lead acid rechargeable battery problem

[miaomiaooh]

if use 8v ( because use voltage regulator 7808 drop down it) to charge a 6v lead acid rechargeable battery,will it spoil or explore the battery? ( because i dun have the battery's data sheet, so many thing i dun understand)

 

[penoy_balut]

most battery labels indicate capacity and charging current if not available charge the battery on a current producing a little bubbling of its electrolyte

 

[HiTech]

You could use a variable DC power supply that has an ammeter to monitor charge current.... which you would then need to monitor and taper it off to a trickle amount. However if you can get ahold of an old discarded camcorder battery charger that has near the needed charge voltage, they often have the capability to trickle charge. Heating up a battery is bad and that's what you need to monitor as well.

 

[fingaz]

Charging a lead acid battery at higher than it's rated voltage will heat up the electrolyte (acid) and can make it evaporate quickly. It Will also (eventually) buckle the plates (which can cause a short circuit) because it's charging too quickly. as hitech suggested, ideally you need a variable power supply so you can reduce the charging current when the battery is nearly charged.

Also remember then whilst charging, a lead acid battery gives off HYDROGEN gas, which is explosive so no sparks or smoking etc

 

[bunghole]

hello i is also trying to find a battery charger for a sealed lead acid battery, this data was on the side of it and it would help if anyone could help me;

Application Charging Voltage Initial Current
Floating Use 13.5~13.8V NO LIMIT
Cycle Use 14.4~15.0v 2.1 a max

Thanks

 

[ericgibbs]

Hi,
" Application Charging Voltage Initial Current
Floating Use 13.5~13.8V NO LIMIT
Cycle Use 14.4~15.0v 2.1 a max "

The charging info on the battery is to suit the way the battery
will be used.
Floating use: this is usualy where the battery is permanently
connected to a charging source and the battery is only used to
power external devices in the event of a mains failure.
The battery charger is a 'constant voltage' type and its charge
voltage MUST be set between 13.5 and 13.8 volts. Within these
charge voltage limits, it can be permanently left on charge.

Cycle use: this is usually where the battery is charged at its
maximum rated voltage/current. The charger is again a
'constant voltage' type, but with a 2.1amp current limiter.
ONCE charged, the battery is disconnected and used to power
external devices. And the cycle is repeated. ie; Charge then use.


For bunghole, divide the above voltages by two for your 6 volt
battery. ie; 6.7 thru 6.9 volts charge for floating use or 7.2v
thru 7.5v for cyclic use with say a 2amp current limiter.

If you use a +8 volt regulator connect two 3 amp diodes in series
with the 8v connection to the +v terminal of the battery.

If you have a +5v reg [7805] in your scrap box, make up a battery
charger to give you a charge voltage of 6.9v. This is done by
inserting a low value variable resistor in the 'gnd' pin
of the 7805 and adjusting the resistor to give you 6.9v,at 1a max.
If you want a diagram let me know.

Regards
EricG

 

[ericgibbs]

Hi,
Modified a drawing of a constant voltage charger for a sealed
lead acid battery. Drawing shows components for 12v or 6v battery.

The charger requires a dc input, at the voltages indicated, for
6v or 12v operation, capable of supplying at least 1amp.

The fuse on the battery output is recommended, if you short out
a fully charged lead acid battery, without a fuse, you will
get a flash and a dark brown smell.

The diode D1 in series with the charger output, this is to
prevent self discharge of the battery via the resistor divider,
when the charger is not connected to a dc input source, also
protects the regulator from high reverse voltages.

It does slightly affect the stability of the constant voltage
output.


If you want to use the circuit for a bog standard bench supply,
where the dc input source is always connected, omit the diode and
the battery. This will give you a bench psu of +12v or 5v.
[set P1 pot to suit] for your project experiments.



Regards
EricG

 

[RODALCO]

If you charge a 6 Volts battery from a 7808, that voltage may be a little too high, and left on for long times the battery may boil dry and will produce excessive hydrogen gas which is explosive.
Put a 1N4004, 1 Amp , or 1N5404, 3 Amp diode in series to reduce the charging voltage to 7.3Volts.
Bear in mind that a 7808 is a 1 Amp regulator so if you run that from a 12 Volts DC supply, 4 Volts will be dissipated in there = 4 Watts, so it requires a reasonable sized heatsink. It will run very hot if not cooled properly and its thermal OL may kick in.

Also a option you can do is put a 12 Volts 5 Watts lamp in series with your 7808, which will drop part of the charging voltage, you still have to check your battery for excessive gassing after 14 hours and do a voltage check with a DC multimeter.

How big is your 6 volt battery ? (Ah)

 

[bunghole]

Hello RODALCO

 

[bunghole]

i don't have a 6v SLA i have a 12v 7.0ah one

 

[bunghole]

EricG, i sees your diagram and some of it looks confusin. Some parts are labeled so they are the second of that part and also the capacitors. I think they are labeled in Mega-Farads, when 1 farad is = to one million uF. Could you clear that up maybe and see if you have a "cycle use" charger in stead of a constant voltage one. Thanks

 

[RODALCO]

Bunghole Hi, i saw you post and that was a 12 Volts SLA, Eric explains that very well how to get about it.

My reply was for the topic starter Miaohmiaooh who has a 6 Volts battery to charge from an 8 volts regulator.
There was not much explanation what supply he had, or what he wanted to achieve.

I assume that he had a 12 volt charger and connected a 7808 IC on the output to reduce the voltage to 8V to charge a 6V battery.

 

[ericgibbs]

hi bunghole
the caps are microfarads.
Edit my drawing with the bits you cannot understanding, repost it and I
will try to expand my explanation.
Dont worry to much at this time about the amp-hour capacity of your
battery. The charger will do the job, just a bit slower. You can always
use a higher power regulator in the future.

REMEMBER: do not exceed the max charge voltage or current of the battery.

Regards
EricG

 

[bunghole]

EricG thanks for the about the caps and also like F2 for fuse #2 but there is no F1 and D2 for diode #2 when i isn't seeing D1
Thanks

 

[bunghole]

-Also this charger is for the floating use isn't it. What kind of power supply do i need for it and can i use this charger to charge the battery and leave it connected, but cut off the power supply and then still use the battery for applications and leave the charger connected?
-Thanks?!?3

 

[ericgibbs]

hi bunghole,
the charger can be used for cyclic or floating battery charging.
Just set the charger output voltage for 13.6/13.8v and thats it.

If you set it for say, 14v output, it will charge the battery faster, BUT dont
leave it set to 14v, once the battery is fully charged. Just back it off
to 13.6/13.8v again.

If you require a faster, cyclic charger, in the future, just add a power
transistor across the 7812, with a resistor in series with the 7812 input,connected to the base/emitter of the power transistor. If you ever
need this addition, post it and I will jpg the modification.
Remember that your dc power source driving the charger needs to have
sufficient power to drive a higher current charger, if you upgrade.

Regards
EricG

 

[ericgibbs]

hi bunghole,
attached original dwg of my charger, showing a pcb layout.
your transformer tags may be different from mine, take care.

hope this helps

Regards
EricG

excuse low dwg quality