Hi Groundloop

Thank you for the circuit and all the information you have been providing. I am in the process of getting the necessary parts to build this charger with the air-core coils. I have some larger batteries that I want to try and condition. As I am quite a newbie I have a few silly questions to ask if you will pardon my ignorance.

1. On the first circuit you posted I assume that the 220nF Cap must be 1000v too?
2. I do not have access to an oscilloscope so was wondering if there is a way to ensure that one connects the coils the correct way around from the onset.
3. What is the resistance of the 50R 5W resistor. 5 Ohms or 50 Ohms?
4. What would be the easiest way to twist the three 18 gauge wires together?
5. How do I know to what value to set the pot initially?
6. Will a 9v 1A DC power supply be sufficient for the circuit?
7. Out of curiosity. What causes the circuit to self oscillate?

Thank you

I made a wire winder out of Plexiglas that I had lying around. I mounted the bobbins with the axis vertically to the plane of the disk as suggested by Groundloop because the disc is a little too small to make it practical and I was in a hurry to get going. As I suspected I was going to have some issues with feeding the wire off the bobbins and it was the case so I ended up feeding a meter or two and then winding it up with my battery drill/screwdriver as I was going along. I had the drill set to screwdriver setting. You need to do this whilst concentrating on the tightness of the winds and trying to keep you fingers out the way of the spinning bobbins. The end product, whilst not professional, should work ok.

I did not know what to use and decided to try using the spools solder wire is supplied on. It turns out that 78 meters of 1mm Magnetic wire fills up the spool almost completely. I simply measured off 78 meters of wire and then ran it onto the spool with my drill. I found that the spool I took the most trouble to roll on the wire slowly and neatly also fed the best in my spinning tool.

I then rolled the twisted wire onto a 2lt soda bottle with an od of 100mm by hand. This was quick but did not come out as neatly as I would have liked. It would be better to make some spooling tool like another post in this thread. I think it should be ok though. I made off the ends of the coils and tested them for continuity. The coils are fine with no short. Unfortunately I do not have a means to measure the inductance of the coils.

I decided on 75 meters as per another post on this thread but used 78 meters to account for the wire shrinking due to winding it up. It ended up a little over 75 meters. The twisted wire only made 184 turns and not 200 as specified. Perhaps because I rolled it a little too thick as the od is slightly over 120mm. I wonder what impact this will have on the circuit?

The only thing I still need is a heat sink for the TO3 transistor and then I can test the circuit. My supplier was out of stock. I am going to build the circuit this week and will hopefully be able to test it soon.

Here are some pics of the tool as well as the completed coil.

I finished building the circuit on Tuesday and eventually had time to test it last night. Success!!! Here are some pictures of my progress to date.

I then tested it the charger on a 6V battery that just to see if it charges. It is an old battery that will not hold a charge above 5.7 V and will be the first one I am going to test the desulphating process on.

I am using a 15v/3A Lab supply and was surpised to feel that it was getting quite hot after about 15 minutes (the large heatsink at the back was quite hot to the touch even if not hot enough to burn) although I have never actually kept it on for more than a few minutes at a time. The diodes were cold and the transistor barely perceptibly hotter than ambient temperature. The pot was feeling warmer to the touch. Is this normal? I set the voltage to 9V and then adjusted the pot until it was indicating 0.6 Amps and then left it there. I noticed that the voltage gradually increased ever so slightly.

Some other observations that may be useful to someone. I could only buy the magnetic wire by weight so had absolutely no idea how much wire to buy. Three lengths of 1mm/18# wire (77 to 78 * 3 = 234 meters) weighs 1.62 Kilograms (3.56 pounds). At least this can provide a guideline to someone who can only buy the wire by weight.

Another was that when I tied off the ends of the coils I left one side longer than the other for easy identification. I found that the trigger coil had to be connected to the opposite of the other two coils. Is this a rule of thumb?

I did not have a 10W 12 lamp so used two 5 Watt lamps in series.

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.

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?