Hello
I hope that this is the correct forum for these questions.
A friend asked me for a battery charger for his car battery recently. I gave him the (very old) one that I had.
However, it seems that it no longer worked. As it was very old, I decided to build a new one and I found this circuit (A)
online.
I acquired all the parts and then (stupidly, as I now had the parts) started to question the circuit.
A reader also says it doesn't work (B).
I asked the following questions in the comments section of the website, but received a strange reply (C).
1. Is this circuit OK in general?
2. Changes I made are indicated on the attached schematic (D) with red blocks and are consistent with the datasheets.
2.1 Inclusion of a current sensing resistor
2.2 Inclusion of input short-circuit and output capacitor discharge protection diodes.
2.3 Addition of 2200uF and 0.1 uF caps on the input, a 10uF cap on the Adjust pin, and a 1uF cap on the output.
3. Can I swop the leds? I wish to have the Red led for charging and the Green led for fully charged.
3.1 Where is the current limiter for the fully charged led?
3.2 Should I change the current limiting resistor for the charging led?
4. Is the 11V 1W Zener diode correct? Shouldn’t it be at least 13V?
5. The author says: "battery charger SHOULD have over voltage protection, short circuit protection and reversed polarity protection"
5.1 Does the following constitute the over-voltage protection? Or should I still do something else?
"Now the base of the transistor gets the sufficient current to turn on so that the output current from the LM317 voltage regulator
is grounded through the transistor Q1. As a result Red LED indicates the full of charge"
6. Rs resistor.
6.1 Is the current sensing resistor a “normal” resistor or is it a special type?
6.2 Will this resistor automatically set the current correctly?
6.3 I couldn’t find a 2 Ohm resistor, only a 2.2 Ohm. Is this ok?
Thank you
Max
I hope that this is the correct forum for these questions.
A friend asked me for a battery charger for his car battery recently. I gave him the (very old) one that I had.
However, it seems that it no longer worked. As it was very old, I decided to build a new one and I found this circuit (A)
online.
I acquired all the parts and then (stupidly, as I now had the parts) started to question the circuit.
A reader also says it doesn't work (B).
I asked the following questions in the comments section of the website, but received a strange reply (C).
1. Is this circuit OK in general?
2. Changes I made are indicated on the attached schematic (D) with red blocks and are consistent with the datasheets.
2.1 Inclusion of a current sensing resistor
2.2 Inclusion of input short-circuit and output capacitor discharge protection diodes.
2.3 Addition of 2200uF and 0.1 uF caps on the input, a 10uF cap on the Adjust pin, and a 1uF cap on the output.
3. Can I swop the leds? I wish to have the Red led for charging and the Green led for fully charged.
3.1 Where is the current limiter for the fully charged led?
3.2 Should I change the current limiting resistor for the charging led?
4. Is the 11V 1W Zener diode correct? Shouldn’t it be at least 13V?
5. The author says: "battery charger SHOULD have over voltage protection, short circuit protection and reversed polarity protection"
5.1 Does the following constitute the over-voltage protection? Or should I still do something else?
"Now the base of the transistor gets the sufficient current to turn on so that the output current from the LM317 voltage regulator
is grounded through the transistor Q1. As a result Red LED indicates the full of charge"
6. Rs resistor.
6.1 Is the current sensing resistor a “normal” resistor or is it a special type?
6.2 Will this resistor automatically set the current correctly?
6.3 I couldn’t find a 2 Ohm resistor, only a 2.2 Ohm. Is this ok?
Thank you
Max