# 14watt 6v solar panel feeding to a TP4056 based charger for charging a Li-ion battery

How to design a solar power based power supply for charging a Li-ion Battery of 3.7v 3500mAh, using TP4056 ?

Specs about Tp4056 based charger using are it is programed for 1.2A current max, and 4.2v constant voltage charging,

A 6v 14watt solar panel to 4056 based charger to charge the Li-ion battey could be feeded?

Will it damage the 4056 based charger?

As the max current produced can reach above 2A.

Our Intention is to provide maximum current available to charge the battery enough and rapidly.

How does the Open circuit voltage of the solar panel affects the 4056 charger? whose operating voltage is 5v to 6v.

The maximum input voltage is 8 V (acc. to p. 2 of the datasheet), so the open circuit voltage of your solar panel has to be lower.

The current will be limited by the charger. The maximum current you could achieve is 1 A (for $R_\mathrm{prog} = 1.2k$).

As far as I can see, there won't be any problem with connecting the solar panel to the charger as you don't exceed its limits.

But i see another problem in your use case. If the output power of the solar panel is dropping due to lower solar radiation (e.g., clouds), the charger's input voltage may drop rapidly if it tries to draw too much current. It has an under voltage lockout which should terminate the charging process in this case. As soon as the charging process is terminated, the input voltage of the charger will rise again as the current is around 0 A (open circuit voltage of the solar panel). This means the charger will start charging again, which leads to an oscillation of charging/not charging.

• The open circuit voltage of the solar panel is 10-11 volts, will this damage the charge controller? How to reduce the open circuit voltage?
– Shiv
Commented Jun 2, 2018 at 16:41

Yes you can use that solar panel. It will have excess power capabilities in sunshine, but that power goes nowhere. Note: You may still need to put two panels in parallel for cloudy seasons.

The max possible current from the panel is not destroying the charger under normal conditions. An analogy: A car battery can give 100 Amps, but still it doesn't blow a 12V 1.2W glove compartment lightbulb. Instead, with the excess possible power, the panel can maybe drive two chargers in parallel.

Yes that panel might destroy your charger under bad circumstances such as bright sunlight in combination with battery full so the input voltage reaches "open circuit" due to no panel load. Maybe not by "overcurrent", but components inside may not be rated for higher voltage and burst or at least deteriorate.

You solve this issue by "clamping down" the voltage by means of Zener diodes. I looked at my local distributor's webpage and they have 7.5V 5W diodes for c:a 0.4Euro each. 7.5V is a reasonable voltage for you, I think. If you are cautious maybe you can select 6,8V. Those apparently cost 0.5Euro each.

3 of those 5W diodes can together take 15W, thereby protecting your circuit without burning up themselves. You put these 3 diodes in parallel with your charger's input. Remember to leave long wires when you solder them, it's their cooling medium. Zener diodes are to be mounted "backwards", you can see it on the internet. These 7.5V diodes work so that at and above c:a 7.5V they will "suddenly" decrease more and more in resistance, effectively stopping a raise in voltage, since more volts will load the source (your panel) with more amps.

I have been using 12V panels and have found that their peak power output is at around 16V. This suggests that your 6V panel works best at 8V (dangerous for your build!). You can achieve keeping those 8V by purchasing an "MPPT" circuit, but allegedly the gain is only 10%. The MPPTs I use are combined with a "buck converter" that can be set at a convenient 5V output, giving you a steady voltage both for panel and charger (if the sun shines). However, without the MPPT, this best performance at c:a 8V suggests that you should have the diode cutoff as high as possible, i.e. at 7.5V. Which, well, may be dangerous. So I suggest you buy 3 of each (6.8V, 7.5V) and try them out.

Also remember that allegedly best charging is only during 4 hours around 12:00. Slanted light and lower sun decreases power rapidly. So those 4 hours define in practice your charging time, or "charging budget". I.e. will those (milli)amps during those hours be sufficient?

(Note: this is written for laymen like me.)