Charge Settings for Flooded Lead Acid Batteries

System · August 2008

I have my cabin inverter system set up and running temporarily at my house. It consists of a Xantrex Prosine 2kW inverter and 4 Energizer 220ah GC2 Batteries in a series/parallel connection to feed 12 VDC to the inverter. I have some questions regarding the settings on the 100A battery charger built into the inverter. Here are the settings that the Charger defaulted to when I selected generic flooded cell and entered 440 ah battery capacity.

Bulk Charge
Max Current 10% of battery ah capacity (Defaulted to 30%, I thought that was too high)
Max Voltage 14.4V
Absorption Charge begins after a time delay of 3 minutes at or above 13.5V

Absorption Charge
Max Current 44A 10% of battery ah capacity (Defaulted to 30%, I thought that was too high)
Max Voltage 14.4V
Max Time 8 hours.
Overcharge begins after a time delay of 3 minutes at or below 2.5% of battery ah capacity

Overcharge ( This is not explained very well in the manual other than it is the second half of the Absorption step)

Overcharge and Float also have settings but I don’t want to get too long with this message.

One question is about the 13.5V setting to begin the absorption charge seems low. Any advice on a typical number there, on what is the overcharge part of the absorption step and any other advice from the gurus here would be appreciated.

Thank you,

Jerry

BB. · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

Wind-Sun's Deep Cycle Battery FAQ does a good job of explaining how to charge the batteries.

As long as the battery is not deeply discharged--and your settings cover that minimum voltage--you are probably covered there.

The other way people damage their batteries is by overcharging them. If you batteries sit unused for week or more at a time--I would really make sure the float settings are correct and check the battery and make sure that it is "floating" when you expect to.

Also, watch battery water usage--if you are refilling your battery with a lot of water every month (or if they are fizzing/bubbling heavily and often)--you probably are overcharging them.

Also, pick up a hydrometer (if you do not use a battery monitor) and check the battery specific gravity is good.

-Bill

System2 · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

TheWire wrote: »

One question is about the 13.5V setting to begin the absorption charge seems low. Any advice on a typical number there, on what is the overcharge part of the absorption step and any other advice from the gurus here would be appreciated.

Thank you,

Jerry

Jerry, I like to absorb at 14.8 @ 77*F and use a temp compensating probe to allow for varying batt temps. Trojan recommends holding this for at least an hour (I like 2-3) before switching to float.

I think the algorithms of most chargers are set way too low for maximizing the systems used by guys that know what they are doing.

That upper 10% of charge is really 30% of your system when you convert to watts available. This is a whole panel, so it makes sense to optimize and do a bit of research. HTH

System2 · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

Bodfish,

I take it your recommendation of 14.8V is the voltage as which to switch from bulk to absorption?

Also, my charger can switch from absorption to float based on time or falling below a current limit. Would a start be to set the charger to switch to float after 2 hours or current below 11A?

Regarding max charging current.

Another forum told me its OK to bulk charge my 440ah bank at 100A (max output on my charger) as long as the batteries don't get to hot.

However the Wind-Sun's Deep Cycle Battery FAQ states "Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps."

Bodfish mentioned "That upper 10% of charge is really 30% of your system when you convert to watts available. This is a whole panel, so it makes sense to optimize and do a bit of research"

What is the consensus here in the forum as to what is the max charge current I should be putting into a 440 ah set of GC2 batteries? Being that my main charging source is a generator for now, I want to maximize my charge current without killing my batteries.

Thanx,

Jerry

mike95490 · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

> Another forum told me its OK to bulk charge my 440ah bank at 100A (max output on my charger) as long as the batteries don't get to hot.

That would be my impression too. If things start getting warm, cut back on current. Since the genset is burning fuel, makes sense to pump as much juice in as possible. 30A vs 100A might shorten lifetimes by half a year, you are moving more material, faster, inside the battery. You have to juggle fuel, vs runtime, vs 5% shorter battery life, vs batteries sitting longer at less than full charge..... But the key is heat, if it heats up, throttle back. Also, after you get to 60% charged, the battery is going to start slowly tapering off the charge current on it's own, it won't stay at 100A for 2 hours, at the end of 2 hours it might be at 20A, and then flip to the next stage of charging.

Brock · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

At the faster charge rates you are less efficient in terms of charging he battery, but more efficient in terms of generator fuel consumption. If you charge at 100 amp rate let’s say you might use 1000 w/hr to totally recharge the bank, if you charge at 25 amps you might only use 950 w/hr's. That extra power just turns in to heat in the battery. But again if it lets you run a genset 2 hours less, it probably worth the trade off in total energy in the system.

