Hello folks!

I am making a solar charge controller circuit for 6V battery and using a 3W solar panel to charge the battery but the output of the charge controller circuit is nil.The circuit diagram is attached. Please help! Its urgent.

Thank you

 

hi IJ,
What are measured voltages on the LM317 In and Out.
Is the open circuit voltage of the solar panel approx 17v when exposed to bright sunshine.?

If you do getting working change the 1k pot to 2k
At full sunlight for 12V, 3W when the battery state is low, you should get about 250mA charge current.

E

 

Just connect the panel to the 6v battery. Nothing else.

 

hi IJ,
What are measured voltages on the LM317 In and Out.
Is the open circuit voltage of the solar panel approx 17v when exposed to bright sunshine.?

If you do getting working change the 1k pot to 2k
At full sunlight for 12V, 3W when the battery state is low, you should get about 250mA charge current.

E

Thanks Eric for your prompt reply. The input voltage on the LM317 In is around 9 volts whereas the output voltage is just 3.5 which is kinda surprising and the open circuit voltage of the solar panel is around 11.2 volts.

 

Just connect the panel to the 6v battery. Nothing else.

I thought of doing that earlier Colin but I am worried what if the panel overcharged the battery! Anything serious can happen.

 

You have only got 250mA to play with. A 4.5 amp-hour battery can be charged at one tenth of its capacity (450mA) for days and days without any damage as the battery will absorb the charging current and not produce bubbles of gas. You will be charging the battery for a maximum of 8 hours a day at a maximum of 250mA so your battery will take this charging current indefinitely without "gassing." Each day will only deliver a maximum of 2 amp-hours and drawing more than this will gradually flatten the battery and drawing less than this will gradually charge the battery.
The only advantage of my design is the fact that the battery will start to charge at lower levels of sunlight, rather than that stupid circuit you are presently using.

 

I agree with @Colin55. If you're concerned about overcharging you can add a disconnect circuit.

 

I agree with @Colin55. If you're concerned about overcharging you can add a disconnect circuit.

That means I can remove the LM317 part and just simply use the Zener diode and transistor circuit.

 

You have only got 250mA to play with. A 4.5 amp-hour battery can be charged at one tenth of its capacity (450mA) for days and days without any damage as the battery will absorb the charging current and not produce bubbles of gas. You will be charging the battery for a maximum of 8 hours a day at a maximum of 250mA so your battery will take this charging current indefinitely without "gassing." Each day will only deliver a maximum of 2 amp-hours and drawing more than this will gradually flatten the battery and drawing less than this will gradually charge the battery.
The only advantage of my design is the fact that the battery will start to charge at lower levels of sunlight, rather than that stupid circuit you are presently using.

Sorry Colin the panel shown in the circuit is not actually that panel which I am using my panel is rated at 350mA current at maximum power and the short circuit current is around 390mA
According to you its safe to connect the battery directly to the solar panel. But still are there any chances of battery damage if I don't use any protection circuit?

 

What is protection going to do?
Anything up to 450mA is absorbed by the battery.

 

I am using my panel is rated at 350mA current at maximum power and the short circuit current is around 390mA

I doubt that the battery could be damaged by your solar panel.

You measured 390mA into a short. You won't get that at the MPP and you're unlikely to actually get 3W from the panel.



To convince yourself that you're not abusing the battery, you can add the disconnect circuit I mentioned.

If you want to reuse as much of the existing circuitry as possible, you'll need to use an N MOSFET between the battery and the solar panel negative terminals.


EDIT: Emitter connection corrected below.

You can reduce R1 and add an LED in series if you want a visual indication of active over voltage protection.

 

If you want to reuse as much of the existing circuitry as possible, you'll need to use an N MOSFET between the battery and the solar panel negative terminals.

I think you want the emitter of Q1 to go to GND, not battery negative.

 

I think you want the emitter of Q1 to go to GND, not battery negative.

Guess that would make more sense...

 

Thanks Eric for your prompt reply. The input voltage on the LM317 In is around 9 volts whereas the output voltage is just 3.5 which is kinda surprising and the open circuit voltage of the solar panel is around 11.2 volts.

hi IJ,
I suspect there is also a problem with your original circuit build.??
If the 1K adjust pot is set to 1K, check the 6.8Vzener.

With a 9V input to the LM317 and the battery disconnected you should get 6.4V out from the LM317.

The open circuit voltage of 11v is low for a 12V panel, can you confirm that you have a 12v Solar panel and not a 6v version.?

E

 

The open circuit voltage of 11v is low for a 12V panel, can you confirm that you have a 12v Solar panel and not a 6v version.?

You don't have to worry about all this "run-around" if you follow my advice. You are helping him move the deck-chairs on the Titanic.

 

The open circuit voltage of 11v is low for a 12V panel, can you confirm that you have a 12v Solar panel and not a 6v version.?

You don't have to worry about all this "run-around" if you follow my advice. You are helping him move the deck-chairs on the Titanic.

thanks for your advice Colin but as my panel output is around 9.5 volts most of the time so there is no need of LM317 therefore I altered the circuit by removing the LM317 section and keeping the other section intact and I think it is working fine.

Thanks a lot for your unconditional help .

 

hi IJ,
I suspect there is also a problem with your original circuit build.??
If the 1K adjust pot is set to 1K, check the 6.8Vzener.

With a 9V input to the LM317 and the battery disconnected you should get 6.4V out from the LM317.

The open circuit voltage of 11v is low for a 12V panel, can you confirm that you have a 12v Solar panel and not a 6v version.?

E

I removed the LM317 because the panel voltage is around 9.5 volts and the current is fine. Thank you for your help.

 

I doubt that the battery could be damaged by your solar panel.

You measured 390mA into a short. You won't get that at the MPP and you're unlikely to actually get 3W from the panel.

View attachment 132274

To convince yourself that you're not abusing the battery, you can add the disconnect circuit I mentioned.

If you want to reuse as much of the existing circuitry as possible, you'll need to use an N MOSFET between the battery and the solar panel negative terminals.

View attachment 132276
EDIT: Emitter connection corrected below.

You can reduce R1 and add an LED in series if you want a visual indication of active over voltage protection.

I got your point and thanks for your help and now I understand that my battery is safe.

 

When connecting a panel directly to the battery is it wise to install a low voltage drop, Shottky diode in series to protect the battery from leakage current through the panel at night?

 

I doubt that the battery could be damaged by your solar panel.

You measured 390mA into a short. You won't get that at the MPP and you're unlikely to actually get 3W from the panel.

View attachment 132274

To convince yourself that you're not abusing the battery, you can add the disconnect circuit I mentioned.

If you want to reuse as much of the existing circuitry as possible, you'll need to use an N MOSFET between the battery and the solar panel negative terminals.

View attachment 132276
EDIT: Emitter connection corrected below.

You can reduce R1 and add an LED in series if you want a visual indication of active over voltage protection.

Haha, well yeah! I have almost killed my solar charger... Thank God I've read your post before doing something wrong. What a lucky day!