteries were tested. They were all flooded,

L-16 type batteries, the most common battery used in

residential-scale RE systems. Tests were repeated so

that the data represents good averages, and the

conclusions are based on good data and methodology.

The study has four conclusions:

1. The finish voltage (sometimes called the absorption

voltage) for a flooded lead-acid battery operating at

12 VDC nominal should be about 15.3 volts (2.55 per

cell) rather than the customary 14.4 volts.

2. Finish charge time should be at least 3 hours and

often longer.

3. The maximum interval between finish charges should

be about five days.

4. Not all brands of L-16s are the same (though the

report names no names).

The general conclusions of the Sandia report are

consistent with the number one problem experienced in

off-grid PV systems—undercharged batteries. Richard

Perez has for many years advocated higher finish

voltages for PV-engine generator systems. As he says,

“I like to run them hot.”

Home Power technical editor Joe Schwartz adds some

good advice regarding flooded lead-acid batteries:

• Higher finish charge rates result in significantly more

gassing and potential for hydrogen buildup. Before

you crank up the finish voltage to 15.3 VDC (for a

nominal 12 volt system), make sure that the battery

containment is well ventilated. The use of powered

battery vents is recommended.

• Batteries charged to a high finish voltage produce a

significant amount of waste heat. Depending on the

type and location of the battery containment, in warm

climates or seasons active ventilation may be required

to keep battery temperature in check. Optimal

operating temperature for lead-acid batteries is 78°F

(25°C). Higher battery temperatures (90°F plus; 32°C)

result in increased self-discharge. Temperatures over

120°F (49°C) can damage lead-acid batteries.

• Batteries charged to a high finish voltage consume a

lot of water. Compared to charging at the traditional

14.4 VDC finish voltage, the time period between

battery watering can easily be cut in half. Automatic

battery watering systems greatly simplify the process.

• Use temperature compensation on all charge

controllers and inverter/chargers.

Finish Charging Is Inefficient

There is one significant downside to the battery

management strategy presented in the Sandia report.

Due to battery charging characteristics, efficiency is

very low during the finish charge phase. Very long

engine generator run times were reported, sometimes

from 6 to 20 hours. These long run times were required

to completely refill the batteries to the manufacturers’

stated ampere-hour capacity.

The state of charge (SOC) of a battery is most

accurately measured with a hydrometer, and is

indicated as specific gravity (SG). Most RE users rely on

amp-hour meters to provide convenient (although

slightly less accurate) battery SOC information. During

the Sandia tests, full batteries had a SG in the range of

1.290. The long, engine generator run times needed to

achieve this SG translate into dollars and pollution (both

audio and atmospheric). Perhaps there is a “middle

way” that preserves the lifetime of the batteries while

reducing the time and cost of engine generator finish

charging.

Revisit the Assumptions

The batteries tested at Sandia were discharged by 60

percent of capacity (to 40% SOC) and then charged

back to rated capacity. In these tests, the rated

capacities were determined empirically, and in most

cases were close to the manufacturer’s stated value (in

the range of 350 AH for an L-16).

These two points require comment. First, this depth of

discharge is not typical of most well-designed, standalone

PV systems. This point is clearly stated by the

author of the study. Most stand-alone PV systems, by

design, cycle batteries by about 25 percent daily, not 60

percent.

Second, the manufacturer’s rated battery capacity and

the way it is determined should be understood. All

manufacturers recharge batteries on the grid. Using the

grid, they can finish charge the batteries for long periods

(on the order of 8 to 12 hours), cramming maximum

ampere-hours into them. For a manufacturer, this

method makes sense because it results in greater AH

capacity figures for their product.

The long engine generator run times required by PV

hybrid systems must mimic the finish charge conditions

the manufacturers use to rate the battery’s capacity.

Perhaps batteries should be rated based on their

application. For instance, a battery used in a standby

application (such as utility backup system with grid

recharging) might specify a full charge SG of 1.290. The

same battery used in an application that regularly

cycles the batteries (such as a PV system with engine

generator backup) might have a recommended SG of

1.250 to be considered full.

It is true that a battery with a SG of 1.290 holds more

charge than the same battery with a SG of 1.250.

Estragon · August 2017

I have US Battery L16s, and use 58.8v for absorb, which seems to work fine, with EQs every month or two. Actual voltage is higher as the bank is almost always under 25°C. I use end amps at~1% of capacity for absorb time.

As the batteries age (currently in their 4th year) I expect I'll need to increase voltage and maybe end amps a bit.

Need help with charging schedule for L16 interstate batteries

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