I charge mainly on grid so I typically charge in the C/15 rates. I also know what my typical daily draw is and that it will recharge in about ½ the time I have cheap power available.

rplarry · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

TheWire
When I had FLA batteries I would charge them to the manufacturers voltage specs, for Trojans that was 14.4-14.8 in bulk, (I don't know what the energizer batts are spec'd at)then have my controller switch to absorb till the batteries will hold that voltage (I charged to 14.8 ) and the charge controller tapered the charge down to 1% of the amp hour capacity of the bank, which in your case is 4.4 amps. Then switch to float. You would need a battery monitor to tell when you have only 4 or 5 amps going into the batteries. Charging your relativly small bank at 100amps is probably a little high, I would follow NAWS guidelines and limit it to C/8 which is 12.5% of the amphour capacity of the bank. Too much amperage could make them over heat and migh possibly warp the plates. The plates on Trojan batteries were only .070" thick.
Anyway, good luck with your system,
Larry

System2 · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

Say, Larry is it hot down there at the beach?:grr

Wire: Larry gave a spot on response. You NEED the higher voltage to push in the last few amps. Just like airing up a tire. You need more psi than what's in the tire to get any volume.

Here's the deal with this upper end and why it's so important. If you don't charge that last 10%, (and it does take a long time), then you have left only 40% usable amps to use (less if you convert the top voltage to amp hours), before charge needs to take place. Most chargers er on the low side. to high is also bad, but 14.8 is not too high for flooded. It will also save you from an equalize.

There are only 2 controllers I know that will give me these settings with a larger system (over 15amps) and they are the Tristar and the Outback. I don't consider any stuff now outsourced to Mexico.........(all the rest)

rplarry · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

Bodfish
Actually I'm in San Diego right now picking up building materials for a new garage that I am building, but it has been warm down there, 95 to 100 deg. The water is clear and warm and lots of whale sharks reight in front of the house so the snorkling is good.
Larry

System2 · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

is there a meter to check battery amp hour available(remaining after used)
thanks,
boon.

BB. · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

Boon,

The typical meter it called a "Battery Monitor" and is about your best friend for ensuring long battery life.

Roughly, it works like a bi-directional gallon meter on your gas tank... As you put electrons (current) in (per unit time)--it adds them up as Amp*Hours. As you draw current out, it subtracts from the total.

The meters also have some "smarts" to figure out when a battery is fully charged (100% State of Charge), temperature factors, and current factors.

Pretty darn close to the "gas gauge" on your car's fuel tank.

Feature wise, the old Xantrex XBM had some love here--and I like the new Xantrex LinkLite and LinkPro features (both new meters include a programmable output signal--handy for a Low Voltage Disconnect based on real State Of Charge, or use as a over/under charge alarm, etc.).

I have not used any of these meters (I don't have an off-grid system)--so do your research.

-Bill

System2 · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

thanks for the link, i could not find a simple meter that will tell me the available amp on battery.

the reason i asked, this morning i went to check deep cycle battery and thinking i can use my Sperry SP-10A to measure the residule of amp hour after used(it rate 115 amph). the meter has DCA tester, i thougt it mean DC Amp hour. i think the meter is now dead.

boon.

BB. wrote: »

Boon,

The typical meter it called a "Battery Monitor" and is about your best friend for ensuring long battery life.

Roughly, it works like a bi-directional gallon meter on your gas tank... As you put electrons (current) in (per unit time)--it adds them up as Amp*Hours. As you draw current out, it subtracts from the total.

The meters also have some "smarts" to figure out when a battery is fully charged (100% State of Charge), temperature factors, and current factors.

Pretty darn close to the "gas gauge" on your car's fuel tank.

Feature wise, the old Xantrex XBM had some love here--and I like the new Xantrex LinkLite and LinkPro features (both new meters include a programmable output signal--handy for a Low Voltage Disconnect based on real State Of Charge, or use as a over/under charge alarm, etc.).

I have not used any of these meters (I don't have an off-grid system)--so do your research.

-Bill

BB. · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

Yes,

It is not easy to measure the actual battery capacity without simply discharging it through a known load, and see how long that takes to do (Amps * Hours)...

Your meter--yes, either dead or a blown fuse in the Amp Meter circuit (it is worth checking).

Volt meters are intended to measure battery voltage directly. Amp Meters (current meters) are intended to measure current through a load ("break" one of the load wires and hook the +/- leads from the meter into the "break"--and the meter has to be rated higher than the current you expect to measure--i.e., a 5 amp load--use a 10 amp rated meter).

Batteries have very high currents available and should never be shorted. The are dangerous devices.

The way to estimate a battery's capacity is to use an accurate voltmeter (typically Digital Volt Meter) when the battery has rested for 3+ hours. You can find the basic chart here (scroll down).

Or, a more accurate way (for use with flooded cell batteries, not sealed/AGM) is a hydrometer (most accurate).

-Bill

rplarry · August 2008

Re: Charge Settings for Flooded Lead Acid Batteries

Boonwsun
A good meter that will do what you are asking about is here: http://www.windsun.com/ChargeControls/Trimetric_2020.htm
and it is on sale! There are alot meters out there, but this is a good one at a good price.
Larry

Charge Settings for Flooded Lead Acid Batteries

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