SLA battery charging with PWM but which frequency

[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.

[showtime]

It sounds like it is very smart technic for a charge system for a changeable source like solar system. I have started research boost technics. Do you use only an MOSFET/TRANSISTOR, inductor and capacitor in output of pic or only a boost IC ?

Maybe every professional charger producer use boost technic to get maximum efficiency in bad situations.

Best regards.

[mackrackit]

The solar charge controllers are built with this idea.

So far I use the LM2588 for most things like this. You could build your own though. Study how the 2588 works.

If you build one an IGBT would work better than a MOSFET as the switching time is normally faster. Controlled by a Gate voltage like a MOSFET.

Things to consider no matter how you do it.

The diode will need to be heat-sinked so on in a TO-220 package works well.

The inductor is critical, you will spend more time sizing this than anything else. One thing about national.com is the web-bench. it will help size things.

The switching frequency is critical also.

This would be a good project for a PIC. Boost, control, and Display all in one.