Model Forum / Radio Controlled / Land Models / September 2003

a few possible/likely faults come to mind:

* blown component
* component exhibiting a thermal fault
* dry solder joint
* loose or corroded mechanical wiring connection in a high-current
application exhibiting positive thermal tendancies
*stuffed battery

easiest to test is the battery - beg/borrow/steal/buy a known-good
pack of about the same capacity (1.4AH to 2AH will be fine).  if you
cant get your hands on another battery, try - and i dont know your
level of skill with electronics here - try hooking a voltmeter
(analogue or digital, cheap or expensive... doesnt matter a damn for
this task) across the battery terminals.  the meter probes can often
be jammed into the "wire" side of plastic multi-pin connectors, ie
"Tamiya" type battery connectors... failing that, a couple of
straightened-out paper clips can usually gain access, and the meter
probes clipped to them using whatever reliable means you have to hand
(small alligator clips with no wires on them can do that task... i
dare say a couple of clothes pegs would serve similarly well - you
could also use a 2-way (or more) screw-type terminal block)

NOTE: DO NOT SHORT OUT THE BATTERY TERMINALS

ok, that bears repeating:

NOTE: DO NOT SHORT OUT THE BATTERY TERMINALS

take great care not to short out the battery terminals - if you short
them out, you stand a good chance of damaging if not destroying the
battery pack, damaging the charger if it's connected, and even
starting a fire.  never take large rechargable cells/batteries for
granted, in some ways theyre as dangerous as the AC mains.

ok, if youve been game enough to hook up a voltmeter...  ;)  monitor
the battery voltage as the charger is powered up:  if the voltage
skyrockets (suddenly climbs to more than 1.5 volts per cell), recycle
the battery and get a new one - even if the charger *is* faulty, so is
the battery if it exhibits that high a terminal voltage soon after
being put on charge.

loose or corroded mechanical wiring connection:  by that i mean screw
terminal, plug&socket, blade (utilux or similar) connector, fuse
holder, terminal strip... whatever.  anything not involving solder.
checking such connections often clears the fault without the repairer
realising until testing, coz simply unscrewing/unplugging then
reconnecting the connection often clears the mild corrosion or
"accidentally" tightens the connection.  if youre not confident with
electrical wiring / electronics, and/or dont have much experience with
mains, i suggest you do NOT open the case of a mains-powered device.
(this doesnt count if the device is powered by a low voltage plugpack
("wall cube" to the americans) - in that case, the unit itself doesnt
contain high voltages.

dry solder joints:  these can be absolute bitches.  if youve cleared
all other faults, with a device as small as a battery charger i
wouldnt bother inspecting solder joints, id just resolder the whole
bloody lot in one hit and clear that question beyond any doubt.  cant
offer much more advice than that - if youve hit a wall re finding
other faults, and wanna have a go, do so - resolder the whole lot.
what have you to lose but an evening and your sanity?  (erm, and your
life... dont mess with mains electricity unless you know what youre
doing)

blown component:  unlikely.  the unit appears to be trying to work,
from your description of the symptoms - that implies a "marginal
tolerence" fault rather than a catastrophic failure.

component exhibiting a thermal fault:  its possible, but this one's
more likely to be a dry solder joint suffering thermal tendancies
(which theyre wont to do - dry joints can be absolute bitches).  a
hairdryer and a can of freezer spray is the go there - heat then cool
areas of the circuit board with the charger powered up, and use
process of elimination to determine if heat plays a part in the fault.
DO NOT USE THIS METHOD IN ANY DEVICE CONTAINING AC MAINS, OR ANY OTHER
HIGH VOLTAGES, UNLESS YOU ***REALLY*** KNOW WHAT YOU ARE DOING.

cant offer much more without a pretty detailed description of the
charger, its methods of operation (charge method, charge termination
method, battery state detection, etc), and a recorded history of the
fault's symptoms.

by the way, the battery wont get warm at all unless its charged in
less than, umm, 'bout 5 hours or so.  an overnight (14-hour)
charger(r) wont cause the battery to become noticably warm unless it
either fails to detect end of charge and keeps going for another 24
hours, or if the battery is stuffed (they can go exothermic when they
reach the end of their useable life and their chemistry is
sufficiently messed up... doesnt apply to shorted cells of course,
they just act like pieces of wire)

hope this helped

*DS*

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