Charge a 3.7v battery directly with solar cell bypassing charger controller?

Other Hardware General Electronics
1

Hi, I've been thinking to connect a 3.5 watt solar cell (6v-580mAh open circuit) directly to the battery cell (3.7v ~1000mAh) bypassing the charger controller because the sun hits the cell only for a couple of ours.

In between the solar cell and battery, I will add a diode of course, and a MOSFET that will be controlled by a ATtiny or ATmega.
When the voltage is more than 4v, the MOSFET will cut the solar cells from the battery, if solar power is lower than battery power, also cut power.

When I use the battery charger I waste an enormous amount of energy. I'm aware of linear and constant charging for Lipos and what the charging controller does. If the battery decreases in life span is also acceptable for me.

2

That's hardly "direct." A better title might be "Please review my charger controller design, but without any schematics or part numbers or datasheets."

It sounds like it will work. Make sure it switches off if you get a few cloudy days in a row and the voltage goes low. LiPo fires are often caused by over-discharge.

3

MorganS:
That's hardly "direct." A better title might be "Please review my charger controller design, but without any schematics or part numbers or datasheets."

It sounds like it will work. Make sure it switches off if you get a few cloudy days in a row and the voltage goes low. LiPo fires are often caused by over-discharge.

Thanks MorganS

4

Any other taker? The circuit I'm using is dependent on batteries and a solar cell. The sun might or might not hit the cell at all in the entire day. This is why I ask. If the cell is producing 4v without direct sunlight, would it be ok to directly connect the solar cell to the battery? Both ends of the terminals from the solar cell and battery will be monitored to decide if it would be convenient to connect them both. A lipo charger controller module requires 4.5v+ to operate and push charge so would it be feasible to do this? Ask what you want! THX

5

Bright sunlight will increase the current, not the voltage, of a solar cell

6

You may want to use something like this "to be sure, to be sure"

http://www.dx.com/p/charge-discharge-protective-circuit-board-for-rechargeable-li-ion-batteries-17-4mm-1-9mm-26112#.VWrjHnDXerU

Weedpharma

7

You wouldn't want to be pumping 6 volts into a LiPo even for short periods of time. Also, considering you are only getting a couple of hours of sunlight you should try to maximise the amount of charge you are getting into the battery by using a MPPT type charge circuit.

Have a look at:

Read about the benefits of MPPT here: Design Notes | USB, DC & Solar Lipoly Charger | Adafruit Learning System

Also: https://www.sparkfun.com/products/12885