In message , "Dave Plowman (News)"
writes
In article ,
Rick Hughes wrote:
On 29/12/2012 00:11, Dave Plowman (News) wrote:
In article ,
Rick Hughes wrote:
I have a relatively new Car Battery Charger (twas a gift) claimed to
be electronic 'smart' charger.
Took the cover off and found it to be a straight transformer to full
wave rectifier set of diodes ... and out to croc leads.

Then it will blow up when you try and use it.

Why ?

220V AC step down transformer full wave rectifier giving DC output
to a pair of croc clip ended leads ..

Display gives some LED indication, and there is an in-line fuse
........... why would it blow up ?

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.

Could the transformer be designed to operate inefficiently; with the
output voltage drooping to limit the current? Inadequate turns or air
gap in the iron circuit?


--
Tim Lamb