On Thu, 26 Nov 2015 23:16:55 -0800, mike wrote:

On 11/26/2015 8:54 PM, wrote:


With reverse polarity protection you don't get 12.2 volts open
circuit. You get NOTHING. If you have a battery charger putting out
12.2 volts open circuit, it won't put out more into a load.

Well, that may be the way you would have designed it.
But, you probably didn't design it.

I don't have a problem with assumptions that you verify.
I have a problem with people who state, with certainty,
stuff they have not experienced on unspecified equipment
in unknown circumstances.

Doesn't it trouble you the least little bit that it's
12.2V? What's the failure mode that results in that
open circuit voltage reading?

Could be several different failure modes, including a bad rectifier,
as most simple battery chargers are very poorly regulated open
circuit, with the impedence/resistancde of the windings limiting
urrent under load. Just like a cheap 12 volt wall wart that may put
out 18 volts open circuit.

My first check would be the bridge rectifier, which is
repairable.replaceable - second would be a shorted secondary winding
in the transformer, which means it is junk.

If it was a sophisticated automatic charger, it could be anything -
but being listed as a dual current rated charger, it is NOT a smart
charger.

Like I said - not rocket science

Good thing that rocket scientists don't think they KNOW everything.

If you understand batteries and electricity you don't have to know
everything to be sure of many things.

Yep, I used to manage very bright engineers with similar arrogance.
Spent much of my time cleaning up after them.

Let's just save the thread the excruciating protracted attempts
to prove how smart you are and turn it into a thought experiment.

Take a random car battery charger.
Plug it into your oscilloscope with no other load.
What would you expect to see on the screen?
A choppy DC - diferrent depending on what kind of rectifier circuit t
has - center tapped full wave, full wave bridge, oe half wave.

If the OP had stated what make and model the charger is, it would be
easier to give a definitive answer - just like if he told us what kind
of "scooterz' he was working on.

and engineers are a lot different breed than those of us who have to
fix their mistakes - or have to work on what they design.

Take your random DC voltmeter and think about how it would
respond to what you see on the screen.

It would read HIGHER than actual voltage if anything.

You are so smart, you explain to me how a DC voltmeter would reaf
lower on an unfiltered rectified voltage than it would when connected
to a "filtering" load like a battery.

If you can adequately explain it, I'll accept your criticism

I agree that understanding of electricity would help...;-)