Hi to one & all!!!
I’m starting to play with solar cells and soon came to the conclusion that I needed to sort out a cheap entry point into the batteries that I will require – junked lead acid batteries; because new ones would just be a money drain and make solar unviable to me.
Which is how I tripped across your stimulating forum – thanks to all those who have already shared their approaches, frustration, insights and route maps – hats off to you for sharing your knowledge.
In return you have stimulated me into taking the first steps – and I’ve spent days, weeks, hours reading through the zillions of posts. So now I would like to share my experiences, pictures, and results - also in the spirit of giving back and hope they are in turn helpful to others.
I arrived at the conclusions that the original AC design, Ron Ingrahms schematic and the Silicon Chip July09 article were all fundamentally the same – not surprising really – the “science” is the same!!
So my grasp of it is: timer circuit with [adjustable] short on-time, long off-time + fast [FET] switch + capacitor charge (electrical energy reservoir)….convert to magnetic energy field in 220uF inductor…collapse the magnetic field and re-create as electrical energy and dump current through diode into battery &…… zap 1000 times a second!!
From all the reading on the forum it was clear that before experimenting I need a base reference design – so I have adapted the use of ferrite inductors into the Silicon Chip design – so I can get to grips with saturation straight away (& not use the air coils originally specified). But keep the LED zapping indicator, over-voltage protection, built in DVM output and use of 1mH choke to protect the charger – I thought these would give me some minimum protection against the “holy smoke” escaping too early in the project!!!
So here are some pics of the final build – circuit already modified to include a trimmer so I can vary the on-time. Oscilloscope traces are of the signal at the FET gate, at the FET drain and also across the battery – all seems to look as it should?
The circuit draws 260mA, the DVM shows 24.8 across the battery, stand-alone battery voltage is about 11.3 volts and its all been zapping away for 10 days, original SG in four cells was 1.275 and 1.225 in two cells – now 1.275 in all cells (but I may not have read it correctly originally)……