12V LM350T Lead Acid battery charger question

[khatus]

Hello friends, I want to make this lead acid battery charger.



Here, I want to use 1000pF polyester film capacitor instead of the electrolytic capacitor C3? My first question is can I use 1000pF polyester film capacitor instead of 1000pF electrolytic capacitor?



if i use the DPDT Self-Locking Push-Button Switch, in the place of the S1 Start pushbutton, will there be any problem?

[Benta]

It's not an electrolytic, the "+" is missing.
Yes, use what you show.

[floobydust]

Yes- a film or ceramic cap is fine for the 1,000pF part C3. The original circuit is from Radio-Electronics I think.

Note the charging circuit has a few weaknesses - if you connect a battery backwards, it is kill.
If power is off or unplugged and you connect a battery, backfeed into LM350 it does not like as well.

[khatus]

What is the purpose of the push button in this circuit?

[floobydust]

The charging circuit has two states controlled by the op-amp. The momentary pushbutton takes the BALANCE/COMP pin 1 low to GND, and forces the op-amp output high. I think this sets the output voltage to the higher setpoint where it stays in CC mode until charging current drops off.
Note output pin 6 is missing from the schematic. LM301 datasheet does not ID pin 1 but NS one does.

more discussion on the same old circuit:
https://www.edaboard.com/threads/using-1n4001-diode-over-1n457-diode-in-a-battery-charging-circuit.411240
https://maker.pro/forums/threads/12v-battery-charger-schematic.267632

[khatus]

Will there be a problem if I use 15 ohm and 230 ohm 1/4 watt resistors? The value of these two resistors must be high wattage or low wattage? If it is high wattage then how much wattage should I use?

[floobydust]

The resistors can all be small 1/4W parts except the current-sense resistor 0.22R needs to be 1-2W. The LM350 needs a big heatsink.

Tony van Roon did his take on the same charger circuit, adding trimpot to adjust the output voltage. This is surely necessary.
https://www.learningelectronics.net/VA3AVR/gadgets/labc2.htm
He says the op-amp output is low for "charge" and high for "float" which opposite to what I said was going on with the pushbutton switch so I might be wrong.

[khatus]

Hello friends,I have completed soldering of the circuit on perfboard according to this Lead acid battery charger diagram, and got the exact output according to the formula given in the datasheet.Here is my resistor value,

R2+R3 = 239.6 k Ω
R1 = 3.276 k Ω 
According to the formula given in the LM350T datasheet,



Vout = 1.25×(1+ 3276/239.6) + 50×10-6×3276
Vout = 18.34+0.1638
vout = 18.50
and I have got exactly this output voltage.
Now my question is ,
1) charging a 12 volt lead-acid battery with this 18.5v output voltage cause any damage to the battery?
2) What is the optimum output voltage to charge the 12V lead acid battery if it is not charged at 18.5 volt.
3) What is the purpose of the 15KΩ resistor in the circuit?
4) If I make the output voltage slightly higher than 12 volts (say 13.5 volts) will the LM301A OPAMP would work properly? Because it requires +/-15 volts at pin 7,4.

[khatus]

Here is my circuit,

[SteveThackery]

1) charging a 12 volt lead-acid battery with this 18.5v output voltage cause any damage to the battery?
2) What is the optimum output voltage to charge the 12V lead acid battery if it is not charged at 18.5 volt.

18.5V is far too high for a 12V lead acid. In fact I think you'd need a LOT of current going into the battery to achieve 18.5V across the terminals.  I'm pretty sure it would do some damage due to gassing.

Lots of vehicles charge their batteries at 14.4V.  Vehicles with "smart" charging will sometimes push the battery voltage up to 15V or so immediately after starting, in order to push as much charge into the battery as quickly as possible. After a few minutes they drop the voltage to around 14.4V.

[SteveThackery]

Here, I want to use 1000pF polyester film capacitor instead of the electrolytic capacitor C3? My first question is can I use 1000pF polyester film capacitor instead of 1000pF electrolytic capacitor?

Does anyone know why the schematic uses the symbol for electrolytic capacitors everywhere?

OP: I think the symbol is wrong - I don't think you can get a 1000pF (1nF) electrolytic.