Hi everyone, I am new to the forum
While searching for a simple circuit for the auto- cut off charger Li-ion battery 3.7v, I found this schema that makes use of a lm339 voltage comparator
I know that Li-ion cells are too sensitive to unfavorable input such as high voltage or high current, I don’t know if Li-on batteries require a complex considerations or no; because some people say absolutely no, and other say don’t play with this monsters, some engineer (say look I have make a Li-on battery charger and he show you big box)!?
please help me to find a save way of charging Li-ion battery

 

Read the datasheet of a Lithium-ion battery charger IC and read about Lithium-ion battery charging at www.batteryuniversity.com to see that a Lithium-ion battery charger has its charging current limited and its voltage limited to 4.20V but when the battery reaches 4.20V it is not fully charged. Instead, it is fully charged when the charger circuit has sensed that the charging current has dropped to a low amount, then the charger cuts off.

Your simple circuit ignores charging current and cuts off the charging when the battery is only half charged, or causes the battery to explode and catch on fire if its voltage is adjusted to be higher than 4.20V. The simple circuit also has no limit for the maximum charging current that might be very high when the battery is discharged.

The simple circuit plays with fire.

 

Indeed, the simple circuit shown needs a resistor to limit the maximum charging current. Probably the current limit is inside that block marked "charger, lithium. " So my question now is what do you have to supply the charging current. That simple circuit will cut off at whatever voltage you set it for, so really you need two things: First, a source of charging voltage that allows you to set the high charging current to the correct level, and Second, another resistor from emitter to collector to allow more charging at a much lower current after the cell is half charged. So now you need to discover what those two current levels are.
And understand that AG is very cautious about everything.

 

Everybody wrongly calls the wall wart with a 5V/1A USB output for a cell phone "the charger". The charger circuit is inside the phone.

 

hello MisterBill2, Audioguru again
I don't have an electrical or electronics engineering but i know some basics about electronic

I'm trying to build a thermostat and I want to add a lithium ion battery 3.7v on it .However I also have to place a charger auto-cut off for this type of battery on the board circuit (thermostat and charger auto-cut off)

For the limited voltage and current I can use simply a good charger but i need the circuit of the cut- off

On my battery is marked 2500mAh and 3.7v, I want to charge the battery with a limited current of C / 3 rate, about 800mA and a voltage of 4.2V

Please see the diagram and help me to finish my project

 

At the price of these why build one bay.com.au/itm/Micro-USB-Lithium-Li-ion-18650-Battery-Charger-Module-Charging-Board-Protection/123275109046?hash=item1cb3c4e2b6:g:794AAOSwZZ5avwFO I buy them in lots of 10 & find they work for me.

 

If you want to put the charging circuit on your board, seriously, you need to use one of the many chips specifically designed for this.

Companies like Apple, Samsung, and Boeing have had disasters with Li Ion chargers. If you think you are smarter than them, go ahead, design this yourself, if not, get a proven solution.

Bob

 

If we had known the application initially you would have had a better answer sooner.
To add a charging circuit for a lithium battery, 3.7 volts, you do not need, nor do you want, a standard battery charging circuit. An electronic thermostat has three modes if for both heating and cooling application, those modes being Heat, OFF, and Cool. IN the heat mode, one set of contacts is closed, in the cool mode a different set, 2 pairs, of contacts are closed, and in the OFF mode the temperature OK condition, all of the contacts are open. One version of thermostat uses a another wire from the opposite end of the 24 volt supply transformer to power the thermostat. Another version uses a very small current from the voltage across the heating contacts to power the thermostat except when it is calling for heat, at which time the battery is supplying the operating power. So the furnace, or heater, power system can be used to charge the battery quite easily. At that point the charger will only be a low current trickle charge, because the battery will not ever be fully discharged. Thus there will be no need to have a circuit to disconnect the high-current charging mode. A series diode and zener diode regulator followed by another diode to prevent drain when the contacts are closed, and another series resistor to limit the charging current. The maximum voltage will need to be set to what ever the float-charge voltage specification is, and also the charging current will need to be limited. But now the whole charger system can be as simple as 4 parts.

 

Depending on what part of the world you are in, a complete electronic thermostat may cost less than the parts for building an electronic thermostat. But you would not learn much from just purchasing and installing one. Calibrating an electronic thermostat will be the larger challenge in the project.

 

IC manufacturers and many knowledge sites say that a lithium battery should never be trickle charged. Also, the battery lasts longer with a higher capacity if it is not always fully charged. Now in winter the Li-PO batteries for my RC radio controlled model airplanes are sitting at a 3.7V storage voltage then I charge them before using them.

