Reversed Joule Thief charger

[boguslaw]

I'd like to post here my experience with this simple DC-DC converter described here :
The "Reverse Joule Thief" Battery Charger

I built a few of those and they work extremely well for charging NiMH or lithium 3.6V batteries from cell phones.

However I would like to convert it into a more useful device with more broad usage : a DC-DC converter or charger which can be used to charge various sizes of batteries from 3V to 12V from solar panel or from 3.6v battery or from 9V battery or to charge large capacitors low voltage rated.

Of course I mean only those smaller 12V batteries like 12V 7Ah max.

The obvious changes is the way to stop charging once the required level of voltage on charged battery/capacitor is obtained.


I used relay with transil to get to this but it's not a perfect solution (because relay coil need some voltage level to work).
I ended up with a small circuit to charge capacitor like 33000uF 40V from some source of electricity like a hand operated "rechargable" flashlight with attached homemade power cord :-)

Here are pictures of my "solar charger": Solar charger pictures by boguslawb - Photobucket

and here are pictures from the circuit with "overcharge" limitation (and you see modified flashlights) : reversed joule thief pictures by boguslawb - Photobucket


I have problems with overheating transistor BC327 probably from coil and relay coil inductive collapse spikes. For the same reason I changed 1N4148 into UF4007 diode . Second problem is to adjust the "cut off" voltage level - it need a better implementation.

Attached is schematic

[Watson]

Looks to me like the LED (D2) is backwards. That's not going to work.

I'd like to post here my experience with this simple DC-DC converter described here :
The "Reverse Joule Thief" Battery Charger

I built a few of those and they work extremely well for charging NiMH or lithium 3.6V batteries from cell phones.

However I would like to convert it into a more useful device with more broad usage : a DC-DC converter or charger which can be used to charge various sizes of batteries from 3V to 12V from solar panel or from 3.6v battery or from 9V battery or to charge large capacitors low voltage rated.

Of course I mean only those smaller 12V batteries like 12V 7Ah max.

The obvious changes is the way to stop charging once the required level of voltage on charged battery/capacitor is obtained.


I used relay with transil to get to this but it's not a perfect solution (because relay coil need some voltage level to work).
I ended up with a small circuit to charge capacitor like 33000uF 40V from some source of electricity like a hand operated "rechargable" flashlight with attached homemade power cord :-)

Here are pictures of my "solar charger": Solar charger pictures by boguslawb - Photobucket

and here are pictures from the circuit with "overcharge" limitation (and you see modified flashlights) : reversed joule thief pictures by boguslawb - Photobucket


I have problems with overheating transistor BC327 probably from coil and relay coil inductive collapse spikes. For the same reason I changed 1N4148 into UF4007 diode . Second problem is to adjust the "cut off" voltage level - it need a better implementation.

Attached is schematic