SLA battery charging with PWM but which frequency

[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.

[showtime]

Ok.

I have a 12V 7.5Ah SLA battery and L200 IC constant voltage charge circuit. My voltmeter shows me 14.5V witout the load.I connect the circuit to the emtpy battery i see 11V and when the battery is full 13.9V. I think everything is normal for this charge technic. Because i use constant voltage charge.

But I don't know what should i do if i use boost type charge. Please correct me if i'm wrong:
-Pic will control the battery voltage for charge status. I think this is easy.
-How can we udjust the i.e LM3588 with a pic ?

Thanks...

[showtime]

hi again.
I see in the lm3588 datasheet. I understand that i can send pic pwm signal to the freq/adj leg (pin 1).

But sould i use lm3588 ADJ version. Because we don't need 12V regulated.

[mackrackit]

I have a 12V 7.5Ah SLA battery and L200 IC constant voltage charge circuit. My voltmeter shows me 14.5V witout the load.I connect the circuit to the emtpy battery i see 11V and when the battery is full 13.9V. I think everything is normal for this charge technic. Because i use constant voltage charge.

Sounds good, but if you can get the no-load voltage down to 14.2 would be perfect.

But I don't know what should i do if i use boost type charge. Please correct me if i'm wrong:
-Pic will control the battery voltage for charge status. I think this is easy.
-How can we udjust the i.e LM3588 with a pic ?

The LM2588 has its own adjustment with resistors, something like the LM317s. Set it as close as you can to 14.2 and that is all you need. For the straight charging, a PIC is not needed if you use LM2588. My main battery bank will go from 11.5 to 14 volts, (400 amp/hr). My chargers built around LM2588 to charge the small batteries will bring them up to 14.2 and hold them there. You could use a PIC to monitor this and when 14.2 is reached the PIC would shut the LM2588 off.

[showtime]

Thank you my friend,
I will set to 14.2V. When i connect the battery the voltage will drop. So will IC set 14.2V itself. Namely will we see 14.2V during charge?

By the way, I think you forget my ask about IC type. Normal LM2588 or LM2588 ADJ ?

[mackrackit]

When the battery is full and connected to the charger you will see 14.2 volts if the battery is healthy. After the battery is off of the charger the voltage will drop to 12.6 to 13 volts. This is the voltage of a fully charged 12 volt battery at rest.

I would go with the adjustable LM2588.

With the adjustable the voltage can be set pretty much where you want it.