In 2007 I have built a replica of the lead-gel battery charger described in Funkamateur 7/2007. What makes this charger special is that it can be operated with a DC voltage of approximately 8.0 V to 16.0 V, meaning it can also be used with a 12 V car socket to charge batteries with a final charging voltage higher than 12V!
Where it all began
I received a pre-etched circuit board from Wolfgang, DJ8ES – many thanks again!
The basic circuits, which Wolfgang also used, are from Linear Technology for the LT1070 and from Prof. H. Schuhmacher for the constant-voltage source with current limiting. I have redrawn the circuit diagrams and added the voltage specifications.
I fitted the charger into an old Eurocard enclosure. However, as the depth of 16 cm was a bit too much for me, I cut all the metal sheets and profiles of the enclosure to size on my table saw. It went surprisingly well.
As I didn’t have any ‘nice’ aluminium sheet for the front panels, I simply cut some offcuts of a red plexiglass sheet to size.
For cooling and mounting, I simply screwed the circuit board – with the two power semiconductors, the LT1070 and the BD235 – onto the base plate. The LT1070 doesn’t actually need cooling, but the BD235 does get quite warm during charging, so the cooling won’t do any harm.
Charging - next generation
The days when lead-acid batteries were used in amateur radio are slowly coming to an end. The performance and price of LiFePO₄ batteries are simply unbeatable.
Of course, with these batteries too, the question arises: how do I charge them if I only have 12V available – for example, in the car?
I remembered the lead-gel battery charger I’d built back in 2007 :-) The output voltage is finely adjustable – the output current is limited to around 500 mA – which made it sound to me as though I could also use the charger for LiFePo4 cells.
After adjusting the output voltage to 14.4 volts, the tests with both a dummy load and a real LiFePo4 battery were very promising.
Of course, it’s not a high-performance charger for LiFePo4 batteries, but if you leave the charger plugged in overnight, even a 5Ah battery will be fully charged by the next morning.