djpark
Enlightened
This is a part-2 of the Super Simple DIY Li-Ion Rechargeable Charger. I have been busy with POP driver and decided to take a short break to cool down the head by making a few chargers.
The basic design is still based on the same Linear LTC4054 single cell li-ion charger controller, but now it has more indicator and I thought I would make a new post. The power is taken from a PC USB port. Please refer to the previous post for the detail.
Whatever was discussed in the previous thread is valid and please refer to it for reverse cell protection by Doug_S and MrAl as well as other charge logging chart and other information.
I will not go through the detail document as the first one, but this needs to be repeated.
I do not guarantee the unit I produce will meet your requirement. I disavow any potential liability for the contents of this document. No responsibility is accepted by me for any loss or damage caused in any way to any person or equipment, as a direct or indirect consequence of following these examples. Use of the concepts, examples, and/or other content of this document is entirely at your own risk.
This new design includes PNP transistor circuit to turn on the charge status LED instead of using the LTC4054 status pin with open drain output. When the charge is complete, the original status pin still let a few uA current to LED and it can be seen as ON when a bright led is used. PNP transistor based inverter removes this and now the charge indicator is ON only when really charging. No mistake..
There is a jumper which select the max constant charging current. With the jumper open, the charge current is 300mA, when closed it is 750mA. 750mA is about 0.5C for Pila and it can charge Pila within 3 hours.
D4 is not used, but it is a good idea to use a schottky diode to drop the input voltage by 0.5V so that the heat generated by LTC4054 chip is less. This reduces the effect of thermal protection by the chip reducing the charging current.
I used a perforated board with 18x5 holes size and arranged the parts as below. Sorry no CAD drawing as I have yet to learn one to do. But this hand drawing should give a good idea. The blue highlighted line is the thread and the red x is to cut.
When the cutting is done, the bottom should look like this (upside down).
Then arrange the parts and solder. Now I solder the chip directly on the board instead of making an adaptor. This should be much easier for anyone.
Then slot into one side of the 2 AA battery holder and connect the wires. The whole board fits in very nicely. The hole for USB cable is tight, so it doesn't move or come out.
Since I ran out of the blue led, I used Nichia white led (the same one used in Arc-AAA) as charging indicator, it is bright. My fellow CPFer Stanley said this charger is the BRIGHTEST charger of all. How true!
Though the holder is meant for AA battery, it can also hold R123. A spacer can be used to charge R123 in the same holder.
I didn't have space to put reverse cell protection circuit using N-channel FET as suggested by Doug_S. So I included just the reverse cell indicator. When the cell is inserted reverse, it turns on the red led.
Be very careful. Don't ever connect the battery reverse when there is power supplied to the charger. It can run as much as 1A (or more) to the charger chip and it may kill the chip, or even affect the PC operation. You have been warned.
The charger has output short circuit protection and it allows only 10% of the max charge current on the short circuit condition.
Any comments are appreciated.
-- dj
The basic design is still based on the same Linear LTC4054 single cell li-ion charger controller, but now it has more indicator and I thought I would make a new post. The power is taken from a PC USB port. Please refer to the previous post for the detail.
Whatever was discussed in the previous thread is valid and please refer to it for reverse cell protection by Doug_S and MrAl as well as other charge logging chart and other information.
I will not go through the detail document as the first one, but this needs to be repeated.
I do not guarantee the unit I produce will meet your requirement. I disavow any potential liability for the contents of this document. No responsibility is accepted by me for any loss or damage caused in any way to any person or equipment, as a direct or indirect consequence of following these examples. Use of the concepts, examples, and/or other content of this document is entirely at your own risk.

This new design includes PNP transistor circuit to turn on the charge status LED instead of using the LTC4054 status pin with open drain output. When the charge is complete, the original status pin still let a few uA current to LED and it can be seen as ON when a bright led is used. PNP transistor based inverter removes this and now the charge indicator is ON only when really charging. No mistake..
There is a jumper which select the max constant charging current. With the jumper open, the charge current is 300mA, when closed it is 750mA. 750mA is about 0.5C for Pila and it can charge Pila within 3 hours.
D4 is not used, but it is a good idea to use a schottky diode to drop the input voltage by 0.5V so that the heat generated by LTC4054 chip is less. This reduces the effect of thermal protection by the chip reducing the charging current.
I used a perforated board with 18x5 holes size and arranged the parts as below. Sorry no CAD drawing as I have yet to learn one to do. But this hand drawing should give a good idea. The blue highlighted line is the thread and the red x is to cut.

When the cutting is done, the bottom should look like this (upside down).

Then arrange the parts and solder. Now I solder the chip directly on the board instead of making an adaptor. This should be much easier for anyone.

Then slot into one side of the 2 AA battery holder and connect the wires. The whole board fits in very nicely. The hole for USB cable is tight, so it doesn't move or come out.
Since I ran out of the blue led, I used Nichia white led (the same one used in Arc-AAA) as charging indicator, it is bright. My fellow CPFer Stanley said this charger is the BRIGHTEST charger of all. How true!

Though the holder is meant for AA battery, it can also hold R123. A spacer can be used to charge R123 in the same holder.

I didn't have space to put reverse cell protection circuit using N-channel FET as suggested by Doug_S. So I included just the reverse cell indicator. When the cell is inserted reverse, it turns on the red led.
Be very careful. Don't ever connect the battery reverse when there is power supplied to the charger. It can run as much as 1A (or more) to the charger chip and it may kill the chip, or even affect the PC operation. You have been warned.
The charger has output short circuit protection and it allows only 10% of the max charge current on the short circuit condition.
Any comments are appreciated.
-- dj