Hi, sorry to wake up this post, but I think that is better than open another one again.

I have simulated this circuit in MultiSim. The project is a litller solar panel (6V 100mA), a Li-Ion battery (3.7V nominal, 4.2V max) and a load.

In this circuit, I have only simulated how I could disconnect the solar panel when the battery goes up 4V, and then,, reconnect it again when battery's voltage goes down to 3.6V.

In this case, the variable voltage source is the source panel, and "load 100ohm" is simulating the battery.

As you know, the battery voltage and solar panel voltage will be the same(minus schottky diode).

If you go up in voltage controlled source until you get Vref = 2.5 in TL431, you will disconnect the battery with the 2n7000 mosfet. R11 mades the neccesary hysteresis and then, when battery's voltage goes low (due to the real load consumption) to 3.6V, the TL431 will reconnect again the mosfet and the battery will be charger again.

Please, experts !!!! do you find anything wrong here??? Or probably all of it is wrong ?
NOTE: I know that TL431 is able to conduct until 100mA, but for this exercise I prefer to use a mosfet. Also I don't know if only with the TL431 and without mosfet I will be able to manage to get some kind of hysteresis.

After this circuit is correct for you, I have to desing a little one with TL431 to disconnect the load from battery if it goes down 3.2V and reconnect load again (hysteresis) when battery goes up to 3.6 or 3.7

Please, help me and comment this circuit.

Regards

Mod edit: new thread created.

 

IMPORTANT: I forget to mention that R2 in the circuit above is "simulating" the current shink of the battery. I don't know how to simulate a rechargeable battery in Multisim (or it is difficult with resistor and capacitor in series), but in this case doesn't mind. SOlar panel output's voltage will be the same as the battery voltage, so I control them with the keyboard-controlled-voltage source from Multisim.

Hi, in order to give you more information, the project is a about and arduino and a SIM800L module. The last one "likes" a lot to work with LiIon batteries, and I will use both deep sleep functions in arduino and SIM800L. I will charge battery with solar panels.

I CAN'T use TP4056 usual modules, as they waste a lot of energy stepping up to 5V from LiIon's 3.7 volts. Besides, SIM800L works perfect with 3.7v, so I want only to connect directly a solar panel to the circuit and use the model that is in the first post as a high voltage cut off to save battery not going up 4V.

After I get this circuit ok, I will post here another one to cut off the loads (arduino and SIM800L) if battery's voltage goes down. It is easy with TL431, but for the first one ... please, could you see it ? is it something wrong ? I want to keep it simple.

Hope your answers,

Regards,

 

There are already chargers on the market that turn on at a certain voltage and turn off at a certain voltage. But you'll have to test them to make sure they turn on and off at the voltages you actually need. Could you use one of those?

See ebay search for "lithium charger board". A large portion of them are designed to charge 1-2 18650s so read the description to find what you want.

 

Hi, thanks. Normally these chargers work with 5v so they are very inefficient, aren't they ?

I prefer to connect it panel directly with battery, with out step up and step down.

Am i wrong ?

 

Hi, anybody ?

 

Is the 6 V normal operating V or OC V ? There is still a requirement to disconnect the SP or short it when battery is full.

 

Is the 6 V normal operating V or OC V ? There is still a requirement to disconnect the SP or short it when battery is full.

Hi Bernard, thanks a lot for your answer.

The SP is about 7VOC. The disconnect and re-connection is made with TL431 and the MOSFET, there is also R11 which give some kind of hidteresys. If I am not wrong, the circuit (MOSFET) conducts until battery voltage is 4V. Solar panel voltage will follow battery voltage.
After that, open MOSFET and reconnects it again when battery falls down to 3.6v.
There is left the other part of the circuit, where I connect or disconnect the load. I will post soon
What do you think about this circuit ? Remember that R2 is simulating the battery.
Regards,