The Natural Philosopher wrote:
Palindrome wrote:

The Natural Philosopher wrote:

Palindrome wrote:

The Natural Philosopher wrote:

Cerumen wrote:

wrote in message
oups.com...
On 27 Jun, 08:45, "the_constructor" wrote:

Hi,

I have two 8Amp battery chargers that I use on my mobility
scooters that
need repairing.

Do you know someone or a company who can repair them please.

Each battery charger new is about £145 and I don't really fancy
binning
them.

There will be a transformer rectifier unit plus a controller of
some sort, a sealed unit full of electronics probably these days.
Without test meters you can't check the rectifier unit or the
electronics and if the transformer isn't burnt out you are stumped.



Huh? most of the ones I have seen for lead acid anyway are just
transformer rectifiers..with enough impedance in them to reduce to
trickle as the battery voltage nears 'fully charged'



The "impedance in them" limits the initial charging current. It does
not cause the current to reduce to a trickle.

Trickle chargers limit the current to a trickle at all times. They
are safe enough, but will typically take 10 hours to charge a battery.

Cheap "transformer rectifier" chargers are unregulated. They may
easily charge at too high a rate during initial charge and have too
high an output voltage to leave "charging", once the battery is
charged. The final "trickle" charge is determined by the charger
output voltage - not the "impedance".

Both actually.


Nope. The impedance of the supply has to be low to deliver a high
normal charging current. Unless that impedance is altered as the
battery reaches its charged state (ie not a cheap
transformer-rectifier charger), the supply impedance remains low - too
low to affect the trickle current level.


You forget that I=Vdiff/R..drive from a low voltage and the current
reduces as the battery charges. However in theory at least, and rather
horrendously in practice sometimes, a low power supply impedance will
ultimately end up in I tending to infinity with the usual result..

Nope. The I decreases because the Vdiff decreases - not because R
increases. R remains constant. Even cheap chargers usually limit Imax
for high VDiff - too many people connect chargers to car batteries with
the 6v12v slide switch set incorrectly. Things have moved on from
selenium rectifiers and moving iron meters..

However, the basic point is that "cheap and cheerful" car battery
chargers should not be used with batteries of the type normally fitted
to mobility scooters. It certainly can end up with things heading
towards infinity - such as bits of the battery.

--
Sue