SLA battery charging with PWM but which frequency

[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

[Acetronics2]

Hi, Showtime

Will you have a look to the CCS 9620 SL ( from BTI ) Datasheet ??? ...

YES ! It's a Pic !!!

Alain

PS: Cost is 16.9 Euros ... @ CONRAD.fr or CONRAD.de ... worth it !!!

[mackrackit]

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

The current will be lower, but will also charge the battery, just slower.

The current from the solar cell will be lower in a cloudy condition so the over all current going to the battery will be lower.

Current is a measurement that involves Time.
I = Current
Q = electric charge in coulombs (ampere seconds)
T = time in seconds

I = Q/T

When the "boost" circuit is working it will take "TIME" to increase the voltage potential so the current over time will be lower than having a constant source. Simple circuits. http://www.intersil.com/engineeringt...ostcircuit.pdf

Basically in battery charging the only way to increase the current is to increase the voltage. If the source was the same voltage as the battery, no current will flow.

So even if the current over time is lower, it is still something. Something that would be going to waste other wise.

Feel free to say that my explanation is unclear and I will try to explain better.