If you have a multimeter then you can turn it to the range at ac 20V, and in series with a 0.1uf~1uf, and then measure two pins of c1, if you can see there is a stable voltage shows up, then the voltage of c1 has ac in it, otherwise it could be ok.

 

Do you know which pins on the BD140 are the base and emitter?

Thx ronv ..... hopefully i thought from front side which is mark details, the left one would be emitter middle one base and last one as collector.. is n't it?

 

If it looks like this one it is Emitter, Collector, base.

 

If it looks like this one it is Emitter, Collector, base.

i fix it on that way too..but some guy said 123 as ebc are you sure 123 is ecb..thx

 

Take a look at the picture on the first page of the data sheet.

https://www.fairchildsemi.com/datasheets/BD/BD140.pdf

PS. sorry, forgot to attach it the first time.

 

still have doubt with this circuit..anybody plz help..i need to know whether this circuit is theoretically correct or not..any expert help me..

 

Do you have a REALLY LARGE heat sink on the LM350? It's going to have to dissipate over 30 Watts of power while charging a battery; which is going to take a LOT of surface area to dissipate. Although it does has some built-in protection against overheating, the thermal stress is really hard on them.

 

If there is a poor connection to R4 or P1 you will get excessive voltage at the regulator output and P1 won't have any effect; symptoms that you're seeing. Check the circuit in that area.
Is the circuit built on a breadboard or on a pcb?

 

Do you have a REALLY LARGE heat sink on the LM350? It's going to have to dissipate over 30 Watts of power while charging a battery; which is going to take a LOT of surface area to dissipate. Although it does has some built-in protection against overheating, the thermal stress is really hard on them.

‍thx...sqtwookie...yep have some heatsink and also fan...but problem is it gives 25v which is same amount as input rather than expected 14.5v..thats the issue..

 

If there is a poor connection to R4 or P1 you will get excessive voltage at the regulator output and P1 won't have any effect; symptoms that you're seeing. Check the circuit in that area.
Is the circuit built on a breadboard or on a pcb?

Thx..alec..ill check ...for your important advice..on pcb which is having tiny lines..

 

Hi,

Swapping base and collector will not give the 24..25V that you measure at the output (you would see around 4.7V or so in that case).

Things that will are the following:

1. Base of Q2 not connected via R5 to pin 3 (in) of the LM350.
2. Emitter of Q2 not connected to ground.
3. An open somewhere in the chain from the collector of Q2 to pin 1 (adjust) of the LM350.
4. Base of Q1 not connected to node R3-R4.
5. R4 or P1 open circuit.
6. Either Q1 or Q2 failed open (unlikely but still possible).

If you measure the voltage at each node (where 2 or more components are joined together) and post the results, we can help you pinpoint the open-circuit.

You mention 3A and thin traces. You'll probably have to solder wires on to the traces that carries 3A then (and don't forget the ground traces).
Measure all traces with an Ohm meter or continuity checker, sometimes you get hair line cracks in the traces, almost invisible to the naked eye.

If at all possible, lower your input voltage to 18V (DC) maximum, unless you want a toaster on the side.

If charging will take place in roughly the same temperature (within eg. a 5°C span) each time, there's no real reason for temperature control - just adjust the max. voltage for the max. temperature it will see.
Lowering the End of Charge voltage a bit (to 14.0V) will allow charge temperatures of up to 30°C or more without compensation.

If you can't find an LM350 to sim, just use an LM317, as long as you are checking voltages.