OK, we've got a small Ryobi cordless screwdriver/drill at work, and the charger has just died - the primary read O/C across the mains input, so I took it to pieces to have a look. As expected, the wires go directly in the transformer, so I carefully peeled the insulation off to reveal a small heat fuse - thinking, it looks fairly easy (for a change) to replace. Anyway, testing it showed it was OK, and it's the actual transformer itself that is O/C
So I looked on Amazon for a replacement charger, to find a few 'alternatives' - all of which were actually 5V 2A Chinese power supplies, and not actually 'chargers' - the circuit of the original Ryobi one I've drawn out below.
The original obviously includes current limiting (the 4.4 ohm) and charging status (the LED), so I'm a bit 'dubious' about just using a 5V 2A power supply in it's place?.
I tried sticking 5V from my bench PSU directly into D1 and the centre tap, and then turned it up until the LED lit, while watching the current, and it took about 7.5V DC to make it charge correctly. After that attempt, I tried resetting the PSU back to 5V, and applied it directly to the output of R1, where it was taking about 250mA (although I've no clue as to the charge status of the tool). It's been running now about 1.5 hours, and it's down to 157mA, the red LED actually on the tool is still lit of course, so I'm keeping an eye on it, to see how it goes.
So what are peoples thoughts about it?, it strikes me as a bad idea just sticking 5V 2A directly in to it, although perhaps there's some kind of limiting inside the tool, as the red LED inside has to be monitoring the current somehow?.
Incidentally, we've ordered a new complete Ryobi screwdriver kit to replace it anyway - but that now uses a 5V USB type charger
So I looked on Amazon for a replacement charger, to find a few 'alternatives' - all of which were actually 5V 2A Chinese power supplies, and not actually 'chargers' - the circuit of the original Ryobi one I've drawn out below.
The original obviously includes current limiting (the 4.4 ohm) and charging status (the LED), so I'm a bit 'dubious' about just using a 5V 2A power supply in it's place?.
I tried sticking 5V from my bench PSU directly into D1 and the centre tap, and then turned it up until the LED lit, while watching the current, and it took about 7.5V DC to make it charge correctly. After that attempt, I tried resetting the PSU back to 5V, and applied it directly to the output of R1, where it was taking about 250mA (although I've no clue as to the charge status of the tool). It's been running now about 1.5 hours, and it's down to 157mA, the red LED actually on the tool is still lit of course, so I'm keeping an eye on it, to see how it goes.
So what are peoples thoughts about it?, it strikes me as a bad idea just sticking 5V 2A directly in to it, although perhaps there's some kind of limiting inside the tool, as the red LED inside has to be monitoring the current somehow?.
Incidentally, we've ordered a new complete Ryobi screwdriver kit to replace it anyway - but that now uses a 5V USB type charger