SLA battery charging with PWM but which frequency

[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.

[showtime]

The end of your comment is most important thing to use the maximum solar energy. But would like turn back to PWM. Generally, what frequency is used for battery charging ?

Best regards

[mackrackit]

The frequency that is used (at least from the so called PWM chargers I know of ) is either 60 or 50 HZ, depending on where you live. They are simply using a half wave rectifier and regulating things from there.

This is from a battery manufacture of VRLA batteries. Same thing as SLA. You can not have a true SLA as it would blow up .

http://www.panasonic.com/industrial/...ingMethods.pdf
The referring page is here. http://www.panasonic.com/industrial/...eal/index.html

As you will see, a recommended frequency is not given as PWM is not one of the recommended ways of charging these batteries.

If you are looking for a boost circuit for those cloudy days, I am using one built around a LM2588T. http://www3.national.com/pf/LM/LM2588.html

[showtime]

mackrackit,
Thank you again and again.
Best regards

[showtime]

Hello again mackrackit,
When we use boost circuit and in a cloudy moment the boost circuit give us what we need. But what about the current? At this moment will the current be enough to continue the charge?

Best regards