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[lukehallbland]

I might be being stupid but this is my first time charging a lead acid battery and I'm a bit worried.

The battery is a new 9AH 12V cell being charged by an Ansmann Xbase Deluxe computer charger with the initial current of 3.4A set as mentioned on the battery, though this has been reduced to a value that fluctuates between about .3A and 1A. The charger is stating that the current voltage of the sell as it's charging is now 14.5V to 14.8V and it's making a faint fizzing noise. Is this what would be expected or is something wrong?

[barriew]

If the current has dropped, it probably means that the cell is charged and the charger is now maintaining a trickle charge. Remove it from the charger and check the voltage. It should be in the order of 13.5v after its settled.

Barrie

[Colin Bishop]

If it is  a sealed lead acid It shouldn't be fizzing which suggests that it is venting from being overcharged. The 14.5 volts you are seeing is probably coming from the charger rather than the battery. As Barrie says, when fully charged and settled (leave it an hour or so) the battery voltage should be around 13.5v.

Colin

[Shipmate60]

The MAX charge on a Gell Cell is 1/10 the capacity, so you are overcharging it.

Bob

[FullLeatherJacket]

The MAX charge on a Gell Cell is 1/10 the capacity, so you are overcharging it.
Bob

Not to cast doubts on the admirable Shipmate 60, but I have just had a look at a Kinetic brand 12v x 7AH SLA battery. It very clearly states the following:
Constant Voltage Charge  Cycle Use 14-4 - 15.0  Float Use 13.5 - 13.8  Initial Charge Current Maximum 2.1A
The same brand 12v x 12AH batteries state a maximum initial charge rate of 3.6A. Weird, huh? I must say that 3.5A does seem a bit excessive, though - especially if it's causing the cells to vent gas. I guess the whole problem is the absence of a definition of how long "initial" is meant to last.
For what it's worth I use either a microprocessor-controlled constant voltage charger, which changes from Bulk to Float Charge after 95% of the full charge, or a cheapo Robbe Multilader @ 500mA. There are numerous different sizes and shapes of sealed lead-acid battery chargers on the market, and mine aren't necessarily the best or the only types to use. They work for me, that's all.

FLJ

[malcolmfrary]

If an SLA is making fizzing noises, it has been venting which means that some of the fluid which belongs inside is now outside.  This is not good.  As you can't replace it , what with it being sealed, the battery now has less electrolyte inside than it should have.  The 7AH capacity will no longer be 7, but something less. 
SLAs respond best to gentle charging, and ideally should be charged by a device that limits both charging current and final voltage.  I would go with Shipmate60's advice, what with him being a buyer and user of batteries rather than a seller of batteries

[Shipmate60]

The SLA Batteries in the Fire Detection Equipment on board my ship are on permanent trickle charge, but not more than 1/2 amp.

Bob

[Colin Bishop]

To add to the comments, I would also treat SLAs fairly gently for charging purposes, and keep them topped up after use of course. However, the internal construction can differ from type to type and the sealed full size battery on my old 1:1 scale boat was designed to take an initial high charge, levelling off as the voltage rose. It was however a "wet" rather than a gel cell. I know marine chargers are designed to pump a fair old amount of current into a discharged battery at first and then use voltage and heat sensing to reduce to a trickle charge as the battery comes up to capacity.

You cannot "fast charge" a SLA cell like you can other types so you might just as well play safe and go for a longer charge period which will help prolong battery life.

Colin

[lukehallbland]

ok, guess the PB setting on the charger must be for unsealed, I'll see if i drop the initial charge current down then the charger will charge it properly. Thanks for the help!

[Peter]

Just to add to Shipmate 60's advice, the generally accepted ideal charge rate for a lead acid battery is 1/10th of the capacity for 15 Hours.

Peter

[stallspeed]

ok, guess the PB setting on the charger must be for unsealed, I'll see if i drop the initial charge current down then the charger will charge it properly. Thanks for the help!

The charger is set for cyclic use of a sealed battery.See the charge voltage vs temperature graph on this link.http://www.yuasa-battery.co.uk/industrial/np.html#

I've heard fizzing on the bulk charge cycle and put it down to the normal charging process,not venting.It may have something to do with periodic reversal which shakes the bubbles away from the plates.

Dedicated Yuasa chargers switch to 13.65 volt float when the charging current falls to .03C.If the charger doesn't perform that then remove the battery after 24 hours.

As has been stated correctly, the bulk charge rate varies from C/10 for standby batteries to higher depending on construction and type of charger

[pk1]

Beware on overcharging, i work in the alarm trade and have seen these batteries looking like balloons and getting red hot, haven't seen one explode though yet, i use an old alarm panel to keep my batteries charged

[wombat]

IIRC A lead-acid battery vent gas when it is fully charged - I always used this as a sign on the car bettery that it was fully charged.

The charge regime to use dpends on the design of the battery - if it is designed for float charge, then float charge it - a gentle charge at no more than 10% of capacity - for your 9AH battery this would mean 0.9A - so the 0.3 to 1A you are seeing is OK - if you charge at this sort of level then you can never overcharge it. However, fast charging is not so good for  a battery designed for float charging.

If a battery is designed for Cyclic charge then you can charge harder - but you have to be more cautious about overcharging, especially if you do not fully discharge.  Even then you need to check the charge current - for example the Yuasa NP series which are designed for float or cyclic charging give a maximum charge rate of 0.25C

Wom