Lead Acid Batteries: When to charge?

MrAl · Post by **MrAl** » Tue Aug 22, 2006 5:22 pm

Hi there,

A while back, someone sent me a nice fluorescent light that ran
off of 4 AA cells. I ran it for a while that way but realized i wasnt
getting the run time i wanted. I switched to NiMH, but still wasnt
happy.
A while later, i had to test someone's lantern so i purchased a
6v lead acid battery. After testing i had no need for the LA battery,
but then it dawned on me that i could use it for the fluor light
and get a pretty long run time.

Ok, so i have a 6v LA battery connected to the fluor lamp, and now
and then it needs to be recharged, so what i am looking for is data
on when the best time to charge is, or what is the longest or lowest
voltage you should allow the LA battery to get to before recharging.

What would be nice is data like this:
5.90 volts A GOOD TIME TO CHARGE
5.80 volts TAKES A LITTLE LIFE OFF THE BATTERY
5.70 volts etc, etc.

Any links would be great, but anything that isnt pretty specific
probably wont help.

Chris Smith · Post by **Chris Smith** » Tue Aug 22, 2006 5:38 pm

What would be nice is data like this:

5.90 volts A GOOD TIME TO CHARGE
5.80 volts TAKES A LITTLE LIFE OFF THE BATTERY
5.70 volts etc, etc.

More like this....

6.10 volts A GOOD TIME TO CHARGE at its bottom.
6.00 volts too late? [getting dead]
5.90 stretching it?

A good battery is always at 12.6 for a 12 volt battery,

or 6.3 [2] for yours.

To charge it nicely with out ripple, 14.7 or 7.2 [4] for yours.

Keep it at this and its happy. [no ripple]

Smoke_Maker · Post by **Smoke_Maker** » Tue Aug 22, 2006 7:51 pm

Here is a link to more information than you ever wanted to know about charging batteries.
Happy digging.
http://www.uuhome.de/william.darden/carfaq9.htm

The battery is full when you reach 2.45 volts per cell and the current stops dropping, and the battery is empty when the voltage drops to 1.75 volts per cell under load. This is assuming you are talking about a deep cycle battery and not a SLA battery.

To test a deep cycle battery condition put a load on it and start a stop watch to see how long it takes to get to 1.75 volts per cell. After you fully charge it first.

MrAl · Post by **MrAl** » Wed Aug 23, 2006 10:42 am

Hi again,

Chris:
how can we be sure of these values? any references?

Smoke:
nice link but couldnt find anything about when it is a good time
to recharge (ie at what voltage). Also, they dont seem to take
into account the charge efficiency of LA batteries when they do
the calculations, which makes me suspect of all their info.

dyarker · Post by **dyarker** » Wed Aug 23, 2006 11:15 am

Try:
http://www.panasonic.com/industrial/bat ... 061R3P.pdf

List of Panasonic batteries:
http://www.panasonic.com/industrial/bat ... .html#data

Pick one close to your battery's AHr rating to use the discharge graph and recommended charge current.

Chris' numbers look pretty good. ( a 1/10th Volt lower while loaded for each condition should be okay too.) The 6.3V value is charged but no load and "rested" after being charged.

And add 5.7V for DISCONNECT LOAD NOW!

Cheers,

Chris Smith · Post by **Chris Smith** » Wed Aug 23, 2006 1:45 pm

Al

These numbers have been used for a long time now for the general Lead acid battery.

The auto [moving] industry first used the 6 volt system and later the 12 volt battery,.... and they have studied, used, and proved these numbers for almost a century now.

This industry includes the 18, 24, and 36 volt systems.

Lower voltages can cause oxidation, chemical break down, flaking, cracking, and all the other battery related problems so sticking "near" to the Ideal voltage is correct way to go.

Too high or too low usually causes premature death in a battery.

Gorgon · Post by **Gorgon** » Wed Aug 23, 2006 2:59 pm

6.8 - 6.9V fixed constant voltage, would keep your battery top charged at 25 deg. C. If you have higher ambient temperature, you should reduce the voltage some. You can see the table her: http://www.powerstream.com/SLA.htm. You could use a NTC to compensate in the power supply. (Thats what we do in our fire alarm panels)

You don't need to cycle the SLA, just keep the voltage within the correct value in regard to the temp. That is important! If you charge with a too high voltage the battery will heat up, the voltage will be much too high, more heat, and so on. You will reduce the working life of the battery or in the worst case short circuit it.

