12V 60A car battery , maybe dead?

Mars67 · January 29, 2015, 11:57:52 PM

Thanks for the feedback Groundloop. I asked for a 3.5W pot but I am not sure that it actually is. I picked up a 5W wirewound pot yesterday but did not get time to test it or the large cap over the output of the power supply last night.

Groundloop · January 30, 2015, 12:21:59 AM

Quote from: Mars67 on January 29, 2015, 11:57:52 PM
Thanks for the feedback Groundloop. I asked for a 3.5W pot but I am not sure that it actually is. I picked up a 5W wirewound pot yesterday but did not get time to test it or the large cap over the output of the power supply last night.

Mars67,

A 5 Watt wire wound pot-meter is a good choice to use. I did look at the picture you posted
and your first pot-meter looks like a 1/4 Watt type. So use your new 5 Watt pot-meter.

I also did download the manual for your power supply. The manual clearly state that the power supply
will get hot on higher power settings. So I guess that 15 Volt 1 Ampere is a high power setting for this
type of supply. Manual attached.

GL.

Mars67 · February 03, 2015, 02:29:30 AM

I built the circuit on Veroboard and incorporated a 9V regulator. I also placed a 1000uF 25V cap over the output of the Voltage Regulator. I cannot really tell if it made a difference to the temperature of the power supply. The heat sink on the LM 7809 goes up to about 63 Celsius and I also had to place a small heat sink on D5 which goes up to about 55C. I'm not sure if that is too hot but I included a 12v fan which keeps everything nice and cool. The 5W wire wound pot also gets a little warm on the side but stays at that temperature. T1 does not get hot at all.

I am using a 12V 2A Laptop power supply. It seems to work really well.

Another question I have is that there is a high pitched whine coming from T1. It is not always there and is not very loud. The pitch seems to go up as one reduces the current drawn by the circuit i.e. as one increases the resistance on the pot. Is this normal?

Groundloop · February 03, 2015, 03:04:16 AM

Quote from: Mars67 on February 03, 2015, 02:29:30 AM
I built the circuit on Veroboard and incorporated a 9V regulator. I also placed a 1000uF 25V cap over the output of the Voltage Regulator. I cannot really tell if it made a difference to the temperature of the power supply. The heat sink on the LM 7809 goes up to about 63 Celsius and I also had to place a small heat sink on D5 which goes up to about 55C. I'm not sure if that is too hot but I included a 12v fan which keeps everything nice and cool. The 5W wire wound pot also gets a little warm on the side but stays at that temperature. T1 does not get hot at all.

I am using a 12V 2A Laptop power supply. It seems to work really well.

Another question I have is that there is a high pitched whine coming from T1. It is not always there and is not very loud. The pitch seems to go up as one reduces the current drawn by the circuit i.e. as one increases the resistance on the pot. Is this normal?

Mars67,

First, measure the voltage out of your Laptop power supply. Most laptop power supplies (than I'm aware of) is closer
to 19 Volt output. So if you is drawing close to 1 Ampere through your linear voltage regulator (LM7809) at 19 Volt
input, then you are at the maximum of what that regulator can handle. What is the exact type marking of that regulator
you are using?

It seems to me that too much base bias current is going to your transistor since the pot meter gets hot.
You large 5 Watt wire wound variable resistor should not be hot at all. Please use you Ohm meter and verify what
resistance the pot meter have. Also measure your two resistor values. Are the resistors in parallel or series? Switch
off the power to the circuit before measuring.

D5 should not get hot. I think you are having too much bias current running through the base of your transistor,
thus too much current going through the power coil.

The high pitched whine from the coil is normal.

GL.

Mars67 · February 03, 2015, 08:29:37 AM

Hi Groundloop

Thanks yet again for your input. I am not sure about the connection of the pot as indicated on your circuit diagram. Again please excuse my ignorance. The pot has three connectors. The sweeper is in the middle. At the moment the 50 Ohm Resistor (2 x 100 Ohm 5W resistors connected in parallel) is connected in serial from the one connector on the side of the pot to the sweeper. The sweeper is then connected to L2. Should the two outside connectors i.e. the full 500 Ohms be in serial with the 50 Ohm with the sweeper going to L2? I will measure all the values and get back to you this evening.