# How to keep the TP4056 Vcc at a constant voltage when using a solar panel?



## SAFIA (May 26, 2017)

I'm using a solar panel (6V - 600mA at peak power) to charge a Li-Ion (3.7V) battery using a TP4056. The TP4056 I'm using has this configuration:









Where the value of the resistor Rprog determines the charging current.









The issue is that the current the solar panel provides is proportional to the light it received and the only way to keep extracting the maximum power from the solar panel is to adjust the load to keep to solar panel voltage around 6V which in my case is controlled by reducing the charging current.

What would be the best circuit to automatically adjust the Rprog resistor to keep the TP4056 Vcc at a constant voltage of around 6V?


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## SOCOM42 (Nov 9, 2012)

Being an ME not an EE, I can only give you my ignorant uneducated opinion.

First, I know nothing about solar, it would be useless to me in my location (troglodyte), so I have not explored it.

After looking at the regulator, most of the input voltages utilize a standard resistor over a wide range.

The input to the regulator is designed to be constant with little fluctuation.

The resistor parameters are based on max allowable current flow into the designated battery, of which capacity you did not specify.

The VCC from the panel could be reduced to a minimum 4.4 OV of the 5VDC, 

by providing a zener regulator at the panel output, as shown.

There is nothing you can do when the OV drops below op spec.

I you wish to remove the Rprog from the circuit, and replace it with a variable, that is above my pay grade.

Sorry not to be of much help, there must be an EE in here to help out.

I assume this is a class assignment, yes?

At these low voltages, anything requiring a semiconductor will result in a 1.2 v loss each device without a bias voltage.

So as I said, above my pay grade.


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## sideKahr (Oct 15, 2014)

Isn't that circuit essentially a PWM charge controller? 

You could probably buy a PWM online for less than the cost of your components. I've seen them on ebay for 9 bucks.


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## SOCOM42 (Nov 9, 2012)

sideKahr said:


> Isn't that circuit essentially a PWM charge controller?
> 
> You could probably buy a PWM online for less than the cost of your components. I've seen them on ebay for 9 bucks.


Buy it for $4.00, she wants to change out the fixed resistor for a variable to automatically restrict the current flow.

The Kobayashi Maru redux.


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## sideKahr (Oct 15, 2014)

SOCOM42 said:


> Buy it for $4.00, she wants to change out the fixed resistor for a variable to automatically restrict the current flow.
> 
> The Kobayashi Maru redux.


LOL. I'm givin' er all I've got, Captain, but she's not chargin'.


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## Coastie dad (Jan 2, 2016)

Candles....I understand candles..
This woman is waaaaayyyyy to smart for several of us..


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## SOCOM42 (Nov 9, 2012)

Coastie dad said:


> Candles....I understand candles..
> This woman is waaaaayyyyy to smart for several of us..


I'm ahead of you, oil lamps and more oil lamps.

Oh, I do have about a hundred pounds of assorted candles.


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