4v SLA battery charger- can i use nokia 5.7v 800ma charger

[robotsmani]

Hi All,

I have 4v 0.5AH(20HR) SLA battery which is used in chinese led lamps. I want to use it for robotics purpose. I need a charger for that. can i use the nokia charger which is rated 5.7v 800ma.

i tried connecting the charger with battery. i am getting some crackle sound in the SLA battery. is it OK?

Is there any charger is available for such batteries or any simple circuit. Is it any auto switch off circuit after full charge of the battery.

Please help me

Thanks,
Robotsmani

 

[Chippie]

Sealed lead acid batteries need a cc/cv charging regime. You cant use any old charger...

Buy a charger suitable for the battery you want charging..

 

[robotsmani]

In the market it is available only for 6v/12v and higher current rating(4.5Ah). Is any circuit available. i searched some. There is LM317 based circuit is available but i am not sure can i use it for 4v battery. i am clueless...

 

[MikeMl]

Crackelling from the SLA does not sound good!

Your SLA requires a current-limited, constant-voltage charger. The initial charging current for your SLA should be limited to 4A or less (check your battery maker's pdf). The highest charging voltage should be limited to 2.42V/cell (4.84V), and then should be reduced to 2.20V/cell (4.40V) for float charging.

 

[robotsmani]

i dont think i can get the charger for my battery in the market. Can you please let me know any simple circuit for charger. I dont have any data sheet for my battery it is a chinese led lamp battery

 

[5uco]

There are circuits for SLA chargers using the L200 regulator. I have used this ic several times for small SLA chargers.

Suggest you download the .pdf for the L200, also the Application Notes for the same .. another .pdf.

D.

 

[arunb]

a suitable charger can be designed if you know the charging characteristics for the battery.

 

[Chippie]

This circuit here:
Gell-Cell Charger

Can be modified to charge your sla battery with a few component changes.

I've used this circuit as is for charging some 12v sla batteries with good results...

 

[robotsmani]

Thanks chippie...
most of the parts available with me. I have a 12v 1A wall adaptor, using this as input and adjusting the R4 in the above circuit to get the 4v(more than this right?what exact is required), can i charge the battery? Is that work?

 

[Chippie]

The combination of R2,R3 and R4 will set the output voltage...You will need to play around with them to arrive at the correct voltage...

The highest charging voltage should be limited to 2.42V/cell (4.84V), and then should be reduced to 2.20V/cell (4.40V) for float charging.

The charge current is set by R1 and should be adjusted to set the charge current to the appropriate value for the capacity of your battery..

 

[MikeMl]

The charger referenced by Chippie does two of the three charging steps for charging SLAs. It limits the initial charging current(good), but then it stops charging when the battery reaches the "float voltage" (bad).

A proper charger does three steps:

(1) limit the initial charging current to a safe level specified by the battery maker,

(2) allow the battery voltage to rise to ~14.5V (2.42V/cell), hold it there until the charging current naturally decreases to ~10% of the initial charging current used in step 1,

(3) then switch to the float voltage of ~13.2V (2.20V/cell).

 

[robotsmani]

Do you have any circuits in mind. Can you please let me know. There is no charger is available with variable voltages like charging for 2v, 4v ,6v, 8v and 12v. So i have to build one myself. Currently i required to charge the 4v 0.5AH battery. Is there any temporary solution? (some guys told me that i can use the dc wall adapter with a diode can charge the battery).

 

[MikeMl]

Do you have an adjustable lab power supply (e.g, a 1A supply based on a LM317?)

 

[robotsmani]

No i don't have...may be i will get one from market this weekend. Last week when i went to search for the charger in the market, one of the shop guy told me that, he is having LM317 based power supply board and it can use as a charger. I think you know how. Can you please guide me

 

[MikeMl]

The maximum charging current for such a small (0.5AH) should be no higher than about 100mA. Set the Power supply to 4.85V with nothing connected. Connect a 10 Ohm, 1/2W resistor (for current-limiting) between the power supply positive terminal and the positive pole of the battery. Connect negative to negative.

Use your Voltmeter to measure the voltage across the battery terminals over the next several hours. The battery is charged when the battery voltage exceeds 4.75V.

 

[robotsmani]

Thanks MikeMI... i will try and let you know...meanwhile if you know a good charger(auto cutoff and indicator) circuit with any voltage, please post here so that i can make it for future use...

Thanks again

 

[robotsmani]

I have done the same above setup...I bought the LM317 supply with 1amp. Adjusted the volt to get 4.85v and connected series with 10ohm 2w resistor with the battery plus and connected minus with the ground of power supply. Starting nothing happend after some i can hear a crackling sound from battery.

Is it dangerous? Is my battery damaged...I have two batteries, both of them giving the crackling sound. Is it normal?

 

[MikeMl]

Sealed Lead Acid batteries are never supposed to "vent" if charged according to the manufacturer's instructions. To me, the crackling sounds like H2 and O are escaping, meaning that the batteries have been previously abused by serious overcharging.

What is the open-circuit battery terminal voltage if they are left unconnected to anything for 24hours prior to being measured?

 

[robotsmani]

The battery voltage showing 3.65v. After bought this i have not used. it was unconnected for 6months i think....

 

[robotsmani]

now i connected the other battery..it does not have the sound. i think it is start charging. How do i quickly test the battery is charged? is it ok to put the charger on over night(~8hours)?