Charging Lead Acid Batteries

Larry1582

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I have seen a lot about whether to leave NiCad and Nihm batteries on chargers 24/7 or not, but what about lead acid battery lights like the lead acid version of the Pelican Big Ed. Will it hurt for it to be on the charger 24/7? Should you ever do a battery run down and recharge conditioning of the lead acid battery?
 

Ginseng

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I have a related question which I hope someone can help with. The battery pack in my Dorcy spot seems to have dropped to about 1/4 of its rated capacity. It is a 6Ah SLA 6V unit and is normally charged with a 12V 300mA wall wart. The last few runs though, instead of giving the rated 30 minutes, I've been getting 7-8 minutes. I have never charged it for longer than 30 hours (the recommended max) from a full discharge but I have discharged it to dimming a few times.

I've run it through a few cycles on the Triton but have not gotten more than 900mAh in or out of it. Also, "fully charged" it now reads 6.5-6.7V and it discharges down to 5.3-5.4V.

Is the cell pranged?

Wilkey
 

Ginseng

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Sorry for the thread-jack. I thought it sort of relevant to your original post.

Wilkey
 

Lynx_Arc

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Lead acid batteries do well on chargers 24/7, They use them as backup for emergency lighting.. alarm systems and your car battery is a lead acid battery. I do not think reconditioning them is needed or wise as it will only possibly damage it.
I don't recommend letting lead acid batteries completely die and fast charge them.... trickle charging them increases the life of the battery.
 

Larry1582

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No problem. I have a question for you about a battery pack you made. PM on the way.
 

Lynx_Arc

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ginseng... what voltage is your SLA getting off the walwart?
Lead acid batteries I believe if you charge them at too high a voltage it can reduce the battery life just as charging too fast will. That is why they do not like it when car charging systems get over about 14.5volt thereabouts.. charging your 6.7v SLA at 12v is the equivelent of charging a car battery at 22.5v if the voltage holds at that level. I am guessing it sags some of the wallwart.
 

Ginseng

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Well,

The batt is most likely screwed up permanently. I was using the wrong wall wart. The plug fit and I never read the label on the wart. Oh well, live and learn.

Wilkey
 

georges80

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Charging an SLA requires a different voltage than maintaining an SLA.

Typical recommendations are to charge (with current limit) to approx 2.45V per cell. Once the charge current drops to a low level - around 60mA for a 6AH SLA then switch to maintenance voltage of 2.25V per cell. The SLA can then be left connected to the maintenance voltage indefinitely.

The charge/maintenance voltage is temperature dependent as well.

Check out some of the datasheets at a gell cell company - for instance power sonic

Benchmarq, now TI, has a decent SLA charger chip (BQ2031), that I've used to build a few 6V gell cell chargers - works a treat. Search for it on www.ti.com - appnotes are there etc.

george.
 

Lynx_Arc

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Most likely you fried that gel cell... unless you like the dorcy spotlight I know harbor freight has 500,000cp spotlights for about 7.99 that have ~6.7v sla in them I could open mine up and look if you want exact size and specs, it may be cheaper than buying the SLA by itself if it is the right size.
 

Doug Owen

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The real danger with these rascals is after all the lead is chemically converted back, each cell is by definition fully charged. If, however, the available voltage is high enough current still flows. Amps of current times Volts across the cell is work being done. If there is no more chemical work to be done ('cuz it's fully charged) it's gonna be heat and (worst still) splitting of the water in the cell by electrolytic action into Hydrogen and Oxygen *gas* that will leave the cell for ever. This kills the part of the cell exposed, eventually the entire battery becomes useless.

Like what you're seeing. The guy that makes it is quite happy to only give you a (cheapest possible) charger and stands ready to sell you the replacement battery it kills.

Lead acid charging *demands* voltage regulation (or extremely careful 'trickle charging') when dealing with gel cell batteries. Ideally, in fact, the voltage needs to be temperature sensitive (lower at higher temperatures).

Doug Owen
 

Lynx_Arc

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would be interesting to make a stick on thermistor hooked to a voltage regulator/current detection circuit that would shut off a charger after it detects it not charging at a certain current level and/or temperature increase. I would have to switch the charger back on when voltage dropped to a certain level.
 
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