[SOLVED] How current is limited in this charge controller?

[Mrunal Ahirrao]

Hi,
I am about to build this kind of PWM charge controller but using PIC MCU. But I am not getting how current is limited in this? In that instructable author says:"The amount of charging current is determined by difference between battery voltage and charge set point voltages". But how? Please guide me.https://www.instructables.com/id/ARDUINO-SOLAR-CHARGE-CONTROLLER-Version-20/

 

[betwixt]

It states:
"3.PWM charging algorithm with auto charge set point according to the battery voltage"

which includes nothing about current limiting, only that it auto detects whether a 6V or 12V battery is connected and selects the charge point (target battery voltage) accordingly.

Brian.

 

[Warpspeed]

Solar panels are a current source, you do not need current limiting.

In fact you can dead short a solar panel and the current will only be slightly higher than at the peak power point.

All you need do is use the solar panel voltage to control the PWM, keep the solar panel voltage at the peak power voltage and you will be putting maximum available charge current into the battery.

Then when the battery voltage rises to the desired maximum fully charged voltage, use that to reduce the PWM duty cycle to then keep the battery voltage constant.

There is absolutely no need to have a current limit if the solar system and battery are sensibly sized.

 

[Mrunal Ahirrao]

Thank you Brian and Warspeed. I was stuck at this point.I am happy that there is no need of current limiting! PWM voltage control is quiet easy.

 

[jtrao]

If you can limit the voltage with PWM control, the current limit also can be done easily. We need to measure the battery charging current.

 

[Mrunal Ahirrao]

If you can limit the voltage with PWM control, the current limit also can be done easily. We need to measure the battery charging current.

How PWM can be used to limit current? PWM can the vary voltage only, isn't it?

 

[Mrunal Ahirrao]

There is absolutely no need to have a current limit if the solar system and battery are sensibly sized.

One more point, I didn't understood what you mean by this? Sensibly sized?

 

[Warpspeed]

One more point, I didn't understood what you mean by this? Sensibly sized?

Well........

If you have 10Kw worth of solar panels, and you are trying to recharge just a laptop battery, the current might be just a bit too high for the battery.

But if size of the solar system, and the size of the battery are both within reasonable limits, you can feed everything that the solar system can provide into the battery without damaging the battery, right up to full battery charge.

You still need to guard against overcharging the battery, but its always best to make best use of whatever sun is available, then cease charging.

Why would anyone want to install 80 Amps worth of solar panels, then limit it to only supply 10 amps maximum to recharge a completely flat battery ?
Current limit is neither necessary or desirable during charging, until full charge is reached.

 

[Mrunal Ahirrao]

Thanks again Warspeed. Now its cleared!

 

[rakeshkatkuri]

if your input current is more than battery charging current example if you have 20A,20V at the input side and your charging current is 1A,14.4V, you need to have a voltage limiter as well as current limiter. both voltage limit and current limit can be done using pwm. that pwm should be scaled from voltage and current

 

[betwixt]

if your input current is more than battery charging current

I'm not sure that makes sense as this design (I can't download it but I can see the parts list) appears to use PWM as a method of voltage reduction as it does not have inductors for storing charge. The input current can therefore not be higher than output current except possibly by the small amount used in the circuit itself.

If I charge a battery at 1A, it makes no difference whether I'm doing it fom a 1A supply or a 100A supply.

Brian.

 

[rakeshkatkuri]

I'm not sure that makes sense as this design (I can't download it but I can see the parts list) appears to use PWM as a method of voltage reduction as it does not have inductors for storing charge. The input current can therefore not be higher than output current except possibly by the small amount used in the circuit itself.

If I charge a battery at 1A, it makes no difference whether I'm doing it fom a 1A supply or a 100A supply.

Brian.

Mr. Brain
Even i am not able to see the circuit. As you said if the input current is same as the output current then no need of any current limit only voltage is enough.