Automatic battery charging circuit

[titch16]

Hi, new to the forums and have a query.
I have done some pcb work before but no major experience and I trying to draw up a curcuit for a 3.7v charger, with a light for fully charged and a light for need charging.
That's my basic needs. More advanced would be if i could then add a second battery and a switch so I can charge one battery at a time (separately). I realise that adding the battery might just need the positive charge to change to each battery but just need clarification. Thanks in advance

 

[BobK]

For charging LiIon batteries, I presume? You can get these on Ebay for a couple of bucks.

Bob

 

[OLIVE2222]

If the needed charging current is in the few hundred mA range, indeed, Ebay is the way to go.
Many of them use USB port as power source. If you want to charge few of them you can go for USB wall plug or a powered usb hub. For DIY one you can use the MAX1555 for example.

Olivier

 

[titch16]

Li-On, yes. The circuit would be put inside a device so ebay offerings aren't ideal.

 

[OLIVE2222]

Ok so if you need something in the few hundred mA range the MAX1555 or the MCP73831 will fit. For higher current it can become more tricky.

Olivier

 

[titch16]

I don't think it would need to be any higher 1A. 800 or so would be fine. What will the 1555 provide?
And would that auto stop the current?

 

[OLIVE2222]

Hi,

No the MAX1555 can handle a maximum of 280mA and max 500mA for the MCP73831.

What are you batteries capacity (the mAh figure) and what charging time do you expect?

Olivier

 

[titch16]

Batteries would be 1800mah. Charge time wouldn't matter too much but overnight would be good.

 

[OLIVE2222]

Batteries would be 1800mah. Charge time wouldn't matter too much but overnight would be good.

OK, "high" charging current are not needed so. You can use MCP73831 (or MCP73832)
They are linear devices in SOT23 package with limited dissipation capabilities.
I suggest to use them at around 350mA , to avoid being on the edge, and to strictly apply the datasheet recommendations about the PCB layout.

Also ensure that you use the version compatible with our Lithium battery type, see the Voltage Regulation Options in the datasheet.
It will cost you less than 1 buck of parts for the charger, so you can build two of them if you need two batteries (according to your first post)

Olivier

 

[titch16]

I searched for the 73831 and found a premade chip, TP4056. The battery is a 3.7v 1800mAh Li-Ion with a max charge current of 0.4A. so would I need to reduce the the output from 1A with a different resistor on the board and reduce the 4V from the charger?

 

[BobK]

I guess you missed this in the first paragraph of the datasheet:

The charge voltage is fixed at 4.2V, and the charge current can be programmed externally with a single resistor.

Bob

 

[OLIVE2222]

Also TPmicro is not very well distributed, when the chip stop to be the trendy charging chip on Ebay you can be in trouble to source it. Those kinds of components are only OK for experiment or for few pieces production to me. Don' t know what is your purpose.