Hi all,
I was given a 'dead' cheapo 20V Lithium drill battery, charger and wall wart to look at by a mate tonight.
Plug PSU (wart) into wall socket, clip 'remote' charger interface onto battery, switch socket on ... nothing.
I took the covers of the charger clip module and connected it onto the battery, measured 19 or so volts on the battery pins but nothing coming from the PSU.
However, after a few minutes I felt the PSU was slightly warm so assumed it was doing something?
I disconnected the PSU output leads from the PSU at the charger module and connected my bench PSU at 20 and with the current limited to the same 400mA as the PSU and the green 'Charged' LED came on constantly.
I rigged up a load (a couple of 12V 60W headlights in series) onto the battery and let it run for a while and then hooked it back up to the charger, charging LED now flashing, indicating it was charging.
DMM on the unloaded o/p of the PSU, nothing.
After leaving it disconnected for a while ... I cracked the PSU open with my toffee hammer and gave the board a look over, nothing obviously burned and no dry joints etc. I checked the bridge rec and a couple diode over and they seemed ok, but an axial series diode (SJ220 from memory) on the output that was driving a cap that went to the remote charger module seemed to be short?
I found the spec somewhere that suggested it was a 2A 1000V (?) device and I have a couple of questions please?
I know Schottky diodes have fast switching times (and a low forward voltage drop but not sure if that would be relevant here?) so is a Schottky required in what I think might be part of a 'charge pump' circuit because of the frequency of the output through the SMPSU and assuming I decoded the markings correctly, why would it need a 1000V device there?
Cheers, T i m