TOK

MrAl · Post by **MrAl** » Wed Aug 23, 2006 3:29 pm

Hi again,

Thanks for the info and the links.

I see from that one link that they are draining the battery down
to 5.4v or even lower (for a 6v 4.5AH LA battery).

For my use i charge the battery, then use it until a certain point
is reached with the battery voltage. I dont need to trickle charge
or anything like that though, just charge it once and put it back into
use, then when time comes charge it again, etc.

Chris Smith · Post by **Chris Smith** » Wed Aug 23, 2006 3:37 pm

If you stick to the approved and upper limits, dont over heat anything etc, your battery wll like you much better.

LA batteries are rugged, but they also break from simple misuse.

MrAl · Post by **MrAl** » Wed Aug 23, 2006 5:56 pm

Hi again,

Chris:
Yeah, and i keep an eye on the current not to exceed an amount
which will not cause any noticable heating in the battery during charge.
I am trying to get the maximum life out of this thing which cost me
almost 15 dollars ha ha. I dont like to pay that much for one battery.
It sure does boost the run time of the fluor light im using though.
The four AA's were almost useless ha ha.
This is s nice light though so i want to keep it, just needed the extra
beefie battery for decent run time before it needs another charge.

If i do get a decent lifetime out of this thing maybe i'll buy another
one when the time does come to chuck it.

I am also waiting for the Eneloop NiMH batteries to some to the USA.
Plan to test them as soon as they become widely available.

Smoke_Maker · Post by **Smoke_Maker** » Wed Aug 23, 2006 6:06 pm

Al, one of the first things you should do is to identify the battery (manufacture, Ah, deep cycle or SLA "starting-lights-accessories") these facts all make a difference to your answer. This battery may not work the way you need it to, a deep cycle battery left partially discharged for a time will start to grow crystals on the plates and will die a early death. If the load is small and the DOD (depth of discharge) is small then this may work for you.

Lead acid batteries will live longest when kept in a fully charged state, a deep cycle battery is considered 100% discharged when it reach's 1.75 volts per cell under load ( in a 6 volt battery this would be 5.25 volts).

80% DOD is the recommended low level of discharge for a deep cycle battery ( 6 volt battery is 5.6 volts under load)

A 6 volt battery with NO load and NO charging is fully charged when it reads 6.3 volts and completely dead when it reads 6.0 volts, that's three tenths of a volt between full charge and completely dead.

So to make it simple, use the battery as you need with out going below 5.6 volts under load (that's 1.82 volts per cell), charge the battery as often as possible and keep asking questions while doing research on lead acid batteries.

Go to the battery manufactures web site and they will give you the numbers they would like you to use for charging and discharge.

All bets are off if you are using a SLA battery, that is a completely different animal.

Chris Smith · Post by **Chris Smith** » Wed Aug 23, 2006 7:47 pm

Al

I have several fluros running off the small D type Lead batteries.

For the main one,....I run the fluro off 8 cells instead of 6, [16v] and the system gets a quick charge rather than leave in it for ever,... type charge.

I run the fluro and when the cells even look low, or the circuit cuts out and blinks, I then hit it fairly hard with a good charge to recuperate the battery.

If the unit wont start, I donâ€™t hit the start circuit over and over just to cheat, I just rotate the cell pack with another and charge one as I use the other.

I can get it to start and fully drain,.... But I donâ€™t.

I usually get more than 4 full hours worth of use per cell pack. [2ah]

Straight or accumulated.

These cells which only cost a buck each were used or recycled when I purchased them and they are over five years old so far. [from me]

Gates was the brand, â€œDâ€

MrAl · Post by **MrAl** » Wed Aug 23, 2006 10:55 pm

HI again,

Chris,
Sounds very ineresting. The one i have is a U tube too but it's only
about 3 inches long (about 7 inches if you were to bend it straight)
but it puts out a lot of light! so i know what you mean. Someone sent
me this light when i purchased some other things and i had been
grateful ever since

take care.

Chris Smith · Post by **Chris Smith** » Thu Aug 24, 2006 8:58 am

Ed

I know the size you mean. My next experiment will be the screw type they make with the small electronic package. The tube is short with two twists built in making the tube long but short in size. I have several tubes with bad bases, so I just unplugged one the tubes. It should be interesting. Ill try it with one of the old drivers and see what happens.

Rodney · Post by **Rodney** » Thu Aug 24, 2006 11:37 am

Another very good source for accurate information on all types of batteries is www.rcbatteryclinic.com.

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Lead Acid Batteries: When to charge?

Lead Acid Batteries: When to charge?

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