Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
Because a lead acid battery has a very low internal resistance. To a
power supply like that virtually a dead short. A crude charger would
have some form of series resistance to limit the maximum current.

Unless they've cunningly used the transformer's impedance to give a
sagging output with increasing load. Saves the regulator and means the
transformer's cheaper, too.

You mean use a thin enough wire in the winding so that acts as the
resistance? Doesn't sound like a recipe for decent life.

As has been mentioned, air gap in the core, a low reluctance core, or
just fiddling with the inductances, all of which work as wattless
droppers, more or less. Transformer designers don't *have* to go for low
impedances all round.

They can also go for low efficiency and cheap, in which case people
don't expect them to last long, and as long as they insert overheating
protection such as a fusible element, they're safe.

--
Tciao for Now!

John.