solar charging setup for a 100ah 3.7v bank?

[bhom9]

Hi all,

I'm looking for recommendations for a way of charging a 100ah 3.7v bank of 18650 cells via 40-50w solar panel. I've done a bunch of googling and have not come up with a higher amperage solution than 3A. Even that solution may be questionable as its coming from an overseas source. Thanks

 

[snoobler]

DC-DC converter. Something that can take a variable DC input and output steady 4.2VDC max.

This:

Amazon.com: Anmbest Constant Current CC CV Buck Converter Module DC 6-40V to 1.2-36V 20A 300W Adjustable Step Down Voltage Regulator Power Supply Module with Short Circuit Protection Function: Electronics

Amazon.com: Anmbest Constant Current CC CV Buck Converter Module DC 6-40V to 1.2-36V 20A 300W Adjustable Step Down Voltage Regulator Power Supply Module with Short Circuit Protection Function: Electronics

www.amazon.com

Though there is some question as to whether that unit will maintain a steady output with a significantly variable input.

Worst case, you could power the above with:

https://www.amazon.com/Automatic-Converter-6A-Waterproof-Transformer/dp/B07WFMG11F

So....

Panel --------> 8-30V to 12V converter --------> regulator outputting 4.2V max

Kinda cobbly and inefficient due to multiple conversions, but there are likely better options out there. Hopefully, this gets you on the right path.

 

[bhom9]

thanks, i've actually been playing around with one of these converters rated at 10a 4.2v. It's actually been working out for me IF i used a 12v battery as a buffer. It seems like the dc to dc converter i was experimenting with was a all or nothing design so when i had it connected to the panel it will output the 4.2v but reading the current i would see it bounce from 0-1a and never actually charge the cells. I'll try picking up a different one. thanks

 

[Mike Jordan]

DC-DC converter. Something that can take a variable DC input and output steady 4.2VDC max.

This:

Amazon.com: Anmbest Constant Current CC CV Buck Converter Module DC 6-40V to 1.2-36V 20A 300W Adjustable Step Down Voltage Regulator Power Supply Module with Short Circuit Protection Function: Electronics

Amazon.com: Anmbest Constant Current CC CV Buck Converter Module DC 6-40V to 1.2-36V 20A 300W Adjustable Step Down Voltage Regulator Power Supply Module with Short Circuit Protection Function: Electronics

www.amazon.com

Though there is some question as to whether that unit will maintain a steady output with a significantly variable input.

Worst case, you could power the above with:

https://www.amazon.com/Automatic-Converter-6A-Waterproof-Transformer/dp/B07WFMG11F

So....

Panel --------> 8-30V to 12V converter --------> regulator outputting 4.2V max

Kinda cobbly and inefficient due to multiple conversions, but there are likely better options out there. Hopefully, this gets you on the right path.

Can you put a converter between a SCC and a batt? How does the SCC know the SOC of the batt?

 

[snoobler]

Can you put a converter between a SCC and a batt? How does the SCC know the SOC of the batt?

No one has mentioned a SCC. This exercise is intended to allow charging a single 3.7V cell to 4.2V. The regulator has this capability, but it may be erratic on the output due to the variable input of the panel. The 12V converter IS designed to accept a wide input range yet output a constant 12V.

Erratic panel voltage ----------> converter providing constant 12V out -------------> regulator providing 4.2V to 3.7V cell.

There is almost certainly a more elegant solution.

 

[bhom9]

2V converter IS designed to accept a wide input range yet output a constant 12V.

No one has mentioned a SCC. This exercise is intended to allow charging a single 3.7V cell to 4.2V. The regulator has this capability, but it may be erratic on the output due to the variable input of the panel. The 12V converter IS designed to accept a wide input range yet output a constant 12V.

Erratic panel voltage ----------> converter providing constant 12V out -------------> regulator providing 4.2V to 3.7V cell.

There is almost certainly a more elegant solution.

in this setup what protects the battery from overcharging? it's own BMS?

 

[snoobler]

4.2V output of the device.

Once the battery reaches the voltage of the charger, it's current tapers to zero. 4.2V is the maximum recommended voltage for typical 3.7V chemistry. You can lower the peak voltage and get lower states of charge and increased cycle life.

 

[Mike Jordan]

No one has mentioned a SCC. This exercise is intended to allow charging a single 3.7V cell to 4.2V. The regulator has this capability, but it may be erratic on the output due to the variable input of the panel. The 12V converter IS designed to accept a wide input range yet output a constant 12V.

Erratic panel voltage ----------> converter providing constant 12V out -------------> regulator providing 4.2V to 3.7V cell.

There is almost certainly a more elegant solution.

I am sorry, I guess I assumed SCC with the panels. I will rephrase, as I have a similar but differing voltage dilemma with Li-Ion solar charging I was trying to work out.

So there is no charge controller in that mix at all? You would have to baby sit that as the batts approached max voltage, as that system has nothing to shut it down.

 

[bhom9]

i

I am sorry, I guess I assumed SCC with the panels. I will rephrase, as I have a similar but differing voltage dilemma with Li-Ion solar charging I was trying to work out.

So there is no charge controller in that mix at all? You would have to baby sit that as the batts approached max voltage, as that system has nothing to shut it down.

from my understanding is that with the dc to dc converter the output max is 4.2v. once the battery reaches that voltage there is an equilibrium that is met so the battery will not continue to charge. please correct me if im wrong but that is how i understand it. For my project I am less worried about it because the device in which the bank powers is on 24/7 so during the night no charging would occur and voltage would drop.

 

[snoobler]

i

from my understanding is that with the dc to dc converter the output max is 4.2v. once the battery reaches that voltage there is an equilibrium that is met so the battery will not continue to charge. please correct me if im wrong but that is how i understand it. For my project I am less worried about it because the device in which the bank powers is on 24/7 so during the night no charging would occur and voltage would drop.

You are correct. Current cannot flow without at least a small voltage differential. Once you hit the set voltage, current will taper as it fills. Once it's full, no current will flow.

 

[Tifoz]

Anyone find the way to charge these 18650 faster than 1A?all i seem to be finding on google are tp4056 modules.