I've got a dac with a separate power supply line into its body, using a 2.1mm plug. Its battery needs to be charged initially from a computer's USB port, but after that it can be continuously recharged either from the USB port or with an external charger (5-12v DC, 500-700mA). After several months of using an external (9v, 600mA), the dac's battery went dead one day; that charger had gone dead. Since then, and after recharging, the dac has yet to stay charged with an external adapter, running only off the USB port. I've tried a few good adapters within specs, all of which have shown the correct voltage using a digital multimeter. That suggests something weird is wrong, but before sending the dac to be checked out, I've wanted to verify the adapters' current output, not just assume it's within range.
My question is, to be accurate, does amperage have to be measured under load, with at least one lead hooked to the dac (e.g., ground or COM)? It's not physically possible to open the dac - opening voids the warranty and is not a good idea in this case, so I've been measuring each adapter's output. They are rated at 500-600 mA output, but the multimeter has been showing ~1A across their 2.1 mm plugs. This made me wonder if I'm measuring incorrectly, that it really needs doing under load, i.e., with the dac involved. Thanks,
Edited by highstream - 11/9/13 at 4:26pm