SLA battery charging with PWM but which frequency

[showtime]

I would like to make a smart SLA battery charger and controller with PWM. Which frequency should i use ?

thank you any comment for now.

[mackrackit]

If you are thinking of pulse charging, do not bother (my opinion ).

Constant Voltage is the best way to go. You can start off with a Constant Current but a CV charger sized correctly will do this automatically.

A maximum voltage of 2.4 volts per cell to bring the battery up to charge, then if you want to "float" if for a back up system or something like that, bring the voltage down to around 2.25 volts per cell.

For the "sizing" of the charger, 20 to 25% of the rated capacity is good. A 5 Amp Hour battery would have a current limiter of 1.25 amps. Even if you have a larger say a 12 AH I do not recommend mare than 2 amps. ( If you have ever replaced batteries from UPS and see the batteries swollen you will know what I am getting at ).

12 Volt example drained to 11 volts.
A charger built like this will when first placed on a "dead" battery will show a voltage close to the battery voltage and the maximum current allowed. As the voltage increases the current will decrease. When 14.2 volts is reached the charger will drop to the float voltage to prevent over charging.

In my experience this will get the most life from this type of battery.

For the past four years my lawn mower and trimmer have ran off of SLAs. This is pretty hard on the batteries but they will still last around two years. By the way, where I live the grass grows year round if I water it

I do use a "boost type" voltage regulator that use PWM to convert the nominal 12 volt from my main battery bank to the 14.2 volts.

[showtime]

Hi again,

Thank you for important informations about SLA charging rules. My SLA is 12V-7.5Ah.
-Yes I will use Constant Voltage.
-As many professional charging device producer say that PWM is the best way to charge SLA batteries. (I don't why it is). So I will do PWM charging system.

I have just uploaded an image. Which is better or any comment will be very very important for me.

[mackrackit]

You can not do PWM and have constant voltage. PWM will go from ZERO to HIGH voltage.

If you have a voltage source of 14.2 for a 12 volt battery and the voltage source is switched via PWM at say a 50% duty cycle, the typical meter will read 7.1 volts. This will take twice as long to charge as the battery is only receiving the needed voltage for half the time. The argument for this is a slow charge is better than a fast charge.

I have seen some of those professional chargers that will read close to the 14 volts with a meter implying a peak voltage well above the maximum limit. (remember the UPS example). The amperage will also be on the high side too. The argument for this is that the average voltage going to the battery is correct.

The image you uploaded.

The LM350 is good for 3 amps (if memory serves ) with a good heat sink. The Could switch between two or change the adjust resistance for float voltage.

Is this for a back up system?

[showtime]

No it is for a solar system. My mini panel supplu 18V without load. And shortcircuit current is 1.5A.

Is PWM usefull for this supply voltage?

[mackrackit]

In that case all you will need would be a way to cut the power from the solar panel when the battery is full. The panel may put out 18 volt open but will pull down to battery voltage.

If you want to get the maximum out of the solar cell, early morning , late afternoon, cloudy day, you can use a boost circuit to bring it up to charging voltage. Then when the cell is producing charging voltage on its own the boost circuit drops out and the solar cell is back to straight into the battery.

[Scampy]

Why are you replying to a post that is almost 7 years old... it's all irrelevant now!

[pedja089]

It is bot...