My home thermostat can be controlled far away by my cell phone if I want. I can control it with my voice on my Google Assistant if I want. It shows the weather and temperature outside on its screen. It shows the time and changes it with Daylight Savings Time.
It aint got and doesn't need a baddry.

 

hello MisterBill2, Audioguru again, debe, BobTPH and Thanks

MisterBill2
I give you the thermostat diagram and the charger diagram please help me

Everybody wrongly calls the wall wart with a 5V/1A USB output for a cell phone "the charger". The charger circuit is inside the phone.

please Audioguru again ; can you give us an example

 

IC manufacturers and many knowledge sites say that a lithium battery should never be trickle charged. Also, the battery lasts longer with a higher capacity if it is not always fully charged. Now in winter the Li-PO batteries for my RC radio controlled model airplanes are sitting at a 3.7V storage voltage then I charge them before using them.

My home thermostat can be controlled far away by my cell phone if I want. I can control it with my voice on my Google Assistant if I want. It shows the weather and temperature outside on its screen. It shows the time and changes it with Daylight Savings Time.
It aint got and doesn't need a baddry.

My home thermostat is not open to hackers on the internet or any wireless connections.
And you are right about lithium batteries. I was thinking of the Nicad ones. It also works with regular cells that are not normally considered rechargable. So really, lithium battery power is not the best choice in thermostats for mains powered systems.

 

A Charger for a Lithium-ion battery uses a smart IC designed to do all the things needed for safety.
Your circuit is simply a variable voltage power supply producing as much current as it can.

Why does your thermostat need a battery?

 

like I said before I don't have an electrical or electronics engineering but i know some basics about electronic .
so Why does my thermostat need a battery?
i thought that it is very simple to integrerate an auto-cut of charger !?

 

like I said before I don't have an electrical or electronics engineering but i know some basics about electronic .
so Why does my thermostat need a battery?
i thought that it is very simple to integrerate an auto-cut of charger !?

An electronic thermostat needs a battery to power the temperature measurement circuit, the output switching circuit, the setpoint circuit, and probably the temperature display circuit. AND many of them will also need power for the memory portion and the real-time clock. Because in normal operation there is only a 2-wire connection to the controlled load, when a command for heat is given the two connections are teid together and so there is no voltage to maintain the clock, memory, or the rest of the circuit.And even if the thermostat was much simpler, there would still be power required for the temperature measuring circuit and the switching circuit, when the contacts wee closed. THAT is why it must have a battery or an alternative power source.

 

I have seen maybe 6 thermostats and I have never seen one that has a battery.
Thermostats use 6 wires so that they are powered and can turn on heating or air conditioning. My thermostat gets its time and weather from wifi.

 

I have seen maybe 6 thermostats and I have never seen one that has a battery.
Thermostats use 6 wires so that they are powered and can turn on heating or air conditioning. My thermostat gets its time and weather from wifi.

I have seen about 500 thermostats that DO require a battery, and I have installed about 20 of them. ALL of those installations use a 5 wire connection or a 4 wire connection. Common feed, Heat , Cool, Fan. Some installations use a second feed for the cooling commands. Certainly there are some installations where the other side of the power feed is brought to the thermostat, but not in this part of the USA.
And it really makes no sense at all to have a WiFi connection that is open to hackers and snoopers and everybody else.

 

Stupid people have everything connected to wifi today. Their cameras in every room and even their baby monitor.
I did not connect my thermostat to wifi for programming, only for receiving weather and time because I set it once then never again.

My new smart TV is connected to wifi and who cares if a hacker sees what I watch.
My google assistant might be hacked one day and a hacker might hear me talking bad about the government.

 

Stupid people have everything connected to wifi today. Their cameras in every room and even their baby monitor.
I did not connect my thermostat to wifi for programming, only for receiving weather and time because I set it once then never again.

My new smart TV is connected to wifi and who cares if a hacker sees what I watch.
My google assistant might be hacked one day and a hacker might hear me talking bad about the government.

Consider the "fun" if some hacker starts switching ALL of the aid conditioners in the area off and on twice a minute for a while. That would be a rather big starting inrush, and quite possibly cause a local blackout as the local grid overloads. Or the same hacker puts everybody's electric stove in the oven clean mode just before dinnertime.
How many folks have actually set a new password on their WiFi toys? And what happens when all of the limited number of channels are all in use?